Respiration Calorimeters for Studying the Respiratory Exchange andEnergy Transformations of Man

BY

FRANCIS G. BENEDICT and THORNE M. CARPENTER

[Illustration]

WASHINGTON, D. C. PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON1910

CARNEGIE INSTITUTION OF WASHINGTONPUBLICATION NO. 123

The Lord Baltimore PressBALTIMORE, MD. , U. S. A. 

PREFACE. 

The immediate development and construction of suitable apparatus forstudying the complicated processes of metabolism in man was obviouslythe first task in equipping the Nutrition Laboratory. As several seriesof experiments have already been made with these respirationcalorimeters, it is deemed advisable to publish the description of theapparatus as used at present. New features in the apparatus are, however, frequently introduced as opportunity to increase accuracy orfacilitate manipulation is noted. 

We wish here to express our sense of obligation to the followingassociates: Mr. W. E. Collins, mechanician of the Nutrition Laboratory, constructed the structural steel framework and contributed manymechanical features to the apparatus as a whole; Mr. J. A. Riche, formerly associated with the researches in nutrition in the chemicallaboratory of Wesleyan University, added his previous experience inconstructing and installing the more delicate of the heating and coolingdevices. Others who have aided in the painstaking construction, testing, and experimenting with the apparatus are Messrs. W. H. Leslie, L. E. Emmes, F. L. Dorn, C. F. Clark, F. A. Renshaw, H. A. Stevens, Jr. , MissH. Sherman, and Miss A. Johnson. 

The numerous drawings were made by Mr. E. H. Metcalf, of our staff. 

 BOSTON, MASSACHUSETTS, _August 10, 1909. _

CONTENTS. 

 PAGE

Introduction 1

Calorimeter laboratory 3 General plan of calorimeter laboratory 3 Heating and ventilating 7

The calorimeter 10 Fundamental principles of the apparatus 10 The calorimeter chamber 11 General construction 14 Prevention of radiation 17 The thermo-electric elements 19 Interior of the calorimeter 20 Heat-absorbing circuit 22 Thermometers 26 Mercurial thermometers 26 Electric-resistance thermometers 28 Air-thermometers 28 Wall thermometers 29 Electrical rectal thermometer 29 Electric-resistance thermometers for the water-current 29 Observer's table 31 Connections to thermal-junction systems 33 Rheostat for heating 34 Wheatstone bridges 34 Galvanometer 35 Resistance for heating coils 35 Temperature recorder 36 Fundamental principle of the apparatus 38 The galvanometer 39 The creeper 40 The clock 42 Installation of the apparatus 42 Temperature control of the ingoing air 43 The heat of vaporization of water 44 The bed calorimeter 45 Measurements of body-temperature 48 Control experiments with the calorimeter 50 Determination of the hydrothermal equivalent of the calorimeter 52

General description of the respiration apparatus 54 Testing the chamber for tightness 54 Ventilation of the chamber 54 Openings in the chamber 55 Ventilating air-current 57 Blower 57 Absorbers for water-vapor 58 Potash-lime cans 60 Balance for weighing absorbers 61 Purification of the air-current with sodium bicarbonate 63 Valves 63 Couplings 64 Absorber table 65 Oxygen supply 67 Automatic control of oxygen supply 69 Tension equalizer 71 Barometer 72 Analysis of residual air 73 Gas-meter 75Calculation of results 76 Analysis of oxygen 76 Advantage of a constant-temperature room and temperature control 77 Variations in the apparent volume of air 77 Changes in volume due to the absorption of water and carbon dioxide 78 Respiratory loss 78 Calculation of the volume of air residual in the chamber 79 Residual analyses 80 Calculation from residual analyses 80 Influence of fluctuations in temperature and pressure on the apparent volume of air in the system 83 Influence of fluctuations in the amounts of carbon dioxide and water-vapor upon residual oxygen 83 Control of residual analyses 84 Nitrogen admitted with the oxygen 84 Rejection of air 85 Interchange of air in the food aperture 85 Use of the residual blank in the calculations 86 Abbreviated method of computation of oxygen admitted to the chamber for use during short experiments 88 Criticism of the method of calculating the volume of oxygen 89 Calculation of total output of carbon dioxide and water-vapor and oxygen absorption 91 Control experiments with burning alcohol 91Balance for weighing subject 93Pulse rate and respiration rate 95Routine of an experiment with man 96 Preparation of subject 96 Sealing in the cover 97 Routine at observer's table 97 Manipulation of the water-meter 98 Absorber table 99 Supplemental apparatus 100

ILLUSTRATIONS. 

