[Illustration: _To face the Title. _]

EXPERIMENTS AND OBSERVATIONS ON DIFFERENT KINDS OF AIR. 

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 Quamobrem, si qua est erga Creatorem humilitas, si qua operum ejus reverentia et magnificatio, si qua charitas in homines, si erga necessitates et ærumnas humanas relevandas studium, si quis amor veritatis in naturalibus, et odium tenebrarum, et intellectus purificandi desiderium; orandi sunt homines iterum atque iterum, ut, missis philosophiis istis volaticis et preposteris, quæ theses hypothesibus anterposuerunt, et experientiam captivam duxerunt, atque de operibus dei triumpharunt, summisse, et cum veneratione quadam, ad volumen creaturarum evolvendum accedant; atque in eo moram faciant, meditentur, et ab opinionibus abluti et mundi, caste et integre versentur. ----In interpretatione ejus eruenda nulli operæ parcant, sed strenue procedant, persistant, immoriantur. 

 LORD BACON IN INSTAURATIONE MAGNA. 

EXPERIMENTS

AND

OBSERVATIONS

ON DIFFERENT KINDS OF

AIR. 

By JOSEPH PRIESTLEY, LL. D. F. R. S. 

The SECOND EDITION Corrected. 

 Fert animus Causas tantarum expromere rerum; Immensumque aperitur opus. 

 LUCAN

LONDON:

Printed for J. JOHNSON, No. 72, in St. Paul's Church-Yard. 

MDCCLXXV. 

 TO THE RIGHT HONOURABLE THE EARL OF SHELBURNE, THIS TREATISE IS WITH THE GREATEST GRATITUDE AND RESPECT, INSCRIBED, BY HIS LORDSHIP's MOST OBLIGED, AND OBEDIENT HUMBLE SERVANT, J. PRIESTLEY. 

Transcriber's Note: Footnotes have been moved to the end of the chapter. The errata listed at the end of the book have been corrected in thetext. In the text, there are places where the apothecary symbols forounce and dram are used. These are changed to oz. And dr. In the textfile. 

THE PREFACE. 

One reason for the present publication has been the favourable receptionof those of my _Observations on different kinds of air_, which werepublished in the Philosophical Transactions for the year 1772, and thedemand for them by persons who did not chuse, for the sake of thosepapers only, to purchase the whole volume in which they were contained. Another motive was the _additions_ to my observations on this subject, in consequence of which my papers grew too large for such a publicationas the _Philosophical Transactions_. 

Contrary, therefore, to my intention, expressed PhilosophicalTransactions, vol. 64. P. 90, but with the approbation of the President, and of my friends in the society, I have determined to send them nomore papers for the present on this subject, but to make a separate andimmediate publication of all that I have done with respect to it. 

Besides, considering the attention which, I am informed, is now given tothis subject by philosophers in all parts of Europe, and the rapidprogress that has already been made, and may be expected to be made inthis branch of knowledge, all unnecessary delays in the publication ofexperiments relating to it are peculiarly unjustifiable. 

When, for the sake of a little more reputation, men can keep broodingover a new fact, in the discovery of which they might, possibly, havevery little real merit, till they think they can astonish the world witha system as complete as it is new, and give mankind a prodigious idea oftheir judgment and penetration; they are justly punished for theiringratitude to the fountain of all knowledge, and for their want of agenuine love of science and of mankind, in finding their boasteddiscoveries anticipated, and the field of honest fame pre-occupied, bymen, who, from a natural ardour of mind, engage in philosophicalpursuits, and with an ingenuous simplicity immediately communicate toothers whatever occurs to them in their inquiries. 

As to myself, I find it absolutely impossible to produce a work on thissubject that shall be any thing like _complete_. My first publication Iacknowledged to be very imperfect, and the present, I am as ready toacknowledge, is still more so. But, paradoxical as it may seem, thiswill ever be the case in the progress of natural science, so long as theworks of God are, like himself, infinite and inexhaustible. Incompleting one discovery we never fail to get an imperfect knowledge ofothers, of which we could have no idea before; so that we cannot solveone doubt without creating several new ones. 

Travelling on this ground resembles Pope's description of travellingamong the Alps, with this difference, that here there is not only_succession_, but an _increase_ of new objects and new difficulties. 

 So pleas'd at first the tow'ring Alps we try, Mount o'er the vales, and seem to tread the sky. Th' eternal snows appear already past, And the first clouds and mountains seem the last, But those attain'd, we tremble to survey The growing labours of the lengthen'd way. Th' increasing prospect tires our wand'ring eyes, Hills peep o'er hills, and Alps on Alps arise. 

 ESSAY ON CRITICISM. 

Newton, as he had very little knowledge of _air_, so he had few doubtsconcerning it. Had Dr. Hales, after his various and valuableinvestigations, given a list of all his _desiderata_, I am confidentthat he would not have thought of one in ten that had occurred to me atthe time of my last publication; and my doubts, queries, and hints fornew experiments are very considerably increased, after a series ofinvestigations, which have thrown great light upon many things of whichI was not able to give any explanation before. 

I would observe farther, that a person who means to serve the cause ofscience effectually, must hazard his own reputation so far as to riskeven _mistakes_ in things of less moment. Among a multiplicity of newobjects, and new relations, some will necessarily pass withoutsufficient attention; but if a man be not mistaken in the principalobjects of his pursuits, he has no occasion to distress himself aboutlesser things. 

In the progress of his inquiries he will generally be able to rectifyhis own mistakes; or if little and envious souls should take a malignantpleasure in detecting them for him, and endeavouring to expose him, heis not worthy of the name of a philosopher, if he has not strength ofmind sufficient to enable him not to be disturbed at it. He who does notfoolishly affect to be above the failings of humanity, will not bemortified when it is proved that he is but a man. 

In this work, as well as in all my other philosophical writings, I havemade it a rule not to conceal the _real views_ with which I have madeexperiments; because though, by following a contrary maxim, I might haveacquired a character of greater sagacity, I think that two very goodends are answered by the method that I have adopted. For it both tendsto make a narrative of a course of experiments more interesting, andlikewise encourages other adventurers in experimental philosophy;shewing them that, by pursuing even false lights, real and importanttruths may be discovered, and that in seeking one thing we often findanother. 

In some respects, indeed, this method makes the narrative _longer_, butit is by making it less tedious; and in other respects I have writtenmuch more concisely than is usual with those who publish accounts oftheir experiments. In this treatise the reader will often find theresult of long processes expressed in a few lines, and of many such in asingle paragraph; each of which, if I had, with the usual parade, described it at large (explaining first the _preparation_, then recitingthe _experiment_ itself, with the _result_ of it, and lastly makingsuitable _reflections_) would have made as many sections or chapters, and have swelled my book to a pompous and respectable size. But I havethe pleasure to think that those philosophers who have but little timeto spare for _reading_, which is always the case with those who _do_much themselves, will thank me for not keeping them too long from theirown pursuits; and that they will find rather more in the volume, thanthe appearance of it promises. 

I do not think it at all degrading to the business of experimentalphilosophy, to compare it, as I often do, to the diversion of _hunting_, where it sometimes happens that those who have beat the ground the most, and are consequently the best acquainted with it, weary themselveswithout starting any game; when it may fall in the way of a merepassenger; so that there is but little room for boasting in the mostsuccessful termination of the chace. 

The best founded praise is that which is due to the man, who, from asupreme veneration for the God of nature, takes pleasure incontemplating his _works_, and from a love of his fellow-creatures, asthe offspring of the same all-wise and benevolent parent, with agrateful sense and perfect enjoyment of the means of happiness of whichhe is already possessed, seeks, with earnestness, but without murmuringor impatience, that greater _command of the powers of nature_, which canonly be obtained by a more extensive and more accurate _knowledge_ ofthem; and which alone can enable us to avail ourselves of the numerousadvantages with which we are surrounded, and contribute to make ourcommon situation more secure and happy. 

Besides, the man who believes that there is a _governor_ as well as a_maker_ of the world (and there is certainly equal reason to believeboth) will acknowledge his providence and favour at least as much in asuccessful pursuit of _knowledge_, as of _wealth_; which is a sentimentthat entirely cuts off all boasting with respect to ourselves, and allenvy and jealousy with respect to others; and disposes us mutually torejoice in every new light that we receive, through whose hands soeverit be conveyed to us. 

I shall pass for an enthusiast with some, but I am perfectly easy underthe imputation, because I am happy in those views which subject me toit; but considering the amazing improvements in natural knowledge whichhave been made within the last century, and the many ages, aboundingwith men who had no other object but study, in which, however, nothingof this kind was done, there appears to me to be a very particularprovidence in the concurrence of those circumstances which have producedso great a change; and I cannot help flattering myself that this will beinstrumental in bringing about other changes in the state of the world, of much more consequence to the improvement and happiness of it. 

This rapid progress of knowledge, which, like the progress of a _wave_of the sea, of _sound_, or of _light_ from the sun, extends itself notthis way or that way only, but _in all directions_, will, I doubt not, be the means, under God, of extirpating _all_ error and prejudice, andof putting an end to all undue and usurped authority in the business of_religion_, as well as of _science_; and all the efforts of theinterested friends of corrupt establishments of all kinds will beineffectual for their support in this enlightened age: though, byretarding their downfal, they may make the final ruin of them morecomplete and glorious. It was ill policy in Leo the Xth to patronizepolite literature. He was cherishing an enemy in disguise. And theEnglish hierarchy (if there be any thing unsound in its constitution)has equal reason to tremble even at an air-pump, or an electricalmachine. 

There certainly never was any period in which _natural knowledge_ madesuch a progress as it has done of late years, and especially in thiscountry; and they who affect to speak with supercilious contempt of thepublications of the present age in general, or of the Royal Society inparticular, are only those who are themselves engaged in the mosttrifling of all literary pursuits, who are unacquainted with all realscience, and are ignorant of the progress and present state of it. [1]

It is true that the rich and the great in this country give lessattention to these subjects than, I believe, they were ever known to do, since the time of Lord Bacon, and much less than men of rank and fortunein other countries give to them. But with us this loss is made up bymen of leisure, spirit, and ingenuity, in the middle ranks of life, which is a circumstance that promises better for the continuance of thisprogress in useful knowledge than any noble or royal patronage. With us, politics chiefly engage the attention of those who stand foremost in thecommunity, which, indeed, arises from the _freedom_ and peculiar_excellence_ of our constitution, without which even the spirit of menof letters in general, and of philosophers in particular, who neverdirectly interfere in matters of government, would languish. 

It is rather to be regretted, however, that, in such a number ofnobility and gentry, so very few should have any taste for scientificalpursuits, because, for many valuable purposes of science, _wealth_ givesa decisive advantage. If extensive and lasting _fame_ be at all anobject, literary, and especially scientifical pursuits, are preferableto political ones in a variety of respects. The former are as much morefavourable for the display of the human faculties than the latter, asthe _system of nature_ is superior to any _political system_ upon earth. 

If extensive _usefulness_ be the object, science has the same advantageover politics. The greatest success in the latter seldom extends fartherthan one particular country, and one particular age; whereas asuccessful pursuit of science makes a man the benefactor of all mankind, and of every age. How trifling is the fame of any statesman that thiscountry has ever produced to that of Lord Bacon, of Newton, or of Boyle;and how much greater are our obligations to such men as these, than toany other in the whole _Biographia Britannica_; and every country, inwhich science has flourished, can furnish instances for similarobservations. 

Here my reader will thank me, and the writer will, I hope, forgive me, if I quote a passage from the postscript of a letter which I happen tohave just received from that excellent, and in my opinion, not tooenthusiastical philosopher, father Beccaria of Turin. 

 _Mi spiace che il mondo politico ch'è pur tanto passeggero, rubbi il grande Franklin al mondo della natura, che non sa ne cambiare, ne mancare. _ In English. "I am sorry that the _political world_, which is so very transitory, should take the great Franklin from the _world of nature_, which can never change, or fail. "

I own it is with peculiar pleasure that I quote this passage, respectingthis truly great man, at a time when some of the infatuated politiciansof this country are vainly thinking to build their wretched anddestructive projects, on the ruins of his established reputation; areputation as extensive as the spread of science itself, and of which itis saying very little indeed, to pronounce that it will last andflourish when the names of all his enemies shall be forgotten. 

I think it proper, upon this occasion, to inform my friends, and thepublic, that I have, for the present, suspended my design of writing_the history and present state of all the branches of experimentalphilosophy_. This has arisen not from any dislike of the undertaking, but, in truth, because I see no prospect of being reasonably indemnifiedfor so much labour and expence, notwithstanding the specimens I havealready given of that work (in the _history of electricity_, and of the_discoveries relating to vision, light, and colours_) have met with amuch more favourable reception from the best judges both at home andabroad, than I expected. Immortality, if I should have any view to it, is not the proper price of such works as these. 

I propose, however, having given so much attention to the subject of_air_, to write, at my leisure, the history and present state ofdiscoveries relating to it; in which case I shall, as a part of it, reprint this work, with such improvements as shall have occurred to meat that time; and I give this notice of it, that no person who intendsto purchase it may have reason (being thus apprised of my intention) tocomplain of buying the same thing twice. If any person chuse it, he maysave his five or six shillings for the present, and wait five or sixyears longer (if I should live so long) for the opportunity of buyingthe same thing, probably much enlarged, and at the same time a completeaccount of all that has been done by others relating to this subject. 

Though for the plain, and I hope satisfactory reason above mentioned, Ishall probably write no other _histories_ of this kind, I shall, asopportunity serves, endeavour to provide _materials_ for such histories, by continuing my experiments, keeping my eyes open to such newappearances as may present themselves, investigating them as far as Ishall be able, and never failing to communicate to the public, by somechannel or other, the result of my observations. 

In the publication of this work I have thought that it would beagreeable to my readers to preserve, in some measure, the order ofhistory, and therefore I have not thrown together all that I haveobserved with respect to each kind of air, but have divided the workinto _two parts_; the former containing what was published before, inthe Philosophical Transactions, with such observations and correctionsas subsequent experience has suggested to me; and I have reserved forthe latter part of the work an account of the experiments which I havemade since that publication, and after a pretty long interruption in myphilosophical pursuits, in the course of the last summer. Besides I amsensible that in the latter part of this work a different arrangement ofthe subjects will be more convenient, for their mutual illustration. 

Some persons object to the term _air_, as applied to _acid_, _alkaline_, and even _nitrous air_; but it is certainly very convenient to have acommon term by which to denote things which have so many commonproperties, and those so very striking; all of them agreeing with theair in which we breathe, and with _fixed air_, in _elasticity_, and_transparency_, and in being alike affected by heat or cold; so that tothe eye they appear to have no difference at all. With much more reason, as it appears to me, might a person object to the common term _metal_, as applied to things so very different from one another as gold, quicksilver, and lead. 

Besides, _acid_ and _alkaline_ air do not differ from _common air_ (inany respect that can countenance an objection to their having a commonappellation) except in such properties as are common to it with _fixedair_, though in a different degree; viz. That of being imbibed by water. But, indeed, all kinds of air, common air itself not excepted, arecapable of being imbibed by water in some degree. 

Some may think the terms acid and alkaline _vapour_ more proper thanacid and alkaline _air_. But the term _vapour_ having always beenapplied to elastic matters capable of being condensed in the temperatureof the atmosphere, especially the vapour of water, it seems harsh toapply it to any elastic substance, which at the same time that it is astransparent as the air we breathe, is no more affected by cold than itis. 

As my former papers were immediately translated into several foreignlanguages, I may presume that this treatise, having a better title toit, will be translated also; and, upon this presumption, I cannot helpexpressing a wish, that it may be done by persons who have a competentknowledge of _subject_, as well as of the _English language_. Themistakes made by some foreigners, have induced me to give this caution. 

 _London, Feb. _ _1774. _

ADVERTISEMENT. 

The _weights_ mentioned in the course of this treatise are _Troy_, andwhat is called _an ounce measure of air_, is the space occupied by anounce weight of water, which is equal to 480 grains, and is, therefore, almost two _cubic inches_ of water; for one cubic inch weighs 254grains. 

FOOTNOTES:

[1] See Sir John Pringle's _Discourse on the different kinds of air_, p. 29, which, if it became me to do it, I would recommend to the reader, ascontaining a just and elegant account of the several discoveries thathave been successively made, relating to the subject of this treatise. 

THE CONTENTS. 

THE INTRODUCTION. 

Section I. _A general view of PRECEDING DISCOVERIES relating to AIR_ Page 1

Sect. II. _An Account of the APPARATUS with which the following Experiments were made_ 6

PART I. 

_Experiments and Observations made in, and before the Year 1772. _ 23

Sect. I. _Of FIXED AIR_ 25

Sect. II. _Of AIR in which a CANDLE, or BRIMSTONE, has burned out_ 43

Sect. III. _Of INFLAMMABLE AIR_ 55

Sect. IV. _Of AIR infected with ANIMAL RESPIRATION, or PUTREFACTION_ 70

Sect. V. _Of AIR in which a mixture of BRIMSTONE and FILINGS of IRON has stood_ 105

Sect. VI. _Of NITROUS AIR_ 108

Sect. VII. _Of AIR infected with the FUMES of BURNING CHARCOAL_ 129

Sect. VIII. _Of the effect of the CALCINATION of METALS, and of the EFFLUVIA of PAINT made with WHITE-LEAD and OIL, on AIR_ 133

Sect. IX. _Of MARINE ACID AIR_ 143

Sect. X. _Miscellaneous Observations_ 154

PART II. 

_Experiments and Observations made in the Year 1773, and the Beginning of1774. _

Sect. I. _Observations on ALKALINE AIR_ 163

Sect. II. _Of COMMON AIR diminished, and made noxious by various processes_ 177

Sect. III. _Of NITROUS AIR_ 203

Sect. IV. _Of MARINE ACID AIR_ 229

Sect. V. _Of INFLAMMABLE AIR_ 242

Sect. VI. _Of FIXED AIR_ 248

Sect. VII. MISCELLANEOUS EXPERIMENTS 252

Sect. VIII. _QUERIES, SPECULATIONS, and HINTS_ 258

THE APPENDIX. 

Number I. _EXPERIMENTS made by Mr. Hey to prove that there is no OIL of VITRIOL in water impregnated with FIXED AIR_ 288

Number II. _A Letter from Mr. HEY to Dr. PRIESTLEY, concerning the effects of fixed Air applied by way of Clyster_ 292

Number III. _Observations on the MEDICINAL USES of FIXED AIR. By THOMAS PERCIVAL, M. D. Fellow of the ROYAL SOCIETY, and of the SOCIETY of ANTIQUARIES in LONDON_ 300

Number IV. _Extract of a Letter from WILLIAM FALCONER, M. D. Of BATH_ 314

Number V. _Extract of a Letter from Mr. WILLIAM BEWLEY, of GREAT MASSINGHAM, NORFOLK_ 317

Num. VI. _A Letter from Dr. FRANKLIN_ 321

Number VII. _Extract of Letter from Mr. HENRY of MANCHESTER_ 323

THE INTRODUCTION. 

SECTION I. 

_A general view of PRECEDING DISCOVERIES relating to air. _

For the better understanding of the experiments and observations ondifferent kinds of air contained in this treatise, it will be useful tothose who are not acquainted with the history of this branch of naturalphilosophy, to be informed of those facts which had been discovered byothers, before I turned my thoughts to the subject; which suggested, andby the help of which I was enabled to pursue, my inquiries. Let it beobserved, however, that I do not profess to recite in this place _all_that had been discovered concerning air, but only those discoveries theknowledge of which is necessary, in order to understand what I have donemyself; so that any person who is only acquainted with the generalprinciples of natural philosophy, may be able to read this treatise, and, with proper attention, to understand every part of it. 

That the air which constitutes the atmosphere in which we live has_weight_, and that it is _elastic_, or consists of a compressible anddilatable fluid, were some of the earliest discoveries that were madeafter the dawning of philosophy in this western part of the world. 

That elastic fluids, differing essentially from the air of theatmosphere, but agreeing with it in the properties of weight, elasticity, and transparency, might be generated from solid substances, was discovered by Mr. Boyle, though two remarkable kinds of factitiousair, at least the effects of them, had been known long before to allminers. One of these is heavier than common air. It lies at the bottomof pits, extinguishes candles, and kills animals that breathe it, onwhich account it had obtained the name of the _choke damp_. The other islighter than common air, taking its place near the roofs ofsubterraneous places, and because it is liable to take fire, andexplode, like gunpowder, it had been called the _fire damp_. The word_damp_ signifies _vapour_ or _exhalation_ in the German and Saxonlanguage. 

Though the former of these kinds of air had been known to be noxious, the latter I believe had not been discovered to be so, having alwaysbeen found in its natural state, so much diluted with common air, as tobe breathed with safety. Air of the former kind, besides having beendiscovered in various caverns, particularly the _grotta del Cane_ inItaly, had also been observed on the surface of fermenting liquors, andhad been called _gas_ (which is the same with _geist_, or _spirit_) byVan Helmont, and other German chymists; but afterwards it obtained thename of _fixed air_, especially after it had been discovered by Dr. Black of Edinburgh to exist, in a fixed state, in alkaline salts, chalk, and other calcareous substances. 

This excellent philosopher discovered that it is the presence of thefixed air in these substances that renders them _mild_, and that whenthey are deprived of it, by the force of fire, or any other process, they are in that state which had been called _caustic_, from theircorroding or burning animal and vegetable substances. 

Fixed air had been discovered by Dr. Macbride of Dublin, after anobservation of Sir John Pringle's, which led to it, to be in aconsiderable degree antiseptic; and since it is extracted in greatplenty from fermenting vegetables, he had recommended the use of _wort_(that is an infusion of malt in water) as what would probably giverelief in the sea-scurvy, which is said to be a putrid disease. 

Dr. Brownrigg had also discovered that the same species of air iscontained in great quantities in the water of the Pyrmont spring at Spain Germany, and in other mineral waters, which have what is called an_acidulous_ taste, and that their peculiar flavour, briskness, andmedicinal virtues, are derived from this ingredient. 

Dr. Hales, without seeming to imagine that there was any materialdifference between these kinds of air and common air, observed thatcertain substances and operations _generate_ air, and others _absorb_it; imagining that the diminution of air was simply a taking away fromthe common mass, without any alteration in the properties of whatremained. His experiments, however, are so numerous, and various, thatthey are justly esteemed to be the solid foundation of all our knowledgeof this subject. 

Mr. Cavendish had exactly ascertained the specific gravities of fixedand inflammable air, shewing the former of them to be 1-1/2 heavierthan common air, and the latter ten times lighter. He also shewed thatwater would imbibe more than its own bulk of fixed air. 

Lastly, Mr. Lane discovered that water thus impregnated with fixed airwill dissolve a considerable quantity of iron, and thereby become astrong chalybeate. 

These, I would observe, are by no means all the discoveries concerningair that have been made by the gentlemen whose names I have mentioned, and still less are they all that have been made by others; but theycomprise all the previous knowledge of this subject that is necessary tothe understanding of this treatise; except a few particulars, which willbe mentioned in the course of the work, and which it is, therefore, unnecessary to recite in this place. 

SECTION II. 

_An account of the APPARATUS with which the following experiments weremade. _

Rather than describe at large the manner in which every particularexperiment that I shall have occasion to recite was made, which wouldboth be very tedious, and require an unnecessary multiplicity ofdrawings, I think it more adviseable to give, at one view, an account ofall my apparatus and instruments, or at least of every thing that canrequire a description, and of all the different operations and processesin which I employ them. 

It will be seen that my apparatus for experiments on air is, in fact, nothing more than the apparatus of Dr. Hales, Dr. Brownrigg, and Mr. Cavendish, diversified, and made a little more simple. Yetnotwithstanding the simplicity of this apparatus, and the ease withwhich all the operations are conducted, I would not have any person, whois altogether without experience, to imagine that he shall be able toselect any of the following experiments, and immediately perform it, without difficulty or blundering. It is known to all persons who areconversant in experimental philosophy, that there are many littleattentions and precautions necessary to be observed in the conducting ofexperiments, which cannot well be described in words, but which it isneedless to describe, since practice will necessarily suggest them;though, like all other arts in which the hands and fingers are made useof, it is only _much practice_ that can enable a person to go throughcomplex experiments, of this or any other kind, with ease and readiness. 

For experiments in which air will bear to be confined by water, I firstused an oblong trough made of earthen ware, as _a_ fig. 1. About eightinches deep, at one end of which I put thin flat stones, _b. B. _ aboutan inch, or half an inch, under the water, using more or fewer of themaccording to the quantity of water in the trough. But I have since foundit more convenient to use a larger wooden trough, of the same generalshape, eleven inches deep, two feet long, and 1-1/2 wide, with a shelfabout an inch lower than the top, instead of the flat stonesabove-mentioned. This trough being larger than the former, I have nooccasion to make provision for the water being higher or lower, the bulkof a jar or two not making so great a difference as did before. 

The several kinds of air I usually keep in _cylindrical jars_, as _c_, _c_, fig. 1, about ten inches long, and 2-1/2 wide, being such as I havegenerally used for electrical batteries, but I have likewise vessels ofvery different forms and sizes, adapted to particular experiments. 

When I want to remove vessels of air from the large trough, I place themin _pots_ or _dishes_, of various sizes, to hold more or less water, according to the time that I have occasion to keep the air, as fig. 2. These I plunge in water, and slide the jars into them; after which theymay be taken out together, and be set wherever it shall be mostconvenient. For the purpose of merely removing a jar of air from oneplace to another, where it is not to stand longer than a few days, Imake use of common _tea-dishes_, which will hold water enough for thattime, unless the air be in a state of diminution, by means of anyprocess that is going on in it. 

If I want to try whether an animal will live in any kind of air, I firstput the air into a small vessel, just large enough to give it room tostretch itself; and as I generally make use of _mice_ for this purpose, I have found it very convenient to use the hollow part of a tallbeer-glass, _d_ fig. 1, which contains between two and three ouncemeasures of air. In this vessel a mouse will live twenty minutes, orhalf an hour. 

For the purpose of these experiments it is most convenient to catch themice in small wire traps, out of which it is easy to take them, andholding them by the back of the neck, to pass them through the waterinto the vessel which contains the air. If I expect that the mouse willlive a considerable time, I take care to put into the vessel somethingon which it may conveniently sit, out of the reach of the water. If theair be good, the mouse will soon be perfectly at its ease, havingsuffered nothing by its passing through the water. If the air besupposed to be noxious, it will be proper (if the operator be desirousof preserving the mice for farther use) to keep hold of their tails, that they may be withdrawn as soon as they begin to shew signs ofuneasiness; but if the air be thoroughly noxious, and the mouse happensto get a full inspiration, it will be impossible to do this before it beabsolutely irrecoverable. 

In order to _keep_ the mice, I put them into receivers open at the topand bottom, standing upon plates of tin perforated with many holes, andcovered with other plates of the same kind, held down by sufficientweights, as fig. 3. These receivers stand upon _a frame of wood_, thatthe fresh air may have an opportunity of getting to the bottoms of them, and circulating through them. In the inside I put a quantity of paper ortow, which must be changed, and the vessel washed and dried, every twoor three days. This is most conveniently done by having anotherreceiver, ready cleaned and prepared, into which the mice may betransferred till the other shall be cleaned. 

Mice must be kept in a pretty exact temperature, for either much heat ormuch cold kills them presently. The place in which I have generally keptthem is a shelf over the kitchen fire-place where, as it is usual inYorkshire, the fire never goes out; so that the heat varies very little, and I find it to be, at a medium, about 70 degrees of Fahrenheit'sthermometer. When they had been made to pass through the water, as theynecessarily must be in order to a change of air, they require, and willbear a very considerable degree of heat, to warm and dry them. 

I found, to my great surprize, in the course of these experiments, thatmice will live intirely without water; for though I have kept them forthree or four months, and have offered them water several times, theywould never taste it; and yet they continued in perfect health andvigour. Two or three of them will live very peaceably together in thesame vessel; though I had one instance of a mouse tearing another almostin pieces, and when there was plenty of provisions for both of them. 

In the same manner in which a mouse is put into a vessel of any kind ofair, a _plant_, or any thing else, may be put into it, viz. By passingit through the water; and if the plant be of a kind that will grow inwater only, there will be no occasion to set it in a pot of earth, whichwill otherwise be necessary. 

There may appear, at first sight, some difficulty in opening the mouthof a phial, containing any substance, solid or liquid, to which watermust not be admitted, in a jar of any kind of air, which is an operationthat I have sometimes had recourse to; but this I easily effect by meansof _a cork cut tapering_, and a strong, wire thrust through it, as infig. 4, for in this form it will sufficiently fit the mouth of anyphial, and by holding the phial in one hand, and the wire in the other, and plunging both my hands into the trough of water, I can easily conveythe phial through the water into the jar; which must either be held byan assistant, or be fastened by strings, with its mouth projecting overthe shelf. When the phial is thus conveyed into the jar, the cork mayeasily be removed, and may also be put into it again at pleasure, andconveyed the same way out again. 

When any thing, as a gallipot, &c. Is to be supported at a considerableheight within a jar, it is convenient to have such _wire stands_ as arerepresented fig. 5. They answer better than any other, because they takeup but little room, and may be easily bended to any shape or height. 

If I have occasion to pour air from a vessel with a wide mouth intoanother with a very narrow one, I am obliged to make use of a funnel, fig. 6, but by this means the operation is exceedingly easy; firstfilling the vessel into which the air is to be conveyed with water, andholding the mouth of it, together with the funnel, both under water withone hand, while the other is employed in pouring the air; which, ascending through the funnel up into the vessel, makes the waterdescend, and takes its place. These funnels are best made of glass, because the air being visible through them, the quantity of it may bemore easily estimated by the eye. It will be convenient to have severalof these funnels of different sizes. 

In order to expel air from solid substances by means of heat, Isometimes put them into a _gun-barrel_, fig. 7, and filling it up withdry sand, that has been well burned, so that no air can come from it, Ilute to the open end the stem of a tobacco pipe, or a small glass tube. Then having put the closed end of the barrel, which contains thematerials, into the fire, the generated air, issuing through the tube, may be received in a vessel of quicksilver, with its mouth immersed in abason of the same, suspended all together in wires, in the mannerdescribed in the figure: or any other fluid substance may be usedinstead of quicksilver. 

But the most accurate method of procuring air from several substances, by means of heat, is to put them, if they will bear it, into phials fullof quicksilver, with the mouths immersed in the same, and then throw thefocus of a burning mirror upon them. For this purpose the phials shouldbe made with their bottoms round, and very thin, that they may not beliable to break with a pretty sudden application of heat. 

If I want to expel air from any liquid, I nearly fill a phial with it, and having a cork perforated, I put through it, and secure with cement, a glass tube, bended in the manner represented at _e_ fig. 1. I then putthe phial into a kettle of water, which I set upon the fire and make toboil. The air expelled by the heat, from the liquor contained in thephial, issues through the tube, and is received in the bason ofquicksilver, fig. 7. Instead of this suspended bason, I sometimescontent myself with tying a flaccid bladder to the end of the tube, inboth these processes, that it may receive the newly generated air. 

In experiments on those kinds of air which are readily imbibed by water, I always make use of quicksilver, in the manner represented fig. 8, inwhich _a_ is the bason of quicksilver, _b_ a glass vessel containingquicksilver, with its mouth immersed in it, _c_ a phial containing theingredients from which the air is to be produced; and _d_ is a smallrecipient, or glass vessel designed to receive and intercept any liquorthat may be discharged along with the air, which is to be transmittedfree from any moisture into the vessel _b_. If there be no apprehensionof moisture, I make use of the glass tube only, without any recipient, in the manner represented _e_ fig. 1. In order to invert the vessel _b_, I first fill it with quicksilver, and then carefully cover the mouth ofit with a piece of soft leather; after which it may be turned upsidedown without any danger of admitting the air, and the leather may bewithdrawn when it is plunged in the quicksilver. 

In order to generate air by the solution of metals, or any process of asimilar nature, I put the materials into a phial, prepared in the mannerrepresented at _e_ fig. 1, and put the end of the glass tube under themouth of any vessel into which I want to convey the air. If heat benecessary I can easily apply to it a candle, or a red hot poker while ithangs in this position. 

When I have occasion to transfer air from a jar standing in the troughof water to a vessel standing in quicksilver, or in any other situationwhatever, I make use of the contrivance represented fig. 9, whichconsists of a bladder, furnished at one end with a small glass tubebended, and at the other with a cork, perforated so as just to admit thesmall end of a funnel. When the common air is carefully pressed out ofthis bladder, and the funnel is thrust tightly into the cork, it may befilled with any kind of air as easily as a glass jar; and then a stringbeing tied above the cork in which the funnel is inserted, and theorifice in the other cork closed, by pressing the bladder against it, itmay be carried to any place, and if the tube be carefully wiped, the airmay be conveyed quite free from moisture through a body of quicksilver, or any thing else. A little practice will make this very usefulmanoeuvre perfectly easy and accurate. 

In order to impregnate fluids with any kind of air, as water with fixedair, I fill a phial with the fluid larger or less as I have occasion (as_a_ fig. 10;) and then inverting it, place it with its mouth downwards, in a bowl _b_, containing a quantity of the same fluid; and havingfilled the bladder, fig. 9, with the air, I throw as much of it as Ithink proper into the phial, in the manner described above. Toaccelerate the impregnation, I lay my hand on the top of the phial, andshake it as much as I think proper. 

If, without having any air previously generated, I would convey it intothe fluid immediately as it arises from the proper materials, I keep thesame bladder in connection with a phial _c_ fig. 10, containing the samematerials (as chalk, salt of tartar, or pearl ashes in diluted oil ofvitriol, for the generation of fixed air) and taking care, lest, in theact of effervescence, any of the materials in the phial _c_ should getinto the vessel _a_, to place this phial on a stand lower than that onwhich the bason was placed, I press out the newly generated air, andmake it ascend directly into the fluid. For this purpose, and that I maymore conveniently shake the phial _c_, which is necessary in someprocesses, especially with chalk and oil of vitriol, I sometimes makeuse of a flexible leathern tube _d_, and sometimes only a glass tube. For if the bladder be of a sufficient length, it will give room for theagitation of the phial; or if not, it is easy to connect two bladderstogether by means of a perforated cork, to which they may both befastened. 

When I want to try whether any kind of air will admit a candle to burnin it, I make use of a cylindrical glass vessel, fig. 11. And a bit ofwax candle _a_ fig. 12, fastened to the end of a wire _b_, and turnedup, in such a manner as to be let down into the vessel with the flameupwards. The vessel should be kept carefully covered till the momentthat the candle is admitted. In this manner I have frequentlyextinguished a candle more than twenty times successively, in a vesselof this kind, though it is impossible to dip the candle into it withoutgiving the external air an opportunity of mixing with the air in theinside more or less. The candle _c_, at the other end of the wire isvery convenient for holding under a jar standing in water, in order toburn as long as the inclosed air can supply it; for the moment that itis extinguished, it may be drawn through the water before any smoke canhave mixed with the air. 

In order to draw air out of a vessel which has its mouth immersed inwater, and thereby to raise the water to whatever height may benecessary, it is very convenient to make use of a glass _syphon_, fig. 13, putting one of the legs up into the vessel, and drawing the air outat the other end by the mouth. If the air be of a noxious quality, itmay be necessary to have a syringe fastened to the syphon, the manner ofwhich needs no explanation. I have not thought it safe to depend upon avalve at the top of the vessel, which Dr. Hales sometimes made use of. 

If, however, a very small hole be made at the top of a glass vessel, itmay be filled to any height by holding it under water, while the air isissuing out at the hole, which may then be closed with wax or cement. 

If the generated air will neither be absorbed by water, nor diminishcommon air, it may be convenient to put part of the materials into acup, supported by a stand, and the other part into a small glassvessel, placed on the edge of it, as at _f_, fig. 1. Then having, bymeans of a syphon, drawn the air to at convenient height, the smallglass vessel may be easily pushed into the cup, by a wire introducedthrough the water; or it may be contrived, in a variety of ways, only todischarge the contents of the small vessel into the larger. The distancebetween the boundary of air and water, before and after the operation, will shew the quantity of the generated air. The effect of processesthat _diminish_ air may also be tried by the same apparatus. 

When I want to admit a particular kind of air to any thing that will notbear wetting, and yet cannot be conveniently put into a phial, andespecially if it be in the form of a powder, and must be placed upon astand (as in those experiments in which the focus of a burning mirror isto be thrown upon it) I first exhaust a receiver, in which it ispreviously placed; and having a glass tube, bended for the purpose, asin fig. 14, I screw it to the stem of a transfer of the air pump onwhich the receiver had been exhausted, and introducing it through thewater into a jar of that kind of air with which I would fill thereceiver, I only turn the cock, and I gain my purpose. In this method, however, unless the pump be very good, and several contrivances, toominute to be particularly described, be made use of a good deal ofcommon air will get into the receiver. 

When I want to measure the goodness of any kind of air, I put twomeasures of it into a jar standing in water; and when I have marked uponthe glass the exact place of the boundary of air and water, I put to itone measure of nitrous air; and after waiting a proper time, note thequantity of its diminution. If I be comparing two kinds of air that arenearly alike, after mixing them in a large jar, I transfer the mixtureinto a long glass tube, by which I can lengthen my scale to what degreeI please. 

If the quantity of the air, the goodness of which I want to ascertain, be exceedingly small, so as to be contained in a part of a glass tube, out of which water will not run spontaneously, as _a_ fig. 15; I firstmeasure with a pair of compasses the length of the column of air in thetube, the remaining part being filled with water, and lay it down upon ascale; and then, thrusting a wire of a proper thickness, _b_, into thetube, I contrive, by means of a thin plate of iron, bent to a sharpangle _c_, to draw it out again, when the whole of this littleapparatus has been introduced through the water into a jar of nitrousair; and the wire being drawn out, the air from the jar must supply itsplace. I then measure the length of this column of nitrous air which Ihave got into the tube, and lay it also down upon the scale, so as toknow the exact length of both the columns. After this, holding the tubeunder water, with a small wire I force the two separate columns of airinto contact, and when they have been a sufficient time together, Imeasure the length of the whole, and compare it with the length of boththe columns taken before. A little experience will teach the operatorhow far to thrust the wire into the tube, in order to admit as much airas he wants and no more. 

In order to take the electric spark in a quantity of any kind of air, which must be very small, to produce a sensible effect upon it, in ashort time, by means of a common machine, I put a piece of wire into theend of a small tube, and fasten it with hot cement, as in fig. 16; andhaving got the air I want into the tube by means of the apparatus fig. 15, I place it inverted in a bason containing either quicksilver, or anyother fluid substance by which I chuse to have the air confined. I then, by the help of the air pump, drive out as much of the air as I thinkconvenient, admitting the quicksilver, &c. To it, as at _a_, andputting a brass ball on the end of the wire, I take the sparks or shocksupon it, and thereby transmit them through the air to the liquor in thetube. 

To take the electric sparks in any kind of fluid, as oil, &c. I use thesame apparatus described above, and having poured into the tube as muchof the fluid as I conjecture I can make the electric spark pass through, I fill the rest with quicksilver; and placing it inverted in a bason ofquicksilver, I take the sparks as before. 

If air be generated very fast by this process, I use a tube that isnarrow at the top, and grows wider below, as fig. 17, that thequicksilver may not recede too soon beyond the striking distance. 

Sometimes I have used a different apparatus for this purpose, represented fig. 18. Taking a pretty wide glass tube, hermeticallysealed at the upper-end, and open below, at about an inch, or at whatdistance I think convenient from the top, I get two holes made in it, opposite to each other. Through these I put two wires, and fasteningthem with warm cement, I fix them at what distance I please from eachother. Between these wires I take the sparks, and the bubbles of airrise, as they are formed, to the top of the tube. 

PART I. 

_Experiments and Observations made in, and before the year 1772. _

In writing upon the subject of _different kinds of air_, I find myselfat a loss for proper _terms_, by which to distinguish them, those whichhave hitherto obtained being by no means sufficiently characteristic, ordistinct. The only terms in common use are, _fixed air_, _mephitic_, and_inflammable_. The last, indeed, sufficiently characterizes anddistinguishes that kind of air which takes fire, and explodes on theapproach of flame; but it might have been termed _fixed_ with as muchpropriety as that to which Dr. Black and others have given thatdenomination, since it is originally part of some solid substance, andexists in an unelastic state. 

All these newly discovered kinds of air may also be called _factitious_;and if, with others, we use the term _fixable_, it is still obvious toremark, that it is applicable to them all; since they are all capable ofbeing imbibed by some substance or other, and consequently of being_fixed_ in them, after they have been in an elastic state. 

The term _mephitic_ is equally applicable to what is called _fixed air_, to that which is _inflammable_, and to many other kinds; since they areequally noxious, when breathed by animals. Rather, however, than eitherintroduce new terms, or change the signification of old ones, I shalluse the term _fixed air_, in the sense in which it is now commonly used, and distinguish the other kinds by their properties, or some otherperiphrasis. I shall be under a necessity, however, of giving names tothose kinds of air, to which no names had been given by others, as_nitrous_, _acid_, and _alkaline_. 

SECTION I. 

_Of FIXED AIR. _

It was in consequence of living for some time in the neighbourhood of apublic brewery, that I was induced to make experiments on fixed air, ofwhich there is always a large body, ready formed, upon the surface ofthe fermenting liquor, generally about nine inches, or a foot in depth, within which any kind of substance may be very conveniently placed; andthough, in these circumstances, the fixed air must be continually mixingwith the common air, and is therefore far from being perfectly pure, yetthere is a constant fresh supply from the fermenting liquor, and it ispure enough for many purposes. 

A person, who is quite a stranger to the properties of this kind of air, would be agreeably amused with extinguishing lighted candles, or chipsof wood in it, as it lies upon the surface of the fermenting liquor; forthe smoke readily unites with this kind of air, probably by means of thewater which it contains; so that very little or none of the smoke willescape into the open air, which is incumbent upon it. It is remarkable, that the upper surface of this smoke, floating in the fixed air, issmooth, and well defined; whereas the lower surface is exceedinglyragged, several parts hanging down to a considerable distance within thebody of the fixed air, and sometimes in the form of balls, connected tothe upper stratum by slender threads, as if they were suspended. Thesmoke is also apt to form itself into broad flakes, parallel to thesurface of the liquor, and at different distances from it, exactly likeclouds. These appearances will sometimes continue above an hour, withvery little variation. When this fixed air is very strong, the smoke ofa small quantity of gunpowder fired in it will be wholly retained by it, no part escaping into the common air. 

Making an agitation in this air, the surface of it, (which stillcontinues to be exactly defined) is thrown into the form of waves, whichit is very amusing to look upon; and if, by this agitation, any of thefixed air be thrown over the side of the vessel, the smoke, which ismixed with it, will fall to the ground, as if it was so much water, thefixed air being heavier than common air. 

The red part of burning wood was extinguished in this air, but I couldnot perceive that a red-hot poker was sooner cooled in it. 

Fixed air does not instantly mix with common air. Indeed if it did, itcould not be caught upon the surface of the fermenting liquor. A candleput under a large receiver, and immediately plunged very deep below thesurface of the fixed air, will burn some time. But vessels with thesmallest orifices, hanging with their mouths downwards in the fixed air, will _in time_ have the common air, which they contain, perfectly mixedwith it. When the fermenting liquor is contained in vessels closecovered up, the fixed air, on removing the cover, readily affects thecommon air which is contiguous to it; so that, candles held at aconsiderable distance above the surface will instantly go out. I havebeen told by the workmen, that this will sometimes be the case, when thecandles are held two feet above the mouth of the vessel. 

Fixed air unites with the smoke of rosin, sulphur, and other electricalsubstances, as well as with the vapour of water; and yet, by holding thewire of a charged phial among these fumes, I could not make anyelectrical atmosphere, which surprized me a good deal, as there was alarge body of this smoke, and it was so confined, that it could notescape me. 

I also held some oil of vitriol in a glass vessel within the fixed air, and by plunging a piece of red-hot glass into it, raised a copious andthick fume. This floated upon the surface of the fixed air like otherfumes, and continued as long. 

Considering the near affinity between water and fixed air, I concludedthat if a quantity of water was placed near the yeast of the fermentingliquor, it could not fail to imbibe that air, and thereby acquire theprincipal properties of Pyrmont, and some other medicinal mineralwaters. Accordingly, I found, that when the surface of the water wasconsiderable, it always acquired the pleasant acidulous taste thatPyrmont water has. The readiest way of impregnating water with thisvirtue, in these circumstances, is to take two vessels, and to keeppouring the water from one into the other, when they are both of themheld as near the yeast as possible; for by this means a great quantityof surface is exposed to the air, and the surface is also continuallychanging. In this manner, I have sometimes, in the space of two or threeminutes, made a glass of exceedingly pleasant sparkling water, whichcould hardly be distinguished from very good Pyrmont, or rather Seltzerwater. 

But the _most effectual_ way of impregnating water with fixed air is toput the vessels which contain the water into glass jars, filled withthe purest fixed air made by the solution of chalk in diluted oil ofvitriol, standing in quicksilver. In this manner I have, in about twodays, made a quantity of water to imbibe more than an equal bulk offixed air, so that, according to Dr. Brownrigg's experiments, it musthave been much stronger than the best imported Pyrmont; for though hemade his experiments at the spring-head, he never found that itcontained quite so much as half its bulk of this air. If a sufficientquantity of quicksilver cannot be procured, _oil_ may be used withsufficient advantage, for this purpose, as it imbibes the fixed air veryslowly. Fixed air may be kept in vessels standing in water for a longtime, if they be separated by a partition of oil, about half an inchthick. Pyrmont water made in these circumstances, is little or nothinginferior to that which has stood in quicksilver. 

The _readiest_ method of preparing this water for use is to agitate itstrongly with a large surface exposed to the fixed air. By this meansmore than an equal bulk of air may be communicated to a large quantityof water in the space of a few minutes. But since agitation promotes thedissipation of fixed air from water, it cannot be made to imbibe sogreat a quantity in this method as in the former, where more time istaken. 

Easy directions for impregnating water with fixed air I have publishedin a small pamphlet, designed originally for the use of seamen in longvoyages, on the presumption that it might be of use for preventing orcuring the sea scurvy, equally with wort, which was recommended by Dr. Macbride for this purpose, on no other account than its property ofgenerating fixed air, by its fermentation in the stomach. 

Water thus impregnated with fixed air readily dissolves iron, as Mr. Lane has discovered; so that if a quantity of iron filings be put to it, it presently becomes a strong chalybeate, and of the mildest and mostagreeable kind. 

I have recommended the use of _chalk_ and oil of vitriol as thecheapest, and, upon the whole, the best materials for this purpose. Butsome persons prefer _pearl ashes_, _pounded marble_, or other calcareousor _alkaline substances_; and perhaps with reason. My own experience hasnot been sufficient to enable me to decide in this case. 

Whereas some persons had suspected that a quantity of the oil of vitriolwas rendered volatile by this process, I examined it, by all thechemical methods that are in use; but could not find that water thusimpregnated contained the least perceivable quantity of that acid. 

Mr. Hey, indeed, who assisted me in this examination, found thatdistilled water, impregnated with fixed air, did not mix so readily withsoap as the distilled water itself; but this was also the case when thefixed air had passed through a long glass tube filled with alkalinesalts, which, it may be supposed, would have imbibed any of the oil ofvitriol that might have been contained in that air[2]. 

Fixed air itself may be said to be of the nature of an acid, though of aweak and peculiar sort. ----Mr. Bergman of Upsal, who honoured me with aletter upon the subject, calls it the _aërial acid_, and, among otherexperiments to prove it to be an acid, he says that it changes the bluejuice of tournesole into red. This Mr. Hey found to be true, and hemoreover discovered that when water tinged blue with the juice oftournesole, and then red with fixed air, has been exposed to the openair, it recovers its blue colour again. 

The heat of boiling water will expel all the fixed air, if a phialcontaining the impregnated water be held in it; but it will oftenrequire above half an hour to do it completely. 

Dr. Percival, who is particularly attentive to every improvement in themedical art, and who has thought so well of this impregnation as toprescribe it in several cases, informs me that it seems to be muchstronger, and sparkles more, like the true Pyrmont water, after it hasbeen kept some time. This circumstance, however, shews that, in time, the fixed air is more easily disengaged from the water; and though, inthis state, it may affect the taste more sensibly, it cannot be of somuch use in the stomach and bowels, as when the air is more firmlyretained by the water. 

By the process described in my pamphlet, fixed air may be readilyincorporated with wine, beer, and almost any other liquor whatever; andwhen beer, wine, or cyder, is become flat or dead (which is theconsequence of the escape of the fixed air they contained) they may berevived by this means; but the delicate and agreeable flavour, oracidulous taste, communicated by fixed air, and which is very manifestin water, can hardly be perceived in wine, or any liquors which havemuch taste of their own. 

I should think that there can be no doubt, but that water thusimpregnated with fixed air must have all the medicinal virtues ofgenuine Pyrmont or Seltzer water; since these depend upon the fixed airthey contain. If the genuine Pyrmont water derives any advantage fromits being a natural chalybeate, this may also be obtained by providing acommon chalybeate water, and using it in these processes, instead ofcommon water. 

Having succeeded so well with this artificial Pyrmont water, I imaginedthat it might be possible to give _ice_ the same virtue, especially ascold is known to promote the absorption of fixed air by water; but inthis I found myself quite mistaken. I put several pieces of ice into aquantity of fixed air, confined by quicksilver, but no part of the airwas absorbed in two days and two nights; but upon bringing it into aplace where the ice melted, the air was absorbed as usual. 

I then took a quantity of strong artificial Pyrmont water, and puttingit into a thin glass phial, I set it in a pot that was filled with snowand salt. This mixture instantly freezing the water that was contiguousto the sides of the glass, the air was discharged plentifully, so thatI catched a considerable quantity, in a bladder tied to the mouth of thephial. 

I also took two quantities of the same Pyrmont water, and placed one ofthem where it might freeze, keeping the other in a cold place, but whereit would not freeze. This retained its acidulous taste, though the phialwhich contained it was not corked; whereas the other being brought intothe same place, where the ice melted very slowly, had at the same timethe taste of common water only. That quantity of water which had beenfrozen by the mixture of snow and salt, was almost as much like snow asice, such a quantity of air-bubbles were contained in it, by which itwas prodigiously increased in bulk. 

The pressure of the atmosphere assists very considerably in keepingfixed air confined in water; for in an exhausted receiver, Pyrmont waterwill absolutely boil, by the copious discharge of its air. This is alsothe reason why beer and ale froth so much _in vacuo_. I do not doubt, therefore, but that, by the help of a condensing engine, water might bemuch more highly impregnated with the virtues of the Pyrmont spring; andit would not be difficult to contrive a method of doing it. 

The manner in which I made several experiments to ascertain theabsorption of fixed air by different fluid substances, was to put theliquid into a dish, and holding it within the body of the fixed air atthe brewery, to set a glass vessel into it, with its mouth inverted. This glass being necessarily filled with the fixed air, the liquor wouldrise into it when they were both taken into the common air, if the fixedair was absorbed at all. 

Making use of _ether_ in this manner, there was a constant bubbling fromunder the glass, occasioned by this fluid easily rising in vapour, sothat I could not, in this method, determine whether it imbibed the airor not. I concluded however, that they did incorporate, from a verydisagreeable circumstance, which made me desist from making any moreexperiments of the kind. For all the beer, over which this experimentwas made, contracted a peculiar taste; the fixed air impregnated withthe ether being, I suppose, again absorbed by the beer. I have alsoobserved, that water which remained a long time within this air hassometimes acquired a very disagreeable taste. At one time it was liketar-water. How this was acquired, I was very desirous of making someexperiments to ascertain, but I was discouraged by the fear of injuringthe fermenting liquor. It could not come from the fixed air only. 

Insects and animals which breathe very little are stifled in fixed air, but are not soon quite killed in it. Butterflies and flies of otherkinds will generally become torpid, and seemingly dead, after being helda few minutes over the fermenting liquor; but they revive again afterbeing brought into the fresh air. But there are very great varietieswith respect to the time in which different kinds of flies will eitherbecome torpid in the fixed air, or die in it. A large strong frog wasmuch swelled, and seemed to be nearly dead, after being held about sixminutes over the fermenting liquor; but it recovered upon being broughtinto the common air. A snail treated in the same manner died presently. 

Fixed air is presently fatal to vegetable life. At least sprigs of mintgrowing in water, and placed over the fermenting liquor, will oftenbecome quite dead in one day, or even in a less space of time; nor dothey recover when they are afterwards brought into the common air. I amtold, however, that some other plants are much more hardy in thisrespect. 

A red rose, fresh gathered, lost its redness, and became of a purplecolour, after being held over the fermenting liquor about twenty-fourhours; but the tips of each leaf were much more affected than the restof it. Another red rose turned perfectly white in this situation; butvarious other flowers of different colours were very little affected. These experiments were not repeated, as I wish they might be done, inpure fixed air, extracted from chalk by means of oil of vitriol. 

For every purpose, in which it was necessary that the fixed air shouldbe as unmixed as possible, I generally made it by pouring oil of vitriolupon chalk and water, catching it in a bladder fastened to the neck ofthe phial in which they were contained, taking care to press out all thecommon air, and also the first, and sometimes the second, produce offixed air; and also, by agitation, making it as quickly as I possiblycould. At other times, I made it pass from the phial in which it wasgenerated through a glass tube, without the intervention of any bladder, which, as I found by experience, will not long make a sufficientseparation between several kinds of air and common air. 

I had once thought that the readiest method of procuring fixed air, andin sufficient purity, would be by the simple process of burning chalk, or pounded lime-stone in a gun-barrel, making it pass through the stemof a tobacco-pipe, or a glass tube carefully luted to the orifice of it. In this manner I found that air is produced in great plenty; but, uponexamining it, I found, to my very great surprise, that little more thanone half of it was fixed air, capable of being absorbed by water; andthat the rest was inflammable, sometimes very weakly, but sometimespretty highly so. 

Whence this inflammability proceeds, I am not able to determine, thelime or chalk not being supposed to contain any other than fixed air. Iconjecture, however, that it must proceed from the iron, and theseparation of it from the calx may be promoted by that small quantity ofoil of vitriol, which I am informed is contained in chalk, if not inlime-stone also. 

But it is an objection to this hypothesis, that the inflammable airproduced in this manner burns blue, and not at all like that which isproduced from iron, or any other metal, by means of an acid. It also hasnot the smell of that kind of inflammable air which is produced frommineral substances. Besides, oil of vitriol without water, will notdissolve iron; nor can inflammable air be got from it, unless the acidbe considerably diluted; and when I mixed brimstone with the chalk, neither the quality nor the quantity of the air was changed by it. Indeed no air, or permanently elastic vapour, can be got from brimstone, or any oil. 

Perhaps this inflammable principle may come from some remains of theanimals, from which it is thought that all calcareous matter proceeds. 

In the method in which I generally made the fixed air (and indeedalways, unless the contrary be particularly mentioned, viz. By dilutedoil of vitriol and chalk) I found by experiment that it was as pure asMr. Cavendish made it. For after it had patted through a large body ofwater in small bubbles, still 1/50 or 1/60 part only was not absorbed bywater. In order to try this as expeditiously as possible, I kept pouringthe air from one glass vessel into another, immersed in a quantity ofcold water, in which manner I found by experience, that almost anyquantity may be reduced as far as possible in a very short time. But themost expeditious method of making water imbibe any kind of air, is toconfine it in a jar; and agitate it strongly, in the manner described inmy pamphlet on the impregnation of water with fixed air, and representedfig. 10. 

At the same time that I was trying the purity of my fixed air, I had thecuriosity to endeavour to ascertain whether that part of it which is notmiscible in water, be equally diffused through the whole mass; and, forthis purpose, I divided a quantity of about a gallon into three parts, the first consisting of that which was uppermost, and the last of thatwhich was the lowest, contiguous to the water; but all these parts werereduced in about an equal proportion, by passing through the water, sothat the whole mass had been of an uniform composition. This I have alsofound to be the case with several kinds of air, which will, not properlyincorporate. 

A mouse will live very well, though a candle will not burn in theresiduum of the purest fixed air that I can make; and I once made a verylarge quantity for the sole purpose of this experiment. This, therefore, seems to be one instance of the generation of genuine common air, thoughvitiated in some degree. It is also another proof of the residuum offixed air being, in part at least, common air, that it becomes turbid, and is diminished by the mixture of nitrous air, as will be explainedhereafter. 

That fixed air only wants some addition to make it permanent, andimmiscible with water if not in all respects, common air, I have beenled to conclude, from several attempts which I once made to mix it withair in which a quantity of iron filings and brimstone, made into a pastewith water, had stood; for, in several mixtures of this kind, I imaginedthat not much more than half of the fixed air could be imbibed by water;but, not being able to repeat the experiment, I conclude that I eitherdeceived myself in it, or that I overlooked some circumstance on whichthe success of it depended. 

These experiments, however, whether they were fallacious or otherwise, induced me to try whether any alteration would be made in theconstitution of fixed air, by this mixture of iron filings andbrimstone. I therefore put a mixture of this kind into a quantity of aspure fixed air as I could make, and confined the whole in quicksilver, lest the water should absorb it before the effects of the mixture couldtake place. The consequence was, that the fixed air was diminished, andthe quicksilver rose in the vessel, till about the fifth part wasoccupied by it; and, as near as I could judge, the process went on, inall respects, as if the air in the inside had been common air. 

What is most remarkable, in the result of this experiment, is, that thefixed air, into which this mixture had been put, and which had been inpart diminished by it, was in part also rendered insoluble in water bythis means. I made this experiment four times, with the greatest care, and observed, that in two of them about one sixth, and in the other twoabout one fourteenth, of the original quantity, was such as could not beabsorbed by water, but continued permanently elastic. Lest I should havemade any mistake with respect to the purity of the fixed air, the lasttime that I made the experiment, I set part of the fixed air, which Imade use of, in a separate vessel, and found it to be exceedingly pure, so as to be almost wholly absorbed by water; whereas the other part, towhich I had put the mixture, was far from being so. 

In one of these cases, in which fixed air was made immiscible withwater, it appeared to be not very noxious to animals; but in anothercase, a mouse died in it pretty soon. This difference probably arosefrom my having inadvertently agitated the air in water rather more inone case than in the other. 

As the iron is reduced to a calx by this process, I once concluded, thatit is phlogiston that fixed air wants, to make it common air; and, forany thing I yet know this may be the case, though I am ignorant of themethod of combining them; and when I calcined a quantity of lead infixed air, in the manner which will be described hereafter, it did notseem to have been less soluble in water than it was before. 

FOOTNOTES:

[2] An account of Mr. Hey's experiments will be found in the Appendix tothese papers. 

SECTION II. 

_Of AIR in which a CANDLE, or BRIMSTONE, has burned out. _

It is well known that flame cannot subsist long without change of air, so that the common air is necessary to it, except in the case ofsubstances, into the composition of which nitre enters, for these willburn _in vacuo_, in fixed air, and even under water, as is evident insome rockets, which are made for this purpose. The quantity of air whicheven a small flame requires to keep it burning is prodigious. It isgenerally said, that an ordinary candle _consumes_, as it is called, about a gallon in a minute. Considering this amazing consumption of air, by fires of all kinds, volcanos, &c. It becomes a great object ofphilosophical inquiry, to ascertain what change is made in theconstitution of the air by flame, and to discover what provision thereis in nature for remedying the injury which the atmosphere receives bythis means. Some of the following experiments will, perhaps, be thoughtto throw light upon the subject. 

The diminution of the quantity of air in which a candle, or brimstone, has burned out, is various; But I imagine that, at a medium, it may beabout one fifteenth, or one sixteenth of the whole; which is one thirdas much as by animal or vegetable substances putrefying in it, by thecalcination of metals, or by any of the other causes of the completediminution of air, which will be mentioned hereafter. 

I have sometimes thought, that flame disposes the common air to depositthe fixed air it contains; for if any lime-water be exposed to it, itimmediately becomes turbid. This is the case, when wax candles, tallowcandles, chips of wood, spirit of wine, ether, and every other substancewhich I have yet tried, except brimstone, is burned in a close glassvessel, standing in lime-water. This precipitation of fixed air (if thisbe the case) may be owing to something emitted from the burning bodies, which has a stronger affinity with the other constituent parts of theatmosphere[3]. 

If brimstone be burned in the same circumstances, the lime-watercontinues transparent, but still there may have been the sameprecipitation of the fixed part of the air; but that, uniting with thelime and the vitriolic acid, it forms a selenetic salt, which is solublein water. Having evaporated a quantity of water thus impregnated, byburning brimstone a great number of times over it, a whitish powderremained, which had an acid taste; but repeating the experiment with aquicker evaporation, the powder had no acidity, but was very much likechalk. The burning of brimstone but once over a quantity of lime-water, will affect it in such a manner, that breathing into it will not make itturbid, which otherwise it always presently does. 

Dr. Hales supposed, that by burning brimstone repeatedly in the samequantity of air, the diminution would continue without end. But this Ihave frequently tried, and not found to be the case. Indeed, when theignition has been imperfect in the first instance, a second firing ofthe same substance will increase the effect of the first, &c. But thisprogress soon ceases. 

In many cases of the diminution of air, the effect is not immediatelyapparent, even when it stands in water; for sometimes the bulk of airwill not be much reduced, till it has passed several times through aquantity of water, which has thereby a better opportunity of absorbingthat part of the air, which had not been perfectly detatched from therest. I have sometimes found a very great reduction of a mass of air, inconsequence of passing but once through cold water. If the air has stoodin quicksilver, the diminution is generally inconsiderable, till it hasundergone this operation, there not being any substance exposed to theair that could absorb any part of it. 

I could not find any considerable alteration in the specific gravity ofthe air, in which candles, or brimstone, had burned out. I am satisfied, however, that it is not heavier than common air, which must have beenmanifest, if so great a diminution of the quantity had been owing, asDr. Hales and others supposed, to the elasticity of the whole mass beingimpaired. After making several trials for this purpose, I concluded thatair, thus diminished in bulk, is rather lighter than common air, whichfavours the supposition of the fixed, or heavier part of the common air, having been precipitated. 

An animal will live nearly, if not quite as long, in air in whichcandles have burned out, as in common air. This fact surprized me verygreatly, having imagined that what is called the _consumption_ of air byflame, or respiration, to have been of the same nature, and in the samedegree; but I have since found, that this fact has been observed by manypersons, and even so early as by Mr. Boyle. I have also observed, thatair, in which brimstone has burned, is not in the least injurious toanimals, after the fumes, which at first make it very cloudy, haveintirely subsided. 

I must, in this place, admonish my reader not to confound the simple_burning of brimstone_, or of matches (_i. E. _ bits of wood dipped init) and the burning of brimstone with a burning mirror, or any _foreignheat_. The effect of the former is nothing more than that of any other_flame_, or _ignited vapour_, which will not burn, unless the air withwhich it is surrounded be in a very pure state, and which is thereforeextinguished when the air begins to be much vitiated. Lighted brimstone, therefore reduces the air to the same state as lighted wood. But thefocus of a burning mirror thrown for a sufficient time either uponbrimstone, or wood, after it has ceased to burn of its own accord, andhas become _charcoal_, will have a much greater effect: of the samekind, diminishing the air to its utmost extent, and making it thoroughlynoxious. In fact, as will be seen hereafter, more phlogiston is expelledfrom these substances in the latter case than in the former. I never, indeed, actually carried this experiment so far with brimstone; but fromthe diminution of air that I did produce by this means, I concludedthat, by continuing the process some time longer, it would have beeneffected. 

Having read, in the Memoirs of the Philosophical Society at Turin, vol. I. P. 41. That air in which candles had burned out was perfectlyrestored, so that other candles would burn in it again as well as ever, after having been exposed to a considerable degree of _cold_, andlikewise after having been compressed in bladders, (for the cold hadbeen supposed to have produced this effect by nothing but_condensation_) I repeated those experiments, and did, indeed, find, that when I compressed the air in _bladders_, as the Count de Saluce, who made the observation, had done, the experiment succeeded: but havinghad sufficient reason to distrust bladders, I compressed the air in aglass vessel standing in water; and then I found, that this process isaltogether ineffectual for the purpose. I kept the air compressed muchmore, and much longer, than the Count had done, but without producingany alteration in it. I also find, that a greater degree of cold thanthat which he applied, and of longer continuance, did by no meansrestore this kind of air: for when I had exposed the phials whichcontained it a whole night, in which the frost was very intense; andalso when I kept it surrounded with a mixture of snow and salt, I foundit, in all respects, the same as before. 

It is also advanced, in the same Memoir, p. 41. That _heat_ only, as thereverse of _cold_, renders air unfit for candles burning in it. But Irepeated the experiment of the Count for that purpose, without findingany such effect from it. I also remember that, many years ago, I filledan exhausted receiver with air, which had passed through a glass tubemade red-hot, and found that a candle would burn in it perfectly well. Also, rarefaction by the air-pump does not injure air in the leastdegree. 

Though this experiment failed, I have been so happy, as by accident tohave hit upon a method of restoring air, which has been injured by theburning of candles, and to have discovered at least one of therestoratives which nature employs for this purpose. It is _vegetation_. This restoration of vitiated air, I conjecture, is effected by plantsimbibing the phlogistic matter with which it is overloaded by theburning of inflammable bodies. But whether there be any foundation forthis conjecture or not, the fact is, I think, indisputable. I shallintroduce the account of my experiments on this subject, by recitingsome of the observations which I made on the growing of plants inconfined air, which led to this discovery. 

One might have imagined that, since common air is necessary tovegetable, as well as to animal life, both plants and animals hadaffected it in the same manner; and I own I had that expectation, when Ifirst put a sprig of mint into a glass jar, standing inverted in avessel of water: but when it had continued growing there for somemonths, I found that the air would neither extinguish a candle, nor wasit at all inconvenient to a mouse, which I put into it. 

The plant was not affected any otherwise than was the necessaryconsequence of its confined situation; for plants growing in severalother kinds of air, were all affected in the very same manner. Everysuccession of leaves was more diminished in size than the preceding, till, at length, they came to be no bigger than the heads of prettysmall pins. The root decayed, and the stalk also, beginning from theroot; and yet the plant continued to grow upwards, drawing itsnourishment through a black and rotten stem. In the third or fourth setof leaves, long and white hairy filaments grew from the insertion ofeach leaf and sometimes from the body of the stem, shooting out as faras the vessel in which it grew would permit, which, in my experiments, was about two inches. In this manner a sprig of mint lived, the oldplant decaying, and new ones shooting up in its place, but less and lesscontinually, all the summer season. 

In repeating this experiment, care must be taken to draw away all thedead leaves from about the plant, lest they should putrefy, and affectthe air. I have found that a fresh cabbage leaf, put under a glassvessel filled with common air, for the space of one night only, has soaffected the air, that a candle would not burn in it the next morning, and yet the leaf had not acquired any smell of putrefaction. 

Finding that candles would burn very well in air in which plants hadgrown a long time, and having had some reason to think, that there wassomething attending vegetation, which restored air that had been injuredby respiration, I thought it was possible that the same process mightalso restore the air that had been injured by the burning of candles. 

Accordingly, on the 17th of August 1771, I put a sprig of mint into aquantity of air, in which a wax candle had burned out, and found that, on the 27th of the same month, another candle burned perfectly well init. This experiment I repeated, without the least variation in theevent, not less than eight or ten times in the remainder of the summer. 

Several times I divided the quantity of air in which the candle hadburned out, into two parts, and putting the plant into one of them, leftthe other in the same exposure, contained, also, in a glass vesselimmersed in water, but without any plant; and never failed to find, thata candle would burn in the former, but not in the latter. 

I generally found that five or six days were sufficient to restore thisair, when the plant was in its vigour; whereas I have kept this kind ofair in glass vessels, immersed in water many months, without being ableto perceive that the least alteration had been made in it. I have alsotried a great variety of experiments upon it, as by condensing, rarefying, exposing to the light and heat, &c. And throwing into it theeffluvia of many different substances, but without any effect. 

Experiments made in the year 1772, abundantly confirmed my conclusionconcerning the restoration of air, in which candles had burned out byplants growing in it. The first of these experiments was made in themonth of May; and they were frequently repeated in that and the twofollowing months, without a single failure. 

For this purpose I used the flames of different substances, though Igenerally used wax or tallow candles. On the 24th of June the experimentsucceeded perfectly well with air in which spirit of wine had burnedout, and on the 27th of the same month it succeeded equally well withair in which brimstone matches had burned out, an effect of which I haddespaired the preceding year. 

This restoration of air, I found, depended upon the _vegetating state_of the plant; for though I kept a great number of the fresh leaves ofmint in a small quantity of air in which candles had burned out, andchanged them frequently, for a long space of time, I could perceive nomelioration in the state of the air. 

This remarkable effect does not depend upon any thing peculiar to_mint_, which was the plant that I always made use of till July 1772;for on the 16th of that month, I found a quantity of this kind of air tobe perfectly restored by sprigs of _balm_, which had grown in it fromthe 7th of the same month. 

That this restoration of air was not owing to any _aromatic effluvia_ ofthese two plants, not only appeared by the _essential oil of mint_having no sensible effect of this kind; but from the equally completerestoration of this vitiated air by the plant called _groundsel_, whichis usually ranked among the weeds, and has an offensive smell. This wasthe result of an experiment made the 16th of July, when the plant hadbeen growing in the burned air from the 8th of the same month. Besides, the plant which I have found to be the most effectual of any that I havetried for this purpose is _spinach_, which is of quick growth, but willseldom thrive long in water. One jar of burned air was perfectlyrestored by this plant in four days, and another in two days. This lastwas observed on the 22d of July. 

In general, this effect may be presumed to have taken place in much lesstime than I have mentioned; because I never chose to make a trial ofthe air, till I was pretty sure, from preceding observations, that theevent which I had expected must have taken place, if it would succeed atall; lest, returning back that part of the air on which I made thetrial, and which would thereby necessarily receive a small mixture ofcommon air, the experiment might not be judged to be quite fair; thoughI myself might be sufficiently satisfied with respect to the allowancethat was to be made for that small imperfection. 

FOOTNOTES:

[3] The supposition, mentioned in this and other passages of the firstpart of this publication, viz. That the diminution of common air, bythis and other processes is, in part at least, owing to theprecipitation of the fixed air from it, the reader will find confirmedby the experiments and observations in the second part. 

SECTION III. 

_Of INFLAMMABLE AIR. _

I have generally made inflammable air in the manner described by Mr. Cavendish, in the Philosophical Transactions, from iron, zinc, or tin;but chiefly from the two former metals, on account of the process beingthe least troublesome: but when I extracted it from vegetable or animalsubstances, or from coals, I put them into a gun-barrel, to the orificeof which I luted a glass tube, or the stem of a tobacco-pipe, and to theend of this I tied a flaccid bladder in order to catch the generatedair; or I received the air in a vessel of quicksilver, in the mannerrepresented Fig. 7. 

There is not, I believe, any vegetable or animal substance whatever, norany mineral substance, that is inflammable, but what will yield greatplenty of inflammable air, when they are treated in this manner, andurged with a strong heat; but, in order to get the most air, the heatmust be applied as suddenly, and as vehemently, as possible. For, notwithstanding the same care be taken in luting, and in every otherrespect, six or even ten times more air may be got by a sudden heat thanby a slow one, though the heat that is last applied be as intense asthat which was applied suddenly. A bit of dry oak, weighing about twelvegrains, will generally yield about a sheep's bladder full of inflammableair with a brisk heat, when it will only give about two or three ouncemeasures, if the same heat be applied to it very gradually. To what thisdifference is owing, I cannot tell. Perhaps the phlogiston beingextricated more slowly may not be intirely expelled, but form anotherkind of union with its base; so that charcoal made with a heat slowlyapplied shall contain more phlogiston than that which is made with asudden heat. It may be worth while to examine the properties of thecharcoal with this view. 

Inflammable air, when it is made by a quick process, has a very strongand offensive smell, from whatever substance it be generated; but thissmell is of three different kinds, according as the air is extractedfrom mineral, vegetable, or animal substances. The last is exceedinglyfetid; and it makes no difference, whether it be extracted from a bone, or even an old and dry tooth, from soft muscular flesh; or any otherpart of the animal. The burning of any substance occasions the samesmell: for the gross fume which arises from them, before they flame, isthe inflammable air they contain, which is expelled by heat, and thenreadily ignited. The smell of inflammable air is the very same, as faras I am able to perceive, from whatever substance of the same kingdom itbe extracted. Thus it makes no difference whether it be got from iron, zinc, or tin, from any kind of wood, or, as was observed before, fromany part of an animal. 

If a quantity of inflammable air be contained in a glass vessel standingin water, and have been generated very fast, it will smell even throughthe water, and this water will also soon become covered with a thinfilm, assuming all the different colours. If the inflammable air havebeen generated from iron, this matter will appear to be a red okre, orthe earth of iron, as I have found by collecting a considerable quantityof it; and if it have been generated from zinc, it is a whitishsubstance, which I suppose to be the calx of the metal. It likewisesettles to the bottom of the vessel, and when the water is stirred, ithas very much the appearance of wool. When water is once impregnated inthis manner, it will continue to yield this scum for a considerable timeafter the air is removed from it. This I have often observed withrespect to iron. 

Inflammable air, made by a violent effervescence, I have observed to bemuch more inflammable than that which is made by a weak effervescence, whether the water or the oil of vitriol prevailed in the mixture. Alsothe offensive smell was much stronger in the former case than in thelatter. The greater degree of inflammability appeared by the greaternumber of successive explosions, when a candle was presented to the neckof a phial filled with it. [4] It is possible, however, that thisdiminution of inflammability may, in some measure, arise from the aircontinuing so much longer in the bladder when it is made very slowly;though I think the difference is too great for this cause to haveproduced the whole of it. It may, perhaps, deserve to be tried by adifferent process, without a bladder. 

Inflammable air is not thought to be miscible with water, and when keptmany months, seems, in general, to be as inflammable as ever. Indeed, when it is extracted from vegetable or animal substances, a part of itwill be imbibed by the water in which it stands; but it may be presumed, that in this case, there was a mixture of fixed air extracted from thesubstance along with it. I have indisputable evidence, however, thatinflammable air, standing long in water, has actually lost all itsinflammability, and even come to extinguish flame much more than thatair in which candles have burned out. After this change it appears to begreatly diminished in quantity, and it still continues to kill animalsthe moment they are put into it. 

This very remarkable fact first occurred to my observation on thetwenty-fifth of May 1771, when I was examining a quantity of inflammableair, which had been made from zinc, near three years before. Upon this, I immediately set by a common quart-bottle filled with inflammable airfrom iron, and another equal quantity from zinc; and examining them inthe beginning of December following, that from the iron was reduced nearone half in quantity, if I be not greatly mistaken; for I found thebottle half full of water, and I am pretty clear that it was full of airwhen it was set by. That which had been produced from zinc was notaltered, and filled the bottle as at first. 

Another instance of this kind occurred to my observation on the 19th ofJune 1772, when a quantity of air, half of which had been inflammableair from zinc, and half air in which mice had died, and which had beenput together the 30th of July 1771, appeared not to be in the leastinflammable, but extinguished flame, as much as any kind of air that Ihad ever tried. I think that, in all, I have had four instances ofinflammable air losing its inflammability, while it stood in water. 

Though air tainted with putrefaction extinguishes flame, I have notfound that animals or vegetables putrefying in inflammable air render itless inflammable. But one quantity of inflammable air, which I had setby in May 1771, along with the others above mentioned, had had someputrid flesh in it; and this air had lost its inflammability, when itwas examined at the same time with the other in the December following. The bottle in which this air had been kept, smelled exactly like verystrong Harrogate water. I do not think that any person could havedistinguished them. 

I have made plants grow for several months in inflammable air made fromzinc, and also from oak; but, though the plants grew pretty well, theair still continued inflammable. The former, indeed, was not so highlyinflammable as when it was fresh made, but the latter was quite as muchso; and the diminution of inflammability in the former case, I attributeto some other cause than the growth of the plant. 

No kind of air, on which I have yet made the experiment, will conductelectricity; but the colour of an electric spark is remarkably differentin some different kinds of air, which seems to shew that they are notequally good non-conductors. In fixed air, the electric spark isexceedingly white; but in inflammable air it is of a purple, or redcolour. Now, since the most vigorous sparks are always the whitest, and, in other cases, when the spark is red, there is reason to think that theelectric matter passes with difficulty, and with less rapidity: it ispossible that the inflammable air may contain particles which conductelectricity, though very imperfectly; and that the whiteness of thespark in the fixed air, may be owing to its meeting with no conductingparticles at all. When an explosion was made in a quantity ofinflammable air, it was a little white in the center, but the edges ofit were still tinged with a beautiful purple. The degree of whiteness inthis case was probably owing to the electric matter rushing with moreviolence in an explosion than in a common spark. 

Inflammable air kills animals as suddenly as fixed air, and, as far ascan be perceived, in the same manner, throwing them into convulsions, and thereby occasioning present death. I had imagined that, by animalsdying in a quantity of inflammable air, it would in time become lessnoxious; but this did not appear to be the case; for I killed greatnumber of mice in a small quantity of this air; which I kept severalmonths for this purpose, without its being at all sensibly mended; thelast, as well as the first mouse, dying the moment it was put into it. 

I once imagined that, since fixed and inflammable air are the reverse ofone another, in several remarkable properties, a mixture of them wouldmake common air; and while I made the mixtures in bladders, I imaginedthat I had succeeded in my attempt; but I have since found that thinbladders do not sufficiently prevent the air that is contained in themfrom mixing with the external air. Also corks will not sufficientlyconfine different kinds of air, unless the phials in which they areconfined be set with their mouths downwards, and a little water lie inthe necks of them, which, indeed, is equivalent to the air standing invessels immersed in water. In this manner, however, I have keptdifferent kinds of air for several years. 

Whatever methods I took to promote the mixture of fixed and inflammableair, they were all ineffectual. I think it my duty, however, to recitethe issue of an experiment or two of this kind, in which equal mixturesof these two kinds of air had stood near three years, as they seem toshew that they had in part affected one another, in that long space oftime. These mixtures I examined April 27, 1771. One of them had stood inquicksilver, and the other in a corked phial, with a little water in it. On opening the latter in water, the water instantly rushed in, andfilled almost half of the phial, and very little more was absorbedafterwards. In this case the water in the phial had probably absorbed aconsiderable part of the fixed air, so that the inflammable air wasexceedingly rarefied; and yet the whole quantity that must have beenrendered non-elastic was ten times more than the bulk of the water, andit has not been found that water can contain much more than its ownbulk of fixed air. But in other cases I have found the diminution of aquantity of air, and especially of fixed air, to be much greater than Icould well account for by any kind of absorption. 

The phial which had stood immersed in quicksilver had lost very littleof its original quantity of air; and being now opened in water, and leftthere, along with another phial, which was just then filled, as this hadbeen three years before, viz. With air half inflammable and half fixed, I observed that the quantity of both was diminished, by the absorptionof the water, in the same proportion. 

Upon applying a candle to the mouths of the phials which had been keptthree years, that which had stood in quicksilver went off at oneexplosion, exactly as it would have done if there had been a mixture ofcommon air with the inflammable. As a good deal depends upon theapertures of the vessels in which the inflammable air is mixed, I mixedthe two kinds of air in equal proportions in the same phial, and afterletting the phial stand some days in water, that the fixed air might beabsorbed, I applied a candle to it, but it made ten or twelve explosions(stopping the phial after each of them) before the inflammable matterwas exhausted. 

The air which had been confined in the corked phial exploded in the verysame manner as an equal and fresh mixture of the two kinds of air in thesame phial, the experiment being made as soon as the fixed air wasabsorbed, as before; so that in this case, the two kinds of air did notseem to have affected one another at all. 

Considering inflammable air as air united to, or loaded with phlogiston, I exposed to it several substances, which are said to have a nearaffinity with phlogiston, as oil of vitriol, and spirit of nitre (theformer for above a month), but without making any sensible alteration init. 

I observed, however, that inflammable air, mixed with the fumes ofsmoking spirit of nitre, goes off at one explosion, exactly like amixture of half common and half inflammable air. This I tried severaltimes, by throwing the inflammable air into a phial full of spirit ofnitre, with its mouth immersed in a bason containing some of the samespirit, and then applying the flame of a candle to the mouth of thephial, the moment that it was uncovered, after it had been taken out ofthe bason. 

This remarkable effect I hastily concluded to have arisen from theinflammable air having been in part deprived of its inflammability, bymeans of the stronger affinity, which the spirit of nitre had withphlogiston, and therefore I imagined that by letting them stand longerin contact, and especially by agitating them strongly together, I shoulddeprive the air of all its inflammability; but neither of theseoperations succeeded, for still the air was only exploded at once, asbefore. 

And lastly, when I passed a quantity of inflammable air, which had beenmixed with the fumes of spirit of nitre, through a body of water, andreceived it in another vessel, it appeared not to have undergone anychange at all, for it went off in several successive explosions, likethe purest inflammable air. The effect above-mentioned must, therefore, have been owing to the fumes of the spirit of nitre supplying the placeof common air for the purpose of ignition, which is analogous to otherexperiments with nitre. 

Having had the curiosity, on the 25th of July 1772, to expose a greatvariety of different kinds of air to water out of which the air itcontained had been boiled, without any particular view; the result was, in several respects, altogether unexpected, and led to a variety of newobservations on the properties and affinities of several kinds of airwith respect to water. Among the rest three fourths of that which wasinflammable was absorbed by the water in about two days, and theremainder was inflammable, but weakly so. 

Upon this, I began to agitate a quantity of strong inflammable air in aglass jar, standing in a pretty large trough of water, the surface ofwhich was exposed to the common air, and I found that when I hadcontinued the operation about ten minutes, near one fourth of thequantity of air had disappeared; and finding that the remainder made aneffervescence with nitrous air, I concluded that it must have become fitfor respiration, whereas this kind of air is, at the first, as noxiousas any other kind whatever. To ascertain this, I put a mouse into avessel containing 2-1/2 ounce measures of it, and observed that it livedin it twenty minutes, which is as long as a mouse will generally live inthe same quantity of common air. This mouse was even taken out alive, and recovered very well. Still also the air in which it had breathed solong was inflammable, though very weakly so. I have even found it to beso when a mouse has actually died in it. Inflammable air thus diminishedby agitation in water, makes but one explosion on the approach of acandle, exactly like a mixture of inflammable air with common air. 

From this experiment I concluded that, by continuing the same process, Ishould deprive inflammable air of all its inflammability, and this Ifound to be the case; for, after a longer agitation, it admitted acandle to burn in it, like common air, only more faintly; and indeed bythe test of nitrous air it did not appear to be near so good as commonair. Continuing the same process still farther, the air which had beenmost strongly inflammable a little before, came to extinguish a candle, exactly like air in which a candle had burned out, nor could they bedistinguished by the test of nitrous air. 

I found, by repeated trials, that it was difficult to catch the time inwhich inflammable air obtained from metals, in coming to extinguishflame, was in the state of common air, so that the transition from theone to the other must be very short. Indeed I think that in many, perhaps in most cases, there may be no proper medium at all, thephlogiston passing at once from that mode of union with its base whichconstitutes inflammable air, to that which constitutes an air thatextinguishes flame, being so much overloaded as to admit of no more. Ireadily, however, found this middle state in a quantity of inflammableair extracted from oak, which air I had kept a year, and in which aplant had grown, though very poorly, for some part of the time. Aquantity of this air, after being agitated in water till it wasdiminished about one half, admitted a candle to burn in it exceedinglywell, and was even hardly to be distinguished from common air by thetest of nitrous air. 

I took some pains to ascertain the quantity of diminution, in fresh madeand very highly-inflammable air from iron, at which it ceased to beinflammable, and, upon the whole, I concluded that it was so when it wasdiminished a little more than one half; for a quantity which wasdiminished exactly one half had something inflammable in it, but in theslightest degree imaginable. It is not improbable, however, but theremay be great differences in the result of this experiment. 

Finding that water would imbibe inflammable air, I endeavoured toimpregnate water with it, by the same process by which I had made waterimbibe fixed air; but though I found that distilled water would imbibeabout one fourteenth of its bulk of inflammable air, I could notperceive that the taste of it was sensibly altered. 

FOOTNOTES:

[4] To try this, after every explosion, which immediately follows thepresenting of the flame, the mouth of the phial should be closed (Igenerally do it with a finger of the hand in which I hold the phial) forotherwise the inflammable air will continue burning, though invisibly inthe day time, till the whole be consumed. 

SECTION IV. 

_Of AIR infected with ANIMAL RESPIRATION, or PUTREFACTION. _

That candles will burn only a certain time, in a given quantity of airis a fact not better known, than it is that animals can live only acertain time in it; but the cause of the death of the animal is notbetter known than that of the extinction of flame in the samecircumstances; and when once any quantity of air has been renderednoxious by animals breathing in it as long as they could, I do not knowthat any methods have been discovered of rendering it fit for breathingagain. It is evident, however, that there must be some provision innature for this purpose, as well as for that of rendering the air fitfor sustaining flame; for without it the whole mass of the atmospherewould, in time, become unfit for the purpose of animal life; and yetthere is no reason to think that it is, at present, at all less fit forrespiration than it has ever been. I flatter myself, however, that Ihave hit upon two of the methods employed by nature for this greatpurpose. How many others there may be, I cannot tell. 

When animals die upon being put into air in which other animals havedied, after breathing in it as long as they could, it is plain that thecause of their death is not the want of any _pabulum vitæ, _ which hasbeen supposed to be contained in the air, but on account of the airbeing impregnated with something stimulating to their lungs; for theyalmost always die in convulsions, and are sometimes affected sosuddenly, that they are irrecoverable after a single inspiration, thoughthey be withdrawn immediately, and every method has been taken to bringthem to life again. They are affected in the same manner, when they arekilled in any other kind of noxious air that I have tried, viz. Fixedair, inflammable air, air filled with the fumes of brimstone, infectedwith putrid matter, in which a mixture of iron filings and brimstone hasstood, or in which charcoal has been burned, or metals calcined, or innitrous air, &c. 

As it is known that _convulsions_ weaken, and exhaust the vital powers, much more than the most vigorous _voluntary_ action of the muscles, perhaps these universal convulsions may exhaust the whole of what we maycall the _vis vitæ_ at once, at least that the lungs may be renderedabsolutely incapable of action, till the animal be suffocated, or beirrecoverable for want of respiration. 

If a mouse (which is an animal that I have commonly made use of for thepurpose of these experiments) can stand the first shock of thisstimulus, or has been habituated to it by degrees, it will live aconsiderable time in air in which other mice will die instantaneously. Ihave frequently found that when a number of mice have been confined in agiven quantity of air, less than half the time that they have actuallylived in it, a fresh mouse being introduced to them has been instantlythrown into convulsions, and died. It is evident, therefore, that if theexperiment of the Black Hole were to be repeated, a man would stand thebetter chance of surviving it, who should enter at the first, than atthe last hour. 

I have also observed, that young mice will always live much longer thanold ones, or than those which are full grown, when they are confined inthe same quantity of air. I have sometimes known a young mouse to livesix hours in the same circumstances in which an old mouse has not livedone. On these accounts, experiments with mice, and, for the same reason, no doubt, with other animals also, have a considerable degree ofuncertainty attending them; and therefore, it is necessary to repeatthem frequently, before the result can be absolutely depended upon. Butevery person of feeling will rejoice with me in the discovery of_nitrous air_, to be mentioned hereafter, which supersedes manyexperiments with the respiration of animals, being a much more accuratetest of the purity of air. 

The discovery of the provision in nature for restoring air, which hasbeen injured by the respiration of animals, having long appeared to meto be one of the most important problems in natural philosophy, I havetried a great variety of schemes in order to effect it. In these myguide has generally been to consider the influences to which theatmosphere is, in fact, exposed; and, as some of my unsuccessful trialsmay be of use to those who are disposed to take pains in the fartherinvestigation of this subject, I shall mention the principal of them. 

The noxious effluvium with which air is loaded by animal respiration, isnot absorbed by standing, without agitation; in fresh or salt water. Ihave kept it many months in fresh water, when, instead of beingmeliorated, it has seemed to become even more deadly, so as to requiremore time to restore it, by the methods which will be explainedhereafter, than air which has been lately made noxious. I have evenspent several hours in pouring this air from one glass vessel intoanother, in water, sometimes as cold, and sometimes as warm, as my handscould bear it, and have sometimes also wiped the vessels many times, during the course of the experiment, in order to take off that part ofthe noxious matter, which might adhere to the glass vessels, and whichevidently gave them an offensive smell; but all these methods weregenerally without any sensible effect. The _motion_, also, which the airreceived in these circumstances, it is very evident, was of no use forthis purpose. I had not then thought of the simple, but most effectualmethod of agitating air in water, by putting it into a tall jar andshaking it with my hand. 

This kind of air is not restored by being exposed to the _light_, or byany other influence to which it is exposed, when confined in a thinphial, in the open air, for some months. 

Among other experiments, I tried a great variety of different_effluvia_, which are continually exhaling into the air, especially ofthose substances which are known to resist putrefaction; but I could notby these means effect any melioration of the noxious quality of thiskind of air. 

Having read, in the memoirs of the Imperial Society, of a plague notaffecting a particular village, in which there was a large sulphur-work, I immediately fumigated a quantity of this kind of air; or (which willhereafter appear to be the very same thing) air tainted withputrefaction, with the fumes of burning brimstone, but without anyeffect. 

I once imagined, that the _nitrous acid_ in the air might be the generalrestorative which I was in quest of; and the conjecture was favoured, byfinding that candles would burn in air extracted from saltpetre. Itherefore spent a good deal of time in attempting, by a burning glass, and other means, to impregnate this noxious air, with some effluvium ofsaltpetre, and, with the same view, introduced into it the fumes of thesmoaking spirit of nitre; but both these methods were altogetherineffectual. 

In order to try the effect of _heat_, I put a quantity of air, in whichmice had died, into a bladder, tied to the end of the stem of atobacco-pipe, at the other end of which was another bladder, out ofwhich the air was carefully pressed. I then put the middle part of thestem into a chafing-dish of hot coals, strongly urged with a pair ofbellows; and, pressing the bladders alternately, I made the air passseveral times through the heated part of the pipe. I have also madethis kind of air very hot, standing in water before the fire. Butneither of these methods were of any use. 

_Rarefaction_ and _condensation_ by instruments were also tried, but invain. 

Thinking it possible that the _earth_ might imbibe the noxious qualityof the air, and thence supply the roots of plants with such putrescentmatter as is known to be nutritive to them, I kept a quantity of air, inwhich mice had died, in a phial, one half of which was filled with finegarden-mould; but, though it stood two months in these circumstances, itwas not the better for it. 

I once imagined that, since several kinds of air cannot be longseparated from common air, by being confined in bladders, in bottleswell corked; or even closed with ground stopples, the affinity betweenthis noxious air and the common air might be so great, that they wouldmix through a body of water interposed between them; the watercontinually receiving from the one, and giving to the other, especiallyas water receives some kind of impregnation from, I believe, every kindof air to which it is contiguous; but I have seen no reason toconclude, that a mixture of any kind of air with the common air can beproduced in this manner. 

I have kept air in which mice have died, air in which candles haveburned out, and inflammable air, separated from the common air, by theslightest partition of water that I could well make, so that it mightnot evaporate in a day or two, if I should happen not to attend to them;but I found no change in them after a month or six weeks. Theinflammable air was still inflammable, mice died instantly in the air inwhich other mice had died before, and candles would not burn where theyhad burned out before. 

Since air tainted with animal or vegetable putrefaction is the samething with air rendered noxious by animal respiration, I shall nowrecite the observations which I have made upon this kind of air, beforeI treat of the method of restoring them. 

That these two kinds of air are, in fact, the same thing, I concludefrom their having several remarkable common properties, and from theirdiffering in nothing that I have been able to observe. They equallyextinguish flame, they are equally noxious to animals, they areequally, and in the same way, offensive to the smell, and they arerestored by the same means. 

Since air which has passed through the lungs is the same thing with airtainted with animal putrefaction, it is probable that one use of thelungs is to carry off a _putrid effluvium_, without which, perhaps, aliving body might putrefy as soon as a dead one. 

When a mouse putrefies in any given quantity of air, the bulk of it isgenerally increased for a few days; but in a few days more it begins toshrink up, and in about eight or ten days, if the weather be prettywarm, it will be found to be diminished 1/6, or 1/5 of its bulk. If itdo not appear to be diminished after this time, it only requires to bepassed through water, and the diminution will not fail to be sensible. Ihave sometimes known almost the whole diminution to take place, upononce or twice passing through the water. The same is the case with air, in which animals have breathed as long as they could. Also, air in whichcandles have burned out may almost always be farther reduced by thismeans. 

All these processes, as I observed before, seem to dispose the compoundmass of air to part with some constituent part belonging to it (whichappears to be the _fixed air_ that enters into its constitution) andthis being miscible with water, must be brought into contact with it, inorder to mix with it to the most advantage, especially when its unionwith the other constituent principles of the air is but partiallybroken. 

I have put mice into vessels which had their mouths immersed inquicksilver, and observed that the air was not much contracted afterthey were dead or cold; but upon withdrawing the mice, and admittinglime water to the air, it immediately became turbid, and was contractedin its dimensions as usual. 

I tried the same thing with air tainted with putrefaction, putting adead mouse to a quantity of common air, in a vessel which had its mouthimmersed in quicksilver, and after a week I took the mouse out, drawingit through the quicksilver, and observed that, for some time, there wasan apparent increase of the air perhaps about 1/20. After this, it stoodtwo days in the quicksilver, without any sensible alteration; and thenadmitting water to it, it began to be absorbed, and continued so, tillthe original quantity was diminished about 1/6. If, instead of commonwater, I had made use of lime-water in this experiment, I make no doubtbut it would have become turbid. 

If a quantity of lime-water in a phial be put under a glass vesselstanding in water, it will not become turbid, and provided the access ofthe common air be prevented, it will continue lime-water, I do not knowhow long; but if a mouse be left to putrefy in the vessel, the waterwill deposit all its lime in a few days. This is owing to the fixed airdeposited by the common air, and perhaps also from more fixed airdischarged from the putrefying substances in some part of the process ofputrefaction. 

The air that is discharged from putrefying substances seems, in somecases, to be chiefly fixed air, with the addition of some othereffluvium, which has the power of diminishing common air. Theresemblance between the true putrid effluvium and fixed air in thefollowing experiment, which is as decisive as I can possibly contriveit, appeared to be very great; indeed much greater than I had expected. I put a dead mouse into a tall glass vessel, and having filled theremainder with quicksilver, and set it, inverted, in a pot ofquicksilver, I let it stand about two months, in which time the putrideffluvium issuing from the mouse had filled the whole vessel, and partof the dissolved blood, which lodged upon the surface of thequicksilver, began to be thrown out. I then filled another glass vessel, of the same size and shape, with as pure fixed air as I could make, andexposed them both, at the same time, to a quantity of lime-water. Inboth cases the water grew turbid alike, it rose equally fast in both thevessels, and likewise equally high; so that about the same quantityremained unabsorbed by the water. One of these kinds of air, however, was exceedingly sweet and pleasant, and the other insufferablyoffensive; one of them also would have made an addition to any quantityof common air, with which it had been mixed, and the other would havediminished it. This, at least, would have been the consequence, if themouse itself had putrefied in any quantity of common air. 

It seems to depend, in some measure, upon the _time_, and othercircumstances, in the dissolution of animal or vegetable substances, whether they yield the proper putrid effluvium, or fixed, or inflammableair; but the experiments which I have made upon this subject, have notbeen numerous enough to enable me to decide with certainty concerningthose circumstances. 

Putrid cabbage, green or boiled, infects the air in the very same manneras putrid animal substances. Air thus tainted is equally contracted inits dimensions, it equally extinguishes flame, and is equally noxious toanimals; but they affect the air very differently, if the heat that isapplied to them be considerable. 

If beef or mutton, raw or boiled, be placed so near to the fire, thatthe heat to which it is exposed shall equal, or rather exceed, that ofthe blood, a considerable quantity of air will be generated in a day ortwo, about 1/7th of which I have generally found to be absorbed bywater, while all the rest was inflammable; but air generated fromvegetables, in the same circumstances, will be almost all fixed air, andno part of it inflammable. This I have repeated again and again, thewhole process being in quicksilver; so that neither common air norwater, had any access to the substance on which the experiment was made;and the generation of air, or effluvium of any kind, except what mightbe absorbed by quicksilver, or resorbed by the substance itself, mightbe distinctly noted. 

A vegetable substance, after standing a day or two in thesecircumstances, will yield nearly all the air that can be extracted fromit, in that degree of heat; whereas an animal substance will continueto give more air, or effluvium, of some kind or other, with very littlealteration, for many weeks. It is remarkable, however, that though apiece of beef or mutton, plunged in quicksilver, and kept in this degreeof heat, yield air, the bulk of which is inflammable, and contracts noputrid smell (at least, in a day or two) a mouse treated in the samemanner, yields the proper putrid effluvium, as indeed the smellsufficiently indicates. 

That the putrid effluvium will mix with water seems to be evident fromthe following experiment. If a mouse be put into a jar full of water, standing with its mouth inverted in another vessel of water, aconsiderable quantity of elastic matter (and which may, therefore, becalled _air_) will soon be generated, unless the weather be so cold asto check all putrefaction. After a short time, the water contracts anextremely fetid and offensive smell, which seems to indicate that theputrid effluvium pervades the water, and affects the neighbouring air;and since, after this, there is often no increase of the air, that seemsto be the very substance which is carried off through the water, as fastas it is generated; and the offensive smell is a sufficient proof thatit is not fixed air. For this has a very agreeable flavour, whether itbe produced by fermentation, or extracted from chalk by oil of vitriol;affecting not only the mouth, but even the nostrils; with a pungencywhich is peculiarly pleasing to a certain degree, as any person mayeasily satisfy himself, who will chuse to make the experiment. 

If the water in which the mouse was immersed, and which is saturatedwith the putrid air, be changed, the greater part of the putrid air, will, in a day or two, be absorbed, though the mouse continues to yieldthe putrid effluvium as before; for as soon as this fresh water becomessaturated with it, it begins to be offensive to the smell, and thequantity of the putrid air upon its surface increases as before. I kepta mouse producing putrid air in this manner for the space of severalmonths. 

Six ounce measures of air not readily absorbed by water, appeared tohave been generated from one mouse, which had been putrefying elevendays in confined air, before it was put into a jar which was quitefilled with water, for the purpose of this observation. 

Air thus generated from putrid mice standing in water, without anymixture of common air, extinguishes flame, and is noxious to animals, but not more so than common air only tainted with putrefaction. It isexceedingly difficult and tedious to collect a quantity of this putridair, not miscible in water, so very great a proportion of what iscollected being absorbed by the water in which it is kept; but what thatproportion is, I have not endeavoured to ascertain. It is probably thesame proportion that that part of fixed air, which is not readilyabsorbed by water, bears to the rest; and therefore this air, which I atfirst distinguished by the name of _the putrid effluvium_, is probablythe same with fixed air, mixed with the phlogistic matter, which, inthis and other processes, diminishes common air. 

Though a quantity of common air be diminished by any substanceputrefying in it, I have not yet found the same effect to be produced bya mixture of putrid air with common air; but, in the manner in which Ihave hitherto made the experiment, I was obliged to let the putrid airpass through a body of water, which might instantly absorb thephlogistic matter that diminished the common air. 

Insects of various kinds live perfectly well in air tainted with animalor vegetable putrefaction, when a single inspiration of it would haveinstantly killed any other animal. I have frequently tried theexperiment with flies and butterflies. The _aphides_ also will thrive aswell upon plants growing in this kind of air, as in the open air. Ihave even been frequently obliged to take plants out of the putrid airin which they were growing, on purpose to brush away the swarms of theseinsects which infected them; and yet so effectually did some of themconceal themselves, and so fast did they multiply, in thesecircumstances, that I could seldom keep the plants quite clear of them. 

When air has been freshly and strongly tainted with putrefaction, so asto smell through the water, sprigs of mint have presently died, uponbeing put into it, their leaves turning black; but if they do not diepresently, they thrive in a most surprizing manner. In no othercircumstances have I ever seen vegetation so vigorous as in this kind ofair, which is immediately fatal to animal life. Though these plants havebeen crouded in jars filled with this air, every leaf has been full oflife; fresh shoots have branched out in various directions, and havegrown much faster than other similar plants, growing in the sameexposure in common air. 

This observation led me to conclude, that plants, instead of affectingthe air in the same manner with animal respiration, reverse the effectsof breathing, and tend to keep the atmosphere sweet and wholesome, whenit is become noxious, in consequence of animals either living andbreathing, or dying and putrefying in it. 

In order to ascertain this, I took a quantity of air, made thoroughlynoxious, by mice breathing and dying in it, and divided it into twoparts; one of which I put into a phial immersed in water; and to theother (which was contained in a glass jar, standing in water) I put asprig of mint. This was about the beginning of August 1771, and aftereight or nine days, I found that a mouse lived perfectly well in thatpart of the air, in which the sprig of mint had grown, but died themoment it was put into the other part of the same original quantity ofair; and which I had kept in the very same exposure, but without anyplant growing in it. 

This experiment I have several times repeated; sometimes using air inwhich animals had breathed and died, and at other times using air, tainted with vegetable or animal putrefaction; and generally with thesame success. 

Once, I let a mouse live and die in a quantity of air which had beennoxious, but which had been restored by this process, and it livednearly as long as I conjectured it might have done in an equal quantityof fresh air; but this is so exceedingly various, that it is not easy toform any judgment from it; and in this case the symptom of _difficultrespiration_ seemed to begin earlier than it would have done in commonair. 

Since the plants that I made use of manifestly grow and thrive in putridair; since putrid matter is well known to afford proper nourishment forthe roots of plants; and since it is likewise certain that they receivenourishment by their leaves as well as by their roots, it seems to beexceedingly probable, that the putrid effluvium is in some measureextracted from the air, by means of the leaves of plants, and thereforethat they render the remainder more fit for respiration. 

Towards the end of the year some experiments of this kind did not answerso well as they had done before, and I had instances of the relapsing ofthis restored air to its former noxious state. I therefore suspended myjudgment concerning the efficacy of plants to restore this kind ofnoxious air, till I should have an opportunity of repeating myexperiments, and giving more attention to them. Accordingly I resumedthe experiments in the summer of the year 1772, when I presently had themost indisputable proof of the restoration of putrid air by vegetation;and as the fact is of some importance, and the subsequent variation inthe state of this kind of air is a little remarkable, I think itnecessary to relate some of the facts pretty circumstantially. 

The air, on which I made the first experiments, was rendered exceedinglynoxious by mice dying in it on the 20th of June. Into a jar nearlyfilled with one part of this air, I put a sprig of mint, while I keptanother part of it in a phial, in the same exposure; and on the 27th ofthe same month, and not before, I made a trial of them, by introducing amouse into a glass vessel, containing 2-1/2 ounce measures filled witheach kind of air; and I noted the following facts. 

When the vessel was filled with the air in which the mint had grown, avery large mouse lived five minutes in it, before it began to shew anysign of uneasiness. I then took it out, and found it to be as strong andvigorous as when it was first put in; whereas in that air which had beenkept in the phial only, without a plant growing in it, a younger mousecontinued not longer than two or three seconds, and was taken out quitedead. It never breathed after, and was immediately motionless. Afterhalf an hour, in which time the larger mouse (which I had kept alive, that the experiment might be made on both the kinds of air with the verysame animal) would have been sufficiently recruited, supposing it tohave received any injury by the former experiment, was put into the samevessel of air; but though it was withdrawn again, after being in ithardly one second, it was recovered with difficulty, not being able tostir from the place for near a minute. After two days, I put the samemouse into an equal quantity of common air, and observed that itcontinued seven minutes without any sign of uneasiness; and being veryuneasy after three minutes longer, I took it out. Upon the whole, Iconcluded that the restored air wanted about one fourth of being aswholesome as common air. The same thing also appeared when I applied thetest of nitrous air. 

In the seven days, in which the mint was growing in this jar of noxiousair, three old shoots had extended themselves about three inches, andseveral new ones had made their appearance in the same time. Dr. Franklin and Sir John Pringle happened to be with me, when the plant hadbeen three or four days in this state, and took notice of its vigorousvegetation, and remarkably healthy appearance in that confinement. 

On the 30th of the same month, a mouse lived fourteen minutes, breathingnaturally all the time, and without appearing to be much uneasy, tillthe last two minutes, in the vessel containing two ounce measures and ahalf of air which had been rendered noxious, by mice breathing in italmost a year before, and which, I had found to be most highly noxiouson the 19th of this month, a plant having grown in it, but notexceedingly well, these eleven days; on which account I had deferredmaking the trial so long. The restored air was affected by a mixture ofnitrous air, almost as much as common air. 

As this putrid air was thus easily restored to a considerable degree offitness for respiration, by plants growing in it, I was in hopes that bythe same means it might in time be so much more perfectly restored, thata candle would burn in it; and for this purpose I kept plants growing inthe jars which contained this air till the middle of August following, but did not take sufficient care to pull out all the old and rottenleaves. The plants, however, had grown, and looked so well upon thewhole, that I had no doubt but that the air must constantly have been ina mending state; when I was exceedingly surprized to find, on the 24thof that month, that though the air in one of the jars had not grownworse, it was no better; and that the air in the other jar was so muchworse than it had been, that a mouse would have died in it in a fewseconds. It also made no effervescence with nitrous air, as it had donebefore. 

Suspecting that the same plant might be capable of restoring putrid airto a certain degree only, or that plants might have a contrary tendencyin some stages of their growth, I withdrew the old plant, and put afresh one in its place; and found that, after seven days, the air wasrestored to its former wholesome state. This fact I consider as a veryremarkable one, and well deserving of a farther investigation, as it maythrow more light upon the principles of vegetation. It is not, however, a single fact; for I had several instances of the same kind in thepreceding year; but it seemed so very extraordinary, that air shouldgrow worse by the continuance of the same treatment by which it hadgrown better, that, whenever I observed it, I concluded that I had nottaken sufficient care to satisfy myself of its previous restoration. 

That plants are capable of perfectly restoring air injured byrespiration, may, I think, be inferred with certainty from the perfectrestoration, by this means, of air which had passed through my lungs, sothat a candle would burn in it again, though it had extinguished flamebefore, and apart of the same original quantity of air still continuedto do so. Of this one instance occurred in the year 1771, a sprig ofmint having grown in a jar of this kind of air, from the 25th of July tothe 17th of August following; and another trial I made, with the samesuccess, the 7th of July 1772, the plant having grown in it from the29th of June preceding. In this case also I found that the effect wasnot owing to any virtue in the leaves of mint; for I kept themconstantly changed in a quantity of this kind of air, for a considerabletime, without making any sensible alteration in it. 

These proofs of a partial restoration of air by plants in a state ofvegetation, though in a confined and unnatural situation, cannot butrender it highly probable, that the injury which is continually done tothe atmosphere by the respiration of such a number of animals, and theputrefaction of such masses of both vegetable and animal matter, is, inpart at least, repaired by the vegetable creation. And, notwithstandingthe prodigious mass of air that is corrupted daily by theabove-mentioned causes; yet, if we consider the immense profusion ofvegetables upon the face of the earth, growing in places, suited totheir nature, and consequently at full liberty to exert all theirpowers, both inhaling and exhaling, it can hardly be thought, but thatit may be a sufficient counterbalance to it, and that the remedy isadequate to the evil. 

Dr. Franklin, who, as I have already observed, saw some of my plants ina very flourishing state, in highly noxious air, was pleased to expressvery great satisfaction with the result of the experiments. In hisanswer to the letter in which I informed him of it, he says, "That the vegetable creation should restore the air which is spoiled bythe animal part of it, looks like a rational system, and seems to be ofa piece with the rest. Thus fire purifies water all the world over. Itpurifies it by distillation, when it raises it in vapours, and lets itfall in rain; and farther still by filtration, when, keeping it fluid, it suffers that rain to percolate the earth. We knew before that putridanimal substances were converted into sweet vegetables, when mixed withthe earth, and applied as manure; and now, it seems, that the sameputrid substances, mixed with the air, have a similar effect. The strongthriving state of your mint in putrid air seems to shew that the air ismended by taking something from it, and not by adding to it. " He adds, "I hope this will give some check to the rage of destroying trees thatgrow near houses, which has accompanied our late improvements ingardening, from an opinion of their being unwholesome. I am certain, from long observation, that there is nothing unhealthy in the air ofwoods; for we Americans have every where our country habitations in themidst of woods, and no people on earth enjoy better health, or are moreprolific. "

Having rendered inflammable air perfectly innoxious by continued_agitation in a trough of water_, deprived of its air, I concluded thatother kinds of noxious air might be restored by the same means; and Ipresently found that this was the case with putrid air, even of morethan a year's standing. I shall observe once for all, that this processhas never failed to restore any kind of noxious air on which I havetried it, viz. Air injured by respiration or putrefaction, air infectedwith the fumes of burning charcoal, and of calcined metals, air in whicha mixture of iron filings and brimstone, that in which paint made ofwhite lead and oil has stood, or air which has been diminished by amixture of nitrous air. Of the remarkable effect which this process hason nitrous air itself, an account will be given in its proper place. 

If this process be made in water deprived of air, either by theair-pump, by boiling, or by distillation, or if fresh rain-water beused, the air will always be diminished by the agitation; and this iscertainly the fairest method of making the experiment. If the water befresh pump-water, there will always be an increase of the air byagitation, the air contained in the water being set loose, and joiningthat which is in the jar. In this case, also, the air has never failedto be restored; but then it might be suspected that the melioration wasproduced by the addition of some more wholesome ingredient. As theseagitations were made in jars with wide mouths, and in a trough which hada large surface exposed to the common air, I take it for granted thatthe noxious effluvia, whatever they be, were first imbibed by the water, and thereby transmitted to the common atmosphere. In some cases this wassufficiently indicated by the disagreeable smell which attended theoperation. 

After I had made these experiments, I was informed that an ingeniousphysician and philosopher had kept a fowl alive twenty-four hours, in aquantity of air in which another fowl of the same size had not been ableto live longer than an hour, by contriving to make the air, which itbreathed, pass through no very large quantity of acidulated water, thesurface of which was not exposed to the common air; and that even whenthe water was not acidulated, the fowl lived much longer than it couldhave done, if the air which it breathed had not been drawn through thewater. 

As I should not have concluded that this experiment would have succeededso well, from any observations that I had made upon the subject, I tooka quantity of air in which mice had died, and agitated it very strongly, first in about five times its own quantity of distilled water, in themanner in which I had impregnated water with fixed air; but though theoperation was continued a long time, it made no sensible change in theproperties of the air. I also repeated the operation with pump-water, but with as little effect. In this case, however, though the air wasagitated in a phial, which had a narrow neck, the surface of the waterin the bason was considerably large, and exposed to the commonatmosphere, which must have tended a little to favour the experiment. 

In order to judge more precisely of the effect of these differentmethods of agitating air, I transferred the very noxious air, which Ihad hot been able to amend in the least degree by the former method, into an open jar, standing in a trough of water; and when I had agitatedit till it was diminished about one third, I found it to be better thanair in which candles had burned out, as appeared by the test of thenitrous air; and a mouse lived in 2-1/2 ounce measures of it a quarterof an hour, and was not sensibly affected the first ten or twelveminutes. 

In order to determine whether the addition of any _acid_ to the water, would make it more capable of restoring putrid air, I agitated aquantity of it in a phial containing very strong vinegar; and after thatin _aqua fortis_, only half diluted with water; but by neither of theseprocesses was the air at all mended, though the agitation was repeated, at intervals, during a whole day, and it was moreover allowed to standin that situation all night. 

Since, however, water in these experiments must have imbibed andretained a certain portion of the noxious effluvia, before they could betransmitted to the external air, I do not think it improbable but thatthe agitation of the sea and large lakes may be of some use for thepurification of the atmosphere, and the putrid matter contained in watermay be imbibed by aquatic plants, or be deposited in some other manner. 

Having found, by several experiments above-mentioned that the properputrid effluvium is something quite distinct from fixed air, andfinding, by the experiments of Dr. Macbride, that fixed air correctsputrefaction; it occured to me, that fixed air, and air tainted withputrefaction, though equally, noxious when separate, might make awholesome mixture, the one, correcting the other; and I was confirmed inthis opinion by, I believe, not less than fifty or sixty instances, inwhich air, that had been made in the highest degree noxious, byrespiration or putrefaction, was so far sweetened, by a mixture of aboutfour times as much fixed air, that afterwards mice lived in itexceedingly well, and in some cases almost as long as in common air. Ifound it, indeed, to be more difficult to restore _old_ putrid air bythis means; but I hardly ever failed to do it, when the two kinds of airhad stood a long time together; by which I mean about a fortnight orthree weeks. 

The reason why I do not absolutely conclude that the restoration of airin these cases was the effect of fixed air, is that, when I made a trialof the mixture, I sometimes agitated the two kinds of air prettystrongly together, in a trough of water, or at least passed it severaltimes through water, from one jar to another, that the superfluous fixedair might be absorbed, not suspecting at that time that the agitationcould have any other effect. But having since found that very violent, and especially long-continued agitation in water, without any mixture offixed air, never failed to render any kind of noxious air in somemeasure fit for respiration (and in one particular instance the meretransferring of the air from one vessel to another through the water, though for a much longer time than I ever used for the mixtures of air, was of considerable use for the same purpose) I began to entertain somedoubt of the efficacy of fixed air in this case. In some cases also themixture of fixed air had by no means so much effect on the putrid airas, from the generality of my observations, I should have expected. 

I was always aware, indeed, that it might be said, that, the residuum offixed air not being very noxious, such an addition must contribute tomend the putrid air; but, in order to obviate this objection, I oncemixed the residuum of as much fixed air as I had found, by a variety oftrials, to be sufficient to restore a given quantity of putrid air, withan equal quantity of that air, without making any sensible meliorationof it. 

Upon the whole, I am inclined to think that this process could hardlyhave succeeded so well as it did with me, and in so great a number oftrials, unless fixed air have some tendency to correct air tainted withrespiration or putrefaction; and it is perfectly agreeable to theanalogy of Dr. Macbride's discoveries, and may naturally be expectedfrom them, that it should have such an effect. 

By a mixture of fixed air I have made wholesome the residuum of airgenerated by putrefaction only, from mice plunged in water. This, onewould imagine, _à priori_, to be the most noxious of all kinds of air. For if common air only tainted with putrefaction be so deadly, much moremight one expect that air to be so, which was generated fromputrefaction only; but it seems to be nothing more than common air (orat least that kind of fixed air which is not absorbed by water) taintedwith putrefaction, and therefore requires no other process to sweetenit. In this case, however, we seem to have an instance of the generationof genuine common air, though mixed with something that is foreign toit. Perhaps the residuum of fixed air may be another instance of thesame nature, and also the residuum of inflammable air, and of nitrousair, especially nitrous air loaded with phlogiston, after long agitationin water. 

Fixed air is equally diffused through the whole mass of any quantity ofputrid air with which it is mixed: for dividing the mixture into twoequal parts, they were reduced in the same proportion by passing throughwater. But this is also the case with some of the kinds of air whichwill not incorporate, as inflammable air, and air in which brimstone hasburned. 

If fixed air tend to correct air which has been injured by animalrespiration or putrefaction, _lime kilns_, which discharge greatquantities of fixed air, may be wholesome in the neighbourhood ofpopulous cities, the atmosphere of which must abound with putrideffluvia. I should think also that physicians might avail themselves ofthe application of fixed air in many putrid disorders, especially as itmay be so easily administered by way of _clyster_, where it would oftenfind its way to much of the putrid matter. Nothing is to be apprehendedfrom the distention of the bowels by this kind of air, since it is soreadily absorbed by any fluid or moist substance. 

Since fixed air is not noxious _per se_, but, like fire, only in excess, I do not think it at all hazardous to attempt to _breathe_ it. It ishowever easily conveyed into the _stomach_, in natural or artificialPyrmont water, in briskly-fermenting liquors, or a vegetable diet. Itis even possible, that a considerable quantity of fixed air might beimbibed by the absorbing vessels of the skin, if the whole body, exceptthe head, should be suspended over a vessel of strongly-fermentingliquor; and in some putrid disorders this treatment might be verysalutary. If the body was exposed quite naked, there would be verylittle danger from the cold in this situation, and the air having freeraccess to the skin might produce a greater effect. Being no physician, Irun no risk by throwing out these random, and perhaps whimsicalproposals. [5]

Having communicated my observations on fixed air, and especially myscheme of applying it by way of _clyster_ in putrid disorders, to Mr. Hey, an ingenious surgeon in Leeds a case presently occurred, in whichhe had an opportunity of giving it a trial; and mentioning it to Dr. Hird and Dr. Crowther, two physicians who attended the patient, theyapproved the scheme, and it was put in execution; both by applying thefixed air by way of clyster, and at the same time making the patientdrink plentifully of liquors strongly impregnated with it. The eventwas such, that I requested Mr. Hey to draw up a particular account ofthe case, describing the whole of the treatment, that the public mightbe satisfied that this new application of fixed air is perfectly safe, and also, have an opportunity of judging how far it had the effect whichI expected from it; and as the application is new, and not unpromising, I shall subjoin his letter to me on the subject, by way of _Appendix_ tothese papers. 

When I began my inquires into the properties of different kinds of air, I engaged my friend Dr. Percival to attend to the _medicinal uses_ ofthem, being sensible that his knowledge of philosophy as well as ofmedicine would give him a singular advantage for this purpose. Theresult of his observations I shall also insert in the Appendix. 

FOOTNOTES:

[5] Some time after these papers were first printed, I was pleased tofind the same proposal in _Dr. Alexander's Experimental Essays_. 

SECTION V. 

_Of AIR in which a mixture of BRIMSTONE and FILINGS of IRON has stood. _

Reading in Dr. Hales's account of his experiments, that there was agreat diminution of the quantity of air in which _a mixture of powderedbrimstone and filings of iron, made into a paste with water_, had stood, I repeated the experiment, and found the diminution greater than I hadexpected. This diminution of air is made as effectually, and asexpeditiously, in quicksilver as in water; and it may be measured withthe greatest accuracy, because there is neither any previous expansionor increase of the quantity of air, and because it is some time beforethis process begins to have any sensible effect. This diminution of airis various; but I have generally found it to be between one fifth andone fourth of the whole. 

Air thus diminished is not heavier, but rather lighter than common air;and though lime-water does not become turbid when it is exposed to thisair, it is probably owing to the formation of a selenitic salt, as wasthe case with the simple burning of brimstone above-mentioned. Thatsomething proceeding from the brimstone strongly affects the water whichis confined in the same place with this mixture, is manifest from thevery strong smell that it has of the volatile spirit of vitriol. 

I conclude that the diminution of air by this, process is of the samekind with the diminution of it in the other cases, because when thismixture is put into air which has been previously diminished, either bythe burning of candles, by respiration, or putrefaction, though it neverfails to diminish it something more, it is, however, no farther thanthis process alone would have done it. If a fresh mixture be introducedinto a quantity of air which had been reduced by a former mixture, ithas little or no farther effect. 

I once observed, that when a mixture of this kind was taken out of aquantity of air in which a candle had before burned out, and in which ithad stood for several days, it was quite cold and black, as it alwaysbecomes in a confined place; but it presently grew very hot, smoakedcopously, and smelled very offensively; and when it was cold, it wasbrown, like the rust of iron. 

I once put a mixture of this kind to a quantity of inflammable air, madefrom iron, by which means it was diminished 1/9 or 1/10 in its bulk;but, as far as I could judge, it was still as inflammable as ever. Another quantity of inflammable air was also reduced in the sameproportion, by a mouse putrefying in it; but its inflammability was notseemingly lessened. 

Air diminished by this mixture of iron filings and brimstone, isexceedingly noxious to animals, and I have not perceived that it growsany better by keeping in water. The smell of it is very pungent andoffensive. 

The quantity of this mixture which I made use of in the precedingexperiments, was from two to four ounce measures; but I did notperceive, but that the diminution of the quantity of air (which wasgenerally about twenty ounce measures) was as great with the smallest, as with the largest quantity. How small a quantity is necessary todiminish a given quantity of air to a _maximum_, I have made noexperiments to ascertain. 

As soon as this mixture of iron filings with, brimstone and water, begins to ferment, it also turns black, and begins to swell, and itcontinues to do so, till it occupies twice as much space as it did atfirst. The force with which it expands is great; but how great it is Ihave not endeavoured to determine. 

When this mixture is immersed in water, it generates no air, though itbecomes black, and swells. 

SECTION VI. 

_Of NITROUS AIR. _

Ever since I first read Dr. Hales's most excellent _Statical Essays_, Iwas particularly struck with that experiment of his, of which an accountis given, VOL. I, p. 224. And VOL. II, p. 280. In which common air, andair generated from the Walton pyrites, by spirit of nitre, made a turbidred mixture, and in which part of the common air was absorbed; but Inever expected to have the satisfaction of seeing this remarkableappearance, supposing it to be peculiar to that particular mineral. Happening to mention this subject to the Hon. Mr. Cavendish, when I wasin London, in the spring of the year 1772, he said that he did notimagine but that other kinds of pyrites, or the metals might answer aswell, and that probably the red appearance of the mixture depended uponthe spirit of nitre only. This encouraged me to attend to the subject;and having no pyrites, I began with the solution of the different metalsin spirit of nitre, and catching the air which was generated in thesolution, I presently found what I wanted, and a good deal more. 

Beginning with the solution of brass, on the 4th of June 1772, I firstfound this remarkable species of air, only one effect of which, wascasually observed by Dr. Hales; and he gave so little attention to it, and it has been so much unnoticed since his time, that, as far as Iknow, no name has been given to it. I therefore found myself, contraryto my first resolution, under an absolute necessity of giving a name tothis kind of air myself. When I first began to speak and write of it tomy friends, I happened to distinguish it by the name of _nitrous air_, because I had procured it by means of spirit of nitre only; and though Icannot say that I altogether like the term, neither myself nor any of myfriends, to whom I have applied for the purpose, have been able to hitupon a better; so that I am obliged, after all, to content myself withit. 

I have found that this kind of air is readily procured from iron, copper, brass, tin, silver, quicksilver, bismuth, and nickel, by thenitrous acid only, and from gold and the regulus of antimony by _aquaregia_. The circumstances attending the solution of each of these metalsare various, but hardly worth mentioning, in treating of the propertiesof the _air_ which they yield; which, from what metal soever it isextracted, has, as far as I have been able to observe, the very sameproperties. 

One of the most conspicuous properties of this kind of air is the greatdiminution of any quantity of common air with which it is mixed, attended with a turbid red, or deep orange colour, and a considerableheat. The _smell_ of it, also, is very strong, and remarkable, but verymuch resembling that of smoking spirit of nitre. 

The diminution of a mixture of this and common air is not an equaldiminution of both the kinds, which is all that Dr. Hales could observe, but of about one fifth of the common air, and as much of the nitrous airas is necessary to produce that effect; which, as I have found by manytrials, is about one half as much as the original quantity of commonair. For if one measure of nitrous air be put to two measures of commonair, in a few minutes (by which time the effervescence will be over, andthe mixture will have recovered its transparency) there will want aboutone ninth of the original two measures; and if both the kinds of air bevery pure, the diminution will still go on slowly, till in a day or two, the whole will be reduced to one fifth less than the original quantityof common air. This farther diminution, by long standing, I had notobserved at the time of the first publication of these papers. 

I hardly know any experiment that is more adapted to amaze and surprizethan this is, which exhibits a quantity of air, which, as it were, devours a quantity of another kind of air half as large as itself, andyet is so far from gaining any addition to its bulk, that it isconsiderably diminished by it. If, after this full saturation of commonair with nitrous air, more nitrous air be put to it, it makes anaddition equal to its own bulk, without producing the least redness, orany other visible effect. 

If the smallest quantity of common air be put to any larger quantity ofnitrous air, though the two together will not occupy so much space asthey did separately, yet the quantity will still be larger than that ofthe nitrous air only. One ounce measure of common air being put to neartwenty ounce measures of nitrous air, made an addition to it of abouthalf an ounce measure. This being a much greater proportion than thediminution of common air, in the former experiment, proves that part ofthe diminution in the former case is in the nitrous air. Besides, itwill presently appear, that nitrous air is subject to a most remarkablediminution; and as common air, in a variety of other cases, suffers adiminution from one fifth to one fourth, I conclude, that in this casealso it does not exceed that proportion, and therefore that theremainder of the diminution respects the nitrous air. 

In order to judge whether the _water_ contributed to the diminution ofthis mixture of nitrous and common air, I made the whole process severaltimes in quicksilver, using one third of nitrous, and two thirds ofcommon air, as before. In this case the redness continued a very longtime, and the diminution was not so great as when the mixtures had beenmade in water, there remaining one seventh more than the originalquantity of common air. 

This mixture stood all night upon the quicksilver; and the next morningI observed that it was no farther diminished upon the admission ofwater to it, nor by pouring it several times through the water, andletting it stand in water two days. 

Another mixture, which had stood about six hours on the quicksilver, wasdiminished a little more upon the admission of water, but was never lessthan the original quantity of common air. In another case however, inwhich the mixture had stood but a very short time in quicksilver, thefarther diminution, which took place upon the admission of water, wasmuch more considerable; so that the diminution, upon the whole, was verynearly as great as if the process had been intirely in water. 

It is evident from these experiments, that the diminution is in partowing to the absorption by the water; but that when the mixture is kepta long time, in a situation in which there is no water to absorb anypart of it, it acquires a constitution, by which it is afterwardsincapable of being absorbed by water, or rather, there is an addition tothe quantity of air by nitrous air produced by the solution of thequicksilver. 

It will be seen, in the second part of this work, that, in thedecomposition of nitrous air by its mixture with common air, there isnothing at hand when the process is made in quicksilver, with which theacid that entered into its composition can readily unite. 

In order to determine whether the fixed part of common air was depositedin the diminution of it by nitrous air, I inclosed a vessel full oflime-water in the jar in which the process was made, but it occasionedno precipitation of the lime; and when the vessel was taken out, afterit had been in that situation a whole day, the lime was easilyprecipitated by breathing into it as usual. 

But though the precipitation of the lime was not sensible in this methodof making the experiment, it is sufficiently so when the whole processis made in lime-water, as will be seen in the second part of this work;so that we have here another evidence of the deposition of fixed airfrom common air. I have made no alteration, however, in the precedingparagraph, because it may not be unuseful, as a caution to futureexperimenters. 

It is exceedingly remarkable that this effervescence and diminution, occasioned by the mixture of nitrous air, is peculiar to common air, or_air fit for respiration_; and, as far as I can judge, from a greatnumber of observations, is at least very nearly, if not exactly, inproportion to its fitness for this purpose; so that by this means thegoodness of air may be distinguished much more accurately than it can bedone by putting mice, or any other animals, to breathe in it. 

This was a most agreeable discovery to me, as I hope it may be an usefulone to the public; especially as, from this time, I had no occasion forso large a stock of mice as I had been used to keep for the purpose ofthese experiments, using them only in those which required to be verydecisive; and in these cases I have seldom failed to know beforehand inwhat manner they would be affected. 

It is also remarkable that, on whatever account air is unfit forrespiration, this same test is equally applicable. Thus there is not theleast effervescence between nitrous and fixed air, or inflammable air, or any species of diminished air. Also the degree of diminution beingfrom nothing at all to more than one third of the whole of any quantityof air, we are, by this means, in possession of a prodigiously large_scale_, by which we may distinguish very small degrees of difference inthe goodness of air. 

I have not attended much to this circumstance, having used this testchiefly for greater differences; but, if I did not deceive myself, Ihave perceived a real difference in the air of my study, after a fewpersons have been with me in it, and the air on the outside of thehouse. Also a phial of air having been sent me, from the neighbourhoodof York, it appeared not to be so good as the air near Leeds; that is, it was not diminished so much by an equal mixture of nitrous air, everyother circumstance being as nearly the same as I could contrive. It mayperhaps be possible, but I have not yet attempted it, to distinguishsome of the different winds, or the air of different times of the year, &c. &c. By this test. 

By means of this test I was able to determine what I was before in doubtabout, viz. The _kind_ as well as the _degree_ of injury done to air bycandles burning in it. I could not tell with certainty, by means ofmice, whether it was at all injured with respect to respiration; and yetif nitrous air may be depended upon for furnishing an accurate test, itmust be rather more than one third worse than common air, and have beendiminished by the same general cause of the other diminutions of air. For when, after many trials, I put one measure of thoroughly putrid andhighly noxious air, into the same vessel with two measures of goodwholesome air, and into another vessel an equal quantity, viz. Threemeasures of air in which a candle had burned out; and then put equalquantities of nitrous air to each of them, the latter was diminishedrather more than the former. 

It agrees with this observation, that _burned air_ is farther diminishedboth by putrefaction, and a mixture of iron filings and brimstone; and Itherefore take it for granted by every other cause of the diminution ofair. It is probable, therefore, that burned air is air so far loadedwith phlogiston, as to be able to extinguish a candle, which it may dolong before it is fully saturated. 

Inflammable air with a mixture of nitrous air burns with a green flame. This makes a very pleasing experiment when it is properly conducted. As, for some time, I chiefly made use of _copper_ for the generation ofnitrous air, I first ascribed this circumstance to that property of thismetal, by which it burns with a green flame; but I was presentlysatisfied that it must arise from the spirit of nitre, for the effect isthe very same from which ever of the metals the nitrous air isextracted, all of which I tried for this purpose, even silver and gold. 

A mixture of oil of vitriol and spirit of nitre in equal proportionsdissolved iron, and the produce was nitrous air; but a less degree ofspirit of nitre in the mixture produced air that was inflammable, andwhich burned with a green flame. It also tinged common air a little red, and diminished it, though not much. 

The diminution of common air by a mixture of nitrous air, is not soextraordinary as the diminution which nitrous air itself is subject tofrom a mixture of iron filings and brimstone, made into a paste withwater. This mixture, as I have already observed, diminishes common airbetween one fifth and one fourth, but has no such effect upon any kindof air that has been diminished, and rendered noxious by any otherprocess; but when it is put to a quantity of nitrous air, it diminishesit so much, that no more than one fourth of the original quantity willbe left. 

The effect of this process is generally perceived in five or six hours, about which time the visible effervesence of the mixture begins; and ina very short time it advances so rapidly, that in about an hour almostthe whole effect will have taken place. If it be suffered to stand a dayor two longer, the air will still be diminished farther, but only a verylittle farther, in proportion to the first diminution. The glass jar, in which the air and this mixture have been confined, has generally beenso much heated in this process, that I have not been able to touch it. 

Nitrous air thus diminished has not so strong a smell as nitrous airitself, but smells just like common air in which the same mixture hasstood; and it is not capable of being diminished any farther, by a freshmixture of iron and brimstone. 

Common air saturated with nitrous air is also no farther diminished bythis mixture of iron filings and brimstone, though the mixture fermentswith great heat, and swells very much in it. 

Plants die very soon, both in nitrous air, and also in common airsaturated with nitrous air, but especially in the former. 

Neither nitrous air, nor common air saturated with nitrous air, differin specific gravity from common air. At least, the difference is sosmall, that I could not be sure there was any; sometimes about threepints of it seeming to be about half a grain heavier, and at other timesas much lighter than common air. 

Having, among other kinds of air, exposed a quantity of nitrous air towater out of which the air had been well boiled, in the experiment towhich I have more than once referred (as having been the occasion ofseveral new and important observations) I found that 19/20 of the wholewas absorbed. Perceiving, to my great surprize, that so very great aproportion of this kind of air was miscible with water, I immediatelybegan to agitate a considerable quantity of it, in a jar standing in atrough of the same kind of water; and, with about four times as muchagitation as fixed air requires, it was so far absorbed by the water, that only about one fifth remained. This remainder extinguished flame, and was noxious to animals. 

Afterwards I diminished a pretty large quantity of nitrous air to oneeighth of its original bulk, and the remainder still retained much ofits peculiar smell, and diminished common air a little. A mouse alsodied in it, but not so suddenly as it would have done in pure nitrousair. In this operation the peculiar smell of nitrous air is verymanifest, the water being first impregnated with the air, and thentransmitting it to the common atmosphere. 

This experiment gave me the hint of impregnating water with nitrous air, in the manner in which I had before done it with fixed air; and Ipresently found that distilled water would imbibe about one tenth of itsbulk of this kind of air, and that it acquired a remarkably acid andastringent taste from it. The smell of water thus impregnated is atfirst peculiarly pungent. I did not chuse to swallow any of it, though, for any thing that I know, it may be perfectly innocent, and perhaps, insome cases, salutary. 

This kind of air is retained very obstinately by water. In an exhaustedreceiver a quantity of water thus saturated emitted a whitish fume, suchas sometimes issues from bubbles of this air when it is first generated, and also some air-bubbles; but though it was suffered to stand a longtime in this situation, it still retained its peculiar taste; but whenit had stood all night pretty near the fire, the water was become quitevapid, and had deposited a filmy kind of matter, of which I had oftencollected a considerable quantity from the trough in which jarscontaining this air had stood. This I suppose to be a precipitate of themetal, by the solution of which the nitrous air was generated. I havenot given so much attention to it as to know, with certainty, in whatcircumstances this _deposit_ is made, any more than I do the matterdeposited from inflammable air above-mentioned; for I cannot get it, atleast in any considerable quantity, when I please; whereas I have oftenfound abundance of it, when I did not expect it at all. 

The nitrous air with which I made the first impregnation of water wasextracted from copper; but when I made the impregnation with air fromquicksilver, the water had the very same taste, though the matterdeposited from it seemed to be of a different kind; for it was whitish, whereas the other had a yellowish tinge. Except the first quantity ofthis impregnated water, I could never deprive any more that I made ofits peculiar taste. I have even let some of it stand more than a week, in phials with their mouths open, and sometimes very near the fire, without producing any alteration in it[6]. 

Whether any of the spirit of nitre contained in the nitrous air be mixedwith the water in this operation, I have not yet endeavoured todetermine. This, however, may probably be the case, as the spirit ofnitre is, in a considerable degree, volatile[7]. 

It will perhaps be thought, that the most _useful_, if not the mostremarkable, of all the properties of this extraordinary kind of air, isits power of preserving animal substances from putrefaction, and ofrestoring those that are already putrid, which it possesses in a fargreater degree than fixed air. My first observation of this wasaltogether casual. Having found nitrous air to suffer so great adiminution as I have already mentioned by a mixture of iron filings andbrimstone, I was willing to try whether it would be equally diminishedby other causes of the diminution of common air, especially byputrefaction; and for this purpose I put a dead mouse into a quantity ofit, and placed it near the fire, where the tendency to putrefaction wasvery great. In this case there was a considerable diminution, viz. From5-1/4 to 3-1/4; but not so great as I had expected, the antiseptic powerof the nitrous air having checked the tendency to putrefaction; forwhen, after a week, I took the mouse out, I perceived, to my very greatsurprize, that it had no offensive smell. 

Upon this I took two other mice, one of them just killed, and the othersoft and putrid, and put them both into the same jar of nitrous air, standing in the usual temperature of the weather, in the months of Julyand August of 1772; and after twenty-five days, having observed thatthere was little or no change in the quantity of the air, I took themice out; and, examining them, found them both perfectly sweet, evenwhen cut through in several places. That which had been put into the airwhen just dead was quite firm; and the flesh of the other, which hadbeen putrid and soft, was still soft, but perfectly sweet. 

In order to compare the antiseptic power of this kind of air with thatof fixed air, I examined a mouse which I had inclosed in a phial full offixed air, as pure as I could make it, and which I had corked veryclose; but upon opening this phial in water about a month after, Iperceived that a large quantity of putrid effluvium had been generated;for it rushed with violence out of the phial; and the smell that camefrom it, the moment the cork was taken out, was insufferably offensive. Indeed Dr. Macbride says, that he could only restore very thin piecesof putrid flesh by means of fixed air. Perhaps the antiseptic power ofthese kinds of air may be in proportion to their acidity. 

If a little pains were taken with this subject, this remarkableantiseptic power of nitrous air might possibly be applied to varioususes, perhaps to the preservation of the more delicate birds, fishes, fruits, &c. Mixing it in different proportions with common or fixed air. Of this property of nitrous air anatomists may perhaps avail themselves, as animal substances may by this means be preserved in their naturalsoft state; but how long it will answer for this purpose, experienceonly can shew. 

I calcined lead and tin in the manner hereafter described in a quantityof nitrous air, but with very little sensible effect; which rathersurprized me; as, from the result of the experiment with the ironfilings and brimstone, I had expected a very great diminution of thenitrous air by this process; the mixture of iron filings and brimstone, and the calcination of metals, having the same effect upon common air, both of them diminishing it in nearly the same proportion. But though Imade the metals _fume_ copiously in nitrous air, there might be no real_calcination_, the phlogiston not being separated, and the propercalcination prevented by there being no _fixed_ _air_, which isnecessary to the formation of the calx, to unite with it. 

Nitrous air is procured from all the proper metals by spirit of nitre, except lead, and from all the semi-metals that I have tried, exceptzinc. For this purpose I have used bismuth and nickel, with spirit ofnitre only, and regulus of antimony and platina, with _aqua regia_. 

I got little or no air from lead by spirit of nitre, and have not yetmade any experiments to ascertain the nature of this solution. With zincI have taken a little pains. 

Four penny-weights and seventeen grains of zinc dissolved in spirit ofnitre, to which as much water was added, yielded about twelve ouncemeasures of air, which had, in some degree, the properties of nitrousair, making a slight effervescence with common air, and diminishing itabout as much as nitrous air, which had been itself diminished one halfby washing in water. The smell of them both was also the same; so that Iconcluded it to be the same thing, that part of the nitrous air, whichis imbibed by water, being retained in this solution. 

In order to discover whether this was the case, I made the solution boilin a sand-heat. Some air came from it in this state, which seemed to bethe same thing, with nitrous air diminished about one sixth, or oneeighth, by washing in water. When the fluid part was evaporated, thereremained a brown fixed substance, which was observed by Mr. Hellot, whodescribes it, Ac. Par. 1735, M. P. 35. A part of this I threw into asmall red-hot crucible; and covering it immediately with a receiver, standing in water, I observed that very dense red fumes rose from it, and filled the receiver. This redness continued about as long as thatwhich is occasioned by a mixture of nitrous and common air; the air wasalso considerably diminished within the receiver. This substance, therefore, must certainly have contained within it the very same thing, or principle, on which the peculiar properties of nitrous air depend. 

It is remarkable, however, that though the air within the receiver wasdiminished about one fifth by this process, it was itself as muchaffected with a mixture of nitrous air, as common air is, and a candleburned in it very well. This may perhaps be attributed to some effect ofthe spirit of nitre, in the composition of that brown substance. 

Nitrous air, I find, will be considerably diminished in its bulk bystanding a long time in water, about as much as inflammable air isdiminished in the same circumstances. For this purpose I kept for somemonths a quart-bottle full of each of these kinds of air; but asdifferent quantities of inflammable air vary very much in this respect, it is not improbable but that nitrous air may vary also. 

From one trial that I made, I conclude that nitrous air may be kept in abladder much better than most other kinds of air. The air to which Irefer was kept about a fortnight in a bladder, through which thepeculiar smell of the nitrous air was very sensible for several days. Ina day or two the bladder became red, and was much contracted in itsdimensions. The air within it had lost very little of its peculiarproperty of diminishing common air. 

I did not endeavour to ascertain the exact quantity of nitrous airproduced from given quantities, of all the metals which yield it; butthe few observations which I did make for this purpose I shall recite inthis place:

 dwt. Gr. 

 6 0 of silver yielded 17-1/2 ounce measures. 5 19 of quicksilver 4-1/2 1 2-1/2 of copper 14-1/2 2 0 of brass 21 0 20 of iron 16 1 5 of bismuth 6 0 12 of nickel 4

FOOTNOTES:

[6] I have since found, that nitrous air has never failed to escape fromthe water, which has been impregnated with it, by long exposure to theopen air. 

[7] This suspicion has been confirmed by the ingenious Mr. Bewley, ofGreat Massingham in Norfolk, who has discovered that the acid taste ofthis water is not the necessary consequence of its impregnation withnitrous air, but is the effect of the _acid vapour_, into which part ofthis air is resolved, when it is decomposed by a mixture with commonair. This, it will be seen, exactly agrees with my own observation onthe constitution of nitrous air, in the second part of this work. A moreparticular account of Mr. Bewley's observation will be given in the_Appendix_. 

SECTION VII. 

_Of AIR infected with the FUMES of BURNING CHARCOAL. _

Air infected with the fumes of burning charcoal is well known to benoxious; and the Honourable Mr. Cavendish favoured me with an account ofsome experiments of his, in which a quantity of common air was reducedfrom 180 to 162 ounce measures, by passing through a red-hot iron tubefilled with the dust of charcoal. This diminution he ascribed to such a_destruction_ of common air as Dr. Hales imagined to be the consequenceof burning. Mr. Cavendish also observed, that there had been ageneration of fixed air in this process, but that it was absorbed bysope leys. This experiment I also repeated, with a small variation ofcircumstances, and with nearly the same result. 

Afterwards, I endeavoured to ascertain, by what appears to me to be aneasier and more certain method, in what manner air is affected with thefumes of charcoal, viz. By suspending bits of charcoal within glassvessels, filled to a certain height with water, and standing invertedin another vessel of water, while I threw the focus of a burning mirror, or lens, upon them. In this manner I diminished a given quantity of airone fifth, which is nearly in the same proportion with other diminutionsof air. 

If, instead of pure water, I used _lime-water_ in this process, it neverfailed to become turbid by the precipitation of the lime, which couldonly be occasioned by fixed air, either discharged from the charcoal, ordeposited by the common air. At first I concluded that it came from thecharcoal; but considering that it is not probable that fixed air, confined in any substance, can bear so great a degree of heat as isnecessary to make charcoal, without being wholly expelled; and that inother diminutions of common air, by phlogiston only, there appears to bea deposition of fixed air, I have now no doubt but that, in this casealso, it is supplied from the same source. 

This opinion is the more probable, from there being the sameprecipitation of lime, in this process, with whatever degree of heat thecharcoal had been made. If, however, the charcoal had not been made witha very considerable degree of heat, there never failed to be a permanentaddition of inflammable air produced; which agrees with what I observedbefore, that, in converting dry wood into charcoal, the greatest partis changed into inflammable air. 

I have sometimes found, that charcoal which was made with the mostintense heat of a smith's fire, which vitrified part of a commoncrucible in which the charcoal was confined, and which had beencontinued above half an hour, did not diminish the air in which thefocus of a burning mirror was thrown upon it; a quantity of inflammableair equal to the diminution of the common air being generated in theprocess: whereas, at other times, I have not perceived that there wasany generation of inflammable air, but a simple diminution of commonair, when the charcoal had been made with a much less degree of heat. This subject deserves to be farther investigated. 

To make the preceding experiment with still more accuracy, I repeated itin quicksilver; when I perceived that there was a small increase of thequantity of air, probably from a generation of inflammable air. Thus itstood without any alteration a whole night, and part of the followingday; when lime-water, being admitted to it, it presently became turbid, and, after some time, the whole quantity of air, which was about fourounce measures, was diminished one fifth, as before. In this case, Icarefully weighed the piece of charcoal, which was exactly two grains, and could not find that it was sensibly diminished in weight by theoperation. 

Air thus diminished by the fumes of burning charcoal not onlyextinguishes flame, but is in the highest degree noxious to animals; itmakes no effervescence with nitrous air, and is incapable of beingdiminished any farther by the fumes of more charcoal, by a mixture ofiron filings and brimstone, or by any other cause of the diminution ofair that I am acquainted with. 

This observation, which respects all other kinds of diminished air, proves that Dr. Hales was mistaken in his notion of the _absorption_ ofair in those circumstances in which he observed it. For he supposed thatthe remainder was, in all cases, of the same nature with that which hadbeen absorbed, and that the operation of the same cause would not havefailed to produce a farther diminution; whereas all my observations shewthat air, which has once been fully diminished by any cause whatever, isnot only incapable of any farther diminution, either from the same orfrom any other cause, but that it has likewise acquired _newproperties_, most remarkably different from those which it had before, and that they are, in a great measure, the same in all the cases. Thesecircumstances give reason to suspect, that the cause of diminution is, in reality, the same in all the cases. What this cause is, may, perhaps, appear in the next course of observations. 

SECTION VIII. 

_Of the effect of the CALCINATION of METALS, and of the EFFLUVIA ofPAINT made with WHITE-LEAD and OIL, on AIR. _

Having been led to suspect, from the experiments which I had made withcharcoal, that the diminution of air in that case, and perhaps in othercases also, was, in some way or other the consequence of its having morethan its usual quantity of phlogiston, it occurred to me, that thecalcination of metals, which are generally supposed to consist ofnothing but a metallic earth united to phlogiston, would tend toascertain the fact, and be a kind of _experimentum crucis_ in the case. 

Accordingly, I suspended pieces of lead and tin in given quantities ofair, in the same manner as I had before treated the charcoal; andthrowing the focus of a burning mirror or lens upon them, so as to makethem fume copiously. I presently perceived a diminution of the air. Inthe first trial that I made, I reduced four ounce measures of air tothree, which is the greatest diminution of common air that I had everobserved before, and which I account for, by supposing that, in othercases, there was not only a cause of diminution, but causes of additionalso, either of fixed or inflammable air, or some other permanentlyelastic matter, but that the effect of the calcination of metals beingsimply the escape of phlogiston, the cause of diminution was alone anduncontrouled. 

The air, which I had thus diminished by calcination of lead, Itransferred into another clean phial, but found that the calcination ofmore lead in it (or at least the attempt to make a farther calcination)had no farther effect upon it. This air also, like that which had beeninfected with the fumes of charcoal, was in the highest degree noxious, made no effervescence with nitrous air, was no farther diminished by themixture of iron filings and brimstone, and was not only renderedinnoxious, but also recovered, in a great measure, the other propertiesof common air, by washing in water. 

It might be suspected that the noxious quality of air in which _lead_was calcined, might be owing to some fumes peculiar to that metal; butI found no sensible difference between the properties of this air, andthat in which _tin_ was calcined. 

The _water_ over which metals are calcined acquires a yellowish tinge, and an exceedingly pungent smell and taste, pretty much (as near as Ican recollect, for I did not compare them together) like that over whichbrimstone has been frequently burned. Also a thin and whitish pelliclecovered both the surface of the water, and likewise the sides of thephial in which the calcination was made; insomuch that, withoutfrequently agitating the water, it grew so opaque by this constantlyaccumulating incrustation, that the sun-beams could not be transmittedthrough it in a quantity sufficient to produce the calcination. 

I imagined, however, that, even when this air was transferred into aclean phial, the metals were not so easily melted or calcined as theywere in fresh air; for the air being once fully saturated withphlogiston, may not so readily admit any more, though it be only totransmit it to the water. I also suspected that metals were not easilymelted or calcined in inflammable, fixed, or nitrous air, or any kindof diminished air. [8] None of these kinds of air suffered any change bythis operation; nor was there any precipitation of lime, when charcoalwas heated in any of these kinds of air standing in lime-water. Thisfurnishes another, and I think a pretty decisive proof, that, in theprecipitation of lime by charcoal, the fixed air does not come from thecharcoal, but from the common air. Otherwise it is hard to assign areason, why the same degree of heat (or at least a much greater) shouldnot expel the fixed air from this substance, though surrounded by thesedifferent kinds of air, and why the fixed air might not be transmittedthrough them to the lime-water. 

Query. May not water impregnated with phlogiston from calcined metals, or by any other method, be of some use in medicine? The effect of thisimpregnation is exceedingly remarkable; but the principle with which itis impregnated is volatile, and intirely escapes in a day or two, if thesurface of the water be exposed to the common atmosphere. 

It should seem that phlogiston is retained more obstinately by charcoalthan it is by lead or tin; for when any given quantity of air is fullysaturated with phlogiston from charcoal, no heat that I have yet appliedhas been able to produce any more effect upon it; whereas, in the samecircumstances, lead and tin may still be calcined, at least be made toemit a copious fume, in which some part of the phlogiston may be setloose. The air indeed, can take no more; but the water receives it, andthe sides of the phial also receive an addition of incrustation. This isa white powdery substance, and well deserves to be examined. I shallendeavour to do it at my leisure. 

Lime-water never became turbid by the calcination of metals over it, thecalx immediately seizing the precipitated fixed air, in preference tothe lime in the water; but the colour, smell, and taste of the water wasalways changed and the surface of it became covered with a yellowpellicle, as before. 

When this process was made in quicksilver, the air was diminished onlyone fifth; and upon water being admitted to it, no more was absorbed;which is an effect similar to that of a mixture of nitrous and commonair, which was mentioned before. 

The preceding experiments on the calcination of metals suggested to me amethod of explaining the cause of the mischief which is known to arisefrom fresh _paint_, made with white-lead (which I suppose is animperfect calx of lead) and oil. 

To verify my hypothesis, I first put a small pot full of this kind ofpaint, and afterwards (which answered much better, by exposing a greatersurface of the paint) I daubed several pieces of paper with it, and putthem under a receiver, and observed, that in about twenty-four hours, the air was diminished between one fifth and one fourth, for I did notmeasure it very exactly. This air also was, as I expected to find, inthe highest degree noxious; it did not effervesce with nitrous air, itwas no farther diminished by a mixture of iron filings and brimstone, and was made wholesome by agitation in water deprived of all air. 

I think it appears pretty evident, from the preceding experiments on thecalcination of metals that air is, some way or other, diminished inconsequence of being highly charged with phlogiston; and that agitationin water restores it, by imbibing a great part of the phlogisticmatter. 

That water has a considerable affinity with phlogiston, is evident fromthe strong impregnation which it receives from it. May not plants alsorestore air diminished by putrefaction by absorbing part of thephlogiston with which it is loaded? The greater part of a dry plant, aswell as of a dry animal substance, consists of inflammable air, orsomething that is capable of being converted into inflammable air; andit seems to be as probable that this phlogistic matter may have beenimbibed by the roots and leaves of plants, and afterwards incorporatedinto their substance, as that it is altogether produced by the power ofvegetation. May not this phlogistic matter be even the most essentialpart of the food and support of both vegetable and animal bodies?

In the experiments with metals, the diminution of air seems to be theconsequence of nothing but a saturation with phlogiston; and in all theother cases of the diminution of air, I do not see but that it may beeffected by the same means. When a vegetable or animal substance isdissolved by putrefaction, the escape of the phlogistic matter (which, together with all its other constituent parts, is then let loose fromit) may be the circumstance that produces the diminution of the air inwhich it putrefies. It is highly improbable that what remains after ananimal body has been thoroughly dissolved by putrefaction, should yieldso great a quantity of inflammable air, as the dried animal substancewould have done. Of this I have not made an actual trial, though I haveoften thought of doing it, and still intend to do it; but I think therecan be no doubt of the result. 

Again, iron, by its fermentation with brimstone and water, is evidentlyreduced to a calx, so that phlogiston must have escaped from it. Phlogiston also must evidently be set loose by the ignition of charcoal, and is not improbably the matter which flies off from paint, composed ofwhite-lead and oil. Lastly, since spirit of nitre is known to have avery remarkable affinity with phlogiston, it is far from beingimprobable that nitrous air may also produce the same effect by the samemeans. 

To this hypothesis it may be objected, that, if diminished air be airsaturated with phlogiston, it ought to be inflammable. But this by nomeans follows; since its inflammability may depend upon some particular_mode of combination_, or degree of affinity, with which we are notacquainted. Besides, inflammable air seems to consist of some otherprinciple, or to have some other constituent part, besides phlogistonand common air, as is probable from that remarkable deposit, which, as Ihave observed, is made by inflammable air, both from iron and zinc. 

It is not improbable, however, but that a greater degree of heat mayinflame that air which extinguishes a common candle, if it could beconveniently applied. Air that is inflammable, I observe, extinguishesred-hot wood; and indeed inflammable substances can only be those which, in a certain degree of heat, have a less affinity with the phlogistonthey contain, than the air, or some other contiguous substance, has withit; so that the phlogiston only quits one substance, with which it wasbefore combined, and enters another, with which it may be combined in avery different manner. This substance, however, whether it be air or anything else, being now fully saturated with phlogiston, and not beingable to take any more, in the same circumstances, must necessarilyextinguish fire, and put a stop to the ignition of all other bodies, that is, to the farther escape of phlogiston from them. 

That plants restore noxious air, by imbibing the phlogiston with whichit is loaded, is very agreeable to the conjectures of Dr. Franklin, made many years ago, and expressed in the following extract from thelast edition of his Letters, p. 346. 

"I have been inclined to think that the fluid _fire_, as well as thefluid _air_, is attracted by plants in their growth, and becomesconsolidated with the other materials of which they are formed, andmakes a great part of their substance; that, when they come to bedigested, and to suffer in the vessels a kind of fermentation, part ofthe fire, as well as part of the air, recovers its fluid active stateagain, and diffuses itself in the body, digesting and separating it;that the fire so re-produced, by digestion and separation, continuallyleaving the body, its place is supplied by fresh quantities, arisingfrom the continual separation; that whatever quickens the motion of thefluids in an animal, quickens the separation, and re-produces more ofthe fire, as exercise; that all the fire emitted by wood, and othercombustibles, when burning, existed in them before in a solid state, being only discovered when separating; that some fossils, as sulphur, sea-coal, &c. Contain a great deal of solid fire; and that, in short, what escapes and is dissipated in the burning of bodies, besides waterand earth, is generally the air and fire, that before made parts of thesolid. "

FOOTNOTES:

[8] I conclude from the experiments of M. Lavoisier, which were madewith a much better burning lens than I had an opportunity of making useof, that there was no _real calcination_ of the metals, though they weremade to _fume_ in inflammable or nitrous air; because he was not able toproduce more than a slight degree of calcination in any given quantityof common air. 

SECTION IX. 

_Of MARINE ACID AIR. _

Being very much struck with the result of an experiment of the Hon. Mr. Cavendish, related Phil. Trans. Vol. LVI. P. 157, by which, though, hesays, he was not able to get any inflammable air from copper, by meansof spirit of salt, he got a much more remarkable kind of air, viz. Onethat lost its elasticity by coming into contact with water, I wasexceedingly desirous of making myself acquainted with it. On thisaccount, I began with making the experiment in quicksilver, which Inever failed to do in any case in which I suspected that air mighteither be absorbed by water, or be in any other manner affected by it;and by this means I presently got a much more distinct idea of thenature and effects of this curious solution. 

Having put some copper filings into a small phial, with a quantity ofspirit of salt; and making the air (which was generated in great plenty, on the application of heat) ascend into a tall glass vessel full ofquicksilver, and standing in quicksilver, the whole produce continued aconsiderable time without any change of dimensions. I then introduced asmall quantity of water to it; when about three fourths of it (the wholebeing about four ounce measures) presently, but gradually, disappeared, the quicksilver rising in the vessel. I then introduced a considerablequantity of water; but there was no farther diminution of the air, andthe remainder I found to be inflammable. 

Having frequently continued this process a long time after the admissionof the water, I was much amused with observing the large bubbles of thenewly generated air, which came through the quicksilver, the suddendiminution of them when they came to the water, and the very smallbubbles which went through the water. They made, however, a continual, though slow, increase of inflammable air. 

Fixed air, being admitted to the whole produce of this air from copper, had no sensible effect upon it. Upon the admission of water, a greatpart of the mixture presently disappeared; another part, which I supposeto have been the fixed air, was absorbed slowly; and in this particularcase the very small permanent residuum did not take fire; but it isvery possible that it might have done so, if the quantity had beengreater. 

The solution of _lead_ in the marine acid is attended with the very samephænomena as the solution of copper in the same acid; about threefourths of the generated air disappearing on the admission of water; andthe remainder being inflammable. 

The solutions of iron, tin, and zinc, in the marine acid, were allattended with the same phænomena as the solutions of copper and lead, but in a less degree; for in iron one eighth, in tin one sixth, and inzinc one tenth of the generated air disappeared on the admission ofwater. The remainder of the air from iron, in this case, burned with agreen, or very light blue flame. 

I had always thought it something extraordinary that a species of airshould _lose its elasticity_ by the mere _contact_ of any thing, andfrom the first suspected that it must have been _imbibed_ by the waterthat was admitted to it; but so very great a quantity of this airdisappeared upon the admission of a very small quantity of water, thatat first I could not help concluding that appearances favoured theformer hypothesis. I found, however, that when I admitted a muchsmaller quantity of water, confined in a narrow glass tube, a part onlyof the air disappeared, and that very slowly, and that more of itvanished upon the admission of more water. This observation put itbeyond a doubt, that this air was properly _imbibed_ by the water, which, being once fully saturated with it, was not capable of receivingany more. 

The water thus impregnated tasted very acid, even when it was muchdiluted with other water, through which the tube containing it wasdrawn. It even dissolved iron very fast, and generated inflammable air. This last observation, together with another which immediately follows, led me to the discovery of the true nature of this remarkable kind ofair. 

Happening, at one time, to use a good deal of copper and a smallquantity of spirit of salt, in the generation of this kind of air, I wassurprized to find that air was produced long after, I could not butthink that the acid must have been saturated with the metal; and I alsofound that the proportion of inflammable air to that which was absorbedby the water continually diminished, till, instead of being one fourthof the whole, as I had first observed, it was not so much as onetwentieth. Upon this, I concluded that this subtle air did not arisefrom the copper, but from the spirit of salt; and presently making theexperiment with the acid only, without any copper, or metal of any kind, this air was immediately produced in as great plenty as before; so thatthis remarkable kind of air is, in fact, nothing more than the vapour, or fumes of spirit of salt, which appear to be of such a nature, thatthey are not liable to be condensed by cold, like the vapour of water, and other fluids, and therefore may be very properly called an _acidair_, or more restrictively, the _marine acid air_. 

This elastic acid vapour, or acid air, extinguishes flame, and is muchheavier than common air; but how much heavier, will not be easy toascertain. A cylindrical glass vessel, about three fourths of an inch indiameter, and four inches deep, being filled with it, and turned upsidedown, a lighted candle may be let down into it more than twenty timesbefore it will burn at the bottom. It is pleasing to observe the colourof the flame in this experiment; for both before the candle goes out, and also when it is first lighted again, it burns with a beautifulgreen, or rather light-blue flame, such as is seen when common salt isthrown into the fire. 

When this air is all expelled from any quantity of spirit of salt, whichis easily perceived by the subsequent vapour being condensed by cold, the remainder is a very weak acid, barely capable of dissolving iron. 

Being now in the possession of a new subject of experiments, viz. Anelastic acid vapour, in the form of a permanent air, easily procured, and effectually confined by glass and quicksilver, with which it did notseem to have any affinity; I immediately began to introduce a variety ofsubstances to it; in order to ascertain its peculiar properties andaffinities, and also the properties of those other bodies with respectto it. 

Beginning with _water_, which, from preceding observations, I knew wouldimbibe it, and become impregnated with it; I found that 2-1/2 grains ofrain-water absorbed three ounce measures of this air, after which it wasincreased one third in its bulk, and weighed twice as much as before; sothat this concentrated vapour seems to be twice as heavy as rain-water:Water impregnated with it makes the strongest spirit of salt that I haveseen, dissolving iron with the most rapidity. Consequently, two thirdsof the best spirit of salt is nothing more than mere phlegm or water. 

Iron filings, being admitted to this air, were dissolved by it prettyfast, half of the air disappearing, and the other half becominginflammable air, not absorbed by water. Putting chalk to it, fixed airwas produced. 

I had not introduced many substances to this air, before I discoveredthat it had an affinity with _phlogiston_, so that it would depriveother substances of it, and form with it such an union as constitutesinflammable air; which seems to shew, that inflammable air universallyconsists of the union of some acid vapour with phlogiston. 

Inflammable air was produced, when to this acid air I put spirit ofwine, oil of olives, oil of turpentine, charcoal, phosphorus, bees-wax, and even sulphur. This last observation, I own, surprized me; for, themarine acid being reckoned the weakest of the three mineral acids, I didnot think that it had been capable of dislodging the oil of vitriol fromthis substance; but I found that it had the very same effect both uponalum and nitre; the vitriolic acid in the former case, and the nitrousin the latter, giving place to the stronger vapour of spirit of salt. 

The rust of iron, and the precipitate of nitrous air made from copper, also imbibed this air very fast, and the little that remained of it wasinflammable air; which proves, that these calces contain phlogiston. Itseems also to be pretty evident, from this experiment, that theprecipitate above mentioned is a real calx of the metal, by the solutionof which the nitrous air is generated. 

As some remarkable circumstances attend the absorption of this acid air, by the substances above-mentioned, I shall briefly mention them. 

Spirit of wine absorbs this air as readily as water itself, and isincreased in bulk by that means. Also, when it is saturated, itdissolves iron with as much rapidity, and still continues inflammable. 

Oil of olives absorbs this air very slowly, and at the same time, itturns almost black, and becomes glutinous. It is also less miscible withwater, and acquires a very disagreeable smell. By continuing upon thesurface of the water, it became white, and its offensive smell went offin a few days. 

Oil of turpentine absorbed this air very fast, turning brown, and almostblack. No inflammable air was formed, till I raised more of the acidair than the oil was able to absorb, and let it stand a considerabletime; and still the air was but weakly inflammable. The same was thecase with the oil of olives, in the last mentioned experiment; and itseems to be probable, that, the longer this acid air had continued incontact with the oil, the more phlogiston it would have extracted fromit. It is not wholly improbable, but that, in the intermediate state, before it becomes inflammable air, it may be nearly of the nature ofcommon air. 

Bees-wax absorbed this air very slowly. About the bigness of a hazel-nutof the wax being put to three ounce measures of the acid air, the airwas diminished one half in two days, and, upon the admission of water, half of the remainder also disappeared. This air was stronglyinflammable. 

Charcoal absorbed this air very fast. About one fourth of it wasrendered immiscible in water, and was but weakly inflammable. 

A small bit of _phosphorus_, perhaps about half a grain, smoked, andgave light in the acid air, just as it would have done in common airconfined. It was not sensibly wasted after continuing about twelvehours in that state, and the bulk of the air was very little diminished. Water being admitted to it absorbed it as before, except about one fifthof the whole. It was but weakly inflammable. 

Putting several pieces of _sulphur_ to this air, it was absorbed butslowly. In about twenty-four hours about one fifth of the quantity haddisappeared; and water being admitted to the remainder, very little morewas absorbed. The remainder was inflammable, and burned with a blueflame. 

Notwithstanding the affinity which this acid air appears to have withphlogiston, it is not capable of depriving all bodies of it. I foundthat dry wood, crusts of bread, and raw flesh, very readily imbibed thisair, but did not part with any of their phlogiston to it. All thesesubstances turned very brown, after they had been some time exposed tothis air, and tasted very strongly of the acid when they were taken out;but the flesh, when washed in water, became very white, and the fibreseasily separated from one another, even more than they would have doneif it had been boiled or roasted[9]. 

When I put a piece of _saltpetre_ to this air it was presentlysurrounded with a white fume, which soon filled the whole vessel, exactly like the fume which bursts from the bubbles of nitrous air, whenit is generated by a vigorous fermentation, and such as is seen whennitrous air is mixed with this acid air. In about a minute, the wholequantity of air was absorbed, except a very little, which might be thecommon air that had lodged upon the surface of the spirit of salt withinthe phial. 

A piece of _alum_ exposed to this air turned yellow, absorbed it as fastas the saltpetre had done, and was reduced by it to the form of apowder. Common salt, as might be expected, had no effect whatever onthis marine acid air. 

I had also imagined, that if air diminished by the processesabove-mentioned was affected in this manner, in consequence of its beingsaturated with phlogiston, a mixture of this acid air might imbibe thatphlogiston, and render it wholesome again; but I put about one fourth ofthis air to a quantity of air in which metals had been calcined, withoutmaking any sensible alteration in it. I do not, however, infer fromthis, that air is not diminished by means of phlogiston, since thecommon air, like some other substances, may hold the phlogiston toofast, to be deprived of it by this acid air. 

I shall conclude my account of these experiments with observing, thatthe electric spark is visible in acid air, exactly as it is in commonair; and though I kept making this spark a considerable time in aquantity of it, I did not perceive that any sensible alteration was madein it. A little inflammable air was produced, but not more than mighthave come from the two iron nails which I made use of in taking thesparks. 

FOOTNOTES:

[9] It will be seen, in the second part of this work, that, in some ofthese processes, I had afterwards more success. 

SECTION X. 

MISCELLANEOUS OBSERVATIONS. 

1. As many of the preceding observations relate to the _vinous_ and_putrefactive_ fermentations, I had the curiosity to endeavour toascertain in what manner the air would be affected by the _acetous_fermentation. For this purpose I inclosed a phial full of small beer ina jar standing in water; and observed that, during the first two orthree days, there was an increase of the air in the jar, but from thattime it gradually decreased, till at length there appeared to be adiminution of about one tenth of the whole quantity. 

During this time the whole surface of it was gradually covered with ascum, beautifully corrugated. After this there was an increase of theair till there was more than the original quantity; but this must havebeen fixed air, not incorporated with the rest of the mass; for, withdrawing the beer, which I found to be sour, after it had stood 18 or20 days under the jar, and passing the air several times through coldwater, the original quantity was diminished about one ninth. In theremainder a candle would not burn, and a mouse would have diedpresently. 

The smell of this air was exceedingly pungent, but different from thatof the putrid effluvium. A mouse lived perfectly well in this air, thusaffected with the acetous fermentation; after it had stood several daysmixed with four times the quantity of fixed air. 

2. All the kinds of factitious air on which I have yet made theexperiment are highly noxious, except that which is extracted fromsaltpetre, or alum; but in this even a candle burned just as in commonair[10]. In one quantity which I got from saltpetre a candle not onlyburned, but the flame was increased, and something was heard like ahissing, similar to the decrepitation of nitre in an open fire. Thisexperiment was made when the air was fresh made, and while it probablycontained some particles of nitre, which would have been depositedafterwards. The air was extracted from these substances by heating themin a gun-barrel, which was much corroded and soon spoiled by theexperiment. What effect this circumstance may have had upon the air Ihave not considered. 

November 6, 1772, I had the curiosity to examine the state of a quantityof this air which had been extracted from saltpetre above a year, andwhich at first was perfectly wholesome; when, to my very great surprize, I found that it was become, in the highest degree, noxious. It made noeffervescence with nitrous air, and a mouse died the moment it was putinto it. I had not, however, washed it in rain-water quite ten minutes(and perhaps less time would have been sufficient) when I found, upontrial, that it was restored to its former perfectly wholesome state. Iteffervesced with nitrous air as much as the best common air ever does;and even a candle burned in it very well, which I had never beforeobserved of any kind of noxious air meliorated by agitation in water. This series of facts, relating to air extracted from nitre, appear to meto be very extraordinary and important, and, in able hands, may lead toconsiderable discoveries. 

3. There are many substances which impregnate common air in a veryremarkable manner, but without making it noxious to animals. Among otherthings I tried volatile alkaline salts, and camphor; the latter of whichI melted with a burning-glass, in air inclosed in a phial. The mouse, which was put into this air, sneezed and coughed very much, especiallyafter it was taken out; but it presently recovered, and did not appearto have been sensibly injured. 

4. Having made several experiments with a mixture of iron filings andbrimstone, kneaded to a paste with water, I had the curiosity to trywhat would be the effect of substituting _brass dust_ in the place ofthe iron filings. The result was, that when this mixture had stood aboutthree weeks, in a given quantity of air, it had turned black, but wasnot increased in bulk. The air also was neither sensibly increased nordecreased, but the nature of it was changed; for it extinguished flame, it would have killed a mouse presently, and was not restored by fixedair, which had been mixed with it several days. 

5. I have frequently mentioned my having, at one time, exposed equalquantities of different kinds of air in jars standing in boiled water. _Common air_ in this experiment was diminished four sevenths, and theremainder extinguished flame. This experiment demonstrates that waterdoes not absorb air equally, but that it decomposes it, taking one part, and leaving the rest. To be quite sure of this fact, I agitated aquantity of common air in boiled water, and when I had reduced it fromeleven ounce measures to seven, I found that it extinguished a candle, but a mouse lived in it very well. At another time a candle barely wentout when the air was diminished one third, and at other times I havefound this effect lake place at other very different degrees ofdiminution. 

This difference I attribute to the differences in the state of the waterwith respect to the air contained in it; for sometimes it had stoodlonger than at other times before I made use of it. I also useddistilled-water, rain-water, and water out of which the air had beenpumped, promiscuously with rain water. I even doubt, not but that, in acertain state of the water, there might be no sensible difference inthe bulk of the agitated air, and yet at the end of the process it wouldextinguish a candle, air being supplied from the water in the place ofthat part of the common air which had been absorbed. 

It is certainly a little extraordinary that the very same process shouldso far mend putrid air, as to reduce it to the standard of air in whichcandles have burned out; and yet that it should so far injure common andwholesome air as to reduce it to about the same standard: but so thefact certainly is. If air extinguish flame in consequence of its beingpreviously saturated with phlogiston, it must, in this case, have beentransferred from the water to the air, and it is by no meansinconsistent with this hypothesis to suppose, that, if the air be oversaturated with phlogiston, the water will imbibe it, till it be reducedto the same proportion that agitation in water would have communicatedto it. 

To a quantity of common air, thus diminished by agitation in water, tillit extinguished a candle, I put a plant, but it did not so far restoreit as that a candle would burn in it again; which to me appeared not alittle extraordinary, as it did not seem to be in a worse state than airin which candles had burned out, and which had never failed to berestored by the same means. 

I had no better success with a quantity of permanent air which I hadcollected from my pump-water. Indeed these experiments were begun beforeI was acquainted with that property of nitrous air, which makes it soaccurate a measure of the goodness of other kinds of air; and it mightperhaps be rather too late in the year when I made the experiments. Having neglected these two jars of air, the plants died and putrefied inboth of them; and then I found the air in them both to be highlynoxious, and to make no effervescence with nitrous air. 

I found that a pint of my pump-water contained about one fourth of anounce measure of air, one half of which was afterwards absorbed bystanding in fresh pump-water. A candle would not burn in this air, but amouse lived in it very well. Upon the whole, it seemed to be in aboutthe same state as air in which a candle had burned out. 

6. I once imagined that, by mere _stagnation_, air might become unfitfor respiration, or at least the burning of candles; but if this be thecase, and the change be produced gradually, it must require a long timefor the purpose. For on the 22d of September 1772, I examined a quantityof common air, which had been kept in a phial, without agitation, fromMay 1771, and found it to be in no respect worse than fresh air, even bythe test of the nitrous air. 

7. The crystallization of nitre makes no sensible alteration in the airin which the process is made. For this purpose I dissolved as much nitreas a quantity of hot water would contain, and let it cool under areceiver, standing in water. 

8. November 6, 1772, a quantity of inflammable air, which, by longkeeping, had come to extinguish flame, I observed to smell very muchlike common air in which a mixture of iron filings and brimstone hadstood. It was not, however, quite so strong, but it was equally noxious. 

9. Bismuth and nickel are dissolved in the marine acid with theapplication of a considerable degree of heat; but little or no air isgot from either of them; but, what I thought a little remarkable, bothof them smelled very much like Harrowgate water, or liver of sulphur. This smell I have met with several times in the course of myexperiments, and in processes very different from one another. 

FOOTNOTES:

[10] Experiments, of which an account will be given in the second partof this work, make it probable, that though a candle burned even _morethan well_ in this air, an animal would not have lived in it. At thetime of this first publication, however, I had no idea of this beingpossible in nature. 

PART II. 

_Experiments and Observations made in the Year 1773, and the Beginningof 1774. _

SECTION I. 

_Observations on ALKALINE AIR. _

After I had made the discovery of the _marine acid air_, which thevapour of spirit of salt may properly enough be called, and had madethose experiments upon it, of which I have given an account in theformer part of this work, and others which I propose to recite in thispart; it occurred to me, that, by a process similar to that by whichthis _acid_ air is expelled from the spirit of salt, an _alkaline_ airmight be expelled from substances containing volatile alkali. 

Accordingly I procured some volatile spirit of sal ammoniac, and havingput it into a thin phial, and heated it with the flame of a candle, Ipresently found that a great quantity of vapour was discharged from it;and being received in a vessel of quicksilver, standing in a bason ofquicksilver, it continued in the form of a transparent and permanentair, not at all condensed by cold; so that I had the same opportunity ofmaking experiments upon it, as I had before on the acid air, being inthe same favourable circumstances. 

With the same ease I also procured this air from _spirit of hartshorn_, and _sal volatile_ either in a fluid or solid form, i. E. From thosevolatile alkaline salts which are produced by the distillation of salammoniac with fixed alkalis. But in this case I soon found that thealkaline air I procured was not pure; for the fixed air, which enteredinto the composition of my materials, was expelled along with it. Also, uniting again with the alkaline air, in the glass tube through whichthey were conveyed, they stopped it up, and were often the means ofbursting my vessels. 

While these experiments were new to me, I imagined that I was able toprocure this air with peculiar advantage and in the greatest abundance, either from the salts in a dry state, when they were just covered withwater, or in a perfectly fluid state; for, upon applying a candle to thephials in which they were contained, there was a most astonishingproduction of air; but having examined it, I found it to be chieflyfixed air, especially after the first or second produce from the samematerials; and removing my apparatus to a trough of water and using thewater instead of quicksilver, I found that it was not presently absorbedby it. 

This, however, appears to be an easy and elegant method of procuringfixed air, from a small quantity of materials, though there must be amixture of alkaline air along with it; as it is by means of itscombination with this principle only, that it is possible, that so muchfixed air should be retained in any liquid. Water, at least, we know, cannot be made to contain much more than its own bulk of fixed air. 

After this disappointment, I confined myself to the use of that volatilespirit of sal ammoniac which is procured by a distillation with slakedlime, which contains no fixed air; and which seems, in a general state, to contain about as much alkaline air, as an equal quantity of spirit ofsalt contains of the acid air. 

Wanting, however, to procure this air in greater quantities, and thismethod being rather expensive, it occurred to me, that alkaline airmight, probably, be procured, with the most ease and convenience, fromthe original materials, mixed in the same proportions that chemists hadfound by experience to answer the best for the production of thevolatile spirit of sal ammoniac. Accordingly I mixed one fourth ofpounded sal ammoniac, with three fourths of slaked lime; and filling aphial with the mixture, I presently found it completely answered mypurpose. The heat of a candle expelled from this mixture a prodigiousquantity of alkaline air; and the same materials (as much as filled anounce phial) would serve me a considerable time, without changing;especially when, instead of a glass phial, I made use of a small irontube, which I find much more convenient for the purpose. 

As water soon begins to rise in this process, it is necessary, if theair is intended to be conveyed perfectly _dry_ into the vessel ofquicksilver, to have a small vessel in which this water (which is thecommon volatile spirit of sal ammoniac) may be received. This smallvessel must be interposed between the vessel which contains thematerials for the generation of the air, and that in which it is to bereceived, as _d_ fig. 8. 

This _alkaline_ air being perfectly analogous to the _acid_ air, I wasnaturally led to investigate the properties of it in the same manner, and nearly in the same order. From this analogy I concluded, as Ipresently found to be the fact, that this alkaline air would be readilyimbibed by water, and, by its union with it, would form a volatilespirit of sal ammoniac. And as the water, when admitted to the air inthis manner, confined by quicksilver, has an opportunity of fullysaturating itself with the alkaline vapour, it is made prodigiouslystronger than any volatile spirit of sal ammoniac that I have ever seen;and I believe stronger than it can be made in the common way. 

In order to ascertain what addition, with respect to quantity andweight, water would acquire by being saturated with alkaline air, I put1-1/4 grains of rain-water into a small glass tube, closed at one endwith cement, and open at the other, the column of water measuring 7/10of an inch; and having introduced it through the quicksilver into avessel containing alkaline air, observed that it absorbed 7/8 of anounce measure of the _air_, and had then gained about half a grain inweight, and was increased to 8-1/2 tenths of an inch in length. I didnot make a second experiment of this kind, and therefore will not answerfor the exactness of these proportions in future trials. What I didsufficiently answered my purpose, in a general view of the subject. 

When I had, at one time, saturated a quantity of distilled water withalkaline air, so that a good deal of the air remained unabsorbed on thesurface of the water, I observed that, as I continued to throw up moreair, a considerable proportion of it was imbibed, but not the whole; andwhen I had let the apparatus stand a day, much more of the air that layon the surface was imbibed. And after the water would imbibe no more ofthe _old_ air, it imbibed _new_. This shews that water requires aconsiderable time to saturate itself with this kind of air, and thatpart of it more readily unites with water than the rest. 

The same is also, probably, the case with all the kinds of air withwhich water can be impregnated. Mr. Cavendish made this observation withrespect to fixed air, and I repeated the whole process above-mentionedwith acid air, and had precisely the same result. The alkaline waterwhich I procured in this experiment was, beyond comparison, stronger tothe smell, than any spirit of sal ammoniac that I had seen. 

This experiment led me to attempt the making of spirit of sal ammoniacin a larger quantity, by impregnating distilled water with this alkalineair. For this purpose I filled a piece of a gun-barrel with thematerials above-mentioned, and luted to the open end of it a small glasstube, one end of which was bent, and put within the mouth of a glassvessel, containing a quantity of distilled water upon quicksilver, standing in a bason of quicksilver, as in fig. 7. In these circumstancesthe heat of the fire, applied gradually, expelled the alkaline air, which, passing through the tube, and the quicksilver, came at last tothe water, which, in time, became fully saturated with it. 

By this means I got a very strong alkaline liquor, from which I couldagain expel the alkaline air which I had put into it, whenever ithappened to be more convenient to me to get it in that manner. Thisprocess may easily be performed in a still larger way; and by this meansa liquor of the same nature with the volatile spirit of sal ammoniac, might be made much stronger, and much cheaper, than it is now made. 

Having satisfied myself with respect to the relation that alkaline airbears to water, I was impatient to find what would be the consequenceof mixing this new air with the other kinds with which I was acquaintedbefore, and especially with _acid_ air; having a notion that these twoairs, being of opposite natures, might compose a _neutral air_, andperhaps the very same thing with common air. But the moment that thesetwo kinds of air came into contact, a beautiful white cloud was formed, and presently filled the whole vessel in which they were contained. Atthe same time the quantity of air began to diminish, and, at length, when the cloud was subsided, there appeared to be formed a solid _whilesalt_, which was found to be the common _sal ammoniac_, or the marineacid united to the volatile alkali. 

The first quantity that I produced immediately deliquesced, upon beingexposed to the common air; but if it was exposed in a very dry and warmplace, it almost all evaporated, in a white cloud. I have, however, since, from the same materials, produced the salt above-mentioned in astate not subject to deliquesce or evaporate. This difference, I find, is owing to the proportion of the two kinds of air in the compound. Itis only volatile when there is more than a due proportion of either ofthe constituent parts. In these cases the smell of the salts isextremely pungent, but very different from one another; being manifestlyacid, or alkaline, according to the prevalence of each of these airsrespectively. 

_Nitrous air_ admitted to alkaline air likewise occasioned a whitishcloud, and part of the air was absorbed; but it presently grew clearagain; leaving only a little dimness on the sides of the vessel. This, however, might be a kind of salt, formed by the union of the two kindsof air. There was no other salt formed that I could perceive. Waterbeing admitted to this mixture of nitrous and alkaline air presentlyabsorbed the latter, and left the former possessed of its peculiarproperties. 

_Fixed air_ admitted to alkaline air formed oblong and slender crystals, which crossed one another, and covered the sides of the vessel in theform of net-work. These crystals must be the same thing with thevolatile alkalis which chemists get in a solid form, by the distillationof sal ammoniac with fixed alkaline salts. 

_Inflammable air_ admitted to alkaline air exhibited no particularappearance. Water, as in the former experiment, absorbed the alkalineair, and left the inflammable air as it was before. It was remarkable, however, that the water which was admitted to them became whitish, andthat this white cloud settled, in the form of a white powder, to thebottom of the vessel. 

Alkaline air mixed with _common air_, and standing together severaldays, first in quicksilver, and then in water (which absorbed thealkaline air) it did not appear that there was any change produced inthe common air: at least it was as much diminished by nitrous air asbefore. The same was the case with a mixture of acid air and common air. 

Having mixed air that had been diminished by the fermentation of amixture of iron filings and brimstone with alkaline air, the waterabsorbed the latter, but left the former, with respect to the test ofnitrous air (and therefore, as I conclude, with respect to all itsproperties) the same that it was before. 

_Spirit of wine_ imbibes alkaline air as readily as water, and seems tobe as inflammable afterwards as before. 

Alkaline air contracts no union with _olive oil_. They were in contactalmost two days, without any diminution of the air. Oil of turpentine, and essential oil of mint, absorbed a very small quantity of alkalineair, but were not sensibly changed by it. 

_Ether_, however, imbibed alkaline air pretty freely; but it wasafterwards as inflammable as before, and the colour was not changed. Italso evaporated as before, but I did not attend to this lastcircumstance very accurately. 

_Sulphur_, _nitre_, _common salt_, and _flints_, were put to alkalineair without imbibing any part of it; but _charcoal_, _spunge_, bits of_linen cloth_, and other substances of that nature, seemed to condensethis air upon their surfaces; for it began to diminish immediately upontheir being put to it; and when they were taken out the alkaline smellthey had contracted was so pungent as to be almost intolerable, especially that of the spunge. Perhaps it might be of use to recoverpersons from swooning. A bit of spunge, about as big as a hazel nut, presently imbibed an ounce measure of alkaline air. 

A piece of the inspissated juice of _turnsole_ was made very dry andwarm, and yet it imbibed a great quantity of the air; by which itcontracted a most pungent smell, but the colour of it was not changed. 

_Alum_ undergoes a very remarkable change by the action of alkaline air. The outward shape and size remain the same, but the internal structureis quite changed, becoming opaque, beautifully white, and, toappearance, in all respects, like alum which had been roasted; and so asnot to be at all affected by a degree of heat that would have reduced itto that state by roasting. This effect is produced slowly; and if apiece of alum be taken out of alkaline air before the operation is over, the inside will be transparent, and the outside, to an equal thickness, will be a white crust. 

I imagine that the alkaline vapour seizes upon the water that entersinto the constitution of crude alum, and which would have been expelledby heat. Roasted alum also imbibes alkaline air, and, like the raw alumthat has been exposed to it, acquires a taste that is peculiarlydisagreeable. 

_Phosphorus_ gave no light in alkaline air, and made no lasting changein its dimensions. It varied, indeed, a little, being sometimesincreased and sometimes diminished, but after a day and a night, it wasin the same state as at the first. Water absorbed this air just as ifnothing had been put to it. 

Having put some _spirit of salt_ to alkaline air, the air was presentlyabsorbed, and a little of the white salt above-mentioned was formed. Alittle remained unabsorbed, and transparent, but upon the admission ofcommon air to it, it instantly became white. 

_Oil of vitriol_, also formed a white salt with alkaline air, and thisdid not rise in white fumes. 

Acid air, as I have observed in my former papers, extinguishes a candle. Alkaline air, on the contrary, I was surprized to find, is slightlyinflammable; which, however, seems to confirm the opinion of chemists, that the volatile alkali contains phlogiston. 

I dipped a lighted candle into a tall cylindrical vessel, filled withalkaline air, when it went out three or four times successively; but ateach time the flame was considerably enlarged, by the addition ofanother flame, of a pale yellow colour; and at the last time this lightflame descended from the top of the vessel to the bottom. At anothertime, upon presenting a lighted candle to the mouth of the same vessel, filled with the same kind of air, the yellowish flame ascended twoinches higher than the flame of the candle. The electric spark taken inalkaline air is red, as it is in common inflammable air. 

Though alkaline air be inflammable, it appeared, by the followingexperiment, to be heavier than the common inflammable air, as well as tocontract no union with it. Into a vessel containing a quantity ofinflammable air, I put half as much alkaline air, and then about thesame quantity of acid air. These immediately formed a white cloud, butit did not rise within the space that was occupied by the inflammableair; so that this latter had kept its place above the alkaline air, andhad not mixed with it. 

That alkaline air is lighter than acid air is evident from theappearances that attend the mixture, which are indeed very beautiful. When acid air is introduced into a vessel containing alkaline air, thewhite cloud which they form appears at the bottom only, and ascendsgradually. But when the alkaline air is put to the acid, the wholebecomes immediately cloudy, quite to the top of the vessel. 

In the last place, I shall observe that alkaline air, as well as acid, dissolves _ice_ as fast as a hot fire can do it. This was tried whenboth the kinds of air, and every instrument made use of in theexperiment, had been exposed to a pretty intense frost several hours. Inboth cases, also, the water into which the ice was melted dissolved moreice, to a considerable quantity. 

SECTION II. 

_Of COMMON AIR diminished and made noxious by various processes. _

It will have been observed that, in the first publication of my papers, I confined myself chiefly to the narration of the new _facts_ which Ihad discovered, barely mentioning any _hypotheses_ that occurred to me, and never seeming to lay much stress upon them. The reason why I was somuch upon my guard in this respect was, left, in consequence ofattaching myself to any hypothesis too soon, the success of my futureinquiries might be obstructed. But subsequent experiments having throwngreat light upon the preceding ones and having confirmed the fewconjectures I then advanced, I may now venture to speak of my hypotheseswith a little less diffidence. Still, however, I shall be ready torelinquish any notions I may now entertain, if new facts shouldhereafter appear not to favour them. 

In a great variety of cases I have observed that there is a remarkable_diminution_ of common, or respirable air, in proportion to which it isalways rendered unfit for respiration, indisposed to effervesce withnitrous air, and incapable of farther diminution from any other cause. The circumstances which produce this effect I had then observed to bethe burning of candles, the respiration of animals, the putrefaction ofvegetables or animal substances, the effervescence of iron filings andbrimstone, the calcination of metals, the fumes of charcoal, theeffluvia of paint made of white-lead and oil, and a mixture of nitrousair. 

All these processes, I observed, agree in this one circumstance, and Ibelieve in no other, that the principle which the chemists call_phlogiston_ is set loose; and therefore I concluded that the diminutionof the air was, in some way or other, the consequence of the airbecoming overcharged with phlogiston, [11] and that water, and growingvegetables, tend to restore this air to a state fit for respiration, byimbibing the superfluous phlogiston. Several experiments which I havesince made tend to confirm this supposition. 

Common air, I find, is diminished, and rendered noxious, by _liver ofsulphur_, which the chemists say exhales phlogiston, and nothing else. The diminution in this case was one fifth of the whole, and afterwards, as in other similar cases, it made no effervescence with nitrous air. 

I found also, after Dr. Hales, that air is diminished by _Homberg'spyrophorus_. 

The same effect is produced by firing _gunpowder_ in air. This I triedby firing the gunpowder in a receiver half exhausted, by which the airwas rather more injured than it would have been by candles burning init. 

Air is diminished by a cement made with one half common coarseturpentine and half bees-wax. This was the result of a very casualobservation. Having, in an air-pump of Mr. Smeaton's construction, closed that end of the syphon-gage, which is exposed to the outward air, with this cement (which I knew would make it perfectly air-light)instead of sealing it hermetically; I observed that, in a course oftime, the quicksilver in that leg kept continually rising, so that themeasures I marked upon it were of no use to me; and when I opened thatend of the tube, and closed it again, the same consequence always tookplace. At length, suspecting that this effect must have arisen from thebit of _cement_ diminishing the air to which it was exposed, I coveredall the inside of a glass tube with it, and one end of it being quiteclosed with the cement, I set it perpendicular, with its open endimmersed in a bason of quicksilver; and was presently satisfied that myconjecture was well founded: for, in a few days, the quicksilver rose somuch within the tube, that the air in the inside appeared to bediminished about one sixth. 

To change this air I filled the tube with quicksilver, and pouring itout again, I replaced the tube in its former situation; when the air wasdiminished again, but not so fast as before. The same lining of cementdiminished the air a third time. How long it will retain this power Icannot tell. This cement had been made several months before I madethis experiment with it. I must observe, however, that another quantityof this kind of cement, made with a finer and more liquid turpentine, had not the power of diminishing air, except in a very small proportion. Also the common red cement has this property in the same small degree. Common air, however, which had been confined in a glass vessel linedwith this cement about a month, was so far injured that a candle wouldnot burn in it. In a longer time it would, I doubt not, have becomethoroughly noxious. 

Iron that has been suffered to rust in nitrous air diminishes common airvery fast, as I shall have occasion to mention when I give acontinuation of my experiments on nitrous air. 

Lastly, the same effect, I find, is produced by the _electric spark_, though I had no expectation of this event when I made the experiment. 

This experiment, however, and those which I have made in pursuance ofit, has fully confirmed another of my conjectures, which relates to the_manner_ in which air is diminished by being overcharged withphlogiston, viz. The phlogiston having a nearer affinity with some ofthe constituent parts of the air than the fixed air which enters intothe composition of it, in consequence of which the fixed air isprecipitated. 

This I first imagined from perceiving that lime-water became turbid byburning candles over it, p. 44. This was also the case with lime-waterconfined in air in which an animal substance was putrefying, or in whichan animal died, p. 79. And that in which charcoal was burned, p. 81. But, in all these cases, there was a possibility of the fixed air beingdischarged from the candle, the putrefying substance, the lungs of theanimal, or the charcoal. That there is a precipitation of lime whennitrous air is mixed with common air, I had not then observed, but Ihave since found it to be the case. 

That there was no precipitation of lime when brimstone was burned, Iobserved, p. 45. Might be owing to the fixed air and the lime unitingwith the vitriolic acid, and making a salt, which was soluble in water;which salt I, indeed, discovered by the evaporation of the water. 

I also observed, p. 46, 105. That diminished air being rather lighterthan common air is a circumstance in favour of the fixed, or theheavier part of the common air, having been precipitated. 

It was upon this idea, together with others similar to it, that I tookso much pains to mix fixed air with air diminished by respiration orputrefaction, in order to make it fit for respiration again; and Ithought that I had, in general, succeeded to a considerable degree, p. 99, &c. I will add, also, what I did not mention before, that I onceendeavoured, but without effect, to preserve mice alive in the sameunchanged air, by supplying them with fixed air, when the air in whichthey were confined began to be injured by their respiration. Withouteffect, also, I confined for some months, a quantity of quick lime in agiven quantity of common air, thinking it might extract the fixed airfrom it. 

The experiments which I made with electricity were solely intended toascertain what has often been attempted, but, as far as I know, hadnever been fully accomplished, viz. To change the blue colour ofliquors, tinged with vegetable juices, red. 

For this purpose I made use of a glass tube, about one tenth of an inchdiameter in the inside, as in fig. 16. In one end of this I cemented apiece of wire _b_, on which I put a brass ball. The lower part from _a_was filled with water tinged blue, or rather purple, with the juice ofturnsole, or archil. This is easily done by an air-pump, the tube beingset in a vessel of the tinged water. 

Things being thus prepared, I perceived that, after I had taken theelectric spark, between the wire _b_, and the liquor at _a_, about aminute, the upper part of it began to look red, and in about two minutesit was very manifestly so; and the red part, which was about a quarterof an inch in length, did not readily mix with the rest of the liquor. Iobserved also, that if the tube lay inclined while I took the sparks, the redness extended twice as far on the lower side as on the upper. 

The most important, though the least expected observation, however, wasthat, in proportion as the liquor became red, it advanced nearer to thewire, so that the space of air in which the sparks were taken wasdiminished; and at length I found that the diminution was about onefifth of the whole space; after which more electrifying produced nosensible effect. 

To determine whether the cause of the change of colour was in the _air_, or in the _electric matter_, I expanded the air which had beendiminished in the tube by means of an air-pump, till it expelled all theliquor, and admitted fresh blue liquor into its place; but after that, electricity produced no sensible effect, either on the air, or on theliquor; so that it was evident that the electric matter had decomposedthe air, and had made it deposite something that was of an acid nature. 

In order to determine whether the _wire_ had contributed any thing tothis effect, I used wires of different metals, iron, copper, brass, andsilver; but the result was the very same with them all. 

It was also the same when, by means of a bent glass tube, I made theelectric spark without any wire at all, in the following manner. Eachleg of the tube, fig. 19. Stood in a bason of quicksilver; which, bymeans of an air-pump, was made to ascend as high as _a, a_, in each leg, while the space between _a_ and _b_ in each contained the blue liquor, and the space between _b_ and _b_ contained common air. Things beingthus disposed, I made the electric spark perform the circuit from oneleg to the other, passing from the liquor in one leg of the tube to theliquor in the other leg, through the space of air. The effect was, thatthe liquor, in both the legs, became red, and the space of air betweenthem was contracted, as before. 

Air thus diminished by electricity makes no effervescence with, and isno farther diminished by a mixture of nitrous air; so that it must havebeen in the highest degree noxious, exactly like air diminished by anyother process. 

In order to determine what the _acid_ was, which was deposited by theair, and which changed the colour of the blue liquor, I exposed a smallquantity of the liquor so changed to the common air, and found that itrecovered its blue colour, exactly as water, tinged with the same blue, and impregnated with fixed air, will do. But the following experimentwas still more decisive to this purpose. Taking the electric spark upon_lime-water_, instead of the blue liquor, the lime was precipitated asthe air diminished. 

From these experiments it pretty clearly follows, that the electricmatter either is, or contains phlogiston; since it does the very samething that phlogiston does. It is also probable, from these experiments, that the sulphureous smell, which is occasioned by electricity, beingvery different from that of fixed air, the phlogiston in the electricmatter itself may contribute to it. 

It was now evident that common air diminished by any one of theprocesses above-mentioned being the same thing, as I have observed, withair diminished by any other of them (since it is not liable to befarther diminished by any other) the loss which it sustains, in all thecases, is, in part, that of the _fixed air_ which entered into itsconstitution. The fixed air thus precipitated from common air by meansof phlogiston unites with lime, if any lime water be ready to receiveit, unless there be some other substance at hand, with which it has agreater affinity, as the _calces of metals_. 

If the whole of the diminution of common air was produced by thedeposition of fixed air, it would be easy to ascertain the quantity offixed air that is contained in any given quantity of common air. But itis evident that the whole of the diminution of common air by phlogistonis not owing to the precipitation of fixed air, because a mixture ofnitrous air will make a great diminution in all kinds of air that arefit for respiration, even though they never were common air, and thoughnothing was used in the process for generating them that can be supposedto yield fixed air. 

Indeed, it appears, from some of the experiments, that the diminution ofsome of these kinds of air by nitrous air is so great, and approaches sonearly to the quantity of the diminution of common air by the sameprocess, as to shew that, unless they be very differently affected byphlogiston, very little is to be allowed to the loss of fixed air in thediminution of common air by nitrous air. 

The kinds of air on which this experiment was made were inflammable air, nitrous air diminished by iron filings and brimstone, and nitrous airitself; all of which are produced by the solution of metals in acids;and also on common air diminished and made noxious, and thereforedeprived of its fixed air by phlogistic processes; and they wererestored to a great degree of purity by agitation in water, out of whichits own air had been carefully boiled. 

To five parts of inflammable air, which had been agitated in water tillit was diminished about one half (at which time part of it fired with aweak explosion) I put one part of nitrous air, which diminished it oneeighth of the whole. This was done in lime-water, without anyprecipitation of lime. To compare this with common air, I mixed the samequantity, viz. Five parts of this, and one part of nitrous air: whenconsiderable crust of lime was formed upon the surface of the limewater, though the diminution was very little more than in the formerprocess. It is possible, however, that the common air might have takenmore nitrous air before it was fully saturated, so as to begin toreceive an addition to its bulk. 

I agitated in water a quantity of nitrous air phlogisticated with ironfilings and brimstone, and found it to be so far restored, that threefourths of an ounce measure of nitrous air being put to two ouncemeasures of it, made no addition to it. 

But the most remarkable of these experiments is that which I made with_nitrous air_ itself which I had no idea of the possibility of reducingto a state fit for respiration by any process whatever, at the time ofmy former publication on this subject. This air, however, itself, without any previous phlogistication, is purified by agitation in watertill it is diminished by fresh nitrous air, and to a very considerabledegree. 

In a pretty long time I agitated nitrous air in water, supplying it fromtime to time with more, as the former quantity diminished, till only oneeighteenth of the whole quantity remained; in which state it was sowholesome, that a mouse lived in two ounce measures of it more than tenminutes, without shewing any sign of uneasiness; so that I concluded itmust have been about as good as air in which candles had burned out. After agitating it again in water, I put one part of fresh nitrous airto five parts of this air, and it was diminished one ninth part. I thenagitated it a third time, and putting more nitrous air to it, it wasdiminished again in the same proportion, and so a fourth time; so that, by continually repeating the process, it would, I doubt not, have beenall absorbed. These processes were made in lime-water, without formingany incrustation on the surface of it. 

Lastly, I took a quantity of common air, which had been diminished andmade noxious by phlogistic processes; and when it had been agitated inwater, I found that it was diminished by nitrous air, though not so muchas it would have been at the first. After cleansing it a second time, itwas diminished again by the same means; and, after that, a third time;and thus there can be no doubt but that, in time, the whole quantitywould have disappeared. For I have never found that agitation in water, deprived of its own air, made any addition to a quantity of noxious air;though, _a priori_, it might have been imagined that, as a saturationwith phlogiston diminishes air, the extraction of phlogiston wouldincrease the bulk of it. On the contrary, agitation in water alwaysdiminished noxious air a little; indeed, if water be deprived of all itsown air, it is impossible to agitate any kind of air in it without someloss. Also, when noxious air has been restored by plants, I neverperceived that it gained any addition to its bulk by that means. Therewas no incrustation of the lime-water in the above-mentioned experiment. 

It is not a little remarkable, that those kinds of air which never hadbeen common air, as inflammable air, phlogisticated nitrous air, andnitrous air itself, when rendered wholesome by agitation in water, should be more diminished by fresh nitrous air, than common air whichhad been made noxious, and restored by the same process; and yet, fromthe few trials that I have made, I could not help concluding that thisis the case. 

In this course of experiments I was very near deceiving myself, inconsequence of transferring the nitrous air which I made use of in abladder, in the manner described, p. 15. Fig. 9. So as to conclude thatthere was a precipitation of lime in all the above-mentioned cases, andthat even nitrous air itself produced that effect. But after repeatedtrials, I found that there was no precipitation of lime, except, in thefirst diminution of common air, when the nitrous air was transferred ina glass vessel. 

That the calces of metals contain air, of some kind or other, and thatthis air contributes to the additional weight of the calces, above thatof the metals from which they are made, had been observed by Dr. Hales;and Mr. Hartley had informed me, that when red-lead is boiled in linseedoil, there is a prodigious discharge of air before they incorporate. Ihad likewise found, that no weight is either gained or lost by thecalcination of tin in a close glass vessel; but I purposely deferredmaking any more experiments on the subject, till we should have someweather in which I could make use of a large burning lens, which I hadprovided for that and other purposes; but, in the mean time, I was ledto the discovery in a different manner. 

Having, by the last-recited experiments, been led to consider theelectric matter as phlogiston, or something containing phlogiston, I wasendeavouring to revivify the calx of lead with it; when I was surprizedto perceive a considerable generation of air. It occurred to me, thatpossibly this effect might arise from the _heat_ communicated to thered-lead by the electric sparks, and therefore I immediately filled asmall phial with the red-lead, and heating it with a candle, I presentlyexpelled from it a quantity of air about four or five times the bulk ofthe lead, the air being received in a vessel of quicksilver. How muchmore air it would have yielded, I did not try. 

Along with the air, a small quantity of _water_ was likewise thrown out;and it immediately occurred to me, that this water and air together mustcertainly be the cause of the addition of weight in the calx. It stillremained to examine what kind of air this was; but admitting water toit, I found that it was imbibed by it, exactly like _fixed air_, which Itherefore immediately concluded it must be[12]. 

After this, I found that Mr. Lavoisier had completely discovered thesame thing, though his apparatus being more complex, and less accuratethan mine, he concluded that more of the air discharged from the calcesof metals was immiscible with water than I found it to be. It appearedto me that I had never obtained fixed air more pure. 

It being now pretty clearly determined, that common air is made todeposit the fixed air which entered into the constitution of it, bymeans of phlogiston, in all the cases of diminished air, it will follow, that in the precipitation of lime, by breathing into lime-water thefixed air, which incorporates with lime, comes not from the lungs, butfrom the common air, decomposed by the phlogiston exhaled from them, anddischarged, after having been taken in with the aliment, and havingperformed its function in the animal system. 

Thus my conjecture is more confirmed, that the cause of the death ofanimals in confined air is not owing to the want of any _pabulum vitæ_, which the air had been supposed to contain, but to the want of adischarge of the phlogistic matter, with which the system was loaded;the air, when once saturated with it, being no sufficient _menstruum_ totake it up. 

The instantaneous death of animals put into air so vitiated, I stillthink is owing to some _stimulus_, which, by causing immediate, universal and violent convulsions, exhausts the whole of the _vis vitæ_at once; because, as I have observed, the manner of their death is thevery same in all the different kinds of noxious air. 

To this section on the subject of diminished, and noxious air, or as itmight have been called _phlogisticated air_, I shall subjoin a letterwhich I addressed to Sir John Pringle, on the noxious quality of theeffluvia of putrid marshes, and which was read at a meeting of the RoyalSociety, December 16, 1773. 

This letter which is printed in the Philosophical Transactions, Vol. 74, p. 90. Is immediately followed by another paper, to which I would refermy reader. It was written by Dr. Price, who has so greatly distinguishedhimself, and done such eminent service to his country, and to mankind, by his calculations relating to the probabilities of human life, and wassuggested by his hearing this letter read at the Royal Society. Itcontains a confirmation of my observations on the noxious effects ofstagnant waters by deductions from Mr. Muret's account of the Bills ofMortality for a parish situated among marshes, in the district of Vaud, belonging to the Canton of Bern in Switzerland. 

 To Sir JOHN PRINGLE, Baronet. 

 DEAR SIR, Having pursued my experiments on different kinds of air considerablyfarther, in several respects, than I had done when I presented the lastaccount of them to the Royal Society; and being encouraged by thefavourable notice which the Society has been pleased to take of them, Ishall continue my communications on this subject; but, without waitingfor the result of a variety of processes, which I have now going on, orof other experiments, which I propose to make, I shall, from time totime, communicate such detached articles, as I shall have given the mostattention to, and with respect to which, I shall have been the mostsuccessful in my inquiries. 

Since the publication of my papers, I have read two treatises, writtenby Dr. Alexander, of Edinburgh, and am exceedingly pleased with thespirit of philosophical inquiry, which they discover. They appear to meto contain many new, curious, and valuable observations; but one of the_conclusions_, which he draws from his experiments, I am satisfied, frommy own observations, is ill founded, and from the nature of it, must bedangerous. I mean his maintaining, that there is nothing to beapprehended from the neighbourhood of putrid marshes. 

I was particularly surprised, to meet with such an opinion as this, in abook inscribed to yourself, who have so clearly explained the greatmischief of such a situation, in your excellent treatise _on thediseases of the army_. On this account, I have thought it not improper, to address to you the following observations and experiments, which Ithink clearly demonstrate the fallacy of Dr. Alexander's reasoning, indisputably establish your doctrine, and indeed justify theapprehensions of all mankind in this case. 

I think it probable enough, that putrid matter, as Dr. Alexander hasendeavoured to prove, will preserve other substances from putrefaction;because, being already saturated with the putrid effluvium, it cannotreadily take any more; but Dr. Alexander was not aware, that air thusloaded with putrid effluvium is exceedingly noxious when taken into thelungs. I have lately, however, had an opportunity of fully ascertaininghow very noxious such air is. 

Happening to use at Calne, a much larger trough of water, for thepurpose of my experiments, than I had done at Leeds, and not havingfresh water so near at hand as I had there, I neglected to change it, till it turned black, and became offensive, but by no means to such adegree, as to deter me from making use of it. In this state of thewater, I observed bubbles of air to rise from it, and especially in oneplace, to which some shelves, that I had in it, directed them; andhaving set an inverted glass vessel to catch them, in a few days Icollected, a considerable quantity of this air, which issuedspontaneously from the putrid water; and putting nitrous air to it, Ifound that no change of colour or diminution ensued, so that it musthave been, in the highest degree, noxious. I repeated the sameexperiment several times afterwards, and always with the same result. 

After this, I had the curiosity to try how wholesome air would beaffected by this water; when, to my real surprise, I found, that afteronly one minute's agitation in it, a candle would not burn in it; and, after three or four minutes, it was in the same state with the air, which had issued spontaneously from the same water. 

I also found, that common air, confined in a glass vessel, in _contact_only with this water, and without any agitation, would not admit acandle to burn in it after two days. 

These facts certainly demonstrate, that air which either arises fromstagnant and putrid water, or which has been for some time in contactwith it, must be very unfit for respiration; and yet Dr. Alexander'sopinion is rendered so plausible by his experiments, that it is verypossible that many persons may be rendered secure, and thoughtless ofdanger, in a situation in which they must necessarily breathe it. Onthis account, I have thought it right to make this communication asearly as I conveniently could; and as Dr. Alexander appears to be aningenuous and benevolent man, I doubt not but he will thank me for it. 

That air issuing from water, or rather from the soft earth, or mud, atthe bottom of pits containing water, is not always unwholesome, I havealso had an opportunity of ascertaining. Taking a walk, about two yearsago, in the neighbourhood of Wakefield, in Yorkshire, I observed bubblesof air to arise, in remarkably great plenty, from a small pool of water, which, upon inquiry, I was informed had been the place, where somepersons had been boring the ground, in order to find coal. Thesebubbles of air having excited my curiosity, I presently returned, with abason, and other vessels proper for my purpose, and having stirred themud with a long stick, I soon got about a pint of this air; and, examining it, found it to be good, common air; at least a candle burnedin it very well. I had not then discovered the method of ascertainingthe goodness of common air, by a mixture of nitrous air. Previous to thetrial, I had suspected that this air would have been found to beinflammable. 

I shall conclude this letter with observing, that I have found aremarkable difference in different kinds of water, with respect to theireffect on common air agitated in them, and which I am not yet able toaccount for. If I agitate common air in the water of a deep well, nearmy house in Calne, which is hard, but clear and sweet, a candle will notburn in it after three minutes. The same is the case with therain-water, which I get from the roof of my house. But in distilledwater, or the water of a spring-well near the house, I must agitate theair about twenty minutes, before it will be so much injured. It may beworth while, to make farther experiments with respect to this propertyof water. 

In consequence of using the rain-water, and the well-water abovementioned, I was very near concluding, contrary to what I have assertedin this treatise, that common air suffers a decomposition by greatrarefaction. For when I had collected a considerable quantity of air, which had been rarefied about four hundred times, by an excellent pumpmade for me by Mr. Smeaton, I always found, that if I filled myreceivers with the water above mentioned, though I did it so graduallyas to occasion as little agitation as possible, a candle would not burnin the air that remained in them. But when I used distilled water, orfresh spring-water, I undeceived myself. 

I think myself honoured by the attention, which, from the first, youhave given to my experiments, and am, with the greatest respect, Dear Sir, Your most obliged

 Humble Servant, London, 7 Dec. 1773. 

 J. PRIESTLEY. 

POSTSCRIPT. 

I cannot help expressing my surprize, that so clear and intelligible anaccount, of Mr. SMEATON'S air-pump, should have been before the publicso long, as ever since the publication of the forty-seventh volume ofthe Philosophical Transactions, printed in 1752, and yet that none ofour philosophical instrument-makers should use the construction. Thesuperiority of this pump, to any that are made upon the common plan, is, indeed, prodigious. Few of them will rarefy more than 100 times, and, ina general way, not more than 60 or 70 times; whereas this instrumentmust be in a poor state indeed, if it does not rarefy 200 or 300 times;and when it is in good order, it will go as far as 1000 times, andsometimes even much farther than that; besides, this instrument isworked with much more ease, than a common air-pump, and either exhaustsor condenses at pleasure. In short, to a person engaged in philosophicalpursuits, this instrument is an invaluable acquisition. I shall haveoccasion to recite some experiments, which I could not have made, andwhich, indeed, I should hardly have dared to attempt, if I had not beenpossessed of such an air-pump as this. It is much to be wished, thatsome person of spirit in the trade would attempt the construction of aninstrument, which would do great credit to himself, as well as be ofeminent service to philosophy. 

FOOTNOTES:

[11] On this account, if it was thought convenient to introduce a newterm (or rather make a new application of a term already in use amongchemists) it might not be amiss to call air that has been diminished, and made noxious by any of the processes above mentioned, or otherssimilar to them, by the common appellation of _phlogisticated air_; and, if it was necessary, the particular process by which it wasphlogisticated might be added; as common air phlogisticated by charcoal, air phlogisticated by the calcination of metals, nitrous airphlogisticated with the liver of sulphur, &c. 

[12] Here it becomes me to ask pardon of that excellent philosopherFather Beccaria of Turin, for conjecturing that the phlogiston, withwhich he revivified metals, did not come from the electric matteritself, but from what was discharged from other pieces of metal withwhich he made the experiment. See History of Electricity, p. 277, &c. This _revivification of metals_ by electricity completes the proof ofthe electric matter being, or containing phlogiston. 

SECTION III. 

_Of NITROUS AIR. _

Since the publication of my former papers I have given more attention tothe subject of nitrous air than to any other species of air; and havingbeen pretty fortunate in my inquiries, I shall be able to lay before myreader a more satisfactory account of the curious phenomena occasionedby it, and also of its nature and constitution, than I could do before, though much still remains to be investigated concerning it, and many newobjects of inquiry are started. 

With a view to discover where the power of nitrous air to diminishcommon air lay, I evaporated to dryness a quantity of the solution ofcopper in diluted spirit of nitre; and having procured from it aquantity of a _green precipitate_, I threw the focus of a burning-glassupon it, when it was put into a vessel of quicksilver, standing invertedin a bason of quicksilver. In this manner I procured air from it, whichappeared to be, in all respects, nitrous air; so that part of the sameprinciple which had escaped during the solution, in the form of _air_, had likewise been retained in it, and had not left it in the evaporationof the water. 

With great difficulty I also procured a small quantity of the same kindof air from a solution of _iron_ in spirit of nitre, by the sameprocess. 

Having, for a different purpose, fired some paper, which had been dippedin a solution of copper in diluted spirit of nitre, in nitrous air, Ifound there was a considerable addition to the quantity of it; uponwhich I fired some of the same kind of paper in quicksilver andpresently observed that air was produced from it in great plenty. Thisair, at the first, seemed to have some singular properties, butafterwards I found that it was nothing more than a mixture of nitrousair, from the precipitate of the solution, and of inflammable air, fromthe paper; but that the former was predominant. 

In the mixture of this kind of air with common air, in a trough of waterwhich had been putrid, but which at that time seemed to have recoveredits former sweetness (for it was not in the least degree offensive tothe smell) a phenomenon sometimes occurred, which for a long timeexceedingly delighted and puzzled me; but which was afterwards the meansof letting me see much farther into the constitution of nitrous air thanI had been able to see before. 

When the diminution of the air was nearly completed, the vessel in whichthe mixture was made began to be filled with the most beautiful _whitefumes_, exactly resembling the precipitation of some white substance ina transparent menstruum, or the falling of very fine snow; except thatit was much thicker below than above, as indeed is the case in allchemical precipitations. This appearance continued two or three minutes. 

At other times I went over the same process, as nearly as possible inthe same manner, but without getting this remarkable appearance, and wasseveral times greatly disappointed and chagrined, when I baulked theexpectations of my friends, to whom I had described, and meant to haveshewn it. This made me give all the attention I possibly could to thisexperiment, endeavouring to recollect every circumstance, which, thoughunsuspected at the time, might have contributed to produce this newappearance; and I took a great deal of pains to procure a quantity ofthis air from the paper above mentioned for the purpose, which, with asmall burning lens, and an uncertain sun, is not a little troublesome. But all that I observed for some time was, that I stood the best chanceof succeeding when I _warmed_ the vessel in which the mixture was made, and _agitated_ the air during the effervescence. 

Finding, at length, that, with the same preparation and attentions, Igot the same appearance from a mixture of nitrous and common air in thesame trough of water, I concluded that it could not depend upon anything peculiar to the precipitate of the _copper_ contained in the_paper_ from which the air was procured, as I had at first imagined, butupon what was common to it, and pure nitrous air. 

Afterwards, having, (with a view to observe whether any crystals wouldbe formed by the union of volatile alkali, and nitrous air, similar tothose formed by it and fixed air, as described by Mr. Smeth in his_Dissertation on fixed Air_) opened the mouth of a phial which was halffilled with a volatile alkaline liquor, in a jar of nitrous air (in themanner described p. 11. Fig. 4. ) I had an appearance which perfectlyexplained the preceding. All that part of the phial which was above theliquor, and which contained common air, was filled with beautiful_white clouds_, as if some fine white powder had been instantly throwninto it, and some of these clouds rose within the jar of nitrous air. This appearance continued about a minute, and then intirely disappeared, the air becoming transparent. 

Withdrawing the phial, and exposing it to the common air, it there alsobecame turbid, and soon after the transparency returned. Introducing itagain into the nitrous air, the clouds appeared as before. In thismanner the white fumes, and transparency, succeeded each otheralternately, as often as I chose to repeat the experiment, and would nodoubt have continued till the air in the jar had been thoroughly dilutedwith common air. These appearances were the same with any substance thatcontained _volatile alkali_, fluid or solid. 

When, instead of the small phial, I used a large and tall glass jar, this appearance was truly fine and striking, especially when the waterin the trough was very transparent. For I had only to put the smallestdrop of a volatile alkaline liquor, or the smallest bit of the solidsalt, into the jar, and the moment that the mouth of it was opened in ajar of nitrous air, the white clouds above mentioned began to be formedat the mouth, and presently descended to the bottom, so as to fill thewhole, were it ever so large, as with fine snow. 

In considering this experiment, I soon perceived that this curiousappearance must have been occasioned by the mixture of the nitrous andcommon air, and therefore that the white clouds must be _nitrousammoniac_, formed by the acid of the nitrous air, set loose in thedecomposition of it by common air, while the phlogiston, which must beanother constituent part of nitrous air, entering the common air, is thecause of the diminution it suffers in this process; as it is the causeof a similar diminution, in a variety of other processes. 

I would observe, that it is not peculiar to nitrous air to be a test ofthe fitness of air for respiration. Any other process by which air isdiminished and made noxious answers the same purpose. Liver of sulphurfor instance, the calcination of metals, or a mixture of iron filingsand brimstone will do just the same thing; but the application of themis not so easy, or elegant, and the effect is not so soon perceived. Infact, it is _phlogiston_ that is the test. If the air be so loaded withthis principle that it can take no more, which is seen by its not beingdiminished in any of the processes above mentioned, it is noxious; andit is wholesome in proportion to the quantity of phlogiston that it isable to take. 

This, I have no doubt, is the true theory of the diminution of commonair by nitrous air, the redness of the appearance being nothing morethan the usual colour of the fumes, of spirit of nitre, which is nowdisengaged from the superabundant phlogiston with which it was combinedin the nitrous air, and ready to form another union with any thing thatis at hand, and capable of it. 

With the volatile alkali it forms nitrous ammoniac, water imbibes itlike any other acid, even quicksilver is corroded by it; but this actionbeing slow, the redness in this mixture of nitrous and common aircontinues much longer when the process is made in quicksilver, than whenit is made in water, and the diminution, as I have also observed; is byno means so great. 

I was confirmed in this opinion when I put a bit of volatile alkalinesalt into the jar of quicksilver in which I made the mixture of nitrousand common air. In these circumstances, the vessel being previouslyfilled with the alkaline fumes, the acid immediately joined them, formedthe white clouds above mentioned, and the diminution proceeded almostas far as when the process was made in water. That it did not proceedquite so far, I attribute chiefly to the small quantity of calx formedby the slight solution of mercury with the acid fumes not being able toabsorb all the fixed air that is precipitated from the common air by thephlogiston. 

In part, also, it may be owing to the small quantify of surface in thequicksilver in the vessels that I made use of; in consequence of whichthe acid fumes could act upon it only in a slow succession, so that partof them, as well as of the fixed air, had an opportunity of forminganother union with the diminished air. 

This, as I have observed before, was so much the case when the processwas made in quicksilver, without any volatile alkali, that when waterwas admitted to it, after some time, it was not capable of dissolvingthat union, tho' it would not have taken place if the process had beenin water from the first. 

In diversifying this experiment, I found that it appeared to very greatadvantage when I suspended a piece of volatile salt in the common air, previous to the admission of nitrous air to it, inclosing it in a bitof gauze, muslin, or a small net of wire. For, presently after theredness of the mixture begins to go off, the white cloud, like snow, begins to descend from the salt, as if a white powder was shaken out ofthe bag that contains it. This white cloud presently fills the wholevessel, and the appearance will last about five minutes. 

If the salt be not put to the mixture of these two kinds of air till ithas perfectly recovered its transparency, the effervescence beingcompletely over, no white cloud will be formed; and, what is rather moreremarkable, there is nothing of this appearance when the salt is putinto the nitrous air itself. The reason of this must be, that the acidof the nitrous air has a nearer affinity with its phlogiston than withthe volatile alkali; though the phlogiston having a nearer affinity withsomething in the common air, the acid being thereby set loose, willunite with the alkaline vapour, if it be at hand to unite with it. 

There is also very little, if any white cloud formed upon holding apiece of the volatile salt within the mouth of a phial containingsmoking spirit of nitre. Also when I threw the focus of a burning mirrorupon some sal ammoniac in nitrous air, and filled the whole vessel withwhite fumes which arose from it, they were soon dispersed, and the airwas neither diminished nor altered. 

I was now fully convinced, that the white cloud which I casuallyobserved, in the first of these experiments, was occasioned by thevolatile alkali emitted from the water, which was in a slight degreeputrid; and that the warming, and agitation of the vessels, had promotedthe emission of the putrid, or alkaline effluvium. 

I could not perceive that the diminution of common air by the mixture ofnitrous air was sensibly increased by the presence of the volatilealkali. It is possible, however, that, by assisting the water to take upthe acid, something less of it may be incorporated with the remainingdiminished air than would otherwise have been; but I did not give muchattention to this circumstance. 

When the phial in which I put the alkaline salts contained any kind ofnoxious air, the opening of it in nitrous air was not followed by anything of the appearance above mentioned. This was the case withinflammable air. But when, after agitating the inflammable air in water, I had brought it to a state in which it was diminished a little by themixture of nitrous air, the cloudy appearance was in the sameproportion; so that this appearance seems to be equally a test of thefitness of air for respiration, with the redness which attends themixture of it with nitrous air only. 

Having generally fastened the small bag which contained the volatilesalt to a piece of brass wire in the preceding experiment, I commonlyfound the end of it corroded, and covered with a blue substance. Alsothe salt itself, and sometimes the bag was died blue. But finding thatthis was not the case when I used an iron wire in the samecircumstances, but that it became _red_, I was satisfied that both themetals had been dissolved by the volatile alkali. At first I had asuspicion that the blue might have come from the copper, out of whichthe nitrous air had been made. But when the nitrous air was made fromiron, the appearances were, in all respects, the same. 

I have observed, in the preceding section, that if nitrous air be mixedwith common air in _lime-water_, the surface of the water, where it iscontiguous to that mixture, will be covered with an incrustation oflime, shewing that some fixed air had been deposited in the process. Itis remarkable, however, as I there also just mentioned, that this isthe case when nitrous air alone is put to a vessel of lime-water, afterit has been kept in a _bladder_, or only transferred from one vessel toanother by a bladder, in the manner described, p. 15. Fig. 9. 

As I had used the same bladder for transferring various kinds of air, and among the rest _fixed air_, I first imagined that this effect mighthave been occasioned by a mixture of this fixed air with the nitrousair, and therefore took a fresh bladder; but still the effect was thesame. To satisfy myself farther, that the bladder had produced thiseffect, I put one into a jar of nitrous air, and after it had continuedthere a day and a night, I found that the nitrous air in this jar, though it was transferred in a glass vessel, made lime-water turbid. 

Whether there was any thing in the preparation of these bladders thatoccasioned their producing this effect, I cannot tell. They were such asI procure from the apothecaries. The thing seems to deserve fartherexamination, as there seems, in this case, to be the peculiar effect offixed air from other causes, or else a production of fixed air frommaterials that have not been supposed to yield it, at least not incircumstances similar to these. 

As fixed air united to water dissolves iron, I had the curiosity to trywhether fixed air alone would do it; and as nitrous air is of an _acid_nature, as well as fixed air, I, at the same time, exposed a largesurface of iron to both the kinds; first filling two eight ounce phialswith nails, and then with quicksilver, and after that displacing thequicksilver in one of the phials by fixed air, and in the other bynitrous air; then inverting them, and leaving them with their mouthsimmersed in basons of quicksilver. 

In these circumstances the two phials stood about two months, when nosensible change at all was produced in the fixed air, or in the ironwhich had been exposed to it, but a most remarkable, and most unexpectedchange was made in the nitrous air; and in pursuing the experiment, itwas transformed into a species of air, with properties which, at thetime of my first publication on this subject, I should not havehesitated to pronounce impossible, viz. Air in which a candle burnsquite naturally and freely, and which is yet in the highest degreenoxious to animals, insomuch that they die the moment they are put intoit; whereas, in general, animals live with little sensible inconveniencein air in which candles have burned out. Such, however, is nitrous air, after it has been long exposed to a large surface of iron. 

It is not less extraordinary, that a still longer continuance of nitrousair in these circumstances (but _how long_ depends upon too many, andtoo minute circumstances to be ascertained with exactness) makes it notonly to admit a candle to burn in it, but enables it to burn with an_enlarged flame_, by another flame (extending every where to an equaldistance from that of the candle, and often plainly distinguishable fromit) adhering to it. Sometimes I have perceived the flame of the candle, in these circumstances, to be twice as large as it is naturally, andsometimes not less than five or six times larger; and yet without anything like an _explosion_, as in the firing of the weakest inflammableair. 

Nor is the farther progress in the transmutation of nitrous air, inthese circumstances, less remarkable. For when it has been brought tothe state last mentioned, the agitation of it in fresh water almostinstantly takes off that peculiar kind of inflammability, so that itextinguishes a candle, retaining its noxious quality. It also retainsits power of diminishing common air in a very great degree. 

But this noxious quality, like the noxious quality of all other kinds ofair that will bear agitation in water, is taken out of it by thisoperation, continued about five minutes; in which process it suffers afarther and very considerable diminution. It is then itself diminishedby fresh nitrous air, and animals live in it very well, about as well asin air in which candles have burned out. 

Lastly, One quantity of nitrous air, which had been exposed to iron inquicksilver, from December 18 to January 20, and which happened to standin water till January 31 (the iron still continuing in the phial) wasfired with an explosion, exactly like a weak inflammable air. At thesame time another quantity of nitrous air, which had likewise beenexposed to iron, standing in quicksilver, till about the same time, andhad then stood in water only, without iron, only admitted a candle toburn in it with an enlarged flame, as in the cases above mentioned. Butwhether the difference I have mentioned in the circumstances of theseexperiments contributed to this difference in the result, I cannot tell. 

Nitrous air treated in the manner above mentioned is diminished aboutone fourth by standing in quicksilver; and water admitted to it willabsorb about half the remainder; but if water only, and no quicksilver, be used from the beginning, the nitrous air will be diminished muchfaster and farther; so that not more than one fourth, one sixth, or onetenth of the original quantity will remain. But I do not know that thereis any difference in the constitution of the air which remains in thesetwo cases. 

The water which has imbibed this nitrous air exposed to iron isremarkably green, also the phial containing it becomes deeply, and, Ibelieve, indelibly tinged with green; and if the water be put intoanother vessel, it presently deposits a considerable quantity of matter, which when dry appears to be the earth or ochre of iron; from which itis evident, that the acid of the nitrous air dissolves the iron; whilethe phlogiston, being set loose, diminishes nitrous air, as in theprocess of the iron filings and brimstone. 

Upon this hint, instead of using _iron_, I introduced a pot of _liver ofsulphur_ into a jar of nitrous air, and presently found, that what I hadbefore done by means of iron in six weeks, or two months, I could do byliver of sulphur (in consequence, no doubt, of its giving its phlogistonmore freely) in less than twenty-four hours, especially when the processwas kept warm. 

It is remarkable, however, that if the process with liver of sulphur besuffered to proceed, the nitrous air will be diminished much farther. At one time not more than one twentieth of the original quantityremained, and how much farther it right have been diminished, I cannottell. In this great diminution, it does not admit a candle to burn in itat all; and I generally found this to be the case whenever thediminution had proceeded beyond three fourths of the originalquantity[13]. 

It is something remarkable, that though the diminution of nitrous air byiron filings and brimstone very much resembles the diminution of it byiron only, or by liver of sulphur, yet the iron filings and brimstonenever bring it to such a state as that a candle will burn in it; andalso that, after this process, it is never capable of diminishing commonair. But when it is considered that these properties are destroyed byagitation in water, this difference in the result of processes, in otherrespects similar, will appear less extraordinary; and they agree inthis, that long agitation in water makes both these kinds of nitrous airequally fit for respiration, being equally diminished by fresh nitrousair. It is possible that there would have been a more exact agreementin the result of these processes, if they had been made in equal degreesof _heat_; but the process with iron was made in the usual temperatureof the atmosphere, and that with liver of sulphur generally near a fire. 

It may clearly, I think, be inferred from these experiments, that allthe difference between fresh nitrous air, that state of it in which itis partially inflammable, or wholly so, that in which it againextinguishes candles, and that in which it finally becomes fit forrespiration, depends upon some difference in the _mode of thecombination_ of its acid with phlogiston, or on the _proportion_ betweenthese two ingredients in its composition; and it is not improbable butthat, by a little more attention to these experiments, the whole mysteryof this proportion and combination may be explained. 

I must not omit to observe that there was something peculiar in theresult of the first experiment which I made with nitrous air exposed toiron; which was that, without any agitation in water, it was diminishedby fresh nitrous air, and that a candle burned in it quite naturally. Towhat this difference was owing I cannot tell. This air, indeed, had beenexposed to the iron a week or two longer than in any of the othercases, but I do not imagine that this circumstance could have producedthat difference. 

When the process is in water with iron, the time in which the diminutionis accomplished is exceedingly various; being sometimes completed in afew days, whereas at other times it has required a week or a fortnight. Some kinds of iron also produced this effect much sooner than others, but on what circumstances this difference depends I do not know. Whatare the varieties in the result of this experiment when it is made inquicksilver I cannot tell, because, on account of its requiring moretime, I have not repeated it so often; but I once found that nitrous airwas not sensibly changed by having been exposed to iron in quicksilvernine days; whereas in water a very considerable alteration was alwaysmade in much less than half that time. 

It may just deserve to be mentioned, that nitrous air extremely rarifiedin an air-pump dissolves iron, and is diminished by it as much as whenit is in its native state of condensation. 

It is something remarkable, though I never attended to it particularlybefore I made these last experiments, and it may tend to throw somelight upon them, that when a candle is extinguished, as it never failsto be, in nitrous air, the flame seems to be a little enlarged at itsedges, by another bluish flame added to it, just before its extinction. 

It is proper to observe in this place, that the electric spark taken innitrous air diminishes it to one fourth of its original quantity, whichis about the quantity of its diminution by iron filings and brimstone, and also by liver of sulphur without heat. The air is also brought byelectricity to the same state as it is by iron filings and brimstone, not diminishing common air. If the electric spark be taken in it when itis confined by water tinged with archil, it is presently changed fromblue to red, and that to a very great degree. 

When the iron nails or wires, which I have used to diminish nitrous air, had done their office, I laid them aside, not suspecting that they couldbe of any other philosophical use; but after having lain exposed to theopen air almost a fortnight; having, for some other purpose, put some ofthem into a vessel containing common air, standing inverted, andimmersed in water, I was surprized to observe that the air in which theywere confined was diminished. The diminution proceeded so fast, thatthe process was completed in about twenty-four hours; for in that timethe air was diminished about one fifth, so that it made no effervescencewith nitrous air, and was, therefore, no doubt, highly noxious, like airdiminished by any other process. 

This experiment I have repeated a great number of times, with the samephials, filled with nails or wires that have been suffered to rust innitrous air, but their power of diminishing common air grows less andless continually. How long it will be before it is quite exhausted Icannot tell. This diminution of air I conclude must arise from thephlogiston, either of the nitrous air or the iron, being some wayentangled in the rust, in which the wires were encrusted, and afterwardsgetting loose from it. 

To the experiments upon iron filings and brimstone in nitrous air, Imust add, that when a pot full of this mixture had absorbed as much asit could of a jar of nitrous air (which is about three fourths of thewhole) I put fresh nitrous air to it, and it continued to absorb, tillthree or four jars full of it disappeared; but the absorption wasexceedingly slow at the last. Also when I drew this pot through thewater, and admitted fresh nitrous air to it, it absorbed another jarfull, and then ceased. But when I scraped off the outer surface of thismixture, which had been so long exposed to the nitrous air, theremainder absorbed more of the air. 

When I took the top of the mixture which I had scraped off and threwupon it the focus of a burning-glass, the air in which it was confinedwas diminished, and became quite noxious; yet when I endeavoured to getair from this matter in a jar full of quicksilver, I was able to procurelittle or nothing. 

It is not a little remarkable that nitrous air diminished by ironfilings and brimstone, which is about one fourth, cannot, by agitationin water, be diminished much farther; whereas pure nitrous air may, bythe same process, be diminished to one twentieth of its whole bulk, andperhaps much more. This is similar to the effect of the same mixture, and of phlogiston in other cases, on fixed air; for it so far changesits constitution, that it is afterwards incapable of mixing with water. It is similar also to the effect of phlogiston in acid air, which ofitself is almost instantly absorbed by water; but by this addition it isfirst converted into inflammable air, which does not readily mix withwater, and which, by long agitation in water, becomes of anotherconstitution, still less miscible with water. 

I shall close this section with a few other observations of amiscellaneous nature. 

Nitrous air is as much diminished both by iron filings, and also byliver of sulphur, when confined in quicksilver, as when it is exposed towater. 

Distilled water tinged blue with the juice of turnsole becomes red onbeing impregnated with nitrous air; but by being exposed a week or afortnight to the common atmosphere, in open and shallow vessels, itrecovers its blue colour; though, in that time, the greater part of thewater will be evaporated. This shews that in time nitrous air escapesfrom the water with which it is combined, just as fixed air does, thoughby no means so readily[14]. 

Having dissolved silver, copper, and iron in equal quantities of spiritof nitre diluted with water, the quantities of nitrous air produced fromthem were in the following proportion; from iron 8, from copper 6-1/4, from silver 6. In about the same proportion also it was necessary tomix water with the spirit of nitre in each case, in order to make itdissolve these metals with equal rapidity, silver requiring the leastwater, and iron the most. 

Phosphorus gave no light in nitrous air, and did not take away from itspower of diminishing common air; only when the redness of the mixturewent off, the vessel in which it was made was filled with white fumes, as if there had been some volatile alkali in it. The phosphorus itselfwas unchanged. 

There is something remarkable in the effect of nitrous air on _insects_that are put into it. I observed before that this kind of air is asnoxious as any whatever, a mouse dying the moment it is put into it; butfrogs and snails (and therefore, probably, other animals whoserespiration is not frequent) will bear being exposed to it aconsiderable time, though they die at length. A frog put into nitrousair struggled much for two or three minutes, and moved now and then fora quarter of an hour, after which it was taken out, but did not recover. _Wasps_ always died the moment they were put into the nitrous air. Icould never observe that they made the least motion in it, nor couldthey be recovered to life afterwards. This was also the case in generalwith _spiders_, _flies_, and _butterflies_. Sometimes, however, spiderswould recover after being exposed about a minute to this kind of air. 

Considering how fatal nitrous air is to insects, and likewise its greatantiseptic power, I conceived that considerable use might be made of itin medicine, especially in the form of _clysters_, in which fixed airhad been applied with some success; and in order to try whether thebowels of an animal would bear the injection of it, I contrived, withthe help of Mr. Hey, to convey a quantity of it up the anus of a dog. But he gave manifest signs of uneasiness, as long as he retained it, which was a considerable time, though in a few hours afterwards he wasas lively as ever, and seemed to have suffered nothing from theoperation. 

Perhaps if nitrous air was diluted either with common air, or fixed air, the bowels might bear it better, and still it might be destructive to_worms_ of all kinds, and be of use to check or correct putrefaction inthe intestinal canal, or other parts of the system. I repeat it oncemore that, being no physician, I run no risk by such proposals as these;and I cannot help flattering myself that, in time, very great medicinaluse will be made of the application of these different kinds of air tothe animal system. Let ingenious physicians attend to this subject, andendeavour to lay hold of the new _handle_ which is now presented them, before it be seized by rash empiricks; who, by an indiscriminate andinjudicious application, often ruin the credit of things and processeswhich might otherwise make an useful addition to the _materia_ and _arsmedica_. 

In the first publication of my papers, having experienced the remarkableantiseptic power of nitrous air, I proposed an attempt to preserveanatomical preparations, &c. By means of it; but Mr. Hey, who made thetrial, found that, after some months, various animal substances wereshriveled, and did not preserve their natural forms in this kind ofair. 

FOOTNOTES:

[13] The result of several of these experiments I had the pleasure oftrying in the presence of the celebrated Mr. De Luc of Geneva, when hewas upon a visit to Lord Shelburne in Wiltshire. 

[14] I have not repeated this experiment with that variation ofcircumstances which an attention to Mr. Bewley's observation willsuggest. 

SECTION IV. 

_Of MARINE ACID AIR. _

In my former experiments on this species of air I procured it fromspirit of salt, but I have since hit upon a much less expensive methodof getting it, by having recourse to the process by which the spirit ofsalt is itself originally made. For this purpose I fill a small phialwith common salt, pour upon it a small quantity of concentrated oil ofvitriol, and receive the fumes emitted by it in a vessel previouslyfilled with quicksilver, and standing in a bason of quicksilver, inwhich it appears in the form of a perfectly _transparent air_, beingprecisely the same thing with that which I had before expelled from thespirit of salt. 

This method of procuring acid air is the more convenient, as a phial, once prepared in this manner, will suffice, for common experiments, manyweeks; especially if a little more oil of vitriol be occasionally put toit. It only requires a little more heat at the last than at the first. Indeed, at the first, the heat of a person's hand will often besufficient to make it throw out the vapour. In warm weather it willeven keep smoking many days without the application of any other heat. 

On this account, it should be placed where there are no instruments, orany thing of metal, that can be corroded by this acid vapour. It is fromdear-bought experience that I give this advice. It may easily beperceived when this phial is throwing out this acid vapour, as it alwaysappears, in the open air, in the form of a light cloud; owing, Isuppose, to the acid attracting to itself, and uniting with, themoisture that is in the common atmosphere. 

By this process I even made a stronger spirit of salt than can beprocured in any other way. For having a little water in the vessel whichcontains the quicksilver, it imbibes the acid vapour, and at lengthbecomes truly saturated with it. Having, in this manner, impregnatedpure water with acid air, I could afterwards expel the same air from it, as from common spirit of salt. 

I observed before that this acid vapour, or air, has a strong affinitywith _phlogiston_, so that it decomposes many substances which containit, and with them forms a permanently inflammable air, no more liable tobe imbibed by water than inflammable air procured by any other process, being in fact the very same thing; and that, in some cases, it evendislodges spirit of nitre and oil of vitriol, which in general appear tobe stronger acids than itself. I have since observed that, by giving itmore time, it will extract phlogiston from substances from which I atfirst concluded that it was not able to do it, as from dry wood, crustsof bread not burnt, dry flesh, and what is more extraordinary fromflints. As there was something peculiar to itself in the process orresult of each of these experiments, it may not be improper to mentionthem distinctly. 

Pieces of dry _cork wood_ being put to the acid air, a small quantityremained not imbibed by water, and was inflammable. 

Very dry pieces of _oak_, being exposed to this air a day and a night, after imbibing a considerable quantity of it, produced air which wasinflammable indeed, but in the slightest degree imaginable. It seemed tobe very nearly in the state of common air. 

A piece of _ivory_ imbibed the acid vapour very slowly. In a day and anight, however, about half an ounce measure of permanent air wasproduced, and it was pretty strongly inflammable. The ivory was notdiscoloured, but was rendered superficially soft, and clammy, tastingvery acid. 

Pieces of _beef_, roasted, and made quite dry, but not burnt, absorbedthe acid vapour slowly; and when it had continued in this situation allnight, from five ounce measures of the air, half a measure waspermanent, and pretty strongly inflammable. This experiment succeeded asecond time exactly in the same manner; but when I used pieces of whitedry _chicken-flesh_ though I allowed the same time, and in otherrespects the process seemed to go on in the same manner, I could notperceive that any part of the remaining air was inflammable. 

Some pieces of a whitish kind of _flint_, being put into a quantity ofacid air, imbibed but a very little of it in a day and a night; but of2-1/2 ounce measures of it, about half a measure remained unabsorbed bywater, and this was strongly inflammable, taking fire just like an equalmixture of inflammable and common air. At another time, however, I couldnot procure any inflammable air by this means, but to what circumstancethese different results were owing I cannot tell. 

That inflammable air is produced from _charcoal_ in acid air I observedbefore. I have since found that it may likewise be procured from _pitcoal_, without being charred. 

Inflammable air I had also observed to arise from the exposure of spiritof wine, and various _oily_ substances, to the vapour of spirit of salt. I have since made others of a similar nature, and as peculiarcircumstances attended some of these experiments, I shall recite themmore at large. 

_Essential oil of mint_ absorbed this air pretty fast, and presentlybecame of a deep brown colour. When it was taken out of this air it wasof the consistence of treacle, and sunk in water, smelling differentlyfrom what it did before; but still the smell of the mint waspredominant. Very little or none of the air was fixed, so as to becomeinflammable; but more time would probably have produced this effect. 

_Oil of turpentine_ was also much thickened, and became of a deep browncolour, by being saturated with acid air. 

_Ether_ absorbed acid air very fast, and became first of a turbid white, and then of a yellow and brown colour. In one night a considerablequantity of permanent air was produced, and it was strongly inflammable. 

Having, at one time, fully saturated a quantity of ether with acid air, I admitted bubbles of common air to it, through the quicksilver, bywhich it was confined, and observed that white fumes were made in it, atthe entrance of every bubble, for a considerable time. 

At another time, having fully saturated a small quantity of ether withacid air, and having left the phial in which it was contained nearlyfull of the air, and inverted, it was by some accident overturned; when, instantly, the whole room was filled with a visible fume, like a whitecloud, which had very much the smell of ether, but peculiarly offensive. Opening the door and window of the room, this light cloud filled a longpassage, and another room. In the mean time the ether was seemingly allvanished, but some time after the surface of the quicksilver in whichthe experiment had been made was covered with a liquor that tasted veryacid; arising, probably, from the moisture in the atmosphere attractedby the acid vapour with which the ether had been impregnated. 

This visible cloud I attribute to the union of the moisture in theatmosphere with the compound of the acid air and ether. I have sincesaturated other quantities of ether with acid air, and found it to beexceedingly volatile, and inflammable. Its exhalation was also visible, but not in so great a degree as in the case above mentioned. 

_Camphor_ was presently reduced into a fluid state by imbibing acid air, but there seemed to be something of a whitish sediment in it. Aftercontinuing two days in this situation I admitted water to it;immediately upon which the camphor resumed its former solid state, and, to appearance, was the very same substance that it had been before; butthe taste of it was acid, and a very small part of the air waspermanent, and slightly inflammable. 

The acid air seemed to make no impression upon a piece of Derbyshire_spar_, of a very dark colour, and which, therefore, seemed to contain agood deal of phlogiston. 

As the acid air has so near an affinity with phlogiston, I expected thatthe fumes of _liver of sulphur_, which chemists agree to be phlogistic, would have united with it, so as to form inflammable air; but I wasdisappointed in that expectation. This substance imbibed half of theacid air to which it was introduced: one fourth of the remainder, afterstanding one day in quicksilver, was imbibed by water, and what was leftextinguished a candle. This experiment, however, seems to prove thatacid air and phlogiston may form a permanent kind of air that is notinflammable. Perhaps it may be air in such a state as common air loadedwith phlogiston, and from which the fixed air has been precipitated. Orrather, it may be the same thing with inflammable air, that has lost itsinflammability by long standing in water. It well deserves a fartherexamination. 

The following experiments are those in which the _stronger acids_ weremade use of, and therefore they may assist us farther to ascertain theiraffinities with certain substances, with respect to this marine acid inthe form of air. 

I put a quantity of strong concentrated _oil of vitriol_ to acid air, but it was not at all affected by it in a day and a night. In order totry whether it would not have more power in a more condensed state, Icompressed it with an additional atmosphere; but upon taking off thispressure, the air expanded again, and appeared to be not at alldiminished. I also put a quantity of strong _spirit of nitre_ to itwithout any sensible effect. We may conclude, therefore, that themarine acid, in this form of air, is not able to dislodge the otheracids from their union with water. 

_Blue vitriol_, which is formed by the union of the vitriolic acid withcopper, turned to a dark green the moment that it was put to the acidair, which it absorbed, though slowly. Two pieces, as big as small nuts, absorbed three ounce measures of the air in about half an hour. Thegreen colour was very superficial; for it was easily wiped or washedoff. 

_Green copperas_ turned to a deeper green upon being put into acid air, which it absorbed slowly. _White copperas_ absorbed this air very fast, and was dissolved in it. 

_Sal ammoniac_, being the union of spirit of salt with volatile alkali, was no more affected with the acid air than, as I have observed before, common salt was. 

I also introduced to the acid air various other substances, without anyparticular expectation; and it may be worth while to give an account ofthe results, that the reader may draw from them such conclusions as heshall think reasonable. 

_Borax_ absorbed acid air about as fast as blue vitriol, but without anything else that was observable. 

Fine white _sugar_ absorbed this air slowly, was thoroughly penetratedwith it, became of a deep brown colour, and acquired a smell that waspeculiarly pungent. 

A piece of _quick lime_ being put to about twelve or fourteen ouncemeasures of acid air, and continuing in that situation about two days, there remained one ounce measure of air that was not absorbed by water, and it was very strongly inflammable, as much so as a mixture of halfinflammable and half common air. Very particular care was taken that nocommon air mixed with the acid air in this process. At another time, from about half the quantity of acid air above mentioned, with much lessquick-lime, and in the space of one day, I got half an ounce measure ofair that was inflammable in a slight degree only. This experiment provesthat some part of the phlogiston which escapes from the fuel, in contactwith which the lime is burned, adheres to it. But I am very far fromthinking that the causticity of quick-lime is at all owing to thiscircumstance. 

I have made a few more experiments on the mixture of acid air with_other kinds of air_, and think that it may be worth while to mentionthem, though nothing of consequence, at least nothing but negativeconclusions, can be drawn from them. 

A quantity of common air saturated with nitrous air was put to aquantity of acid air, and they continued together all night, without anysensible effect. The quantity of both remained the same, and water beingadmitted to them, it absorbed all the acid air, and left the other justas before. 

A mixture of two thirds of air diminished by iron filings and brimstone, and one third acid air, were mixed together, and left to stand fourweeks in quicksilver. But when the mixture was examined, water presentlyimbibed all the acid air, and the diminished air was found to be justthe same that it was before. I had imagined that the acid air might haveunited with the phlogiston with which the diminished air wasovercharged, so as to render it wholsome; and I had read an account ofthe stench arising from putrid bodies being corrected by acid fumes. 

The remaining experiments, in which the acid air was principallyconcerned, are of a miscellaneous nature. 

I put a piece of dry _ice_ to a quantity of acid air (as was observed inthe section concerning _alkaline_ air) taking it with a forceps, which, as well as the air itself, and the quicksilver by which it had beenconfined; had been exposed to the open air for an hour, in a prettystrong frost. The moment it touched the air it was dissolved as fast asit would have been by being thrown into a hot fire, and the air waspresently imbibed. Putting fresh pieces of ice to that which wasdissolved before, they were also dissolved immediately, and the waterthus procured did not freeze again, though it was exposed a whole night, in a very intense frost. 

Flies and spiders die in acid air, but not so quickly as in nitrous air. This surprized me very much; as I had imagined that nothing could bemore speedily fatal to all animal life than this pure acid vapour. 

As inflammable air, I have observed, fires at one explosion in thevapour of smoking spirit of nitre, just like an equal mixture ofinflammable and common air, I thought it was possible that the fumewhich naturally rises from common spirit of salt might have the sameeffect, but it had not. For this purpose I treated the spirit of salt, as I had before done the smoking spirit of nitre; first filling a phialwith it, then inverting it in a vessel containing a quantity of the sameacid; and having thrown the inflammable air into it, and thereby drivenout all the acid, turning it with its mouth upwards, and immediatelyapplying a candle to it. 

Acid air not being so manageable as most of the other kinds of air, Ihad recourse to the following peculiar method, in order to ascertain its_specific gravity_. Having filled an eight ounce phial with this air, and corked it up, I weighed it very accurately; and then, taking out thecork, I blew very strongly into it with a pair of bellows, that thecommon air might take place of the acid; and after this I weighed itagain, together with the cork, but I could not perceive the leastdifference in the weight. I conclude, however, from this experiment, that the acid air is heavier than the common air, because the mouth ofthe phial and the inside of it were evidently moistened by the waterwhich the acid vapour had attracted from the air, which moisture musthave added to the weight of the phial. 

SECTION V. 

_Of INFLAMMABLE AIR. _

It will have appeared from my former experiments, that inflammable airconsists chiefly, if not wholly, of the union of an acid vapour withphlogiston; that as much of the phlogiston as contributes to make airinflammable is imbibed by the water in which it is agitated; that inthis process it soon becomes fit for respiration, and by the continuanceof it comes at length to extinguish flame. These observations, andothers which I have made upon this kind of air, have been confirmed bymy later experiments, especially those in which I have connected_electrical experiments_ with those on air. 

The electric spark taken in any kind of _oil_ produces inflammable air, as I was led to observe in the following manner. Having found, as willbe mentioned hereafter, that ether doubles the quantity of any kind ofair to which it is admitted; and being at that time engaged in a courseof experiments to ascertain the effect of the electric matter on all thedifferent kinds of air, I had the curiosity to try what it would do with_common air_, thus increased by means of ether. The very first spark, Iobserved, increased the quantity of this air very considerably, so thatI had very soon six or eight times as much as I began with; and whereaswater imbibes all the ether that is put to any kind of air, and leavesit without any visible change, with respect to quantity or quality, thisair, on the contrary, was not imbibed by water. It was also very littlediminished by the mixture of nitrous air. From whence it was evident, that it had received an addition of some other kind of air, of which itnow principally consisted. 

In order to determine whether this effect was produced by the _wire_, orthe _cement_ by which the air was confined (as I thought it possiblethat phlogiston might be discharged from them) I made the experiment ina glass syphon, fig. 19, and by that means I contrived to make theelectric spark pass from quicksilver through the air on which I made theexperiment, and the effect was the same as before. At one time therehappened to be a bubble of common air, without any ether, in one part ofthe syphon, and another bubble with ether in another part of it; and itwas very amusing to observe how the same electric sparks diminished theformer of these bubbles, and increased the latter. 

It being evident that the _ether_ occasioned the difference that wasobservable in these two cases, I next proceeded to take the electricspark in a quantity of ether only, without any air whatever; andobserved that every spark produced a small bubble; and though, while thesparks were taken in the ether itself, the generation of air was slow, yet when so much air was collected, that the sparks were obliged to passthrough it, in order, to come to the ether and the quicksilver on whichit rested, the increase was exceedingly rapid; so that, making theexperiment in small tubes, as fig. 16, the quicksilver soon recededbeyond the striking distance. This air, by passing through water, wasdiminished to about one third, and was inflammable. 

One quantity of air produced in this manner from ether I suffered tostand two days in water, and after that I transferred it several timesthrough the water, from one vessel to another, and still found that itwas very strongly inflammable; so that I have no doubt of its beinggenuine inflammable air, like that which is produced from metals byacids, or by any other chemical process. 

Air produced from ether, mixed both with common and nitrous air, waslikewise inflammable; but in the case of the nitrous air, the originalquantity bore a very small proportion to the quantity generated. 

Concluding that the inflammable matter in this air came from the ether, as being of the class of _oils_, I tried other kinds of oil, as _oil ofolives_, _oil of turpentine_, and _essential oil of mint_, taking theelectric spark in them, without any air to begin with, and found thatinflammable air was produced in this manner from them all. Thegeneration of air from oil of turpentine was the quickest, and from theoil of olives the slowest in these three cases. 

By the same process I got inflammable air from _spirit of wine_, andabout as copiously as from the essential oil of mint. This air continuedin water a whole night, and when it was transferred into another vesselwas strongly inflammable. 

In all these cases the inflammable matter might be supposed to arisefrom the inflammable substances on which the experiments were made. Butfinding that, by the same process I could get inflammable air from the_volatile spirit of sal ammoniac_, I conclude that the phlogiston was inpart supplied by the electric matter itself. For though, as I haveobserved before, the alkaline air which is expelled from the spirit ofsal ammoniac be inflammable, it is so in a very slight degree, and canonly be perceived to be so when there is a considerable quantity of it. 

Endeavouring to procure air from a caustic alkaline liquor, accuratelymade for me by Mr. Lane, and also from spirit of salt, I found that theelectric spark could not be made visible in either of them; so that theymust be much more perfect conductors of electricity than water, or otherfluid substances. This experiment well deserves to be prosecuted. 

I observed before that inflammable air, by standing long in water, andespecially by agitation in water, loses its inflammability; and that inthe latter case, after passing through a state in which it makes someapproach to common air (just admitting a candle to burn in it) it comesto extinguish a candle. I have since made another observation of thiskind, which well deserves to be recited. It relates to the inflammableair generated from oak the 27th of July 1771, of which I have mademention before. 

This air I have observed to have been but weakly inflammable some monthsafter it was generated, and to have been converted into pretty good orwholesome air by no great degree of agitation in water; but on the 27thof March 1773, I found the remainder of it to be exceedingly good air. Acandle burned in it perfectly well, and it was diminished by nitrous airalmost as much as common air. 

I shall conclude this section with a few miscellaneous observations ofno great importance. 

Inflammable air is not changed by being made to pass many times througha red-hot iron tube. It is also no more diminished or changed by thefumes of liver of sulphur, or by the electric spark, than I have beforeobserved it to have been by a mixture of iron filings and brimstone. When the electric spark was taken in it, it was confined by a quantityof water tinged blue with the juice of archil, but the colour remainedunchanged. 

I put two _wasps_ into inflammable air, and let them remain there aconsiderable time, one of them near an hour. They presently ceased tomove, and seemed to be quite dead for about half an hour after they weretaken into the open air; but then they came to life again, and presentlyafter seemed to be as well as ever they had been. 

SECTION VI. 

_Of FIXED AIR. _

The additions I have made to my observations on _fixed air_ are neithernumerous nor considerable. 

The most important of them is a confirmation of my conjecture, thatfixed air is capable of forming an union with phlogiston, and therebybecoming a kind of air that is not miscible with water. I had producedthis effect before by means of iron filings and brimstone, fermenting inthis kind of air; but I have since had a much more decisive and elegantproof of it by _electricity_. For after taking a small electricexplosion, for about an hour, in the space of an inch of fixed air, confined in a glass tube one tenth of an inch in diameter, fig. 16, Ifound that when water was admitted to it, only one fourth of the air wasimbibed. Probably the whole of it would have been rendered immiscible inwater, if the electrical operation had been continued a sufficient time. This air continued several days in water, and was even agitated in waterwithout any farther diminution. It was not, however, common air, for itwas not diminished by nitrous air. 

By means of iron filings and brimstone I have, since my formerexperiments, procured a considerable quantity of this kind of air in amethod something different from that which I used before. For havingplaced a pot of this mixture under a receiver, and exhausted it with apump of Mr. Smeaton's construction, I filled it with fixed air, and thenleft it plunged under water; so that no common air could have access toit. In this manner, and in about a week, there was, as near as I canrecollect, one sixth, or at least one eighth of the whole converted intoa permanent air, not imbibed by water. 

From this experiment I expected that the same effect would have beenproduced on fixed air by the fumes of _liver of sulphur_; but I wasdisappointed in that expectation, which surprised me not a little;though this corresponds in some measure, to the effect of phlogistonexhaled from this substance on acid air. Perhaps more time may berequisite for this purpose, for this process was not continued more thana day and a night. 

Iron filings and brimstone, I have observed, ferment with great heat innitrous air, and I have since observed that this process is attendedwith greater heat in fixed air than in common air. 

Though fixed air incorporated with water dissolves iron, fixed airwithout water has no such power, as I observed before. I imagined that, if it could have dissolved iron, the phlogiston would have united withthe air, and have made it immiscible with water, as in the formerinstances; but after being confined in a phial full of nails from the15th of December to the 4th of October following, neither the iron northe air appeared to have been affected by their mutual contact. 

Having exposed equal quantities of common and fixed air, in equal andsimilar cylindrical glass vessels, to equal degrees of heat, by placingthem before a fire, and frequently changing their situations, I observedthat they were expanded exactly alike, and when removed from the firethey both recovered their former dimensions. 

Having had some small suspicion that liver of sulphur, besides emittingphlogiston, might also yield some fixed air (which is known to becontained in the salt of tartar from which it is made) I mixed the twoingredients, viz. Salt of tartar and brimstone, and putting them into athin phial, and applying the flame of a candle to it, so as to form theliver of sulphur, I received the air that came from it in this processin a vessel of quicksilver. In this manner I procured a veryconsiderable quantity of fixed air, so that I judged it was alldischarged from the tartar. But though it is possible that a smallquantity of it may remain in liver of sulphur, when it is made in themost perfect manner, it is not probable that it can be expelled withoutheat. 

SECTION VII. 

MISCELLANEOUS EXPERIMENTS. 

1. It is something extraordinary that, though ether, as I found, cannotbe made to assume the form of air (the vapour arising from it by heat, being soon condensed by cold, even in quicksilver) yet that a very smallquantity of ether put to any kind of air, except the acid, and alkaline, which it imbibes, almost instantly doubles the apparent quantity of it;but upon passing this air through water, it is presently reduced to itsoriginal quantity again, with little or no change of quality. 

I put about the quantity of half a nut-shell full of ether, inclosed ina glass tube, through a body of quicksilver, into an ounce measure ofcommon air, confined by quicksilver; upon which it presently began toexpand, till it occupied the space of two ounce measures. It thengradually contracted about one sixth of an ounce measure. Putting moreether to it, it again expanded to two ounce measures; but no moreaddition of ether would make it expand any farther. Withdrawing thequicksilver, and admitting water to this air, without any agitation, itbegan to be absorbed; but only about half an ounce measure haddisappeared after it had stood an hour in the water. But by once passingit through water the air was reduced to its original dimensions. Beingtried by a mixture of nitrous air, it appeared not to be so good asfresh air, though the injury it had received was not considerable. 

All the phenomena of dilatation and contraction were nearly the same, when, instead of common air, I used nitrous air, fixed air, inflammableair, or any species of phlogisticated common air. The quantity of eachof these kinds of air was nearly doubled while they were kept inquicksilver, but fixed air was not so much increased as the rest, andphlogisticated air less; but after passing through the water, theyappeared not to have been sensibly changed by the process. 

2. Spirit of wine yields no air by means of heat, the vapours being sooncondensed by cold, like the vapour of water; yet when, in endeavouringto procure air from it, I made it boil, and catched the air which hadrested on the surface of the spirit, and which had been expelled by theheat together with the vapour, in a vessel of quicksilver, andafterwards admitted acid air to it, the vessel was filled with whitefumes, as if there had been a mixture of alkaline air along with it. Towhat this appearance was owing I cannot tell, and indeed I did notexamine into it. 

3. Having been informed by Dr. Small and Mr. Bolton of Birmingham, thatpaper dipped in a solution of copper in spirit of nitre would take firewith a moderate heat (a fact which I afterwards found mentioned in thePhilosophical Transactions) it occurred to me that this would be veryconvenient for experiments relating to _ignition_ in different kinds ofair; and indeed I found that it was easily fired, either by a burninglens, or the approach of red-hot iron on the outside of the phial inwhich it was contained, and that any part of it being once fired, thewhole was presently reduced to ashes; provided it was previously madethoroughly dry, which, however, it is not very easy to do. 

With this preparation, I found that this paper burned freely in allkinds of air, but not in _vacuo_, which is also the case with gunpowder;and, as I have in effect observed before, all the kinds of air in whichthis paper was burned received an addition to their bulk, whichconsisted partly of nitrous air, from the nitrous precipitate, andpartly of inflammable air, from the paper. As some of the circumstancesattending the ignition of this paper in some of the kinds of air were alittle remarkable, I shall just recite them. 

Firing this paper in _inflammable_ air, which it did without anyignition of the inflammable air itself, the quantity increasedregularly, till the phial in which the process was made was nearly full;but then it began to decrease, till one third of the whole quantitydisappeared. 

A piece of this paper being put to three ounce measures of _acid_ air, agreat part of it presently turned yellow, and the air was reduced to onethird of the original quantity, at the same time becoming reddish, exactly like common air in a phial containing smoking spirit of nitre. After this, by the approach of hot iron, I set fire to the paper;immediately upon which there was a production of air which more thanfilled the phial. This air appeared, upon examination, to be very littledifferent from pure nitrous air. I repeated this experiment with thesame event. 

Paper dipped in a solution of mercury, zinc, or iron, in nitrous acid, has, in a small degree, the same property with paper dipped in asolution of copper in the same acid. 

4. Gunpowder is also fired in all kinds of air, and, in the quantity inwhich I tried it, did not make any sensible change in them, except thatthe common air in which it was fired would not afterwards admit a candleto burn in it. In order to try this experiment I half exhausted areceiver, and then with a burning-glass fired the gunpowder which hadbeen previously put into it. By this means I could fire a greaterquantity of gunpowder in a small quantity of air, and avoid the hazardof blowing up, and breaking my receiver. 

I own that I was rather afraid of firing gunpowder in inflammable air, but there was no reason for my fear; for it exploded quite freely inthis air, leaving it, in all respects, just as it was before. 

In order to make this experiment, and indeed almost all the experimentsof firing gunpowder in different kinds of air, I placed the powder upona convenient stand within my receiver, and having carefully exhausted itby a pump of Mr. Smeaton's construction, I filled the receiver with anykind of air by the apparatus described, p. 19, fig. 14, taking thegreatest care that the tubes, &c. Which conveyed the air should containlittle or no common air. In the experiment with inflammable air aconsiderable mixture of common air would have been exceedinglyhazardous: for, by that assistance, the inflammable air might haveexploded in such a manner, as to have been dangerous to the operator. Indeed, I believe I should not have ventured to have made the experimentat all with any other pump besides Mr. Smeaton's. 

Sometimes, I filled a glass vessel with quicksilver, and introduced theair to it, when it was inverted in a bason of quicksilver. By this meansI intirely avoided any mixture of common air; but then it was not easyto convey the gunpowder into it, in the exact quantity that wasrequisite for my purpose. This, however, was the only method by which Icould contrive to fire gunpowder in acid or alkaline air, in which itexploded just as it did in nitrous or fixed air. 

I burned a considerable quantity of gunpowder in an exhausted receiver(for it is well known that it will not explode in it) but the air I gotfrom it was very inconsiderable, and in these circumstances wasnecessarily mixed with common air. A candle would not burn in it. 

SECTION VIII. 

_QUERIES, SPECULATIONS, and HINTS. _

I begin to be apprehensive lest, after being considered as a _dryexperimenter_, I should pass, with many of my readers, into the oppositecharacter of a _visionary theorist_. A good deal of theory has beeninterspersed in the course of this work, but, not content with this, Iam now entering upon a long section, which contains nothing else. 

The conjectures that I have ventured to advance in the body of the workwill, I hope, be found to be pretty well supported by facts; but thepresent section will, I acknowledge, contain many _random thoughts_. Ihave, however, thrown them together by themselves, that readers of lessimagination, and who care not to advance beyond the regions of plainfact, may, if they please, proceed no farther, that their delicacy benot offended. 

In extenuation of my offence, let it, however, be considered, that_theory_ and _experiment_ necessarily go hand in hand, every processbeing intended to ascertain some particular _hypothesis_, which, infact, is only a conjecture concerning the circumstances or the cause ofsome natural operation; consequently that the boldest and most originalexperimenters are those, who, giving free scope to their imaginations, admit the combination of the most distant ideas; and that though many ofthese associations of ideas, will be wild and chimerical, yet thatothers will have the chance of giving rise to the greatest and mostcapital discoveries; such as very cautious, timid, sober, andslow-thinking people would never have come at. 

Sir Isaac Newton himself, notwithstanding the great advantage which hederived from a habit of _patient thinking_, indulged bold and excentricthoughts, of which his Queries at the end of his book of Optics are asufficient evidence. And a quick conception of distant analogies, whichis the great key to unlock the secret of nature, is by no meansincompatible with the spirit of _perseverance_, in investigationscalculated to ascertain and pursue those analogies. 

§ 1. _Speculations concerning the CONSTITUENT PRINCIPLES of thedifferent kinds of AIR, and the CONSTITUTION and ORIGIN of theATMOSPHERE, &c. _

All the kinds of air that appear to me to be essentially distinct fromeach other are _fixed air_, _acid_ and _alkaline_; for these, andanother principle, called _phlogiston_, which I have not been able toexhibit in the form of _air_, and which has never yet been exhibited byitself in _any form_, seem to constitute all the kinds of air that I amacquainted with. 

Acid air and phlogiston constitute an air which either extinguishesflame, or is itself inflammable, according, probably, to the quantity ofphlogiston combined in it, or the mode of combination. When itextinguishes flame, it is probably so much charged with the phlogisticmatter, as to take no more from a burning candle, which must, therefore, necessarily go out in it. When it is inflammable, it is probably so muchcharged with phlogiston, that the heat communicated by a burning candlemakes it immediately separate itself from the other principle with whichit was united, in which separation _heat_ is produced, as in other casesof ignition; the action and reaction, which necessarily attends theseparation of the constituent principles, exciting probably a vibratorymotion in them. 

Since inflammable, air, by agitation in water, first comes to lose itsinflammability, so as to be fit for respiration, and even to admit acandle to burn in it, and then comes to extinguish a candle; it seemsprobable that water imbibes a great part of this extraordinary charge ofphlogiston. And that water _can_ be impregnated with phlogiston, isevident from many of my experiments, especially those in which metalswere calcined over it. 

Water having this affinity with phlogiston, it is probable that italways contains a considerable portion of it; which phlogiston having astronger affinity with the acid air, which is perhaps the basis ofcommon air, may by long agitation be communicated to it, so as to leaveit over saturated, in consequence of which it will extinguish a candle. 

It is possible, however, that inflammable air and air which extinguishesa candle may differ from one another in the _mode_ of the combination ofthese two constituent principles, as well as in the proportionalquantity of each; and by agitation in water, or long standing, that modeof combination may change. This we know to be the case with othersubstances, as with _milk_, from which, by standing only, _cream_ isseparated; which by agitation becomes _butter_. Also many substances, being at rest, putrefy, and thereby become quite different from whatthey were before. If this be the case with inflammable air, the watermay imbibe either of the constituent parts, whenever any proportion ofit is spontaneously separated from the rest; and should this ever bethat phlogiston, with which air is but slightly overcharged, as by theburning of a candle, it will be recovered to a state in which a candlemay burn in it again. 

It will be observed, however, that it was only in one instance that Ifound that strong inflammable air, in its transition to a state in whichit extinguishes a candle, would admit a candle to burn in it, and thatwas very faintly; that then the air was far from being pure, as appearedby the test of nitrous air; and that it was only from a particularquantity of inflammable air which I got from oak, and which had stood along time in water, that I ever got air which was as pure as common air. Indeed, it is much more easy to account for the passing of inflammableair into a state in which it extinguishes candles, without anyintermediate state, in which it will admit a candle to burn in it, thanotherwise. This subject requires and deserves farther investigation. Itwill also be well worth while to examine what difference the agitationof air in natural or artificial _sea-water_ will occasion. 

Since acid air and phlogiston make inflammable air, and sinceinflammable air is convertible into air fit for respiration, it seemsnot to be improbable, that these two ingredients are the only essentialprinciples of common air. For this change is produced by agitation inwater only, without the addition of any fixed air, though this kind ofair, like various other things of a foreign nature, may be combined withit. 

Considering also what prodigious quantities of inflammable air areproduced by the burning of small pieces of wood or pit-coal, it may notbe improbable but that the _volcanos_, with which there are evidenttraces of almost the whole surface of the earth having been overspread, may have been the origin of our atmosphere, as well as (according to theopinion of some) of all the solid land. 

The superfluous phlogiston of the air, in the state in which it issuesfrom volcanos, may have been imbibed by the waters of the sea, which itis probable originally covered the surface of the earth, though part ofit might have united with the acid vapour exhaled from the sea, and bythis union have made a considerable and valuable addition to the commonmass of air; and the remainder of this over-charge of phlogiston mayhave been imbibed by plants as soon as the earth was furnished withthem. 

That an acid vapour is really exhaled from the sea, by the heat of thesun, seems to be evident from the remarkably different states of theatmosphere, in this respect, in hot and cold climates. In Hudson's bay, and also in Russia, it is said, that metals hardly ever rust, whereasthey are remarkably liable to rust in Barbadoes, and other islandsbetween the tropics. See Ellis's Voyage, p. 288. This is also the casein places abounding with salt-springs, as Nantwich in Cheshire. 

That mild air should consist of parts of so very different a nature asan acid vapour and phlogiston, one of which is so exceedingly corrosive, will not appear surprising to a chemist, who considers the very strongaffinity which these two principles are known to have with each other, and the exceedingly different properties which substances composed bythem possess. This is exemplified in common _sulphur_, which is as mildas air, and may be taken into the stomach with the utmost safety, thoughnothing can be more destructive than one of its constituent parts, separately taken, viz. Oil of vitriol. Common air, therefore, notwithstanding its mildness, may be composed of similar principles, andbe a real _sulphur_. 

That the fixed air which makes part of the atmosphere is not presentlyimbibed by the waters of the sea, on which it rests, may be owing to theunion which this kind of air also appears to be capable of forming withphlogiston. For fixed air is evidently of the nature of an acid; and itappears, in fact, to be capable of being combined with phlogiston, andthereby of constituting a species of air not liable to be imbibed bywater. Phlogiston, however, having a stronger affinity with acid air, which I suppose to be the basis of common air, it is not surprisingthat, uniting with this, in preference to the fixed air, the lattershould be precipitated, whenever a quantity of common air is madenoxious by an over-charge of phlogiston. 

The fixed air with which our atmosphere abounds may also be supplied byvolcanos, from the vast masses of calcareous matter lodged in the earth, together with inflammable air. Also a part of it may be supplied fromthe fermentation of vegetables upon the surface of it. At present, asfast as it is precipitated and imbibed by one process, it may be setloose by others. 

Whether there be, upon, the whole, an increase or a decrease of thegeneral mass of the atmosphere is not easy to conjecture, but I shouldimagine that it rather increases. It is true that many processescontribute to a great visible diminution of common air, and that when byother processes it is restored to its former wholesomeness, it is notincreased in its dimensions; but volcanos and fires still supply vastquantities of air, though in a state not yet fit for respiration; and itwill have been seen in my experiments, that vegetable and animalsubstances, dissolved by putrefaction, not only emit phlogiston, butlikewise yield a considerable quantity of permanent elastic air, overloaded indeed with phlogiston, as might be expected, but capable ofbeing purified by those processes in nature by which other noxious airis purified. 

That particles are continually detaching themselves from the surfaces ofall solid bodies, even the metallic ones, and that these particlesconstitute the most permanent part of the atmosphere, as Sir IsaacNewton supposed, does not appear to me to be at all probable. 

My readers will have observed, that not only is common air liable to bediminished by a mixture of nitrous air, but likewise air originallyproduced from inflammable air, and even from nitrous air itself, whichnever contained any fixed air. From this it may be inferred, that thewhole of the diminution of common air by phlogiston is not owing to theprecipitation of fixed air, but from a real contraction of itsdimensions, in consequence of its union with phlogiston. Perhaps anaccurate attention to the specific gravity of air procured from thesedifferent materials, and in these different states, may determine thismatter, and assist us in investigating the nature of phlogiston. 

In what _manner_ air is diminished by phlogiston, independent of theprecipitation of any of its constituent parts, is not easy to conceive;unless air thus diminished be heavier than air not diminished, which Idid not find to be the case. It deserves, however, to be tried with moreattention. That phlogiston should communicate absolute _levity_ to thebodies with which it is combined, is a supposition that I am not willingto have recourse to, though it would afford an easy solution of thisdifficulty. 

I have likewise observed, that a mouse will live almost as long ininflammable air, when it has been agitated in water, and even before ithas been deprived of all its inflammability, as in common air; and yetthat in this state it is not, perhaps, so much diminished by nitrous airas common air is. In this case, therefore, the diminution seems to havebeen occasioned by a contraction of dimensions, and not by a loss of anyconstituent part; so that the air is really better, that is, more fitfor respiration, than, by the test of nitrous air, it would seem to be. 

If this be the case (for it is not easy to judge with accuracy byexperiments with small animals) nitrous air will be an accurate test ofthe goodness of _common air_ only, that is, air containing aconsiderable proportion of fixed air. But this is the most valuablepurpose for which a test of the goodness of air can be wanted. It willstill, indeed, serve for a measure of the goodness of air that does notcontain fixed air; but, a smaller degree of diminution in this case, must be admitted to be equivalent to a greater diminution in the other. 

As I could never, by means of growing vegetables, bring air which hadbeen thoroughly noxious to so pure a state as that a candle would burnin it, it may be suspected that something else besides _vegetation_ isnecessary to produce this effect. But it should be considered, that nopart of the common atmosphere can ever be in this highly noxious state, or indeed in a state in which a candle will not burn in it; but thateven air reduced to this state, either by candles actually burning outin it, or by breathing it, has never failed to be perfectly restored byvegetation, at least so far that candles would burn in it again, and, toall appearance, as well, and as long as ever; so that the growingvegetables, with which the surface of the earth is overspread, may, forany thing that appears to the contrary, be a cause of the purificationof the atmosphere sufficiently adequate to the effect. 

It may likewise be suspected, that since _agitation in water_ injurespure common air, the agitation of the sea may do more harm than good inthis respect. But it requires a much more violent and longer continuedagitation of air in water than is ever occasioned by the waves of thesea to do the least sensible injury to it. Indeed a light agitation ofair in _putrid water_ injures it very materially; but if the water besweet, this effect is not produced, except by a long and tediousoperation, whereas it requires but a very short time, in comparison, torestore a quantity of any of the most noxious kinds of air to a verygreat degree of wholesomeness by the same process. 

Dr. Hales found that he could breathe the same air much longer when, inthe course of his respiration, it was made to pass through several foldsof cloth dipped in vinegar, in a solution of sea-salt, or in salt oftartar, especially the last. Statical Essays, vol. 1. P. 266. Theexperiment is valuable, and well deserves to be repeated with a greatervariety of circumstances. I imagine that the effect was produced bythose substances, or by the _water_ which they attracted from the air, imbibing the phlogistic matter discharged from the lungs. Perhaps thephlogiston may unite with the watery part of the atmosphere, inpreference to any other part of it, and may by that means be more easilytransferred to such salts as imbibe moisture. 

Sir Isaac Newton defines _flame_ to be _fumus candens_, considering all_smoke_ as being of the same nature, and capable of ignition. But thesmoke of common fuel consists of two very different things. That whichrises first is mere _water_, loaded with some of the grosser parts ofthe fuel, and is hardly more capable of becoming red hot than wateritself; but the other kind of smoke, which alone is capable of ignition, is properly _inflammable air_, which is also loaded with otherheterogeneous matter, so as to appear like a very dense smoke. A lightedcandle soon shews them to be essentially different from each other. Forone of them instantly takes fire, whereas the other extinguishes acandle. 

It is remarkable that gunpowder will take fire, and explode in all kindsof air, without distinction, and that other substances which contain_nitre_ will burn freely in those circumstances. Now since nothing canburn, unless there be something at hand to receive the phlogiston, whichis set loose in the act of ignition, I do not see how this fact can beaccounted for, but by supposing that the acid of nitre, being peculiarlyformed to unite with phlogiston, immediately receives it. And if thesulphur, which is thereby formed, be instantly decomposed again, as thechemists in general say, thence comes the explosion of gunpowder, which, however, requires the reaction of some incumbent atmosphere, and withoutwhich the materials will only _melt_, and be _dispersed_ withoutexplosion. 

Nitrous air seems to consist of the nitrous acid vapour united tophlogiston, together, perhaps, with some small portion of the metalliccalx; just as inflammable air consists of the vitriolic or marine acid, and the same phlogistic principle. It should seem, however, thatphlogiston has a stronger affinity with the marine acid, if that be thebasis of common air; for nitrous air being admitted to common air, it isimmediately decomposed; probably by the phlogiston joining with the acidprinciple of the common air, while the fixed air which it contained isprecipitated, and the acid of the nitrous air is absorbed by the waterin which the mixture is made, or unites with any volatile alkali thathappens to be at hand. 

This, indeed, is hardly agreeable to the hypothesis of most chemists, who suppose that the nitrous acid is stronger than the marine, so as tobe capable of dislodging it from any base with which it may be combined;but it agrees with my own experiments on marine acid air, which shewthat, in many cases, this _weaker acid_, as it is called, is capable ofseparating both the vitriolic and the nitrous acids from the phlogistonwith which they are combined. 

On the other hand, the solution of metals in the different acids seemsto shew, that the nitrous acid forms a closer union with phlogiston thanthe other two; because the air which is formed by the nitrous acid isnot inflammable, like that which is produced by the oil of vitriol, orthe spirit of salt. Also, the same weight of iron does not yield halfthe quantity of nitrous air that it does of inflammable. 

The great diminution of nitrous air by phlogiston is not easilyaccounted for, unless we suppose that its superabundant acid, unitingmore intimately with the phlogiston, constitutes a species of _sulphur_that is not easily perceived or catched; though, in the process withiron, and also in that with liver of sulphur, part of the redundantphlogiston forms such an union with the acid as gives it a kind ofinflammability. 

It appears to me to be very probable, that the spirit of nitre might beexhibited in the form of _air_, if it were possible to find any fluid bywhich it could be confined; but it unites with quicksilver as well aswith water, so that when, by boiling the spirit of nitre, the fumes aredriven through the glass tube, fig. 8, they instantly seize upon thequicksilver through which they are to be conveyed, and uniting with it, form a substance that stops up the tube: a circumstance which has morethan once exposed me to very disagreeable accidents, in consequence ofthe bursting of the phials. 

I do not know any inquiry more promising than the investigation of theproperties of _nitre_, the _nitrous acid_, and _nitrous air_. Some ofthe most wonderful phenomena in nature are connected with them, and thesubject seems to be fully within our reach. 

§ 2. _Speculations arising from the consideration of the similarity ofthe ELECTRIC MATTER and PHLOGISTON. _

There is nothing in the history of philosophy more striking than therapid progress of _electricity_. Nothing ever appeared more triflingthan the first effects which were observed of this agent in nature, asthe attraction and repulsion of straws, and other light substances. Itexcited more attention by the flashes of _light_ which it exhibited. Wewere more seriously alarmed at the electrical _shock_, and the effectsof the electrical _battery_; and we were astonished to the highestdegree by the discovery of the similarity of electricity with_lightning_, and the _aurora borealis_, with the connexion it seems tohave with _water-spouts_, _hurricanes_, and _earthquakes_, and also withthe part that is probably assigned to it in the system of _vegetation_, and other the most important processes in nature. 

Yet, notwithstanding all this, we have been, within a few years, morepuzzled than ever with the electricity of the _torpedo_, and of the_anguille temblante_ of Surinam, especially since that most curiousdiscovery of Mr. Walsh's, that the former of these wonderful fishes hasthe power of giving a proper electrical shock; the electrical matterwhich proceeds from it performing a real circuit from one part of theanimal to the other; while both the fish which performs this experimentand all its apparatus are plunged in water, which is known to be aconducting substance. 

Perhaps, however, by considering this fact in connexion with a fewothers, and especially with what I have lately observed concerning theidentity of electricity and phlogiston, a little light may be thrownupon this subject, in consequence of which we may be led to considerelectricity in a still more important light. Many of my readers, I amaware, will smile at what I am going to advance; but the apprehension ofthis shall not interrupt my speculations, how chimerical soever they maybe thought to be. 

The facts, the consideration of which I would combine with that of theelectricity of the torpedo, are the following. 

First, The remarkable electricity of the feathers of a paroquet, observed by Mr. Hartmann, an account of which may be seen in Mr. Rozier's Journal for Sept. 1771. P. 69. This bird never drinks, butoften washes itself; but the person who attended it having neglected tosupply it with water for this purpose, its feathers appeared to beendued with a proper electrical virtue, repelling one another, andretaining their electricity a long time after they were plucked from thebody of the bird, just as they would have done if they had receivedelectricity from an excited glass tube. 

Secondly, The electric matter directed through the body of any muscleforces it to contract. This is known to all persons who attend to whatis called the electrical shock; which certainly occasions a proper_convulsion_, but has been more fully illustrated by Father Beccaria. See my _History of Electricity_, p. 402. 

Lastly, Let it be considered that the proper nourishment of an animalbody, from which the source and materials of all muscular motion must bederived, is probably some modification of phlogiston. Nothing willnourish that does not contain phlogiston, and probably in such a stateas to be easily separated from it by the animal functions. 

That the source of muscular motion is phlogiston is still more probable, from the consideration of the well known effects of vinous andspirituous liquors, which consist very much of phlogiston, and whichinstantly brace and strengthen the whole nervous and muscular system;the phlogiston in this case being, perhaps, more easily extricated, andby a less tedious animal process, than in the usual method of extractingit from mild aliments. Since, however, the mildest aliments do the samething more slowly and permanently, that spirituous liquors do suddenlyand transiently, it seems probable that their operation is ultimatelythe same. 

This conjecture is likewise favoured by my observation, that respirationand putrefaction affect common air in the same manner, and in the samemanner in which all other processes diminish air and make it noxious, and which agree in nothing but the emission of phlogiston. If this bethe case, it should seem that the phlogiston which we take in with ouraliment, after having discharged its proper function in the animalsystem (by which it probably undergoes some unknown alteration) isdischarged as _effete_ by the lungs into the great common _menstruum_, the atmosphere. 

My conjecture suggested (whether supported or not) by these facts, is, that animals have a power of converting phlogiston, from the state inwhich they receive it in their nutriment, into that state in which it iscalled the electrical fluid; that the brain, besides its other properuses, is the great laboratory and repository for this purpose; that bymeans of the nerves this great principle, thus exalted, is directed intothe muscles, and forces them to act, in the same manner as they areforced into action when the electric fluid is thrown into them _abextra_. 

I farther suppose, that the generality of animals have no power ofthrowing this generated electricity any farther than the limits of theirown system; but that the _torpedo_, and animals of a similarconstruction, have likewise the power, by means of an additionalapparatus, of throwing it farther, so as to affect other animals, andother substances at a distance from them. 

In this case, it should seem that the electric matter discharged fromthe animal system (by which it is probably more exhausted and fatiguedthan by ordinary muscular motion) would never return to it, at least soas to be capable of being made use of a second time, and yet if thestructure of these animals be such as that the electric matter shalldart from one part of them only, while another part is left suddenlydeprived of it, it may make a circuit, as in the Leyden phial. 

As to the _manner_ in which the electric matter makes a muscle contract, I do not pretend to have any conjecture worth mentioning. I only imaginethat whatever can make the muscular fibres recede from one anotherfarther than the parts of which they consist, must have this effect. 

Possibly, the _light_ which is said to proceed from some animals, asfrom cats and wild beasts, when they are in pursuit of their prey in thenight, may not only arise, as it has hitherto been supposed to do, fromthe friction of their hairs or bristles, &c. But that violent muscularexertion may contribute to it. This may assist them occasionally tocatch their prey; as glow-worms, and other insects, are provided with aconstant light for that purpose, to the supply of which light theirnutriment may also contribute. 

I would not even say that the light which is said to have proceeded fromsome human bodies, of a particular temperament, and especially on someextraordinary occasions, may not have been of the electrical kind, thatis, produced independently of friction, or with less friction thanwould have produced it in other persons; as in those cases related byBartholin in his treatice _De luce animalium_. See particularly what hesays concerning Theodore king of the Goths, p. 54, concerning Gonzagaduke of Mantua, p. 57, and Gothofred Antonius, p. 123: But I would nothave my readers suppose that I lay much stress upon stories no betterauthenticated than these. 

The electric matter in passing through non-conducting substances alwaysemits _light_. This light I have been sometimes inclined to suspectmight have been supplied from the substance through which it passes. ButI find that after the electric spark has diminished a quantity of air asmuch as it possibly can, so that it has no more visible effect upon it, the electric light in that air is not at all lessened. It is probable, therefore, that electric light comes from the electric matter itself;and this being a modification of phlogiston, it is probable that _alllight_ is a modification of phlogiston also. Indeed, since no othersubstances besides such as contain phlogiston are capable of ignition, and consequently of becoming luminous, it was on this account prettyevident, prior to these deductions from electrical phenomena, that lightand phlogiston are the same thing, in different forms or states. 

It appears to me that _heat_ has no more proper connexion withphlogiston than it has with water, or any other constituent part ofbodies; but that it is a state into which the parts of bodies are thrownby their action and reaction with respect to one another; and probably(as the English philosophers in general have supposed) the heated stateof bodies may consist of a subtle vibratory motion of their parts. Sincethe particles which constitute light are thrown from luminous bodieswith such amazing velocity, it is evident that, whatever be the cause ofsuch a projection, the reaction consequent upon it must be considerable. This may be sufficient not only to keep up, but also to increase thevibration of the parts of those bodies in which the phlogiston is notvery firmly combined; and the difference between the substances whichare called _inflammable_ and others which also contain phlogiston may bethis, that in the former the heat, or the vibration occasioned by theemission of their own phlogiston, may be sufficient to occasion theemission of more, till the whole be exhausted; that is, till the body bereduced to ashes. Whereas in bodies which are not inflammable, the heatoccasioned by the emission of their own phlogiston may not be sufficientfor this purpose, but an additional heat _ab extra_ may be necessary. 

Some philosophers dislike the term _phlogiston_; but, for my part, I cansee no objection to giving that, or any other name, to a _realsomething_, the presence or absence of which makes so remarkabledifference in bodies, as that of _metallic calces_ and _metals_, _oil ofvitriol_ and _brimstone_, &c. And which may be transferred from onesubstance to another, according to certain known laws, that is, incertain definite circumstances. It is certainly hard to conceive how anything that answers this description can be only a mere _quality_, ormode of bodies, and not _substance_ itself, though incapable of beingexhibited alone. At least, there can be no harm in giving this name toany _thing_, or any _circumstance_ that is capable of producing theseeffects. If it should hereafter appear not to be a substance, we maychange our phraseology, if we think proper. 

On the other hand I dislike the use of the term _fire_, as a constituentprinciple of natural bodies, because, in consequence of the use that hasgenerally been made of that term, it includes another thing orcircumstance, viz. _heat_, and thereby becomes ambiguous, and is indanger of misleading us. When I use the term phlogiston, as a principlein the constitution of bodies, I cannot mislead myself or others, because I use one and the same term to denote only one and the same_unknown cause_ of certain well-known effects. But if I say that _fire_is a principle in the constitution of bodies, I must, at least, embarrass myself with the distinction of fire _in a state of action_, and fire _inactive_, or quiescent. Besides I think the term phlogistonpreferable to that of fire, because it is not in common use, butconfined to philosophy; so that the use of it may be more accuratelyascertained. 

Besides, if phlogiston and the electric matter be the same thing, thoughit cannot be exhibited alone, in a _quiescent state_, it may beexhibited alone under one of its modifications, when it is in _motion_. And if light be also phlogiston, or some modification or subdivision ofphlogiston, the same thing is capable of being exhibited alone in thisother form also. 

In my paper on the _conducting power of charcoal_, (See PhilosophicalTransactions, vol. 60. P. 221) I observed that there is a remarkableresemblance between metals and charcoal; as in both these substancesthere is an intimate union of phlogiston with an earthy base; and I saidthat, had there been any phlogiston in _water_, I should have concluded, that there had been no conducting power in nature, but in consequence ofan union of this principle with some base; for while metals havephlogiston they conduct electricity, but when they are deprived of itthey conduct no longer. Now the affinity which I have observed betweenphlogiston and water leads me to conclude that water, in its naturalstate, does contain some portion of phlogiston; and according to thehypothesis just now mentioned they must be intimately united, becausewater is not inflammable. 

I think, therefore, that after this state of hesitation and suspence, Imay venture to lay it down as a characteristic distinction betweenconducting and non-conducting substances, that the former containphlogiston intimately united with some base, and that the latter, ifthey contain phlogiston at all, retain it more loosely. In what mannerthis circumstance facilitates the passing of the electric matter throughone substance, and obstructs its passage through another, I do notpretend to say. But it is no inconsiderable thing to have advanced but_one step_ nearer to an explanation of so very capital a distinction ofnatural bodies, as that into conductors and non-conductors ofelectricity. 

I beg leave to mention in this place, as favourable to this hypothesis, a most curious discovery made very lately by Mr. Walsh, who beingassisted by Mr. De Luc to make a more perfect vacuum in the double orarched barometer, by boiling the quicksilver in the tube, found that theelectric spark or shock would no more pass through it, than through astick of solid glass. He has also noted several circumstances thataffect this vacuum in a very extraordinary manner. But supposing thatvacuum to be perfect, I do not see how we can avoid inferring from thefact, that some _substance_ is necessary to conduct electricity; andthat it is not capable, by its own expansive power, of extending itselfinto spaces void of all matter, as has generally been supposed, on theidea of there being nothing to obstruct its passage. 

Indeed if this was the case, I do not see how the electric matter couldbe retained within the body of the earth, or any of the planets, orsolid orbs of any kind. In nature we see it make the most splendidappearance in the upper and thinner regions of the atmosphere, just asit does in a glass tube nearly exhausted; but if it could expand itselfbeyond that degree of rarity, it would necessarily be diffused into thesurrounding vacuum, and continue and be condensed there, at least in agreater proportion than in or near any solid body, as Newton supposedconcerning his _ether_. 

If that mode of vibration which constitutes heat be the means ofconverting phlogiston from that state in which it makes a part of solidbodies, and eminently contributes to the firmness of their texture intothat state in which it diminishes common air; may not that peculiar kindof vibration by which Dr. Hartley supposes the brain to be affected, andby which he endeavours to explain all the phenomena of sensation, ideas, and muscular motion, be the means by which the phlogiston, which isconveyed into the system by nutriment, is converted into that form ormodification of it of which the electric fluid consists. 

These two states of phlogiston may be conceived to resemble, in somemeasure, the two states of fixed air, viz. Elastic, or non-elastic; asolid, or a fluid. 

THE APPENDIX. 

In this Appendix I shall present the reader with the communications ofseveral of my friends on the subject of the preceding work. Among them Ishould with pleasure have inserted some curious experiments, made by Dr. Hulme of Halifax, on the air extracted from Buxton water, and on theimpregnation of several fluids, with different kinds of air; but that heinforms me he proposes to make a separate publication on the subject. 

NUMBER I. 

 _EXPERIMENTS made by Mr. Hey to prove that there is no OIL of VITRIOL in water impregnated with FIXED AIR. _

It having been suggested, that air arising from a fermenting mixture ofchalk and oil of vitriol might carry up with it a small portion of thevitriolic acid, rendered volatile by the act of fermentation; I made thefollowing experiments, in order to discover whether the acidulous taste, which water impregnated with such air affords, was owing to the presenceof any acid, or only to the fixed air it had absorbed. 

EXPERIMENT I. 

I mixed a tea-spoonful of syrup of violets with an ounce of distilledwater, saturated with fixed air procured from chalk by means of thevitriolic acid; but neither upon the first mixture, nor after standing24 hours, was the colour of the syrup at all changed, except by itssimple dilution. 

EXPERIMENT II. 

A portion of the same distilled water, unimpregnated with fixed air, wasmixed with the syrup in the same proportion: not the least difference incolour could be perceived betwixt this and the above-mentioned mixture. 

EXPERIMENT III. 

One drop of oil of vitriol being mixed with a pint of the same distilledwater, an ounce of this water was mixed with a tea-spoonful of thesyrup. This mixture was very distinguishable in colour from the twoformer, having a purplish cast, which the others wanted. 

EXPERIMENT IV. 

The distilled water impregnated with so small a quantity of vitriolicacid, having a more agreeable taste than when alone, and yet manifestingthe presence of an acid by means of the syrup of violets; I subjected itto some other tests of acidity. It formed curds when agitated with soap, lathered with difficulty, and very imperfectly; but not the leastebullition could be discovered upon dropping in spirit of sal ammoniac, or solution of salt of tartar, though I had taken care to render thelatter free from causticity by impregnating it with fixed air. 

EXPERIMENT V. 

The distilled water saturated with fixed air neither effervesced, norshewed any clouds, when mixed with the fixed or volatile alkali. 

EXPERIMENT VI. 

No curd was formed by pouring this water upon an equal quantity of milk, and boiling them together. 

EXPERIMENT VII. 

When agitated with soap, this water produced curds, and lathered withsome difficulty; but not so much as the distilled water mixed withvitriolic acid in the very small proportion above-mentioned. The samedistilled water without any impregnation of fixed air lathered with soapwithout the least previous curdling. River-water, and a pleasantpump-water not remarkably hard, were compared with these. The formerproduced curds before it lathered, but not quite in so great a quantityas the distilled water impregnated with fixed air: the latter caused astronger curd than any of the others above-mentioned. 

EXPERIMENT VIII. 

Apprehending that the fixed air in the distilled water occasioned thecoagulation, or separation of the oily part of the soap, only bydestroying the causticity of the _lixivium_, and thereby rendering theunion less perfect betwixt that and the tallow, and not by the presenceof any acid; I impregnated a fresh quantity of the same distilled waterwith fixed air, which had passed through half a yard of a widebarometer-tube filled with salt of tartar; but this water caused thesame curdling with soap as the former had done, and appeared in everyrespect to be exactly the same. 

EXPERIMENT IX. 

Distilled water saturated with fixed air formed a white cloud andprecipitation, upon being mixed with a solution of _saccharum saturni_. I found likewise, that fixed air, after passing through the tube filledwith alkaline salt, upon being let into a phial containing a solution ofthe metalic salt in distilled water, caused a perfect separation of thelead, in the form of a white powder; for the water, after thisprecipitation, shewed no cloudiness upon a fresh mixture of thesubstances which had before rendered it opaque. 

NUMBER II. 

 _A Letter from Mr. HEY to Dr. PRIESTLEY, concerning the Effects of fixed Air applied by way of Clyster. _

 Leeds, Feb. 15th, 1772. 

 Reverend Sir, Having lately experienced the good effects of fixed air in a putridfever, applied in a manner, I believe not heretofore made use of, Ithought it proper to inform you of the agreeable event, as the method ofapplying this powerful corrector of putrefaction took its riseprincipally from your observations and experiments on factitious air;and now, at your request, I send the particulars of the case I mentionedto you, as far as concerns the administration of this remedy. 

January 8, 1772, Mr. Lightbowne, a young gentleman who lives with me, was seized with a fever, which, after continuing about ten days, beganto be attended with those symptoms that indicate a putrescent state ofthe fluids. 

18th, His tongue was black in the morning when I first visited him, butthe blackness went off in the day-time upon drinking: He had begun todoze much the preceding day, and now he took little notice of those thatwere about him: His belly was loose, and had been so for some days: hispulse beat 110 strokes in a minute, and was rather low: he was orderedto take twenty-five grains of Peruvian bark with five of tormentil-rootin powder every four hours, and to use red wine and water cold as hiscommon drink. 

19th, I was called to visit him early in the morning, on account of ableeding at the nose which had come on: he lost about eight ounces ofblood, which was of a loose texture: the hæmorrhage was suppressed, though not without some difficulty, by means of tents made of soft lint, dipped in cold water strongly impregnated with tincture of iron, whichwere introduced within the nostrils quite through to their posteriorapertures; a method which has never yet failed me in like cases. Histongue was now covered with a thick black pellicle, which was notdiminished by drinking: his teeth were furred with the same kind ofsordid matter, and even the roof of his mouth and sauces were not freefrom it: his looseness and stupor continued, and he was almostincessantly muttering to himself: he took this day a scruple of thePeruvian bark with ten grains of tormentil every two or three hours: astarch clyster, containing a drachm of the compound powder of bole, without opium, was given morning and evening: a window was set open inhis room, though it was a severe frost, and the floor was frequentlysprinkled with vinegar. 

20th, He continued nearly in the same state: when roused from hisdozing, he generally gave a sensible answer to the questions asked him;but he immediately relapsed, and repeated his muttering. His skin wasdry, and harsh, but without _petechiæ_. He sometimes voided his urineand _fæces_ into the bed, but generally had sense enough to ask for thebed-pan: as he now nauseated the bark in substance, it was exchangedfor Huxham's tincture, of which he took a table spoonful every two hoursin a cup full of cold water: he drank sometimes a little of the tinctureof roses, but his common liquors were red wine and water, or rice-waterand brandy acidulated with elixir of vitriol: before drinking, he wascommonly requested to rinse his mouth with water to which a little honeyand vinegar had been added. His looseness rather increased, and thestools were watery, black, and foetid: It was judged necessary tomoderate this discharge, which seemed to sink him, by mixing a drachm ofthe _theriaca Andromachi_ with each clyster. 

21st. The same putrid symptoms remained, and a _subsultus tendinum_ cameon: his stools were more foetid; and so hot, that the nurse assured meshe could not apply her hand to the bed-pan, immediately after they weredischarged, without feeling pain on this account: The medicine andclysters were repeated. 

Reflecting upon the disagreeable necessity we seemed to lie under ofconfining this putrid matter in the intestines, lest the evacuationshould destroy the _vis vitæ_ before there was time to correct its badquality, and overcome its bad effects, by the means we were using; Iconsidered, that, if this putrid ferment could be more immediatelycorrected, a stop would probably be put to the flux, which seemed toarise from, or at least to be encreased by it; and the _fomes_ of thedisease would likewise be in a great measure removed. I thought nothingwas so likely to effect this, as the introduction of fixed air into thealimentary canal, which, from the experiments of Dr. Macbride, andthose you have made since his publication, appears to be the mostpowerful corrector of putrefaction hitherto known. I recollected whatyou had recommended to me as deserving to be tried in putrid diseases, Imean, the injection of this kind of air by way of clyster, and judgedthat in the present case such a method was clearly indicated. 

The next morning I mentioned my reflections to Dr. Hird and Dr. Crowther, who kindly attended this young gentleman at my request, andproposed the following method of treatment, which, with theirapprobation, was immediately entered upon. We first gave him five grainsof ipecacuanha, to evacuate in the most easy manner part of the putrid_colluvies_: he was then allowed to drink freely of brisk orange-wine, which contained a good deal of fixed air, yet had not lost itssweetness. The tincture of bark was continued as before; and the waterwhich he drank along with it, was impregnated with fixed air from theatmosphere of a large vat of fermenting wort, in the manner I hadlearned from you. Instead of the astringent clyster, air alone wasinjected, collected from a fermenting mixture of chalk and oil ofvitriol: he drank a bottle of orange-wine in the course of this day, butrefused any other liquor except water and his medicine: two bladdersfull of air were thrown up in the afternoon. 

23d. His stools were less frequent; their heat likewise and peculiar_foetor_ were considerably diminished; his muttering was much abated, and the _subsultus tendinum_ had left him. Finding that part of the airwas rejected when given with a bladder in the usual way, I contrived amethod of injecting it which was not so liable to this inconvenience. Itook the flexible tube of that instrument which is used for throwing upthe fume of tobacco, and tied a small bladder to the end of it that isconnected with the box made for receiving the tobacco, which I hadpreviously taken off from the tube: I then put some bits of chalk into asix ounce phial until it was half filled; upon these I poured such aquantity of oil of vitriol as I thought capable of saturating the chalk, and immediately tied the bladder, which I had fixed to the tube, roundthe neck of the phial: the clyster-pipe, which was fastened to the otherend of the tube, was introduced into the _anus_ before the oil ofvitriol was poured upon the chalk. By this method the air passedgradually into the intestines as it was generated; the rejection of itwas in a great measure prevented; and the inconvenience of keeping thepatient uncovered during the operation was avoided. 

24th, He was so much better, that there seemed to be no necessity forrepeating the clysters: the other means were continued. The window ofhis room was now kept shut. 

25th, All the symptoms of putrescency had left him; his tongue and teethwere clean; there remained no unnatural blackness or _foetor_ in hisstool, which had now regained their proper consistence; his dozing andmuttering were gone off; and the disagreeable odour of his breath andperspiration was no longer perceived. He took nourishment to-day, withpleasure; and, in the afternoon, sat up an hour in his chair. 

His fever, however, did not immediately leave him; but this weattributed to his having caught cold from being incautiously uncovered, when the window was open, and the weather extremely severe; for a cough, which had troubled him in some degree from the beginning, increased, andhe became likewise very hoarse for several days, his pulse, at the sametime, growing quicker: but these complaints also went off, and herecovered, without any return of the bad symptoms above-mentioned. 

 I am, Reverend Sir, Your obliged humble Servant, WM. HEY. 

POSTSCRIPT

 October 29, 1772. 

Fevers of the putrid kind have been so rare in this town, and in itsneighbourhood, since the commencement of the present year, that I havenot had an opportunity of trying again the effects of fixed air, givenby way of clyster, in any case exactly similar to Mr. Lightbowne's. Ihave twice given water saturated with fixed air in a fever of theputrescent kind, and it agreed very well with the patients. To one ofthem the aërial clysters were administred, on account of a looseness, which attended the fever, though the stools were not black, norremarkably hot or foetid. 

These clysters did not remove the looseness, though there was often agreater interval than usual betwixt the evacuations, after the injectionof them. The patient never complained of any uneasy distention of thebelly from the air thrown up, which, indeed, is not to be wondered at, considering how readily this kind of air is absorbed by aqueous andother fluids, for which sufficient time was given, by the gradual mannerof injecting it. Both those patients recovered though the use of fixedair did not produce a crisis before the period at which such feversusually terminate. They had neither of them the opportunity of drinkingsuch wine as Mr. Lightbowne took, after the use of fixed air was enteredupon; and this, probably, was some disadvantage to them. 

I find the methods of procuring fixed air, and impregnating water withit, which you have published, are preferable to those I made use of inMr. Lightbowne's case. 

The flexible tube used for conveying the fume of tobacco into theintestines, I find to be a very convenient instrument in this case, bythe method before-mentioned (only adding water to the chalk, before theoil of vitriol is instilled, as you direct) the injection of air may becontinued at pleasure, without any other inconvenience to the patient, than what may arise from his continuing in one position during theoperation, which scarcely deserves to be mentioned, or from thecontinuance of the clyster-pipe within the anus, which is but trifling, if it be not shaken much, or pushed against the rectum. 

When I said in my letter, that fixed air appeared to be the greatestcorrector of putrefaction hitherto known, your philosophical researcheshad not then made you acquainted with that most remarkably antisepticproperty of nitrous air. Since you favoured me with a view of someastonishing proofs of this, I have conceived hopes, that this kind ofair may likewise be applied medicinally to great advantage. 

 W. H. 

NUMBER III. 

 _Observations on the MEDICINAL USES of FIXED AIR. By THOMAS PERCIVAL, M. D. Fellow of the ROYAL SOCIETY, and of the SOCIETY of ANTIQUARIES in LONDON. _

These Observations on the MEDICINAL USES OF FIXED AIR have been beforepublished in the Second Volume of my Essays; but are here reprinted withconsiderable additions. They form a part of an experimental inquiry intothis interesting and curious branch of Physics; in which the friendshipof Dr. Priestley first engaged me, in concert with himself. 

 Manchester, March 16, 1774. 

In a course of Experiments, which is yet unfinished, I have had frequentopportunities of observing that FIXED AIR may in no inconsiderablequantity be breathed without danger or uneasiness. And it is aconfirmation of this conclusion, that at Bath, where the waterscopiously exhale this mineral spirit, [15] the bathers inspire it withimpunity. At Buxton also, where the Bath is in a close vault, theeffects of such _effluvia_, if noxious, must certainly be perceived. 

Encouraged by these considerations, and still more by the testimony of avery judicious Physician at Stafford, in favour of this powerfulantiseptic remedy, I have administered fixed air in a considerablenumber of cases of the PHTHISIS PULMONALIS, by directing my patients toinspire the steams of an effervescing mixture of chalk and vinegar; orwhat I have lately preferred, of vinegar and potash. The hectic feverhas in several instances been considerably abated, and the matterexpectorated has become less offensive, and better digested. I have notyet been so fortunate in any one case, as to effect a cure; although theuse of mephitic air has been accompanied with proper internal medicines. But Dr. Withering, the gentleman referred to above, informs me, that hehas been more successful. One Phthisical patient under his care has by asimilar course intirely recovered; another was rendered much better; anda third, whose case was truly deplorable, seemed to be kept alive by itmore than two months. It may be proper to observe that fixed air canonly be employed with any prospect of success, in the latter stages ofthe _phthisis pulmonalis_, when a purulent expectoration takes place. After the rupture and discharge of a VOMICA also, such a remedy promisesto be a powerful palliative. Antiseptic fumigations and vapours havebeen long employed, and much extolled in cases of this kind. I made thefollowing experiment, to determine whether their efficacy, in anydegree, depends on the separation of fixed air from their substance. 

One end of a bent tube was fixed in a phial full of lime-water; theother end in a bottle of the tincture of myrrh. The junctures werecarefully luted, and the phial containing the tincture of myrrh wasplaced in water, heated almost to the boiling point, by the lamp of atea-kettle. A number of air-bubbles were separated, but probably not ofthe mephitic kind, for no precipitation ensued in the lime water. Thisexperiment was repeated with the _tinct. Tolutanæ, ph. Ed. _ and with_sp, vinos. Camp. _ and the result was entirely the same. The medicinalaction therefore of the vapours raised from such tinctures, cannot beascribed to the extrication of fixed air; of which it is probable bodiesare deprived by _chemical solution_ as well as by _mixture_. 

If mephitic air be thus capable of correcting purulent matter in thelungs, we may reasonably infer it will be equally useful when appliedexternally to foul ULCERS. And experience confirms the conclusion. Eventhe sanies of a CANCER, when the carrot poultice failed, has beensweetened by it, the pain mitigated, and a better digestion produced. The cases I refer to are now in the Manchester infirmary, under thedirection of my friend Mr. White, whose skill as a surgeon, andabilities as a writer are well known to the public. 

Two months have elapsed since these observations were written, [16] andthe same remedy, during that period, has been assiduously applied, butwithout any further success. The progress of the cancers seems to bechecked by the fixed air; but it is to be feared that a cure will not beeffected. A palliative remedy, however, in a disease so desperate andloathsome, may be considered as a very valuable acquisition. PerhapsNITROUS AIR might be still more efficacious. This species of factitiousair is obtained from all the metals except zinc, by means of the nitrousacid; and Dr. Priestley informs me, that as a sweetener and antisepticit far surpasses fixed air. He put two mice into a quantity of it, onejust killed, the other offensively putrid. After twenty-five days theywere both perfectly sweet. 

In the ULCEROUS SORE THROAT much advantage has been experienced from thevapours of effervescing mixtures drawn into the _fauces_[17]. But thisremedy should not supersede the use of other antisepticapplications. [18]

A physician[19] who had a very painful APTHOUS ULCER at the point of histongue, found great relief, when other remedies failed, from theapplication of fixed air to the part affected. He held his tongue overan effervescing mixture of potash and vinegar; and as the pain wasalways mitigated, and generally removed by this vaporisation, herepeated it, whenever the anguish arising from the ulcer was more thanusually severe. He tried a combination of potash and oil of vitriol welldiluted with water; but this proved stimulant and increased his pain;probably owing to some particles of the acid thrown upon the tongue, bythe violence of the effervescence. For a paper stained with the purplejuice of radishes, when held at an equal distance over two vessels, theone containing potash and vinegar, the other the same alkali and_Spiritus vitrioli tenuis_, was unchanged by the former, but was spottedwith red, in various parts, by the latter. 

In MALIGNANT FEVERS wines abounding with fixed air may be administered, to check the septic ferment, and sweeten the putrid _colluvies_ in the_primæ viæ_. If the laxative quality of such liquors be thought anobjection to the use of them, wines of a greater age may be given, impregnated with mephitic air, by a simple but ingenious contrivance ofmy friend Dr. Priestley. [20]

The patient's common drink might also be medicated in the same way. Aputrid DIARRH[OE]A frequently occurs in the latter stage of suchdisorder, and it is a most alarming and dangerous symptom. If thedischarge be stopped by astringents, a putrid _fomes_ is retained in thebody, which aggravates the delirium and increases the fever. On thecontrary, if it be suffered to take its course, the strength of thepatient must soon be exhausted, and death unavoidably ensue. Theinjection of mephitic air into the intestines, under thesecircumstances, bids fair to be highly serviceable. And a case of thisdeplorable kind, has lately been communicated to me, in which the vapourof chalk and oil of vitriol conveyed into the body by the machineemployed for tobacco clysters, quickly restrained the _diarrhoea_, corrected the heat and foetor of the stools, and in two days removedevery symptom of danger[21]. Two similar instances of the salutaryeffects of mephitic air, thus administered, have occurred also in my ownpractice, the history of which I shall briefly lay before the reader. May we not presume that the same remedy would be equally useful in theDYSENTERY? The experiment is at least worthy of trial. 

Mr. W----, aged forty-four years, corpulent, inactive, with a shortneck, and addicted to habits of intemperance, was attacked on the 7th ofJuly 1772, with symptoms which seemed to threaten an apoplexy. On the8th, a bilious looseness succeeded, with a profuse hoemorrhage fromthe nose. On the 9th, I was called to his assistance. His countenancewas bloated, his eyes heavy, his skin hot, and his pulse hard, full, andoppressed. The diarrhoea continued; his stools were bilious and veryoffensive; and he complained of griping pains in his bowels. He hadlost, before I saw him, by the direction of Mr. Hall, a surgeon ofeminence in Manchester, eight ounces of blood from the arm, which was ofa lax texture; and he had taken a saline mixture every sixth hour. Thefollowing draught was prescribed, and a dose of rhubarb directed to beadministered at night. 

 Rx. _Aq. Cinnam. Ten. _ oz. J. _Succ. Limon. Recent. _ oz. ß. _Salis Nitri gr. Xij. Syr. è Succo Limon. Dr. J. M. F. Haust. _ _4tis horis sumendus. _

July 11. The _Diarrhoea_ was more moderate; his griping pains wereabated; and he had less stupor and dejection in his countenance. Pulse90, not so hard or oppressed. As his stools continued to be foetid, the dose of rhubarb was repeated; and instead of simple cinnamon-water, his draughts were prepared with an infusion of columbo root. 

12. The _Diarrhoea_ continued; his stools were involuntary; and hedischarged in this way a quantity of black, grumous, and foetid blood. Pulse hard and quick; skin hot; tongue covered with a dark fur; abdomenswelled; great stupor. Ten grains of columbo root, and fifteen of the_Gummi rubrum astringens_ were added to each draught. Fixed air, underthe form of clysters, was injected every second or third hour; anddirections were given to supply the patient plentifully with water, artificially impregnated with mephitic air. A blister was also laidbetween his shoulders. 

13. The Diarrhoea continued, with frequent discharges of blood; butthe stools had now lost their foetor. Pulse 120; great flatulence inthe bowels, and fulness in the belly. The clysters of fixed air alwaysdiminished the tension of the _Abdomen_, abated flatulence, and made thepatient more easy and composed for some time after their injection. Theywere directed to be continued, together with the medicated water. Thenitre was omitted, and a scruple of the _Confect. Damocratis_ was givenevery fourth hour, in an infusion of columbo root. 

14. The Diarrhoea was how checked, His other symptoms continued asbefore. Blisters were applied to the arms; and a drachm and a half ofthe _Tinctura Serpentariæ_ was added to each draught. 

15. His pulse was feeble, quicker and more irregular. He dosed much;talked incoherently; and laboured under a slight degree of _Dyspnæa_. His urine, which had hitherto assumed no remarkable appearance, nowbecame pale. Though he discharged wind very freely, his belly was muchswelled, except for a short time after the injection of theair-clysters. The following draughts were then prescribed. 

 Rx _Camphoræ mucilag. G. Arab, solutæ gr. Viij. Infus. Rad. Columbo oz. Jfs Tinct. Serpent. Dr. Ij Confect. Card. Scruple j Syr. è Cort. Aurant dr. I m. F. Haust. 4tis horis sumendus. _

Directions were given to foment his feet frequently with vinegar andwarm water. 

16. He has had no stools since the 14th. His _Abdomen_ is tense. Nochange in the other symptoms. The _Tinct. Serpent. _ was omitted in hisdraughts, and an equal quantity of _Tinct. Rhæi Sp. _ substituted in itsplace. 

In the evening he had a motion to stool, of which he was for the firsttime so sensible, as to give notice to his attendants. But thedischarge, which was considerable and slightly offensive, consistedalmost entirely of blood, both in a coagulated and in a liquid state. His medicines were therefore varied as follows:

 Rx. _Decoct. Cort. Peruv. Oz. Iss Tinct. Cort. Ejusd. Dr. Ij. Confect. Card. Scruple j Gum. Rubr. Astring. Gr. Xv. Pulv. Alnmin. Gr. Vij. M. F. Haustus 4tis horis sumendus. _

Red Port wine was now given more freely in his medicated water; and hisnourishment consisted of sago and salep. 

In this state, with very little variation, he continued for severaldays; at one time ostive, and at another discharging small quantities offæces, mixed with grumous blood. The air-clysters were continued, andthe astringents omitted. 

20. His urine was now of an amber colour, and deposited a slightsediment. His pulse was more regular, and although still very quick, abated in number ten strokes in a minute. His head was less confused, and his sleep seemed to be refreshing. No blood appeared in his stools, which were frequent, but small in quantity; and his _Abdomen_ was lesstense than usual. He was extremely deaf; but gave rational answers tothe few questions which were proposed to him; and said he felt no pain. 

21. He passed a very restless night; his delirium recurred; his pulsebeat 125 strokes in a minute; his urine was of a deep amber colour whenfirst voided; but when cold assumed the appearance of cow's whey. The_Abdomen_ was not very tense, nor had he any further discharge of blood. 

Directions were given to shave his head, and to wash it with a mixtureof vinegar and brandy; the quantity of wine in his drink was diminished;and the frequent use of the pediluvium was enjoined. The air-clysterswere discontinued, as his stools were not offensive, and his _Abdomen_less distended. 

22. His pulse was now small, irregular, and beat 130 strokes in aminute. The _Dyspnoea_ was greatly increased; his skin was hot, andbedewed with a clammy moisture; and every symptom seemed to indicate theapproach of death. In this state he continued till evening, when herecruited a little. The next day he had several slight convulsions. Hisurine which was voided plentifully, still put on the appearance of wheywhen cold. Cordial and antispasmodic draughts, composed of camphor, tincture of castor, and _Sp. Vol. Aromat. _ were now directed; and winewas liberally administered. 

24. He rose from his bed, and by the assistance of his attendants walkedacross the chamber. Soon after he was seized with a violent convulsion, in which he expired. 

To adduce a case which terminated fatally as a proof of the efficacy ofany medicine, recommended to the attention of the public, may perhapsappear singular; but cannot be deemed absurd, when that remedy answeredthe purposes for which it was intended. For in the instance before us;fixed air was employed, not with an expectation that it would cure thefever, but to obviate the symptoms of putrefaction, and to allay theuneasy irritation in the bowels. The disease was too malignant, thenervous system too violently affected, and the strength of the patienttoo much exhausted by the discharges of blood which he suffered, toafford hopes of recovery from the use of the most powerful antiseptics. 

But in the succeeding case the event proved more fortunate. 

Elizabeth Grundy, aged seventeen, was attacked on the 10th of December1772, with the usual symptoms of a continued fever. The common method ofcure was pursued; but the disease increased, and soon assumed a putridtype. 

On the 23d I found her in a constant delirium, with a _subsultustendinum_. Her skin was hot and dry, her tongue black, her thirstimmoderate, and her stools frequent, extremely offensive, and for themost part involuntary. Her pulse beat 130 strokes in a minute; she dosedmuch; and was very deaf. I directed wine to be administered freely; ablister to be applied to her back; the _pediluvium_ to be used severaltimes in the day; and mephitic air to be injected under the form of aclyster every two hours. The next day her stools were less frequent, hadlost their foetor, and were no longer discharged involuntarily; herpulse was reduced to 110 strokes in the minute; and her delirium wasmuch abated. Directions were given to repeat the clysters, and to supplythe patient liberally with wine. These means were assiduously pursuedseveral days; and the young woman was so recruited by the 28th, that theinjections were discontinued. She was now quite rational, and not averseto medicine. A decoction of Peruvian bark was therefore prescribed, bythe use of which she speedily recovered her health. 

I might add a third history of a putrid disease, in which the mephiticair is now under trial, and which affords the strongest proof both ofthe _antiseptic_, and of the _tonic_ powers of this remedy; but as theissue of the case remains yet undetermined (though it is highlyprobable, alas! that it will be fatal) I shall relate only a fewparticulars of it. Master D. A boy of about twelve years of age, endowedwith an uncommon capacity, and with the most amiable dispositions, haslaboured many months under a hectic fever, the consequence of severaltumours in different parts of his body. Two of these tumours were laidopen by Mr. White, and a large quantity of purulent matter wasdischarged from them. The wounds were very properly treated by thisskilful surgeon, and every suitable remedy, which my best judgment couldsuggest, was assiduously administered. But the matter became sanious, ofa brown colour, and highly putrid. A _Diarrhoea_ succeeded; thepatient's stools were intolerably offensive, and voided without hisknowledge. A black fur collected about his teeth; his tongue was coveredwith _Aphthæ_; and his breath was so foetid, as scarcely to beendured. His strength was almost exhausted; a _subsultus tendinum_ cameon; and the final period of his sufferings seemed to be rapidlyapproaching. As a last, but almost hopeless, effort, I advised theinjection of clysters of mephitic air. These soon corrected the foetorof the patient's stools; restrained his _Diarrhoea_; and seemed torecruit his strength and spirits. Within the space of twenty-four hourshis wounds assumed a more favourable appearance; the matter dischargedfrom them became of a better colour and consistence; and was no longerso offensive to the smell. The use of this remedy has been continuedseveral days, but is now laid aside. A large tumour is suddenly formedunder the right ear; swallowing is rendered difficult and painful; andthe patient refuses all food and medicine. Nourishing clysters aredirected; but it is to be feared that these will renew the looseness, and that this amiable youth will quickly sink under his disorder[22]. 

The use of _wort_ from its saccharine quality, and disposition toferment, has lately been proposed as a remedy for the SEA SCURVY. Wateror other liquors, already abounding with fixed air in a separate state, should seem to be better adapted to this purpose; as they will morequickly correct the putrid disposition of the fluids, and at the sametime, by their gentle stimulus[23] increase the powers of digestion, andgive new strength to the whole system. 

Dr. Priestley, who suggested both the idea and the means of executingit, has under the sanction of the College of Physicians, proposed thescheme to the Lords of the Admiralty, who have ordered trial to be madeof it, on board some of his Majesty's ships of war. Might it not howevergive additional efficacy to this remedy, if instead of simple water, theinfusion of malt were to be employed?

I am persuaded such a medicinal drink might be prescribed also withgreat advantage in SCROPHULOUS COMPLAINTS, when not attended with ahectic fever; and in other disorders in which a general acrimonyprevails, and the crasis of the blood is destroyed. Under suchcircumstances, I have seen _vibices_ which spread over the body, disappear in a few days from the use of wort. 

A gentleman who is subject to a scorbutic eruption in his face, forwhich he has used a variety of remedies with no very beneficial effect, has lately applied the fumes of chalk and oil of vitriol to the partsaffected. The operation occasions great itching and pricking in theskin, and some degree of drowsiness, but evidently abates the serousdischarge, and diminishes the eruption. This patient has severalsymptoms which indicate a genuine scorbutic DIATHESIS; and it isprobable that fixed air, taken internally, would be an useful medicinein this case. 

The saline draughts of Riverius are supposed to owe their antiemeticeffects to the air, which is separated from the salt of wormwood duringthe act of effervescence. And the tonic powers of many mineral watersseem to depend on this principle. I was lately desired to visit a ladywho had most severe convulsive REACHINGS. Various remedies had beenadministered without effect, before I saw her. She earnestly desired adraught of malt liquor, and was indulged with half a pint of Burton beerin brisk effervescence. The vomitings ceased immediately, and returnedno more. Fermenting liquors, it is well known, abound with fixed air. Tothis, and to the cordial quality of the beer, the favourable effectwhich it produced, may justly be ascribed. But I shall exceed my designby enlarging further on this subject. What has been advanced it ishoped, will suffice to excite the attention of physicians to a remedywhich is capable of being applied to so many important medicinalpurposes. 

NUMBER IV. 

_Extract of a Letter from WILLIAM FALCONER, M. D. Of BATH. _

 Jan 6, 1774, Reverend Sir, I once observed the same taste you mention (Philosophical Transactions, p. 156. Of this Volume, p. 35. ) viz. Like tar water, in some water thatI impregnated with fixed air about three years ago. I did not then knowto what to attribute it, but your experiment seems to clear it up. Ihappened to have spent all my acid for raising effervescence, and tosupply its place I used a bottle of dulcified spirit of nitre, which Iknew was greatly under-saturated with spirit of wine; from which, asanalogous to your observation, I imagine the effect proceeded. 

As[24] to the coagulation of the blood of animals by fixed Air, I fearit will scarce stand the test of experiment, as I this day gave it, Ithink, a fair trial, in the following manner. 

A young healthy man, at 20 years old, received a contusion by a fall, was instantly carried to a neighbouring surgeon, and, at my request, bled in the following manner. 

I inserted a glass funnel into the neck of a large clear phial about oz. X. Contents, and bled him into it to about oz. Viii. By these means theblood was exposed to the air as little a time as possible, as it flowedinto the bottle as it came from the orifice. 

As soon as the quantity proposed was drawn, the bottle was carefullycorked, and brought to me. It was then quite fluid, nor was there theleast separation of its parts. 

On the surface of this I conveyed several streams of fixed air (havingfirst placed the bottle with the blood in a bowl of water, heated asnearly to the human heat as possible) from the mixture of the vitriolicacid and lixiv. Tartar, which I use preferably to other alkalines, asbeing (as Dr. Cullen observes) in the mildest state, and therefore mostlikely to generate most air. 

I shook the phial often, and threw many streams of air on the blood, asI have often practised with success for impregnating water; but couldnot perceive the smallest signs of coagulation, although it stood in anatmosphere of fixed air 20 minutes or more. I then uncorked the bottles, and poured off about oz. Ii to which I added about 6 or 7 gtts of spiritof vitriol, which coagulated it immediately. I set the remainder in acold place and it coagulated, as near as I could judge, in the same timethat blood would have done newly drawn from the vein. 

P. 82. Perhaps the circumilance of putrid vegetables yielding all fixedand no inflammable air may be the causes of their proving so antiseptic, even when putrid, as appears by Mr. Alexander's Experiments. 

P. 86. Perhaps the putrid air continually exhaled may be one cause ofthe luxuriancy of plants growing on dunghills or in very rich soils. 

P. 146. Your observation that inflammable air consists of the union ofsome acid vapour with phlogiston, puts me in mind of an old observationof Dr. Cullen, that the oil separated from soap by an acid was much moreinflammable than before, resembling essential oil, and soluble in V. Sp. 

I have tried fixed air as an antiseptic taken in by respiration, butwith no great success. In one case it seemed to be of service, in two itseemed indifferent, and in one was injurious, by exciting a cough. 

NUMBER V. 

_Extract of a Letter from Mr. WILLIAM BEWLEY, of GREAT MASSINGHAM, NORFOLK. _

 March 23, 1774. 

 Dear Sir, When I first received your paper, I happened to have a process going onfor the preparation of _nitrous ether_, without distillation. [25] I hadheretofore always taken for granted that the elastic fluid generated inthat preparation was _fixed_ air: but on examination I found thiscombination of the nitrous acid with inflammable spirits, produced anelastic fluid that had the same general properties with the air that youunwillingly, though very properly, in my opinion, term _nitrous_; as Ibelieve it is not to be procured without employing the _nitrous_ acid, either in a simple state, or compounded, as in _aqua regia_. I shallsuggest, however, by and by some doubts with respect to it's title tothe appellation of _air_. 

Water impregnated with your nitrous air _certainly_, as you suspectedfrom it's taste, contains the nitrous acid. On saturating a quantity ofthis water with a fixed alcali, and then evaporating, &c. I haveprocured two chrystals of nitre. But the principal observations thathave occurred to me on the subject of nitrous air are the following. Myexperiments have been few and made by snatches, under every disadvantageas to apparatus, &c. And with frequent interruptions; and yet I thinkthey are to be depended upon. 

My first remark is, that nitrous air does not give water a sensibly acidimpregnation, unless it comes into contact, or is mixed with a portionof common or atmospherical air: and my second, that nitrous airprincipally consists of the nitrous acid itself, reduced to the state ofa _permanent_ vapour not condensable by cold, like other vapours, butwhich requires the presence and admixture of common air to restore it toits primitive state of a liquid. I am beholden for this idea, you willperceive, to your own very curious discovery of the true nature of Mr. Cavendish's _marine_ vapour. 

When I first repeated your experiment of impregnating water with nitrousair, the water, I must own tasted acid; as it did in one, or perhaps twotrials afterwards; but, to my great astonishment, in all the followingexperiments, though some part of the factitious air, or vapour, wasvisibly absorbed by the water, I could not perceive the latter to haveacquired any sensible acidity. I at length found, however, that I couldrender this same water _very_ acid, by means only of the nitrous airalready included in the phial with it. Taking the inverted phial out ofthe water, I remove my finger from the mouth of it, to admit a littleof the common air, and instantly replace my finger. The redness, effervescence, and diminution take place. Again taking off my finger, and instantly replacing it, more common, air rushes in, and the samephenomena recur. The process sometimes requires to be seven or eighttimes repeated, before the whole of the nitrous _vapour_ (as I shallventure to call it) is condensed into nitrous _acid_, by the successiveentrance of fresh parcels of common air after each effervescence; andthe water becomes evidently more and more acid after every such freshadmission of the external air, which at length ceases to enter, when thewhole of the vapour has been condensed. No agitation of the water isrequisite, except a gentle motion, just sufficient to rince the sides ofthe phial, in order to wash off the condensed vapour. 

The acidity which you (and I likewise, at first) observed in the wateragitated with nitrous air _alone_, I account for thus. On bringing thephial to the mouth, the common air meeting with the nitrous vapour inthe neck of the phial, condenses it, and impregnates the water with theacid, in the very act of receiving it upon the tongue. On stopping themouth of the phial with my tongue for a short time and afterwardswithdrawing it a very little, to suffer the common air to rush past itinto the phial, the sensation of acidity has been sometimes intolerable:but taking a large gulph of the water at the same time, it has beenfound very slightly acid. --The following is one of the methods by whichI have given water a very strong acid impregnation, by means of amixture of nitrous and common air. 

Into a small phial, containing only common air, I force a quantity ofnitrous air at random, out of a bladder, and instantly clap my finger onthe mouth of the bottle. I then immerse the neck of it into water, asmall quantity of which I suffer to enter, which squirts into it withviolence; and immediately replacing my finger, remove the phial. Thewater contained in it is already _very_ acid, and it becomes more andmore so (if a sufficient quantity of nitrous air was at first thrown in)on alternately stopping the mouth of the phial, and opening it, as oftenas fresh air will enter. 

Since I wrote the above, I have frequently converted a small portion ofwater in an ounce phial into a weak _Aqua fortis_, by repeated mixturesof common and nitrous air; throwing in alternately the one or the other, according to the circumstances; that is, as long as there was asuperabundance of nitrous air, suffering the common air to enter andcondense it; and, when that was effected, forcing in more nitrous airfrom the bladder, to the common air which now predominated in thephial--and so alternately. I have wanted leisure, and conveniences, tocarry on this process to its _maximum_, or to execute it in a differentand better manner; but from what I have done, I think we may concludethat nitrous air consists principally of the nitrous acid, phlogisticated, or otherwise so modified, by a previous commenstruationwith metals, inflammable spirits, &c. As to be reduced into a durablyelastic vapour: and that, in order to deprive it of its elasticity, andrestore it to its former state, an addition of common air is requisite, and, as I suspect, of water likewise, or some other fluid: as in thecourse of my few trials, I have not yet been able to condense it in aperfectly dry bottle. 

NUMBER VI. 

_A Letter from_ Dr. FRANKLIN. 

 Craven Street, April 10, 1774. 

 Dear Sir, In compliance with your request, I have endeavoured to recollect thecircumstances of the American experiments I formerly mentioned to you, of raising a flame on the surface of some waters there. 

When I passed through New Jersey in 1764, I heard it several timesmentioned, that by applying a lighted candle near the surface of some oftheir rivers, a sudden flame Would catch and spread on the water, continuing to burn for near half a minute. But the accounts I receivedwere so imperfect that I could form no guess at the cause of such aneffect, and rather doubted the truth of it. I had no opportunity ofseeing the experiment; but calling to see a friend who happened to bejust returned home from making it himself, I learned from him the mannerof it; which was to choose a shallow place, where the bottom could bereached by a walking-stick, and was muddy; the mud was first to bestirred with the stick, and when a number of small bubbles began toarise from it, the candle was applied. The flame was so sudden and sostrong, that it catched his ruffle and spoiled it, as I saw. New-Jerseyhaving many pine-trees in different parts of it, I then imagined thatsomething like a volatile oil of turpentine might be mixed with thewaters from a pine-swamp, but this supposition did not quite satisfy me. I mentioned the fact to some philosophical friends on my return toEngland, but it was not much attended to. I suppose I was thought alittle too credulous. 

In 1765, the Reverend Dr. Chandler received a letter from Dr. Finley, President of the College in that province, relating the same experiment. It was read at the Royal Society, Nov. 21, of that year, but not printedin the Transactions; perhaps because it was thought too strange to betrue, and some ridicule might be apprehended if any member shouldattempt to repeat it in order to ascertain or refute it. The followingis a copy of that account. 

"A worthy gentleman, who lives at a few miles distance, informed me thatin a certain small cove of a mill-pond, near his house, he was surprizedto see the surface of the water blaze like inflamed spirits. I soonafter went to the place, and made the experiment with the same success. The bottom of the creek was muddy, and when stirred up, so as to cause aconsiderable curl on the surface, and a lighted candle held within twoor three inches of it, the whole surface was in a blaze, as instantly asthe vapour of warm inflammable spirits, and continued, when stronglyagitated, for the space of several seconds. It was at first imagined tobe peculiar to that place; but upon trial it was soon found, that such abottom in other places exhibited the same phenomenon. The discovery wasaccidentally made by one belonging to the mill. "

I have tried the experiment twice here in England, but without success. The first was in a slow running water with a muddy bottom. The second ina stagnant water at the bottom of a deep ditch. Being some time employedin stirring this water, I ascribed an intermitting fever, which seizedme a few days after, to my breathing too much of that foul air which Istirred up from the bottom, and which I could not avoid while I stoopedin endeavouring to kindle it. --The discoveries you have lately made ofthe manner in which inflammable air is in some cases produced, may throwlight on this experiment, and explain its succeeding in some cases, andnot in others. With the highest esteem and respect, I am, Dear Sir, Your most obedient humble servant, B. FRANKLIN. 

NUMBER VII. 

_Extract of a Letter from_ Mr. HENRY _of_ Manchester. 

It is with great pleasure I hear of your intended publication _on air_, and I beg leave to communicate to you an experiment or two which Ilately made. 

Dr. Percival had tried, without effect, to dissolve lead in waterimpregnated with fixed air. I however thought it probable, that theexperiment might succeed with nitrous air. Into a quantity of waterimpregnated with it, I put several pieces of sheet-lead, and sufferedthem, after agitation, to continue immersed about two hours. A few dropsof vol. Tincture of sulphur changed the water to a deep orange colour, but not so deep as when the same tincture was added to a glass of thesame water, into which one drop of a solution of sugar of lead had beeninstilled. The precipitates of both in the morning, were exactly of thesame kind; and the water in which the lead had been infused all night, being again tried by the same test, gave signs of a still strongersaturnine impregnation--Whether the nitrous air acts as an acid on thelead, or in the same manner that fixed air dissolves iron, I do notpretend to determine. Syrup of violets added to the nitrous water becameof a pale red, but on standing about an hour, grew of a turbid browncast. 

Though the nitrous acid is not often found, except produced by art, yetas there is a probability that nitre may be formed in the earth in largetowns, and indeed fossile nitre has been actually found in suchsituations, it should be an additional caution against the use of leadenpumps. 

I tried to dissolve mercury by the same means, but without success. 

 I am, with the most sincere esteem, Dear Sir, Your obliged and obedient servant, THO. HENRY. 

_FINIS. _

FOOTNOTES:

[15] See Dr. Falconer's very useful and ingenious treatise on the Bathwater, 2d edit. P. 313. 

[16] May, 1772. 

[17] Vid. Mr. White's useful treatise on the management of pregnant andlying-in women, p. 279. 

[18] See the author's observations on the efficacy of externalapplications in the ulcerous sore throats, Essays medical andexperimental, Vol. I. 2d edit. P. 377. 

[19] The author of these observations. 

[20] Directions for impregnating water with fixed air, in order tocommunicate to it the peculiar spirit and virtues of Pyrmont water, andother mineral waters of a similar nature. 

[21] Referring to the case communicated by Mr. Hey. 

[22] He languished about a week, and then died. 

[23] The vegetables which are most efficacious in the cure of thescurvy, possess some degree of a stimulating power. 

[24] This refers, to an experiment mentioned in the first publication ofthese papers in the Philosophical Transactions, but omitted in thisvolume. 

[25] The first account of this curious process was, I believe, given inthe Mem. De l'Ac. De Sc. De Paris for 1742. Though seemingly lessvolatile than the vitriolic ether, it boils with a much smaller degreeof heat. One day last summer, it boiled in the coolest room of my house;as it gave me notice by the explosion attending its driving out thecork. To save the bottle, and to prevent the total loss of the liquor byevaporation, I found myself obliged instantly to carry it down to mycellar. 

ERRATA. 

 P. 15. L. 13. _for_ it to _read_ to it

 p. 24. L. 20. ---- has ---- had

 p. 60. L. 22. ---- inflammable ---- in inflammable

 p. 84. L. 5. ---- experiments ---- experiment

 p. 145. L. 16. ---- with ---- of

 p. 153. L. 1. ---- that is ---- this air

 p. 199. L. 17. ---- ingenious ---- ingenuous

 p. 211. L. 23. ---- of ----, if

 p. 243. L. 27. ---- diminishing ---- diminished

 p. 272. L. 21. ---- seem ---- seems

 p. 301. L. 31. ---- ---- ---- one end

 p. 303. L. 5. ---- ---- ---- the nitrous

 p. 304. L. 21. ---- deslrium ---- delirium

 p. 306. L. 2. ---- recet. ---- recent. 

 p. 308. L. 7. ---- per ---- Peruv. 

 p. 313. L. 27. ---- usual ---- useful

 p. 300. To 314. Passim ---- Diarrhæa ---- Diarrhoea

 p. 316. L. 11. ---- remains ---- remainder

 p. 524. L. 15. ---- it ---- iron. 

A CATALOGUE of BOOKS written by

JOSEPH PRIESTLEY, LL. D. F. R. S. , _And printed for_

J. JOHNSON, BOOKSELLER, at No. 72, St. Paul's Church-Yard, London. 

1. The HISTORY and PRESENT STATE of ELECTRICITY, with originalExperiments, illustrated with Copper Plates. 4th Edit, corrected andenlarged, 4to. 1l. 1s. 

2. A FAMILIAR INTRODUCTION to the STUDY of ELECTRICITY, 2d Edit. 8vo. 2s. 6d. 

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 Consisting of original Essays, Hints, Queries, &c. Calculated to promote religious Knowledge, in 3 Volumes, 8vo, Price 18s. In Boards. 

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