 PAGE

Fig. 1. General plan of respiration calorimeter laboratory 4

 2. General view of laboratory taken near main door 4

 3. General view of laboratory taken near refrigeration room 4

 4. General view of laboratory taken near temperature recorder 4

 5. View of laboratory taken from entrance of bed calorimeter 4

 6. Plan of heating and ventilating the calorimeter laboratory 6

 7. Horizontal cross-section of chair calorimeter 11

 8. Vertical cross-section of chair calorimeter 12

 9. Vertical cross-section of chair calorimeter from front to back 13

 10. Photograph of framework of chair calorimeter 14

 11. Photograph of portion of framework and copper shell 14

 12. Cross-section in detail of walls of calorimeter 16

 13. Detail of drop-sight feed-valve and arrangement of outside cooling circuit 18

 14. Schematic diagram of water-circuit for the heat-absorbers of the calorimeter 22

 15. Detail of air-resistance thermometer 28

 16. Details of resistance thermometers for water-circuit 30

 17. Diagram of wiring of observer's table 32

 18. Diagram of rheostat and resistances in series with it 36

 19. Diagram of wiring of differential circuit with shunts used with resistance thermometers for water-circuit 38

 20. Diagram of galvanometer coil, used with recording apparatus for resistance thermometers in water-circuit 40

 21. Diagram of wiring of circuits actuating plunger and creeper 41

 22. Diagram of wiring of complete 110-volt circuit 41

 23. Temperature recorder 42

 24. Detailed wiring diagram showing all parts of the recording apparatus, together with wiring to thermometers 42

 25. Section of calorimeter walls and portion of ventilating air-circuit 43

 26. Cross-section of bed calorimeter 46

 27. Diagram of ventilation of the respiration calorimeter 57

 28. Cross-section of sulphuric acid absorber 59

 29. Balance for weighing absorbers 62

 30. Diagram of absorber table 66

 31. Diagram of oxygen balance and cylinders 68

 32. The oxygen cylinder and connections to tension equalizer 70

RESPIRATION CALORIMETERS FOR STUDYING THE RESPIRATORY EXCHANGE ANDENERGY TRANSFORMATIONS IN MAN. 

INTRODUCTION. 

The establishment in Boston of an inquiry into the nutrition of man withthe construction of a special laboratory for that purpose is a directoutcome of a series of investigations originally undertaken in thechemical laboratory of Wesleyan University, in Middletown, Connecticut, by the late Prof. W. O. Atwater. Appreciating the remarkable results ofPettenkofer and Voit[1] and their associates, as early as 1892 he madeplans for the construction of a respiration apparatus accompanied bycalorimetric features. The apparatus was designed on the generalventilation plan of the above investigators, but in the firstdescription of this apparatus[2] it is seen that the method used for thedetermination of carbon dioxide and water-vapor was quite other thanthat used by Voit. Each succeeding year of active experimenting broughtabout new developments until, in 1902, the apparatus was essentiallymodified by changing it from the open-circuit type to the closed-circuittype of Regnault and Reiset. This apparatus, thus modified, has beencompletely described in a former publication. [3] The calorimetricfeatures likewise underwent gradual changes and, as greater accuracy wasdesired, it was found impracticable to conduct calorimetricinvestigations to the best advantage in the basement of a chemicallaboratory. With four sciences crowded into one building it waspractically impossible to devote more space to these researches. Furthermore, the investigations had proceeded to such an extent that itseemed desirable to construct a special laboratory for the purpose ofcarrying out the calorimetric and allied investigations on the nutritionof man. 

In designing this laboratory it was planned to overcome the difficultiesexperienced in Middletown with regard to control of the room-temperatureand humidity, and furthermore, while the researches had heretofore beencarried on simultaneously with academic duties, it appeared absolutelynecessary to adjust the research so that the uninterrupted time of theexperimenters could be given to work of this kind. Since theseexperiments frequently continued from one to ten days, theirsatisfactory conduct was not compatible with strenuous academic duties. 

As data regarding animal physiology began to be accumulated, it was soonevident that there were great possibilities in studying abnormalmetabolism, and hence the limited amount of pathological materialavailable in Middletown necessitated the construction of the laboratoryin some large center. 

A very careful consideration was given to possible sites in a number ofcities, with the result that the laboratory was constructed on a plot ofground in Boston in the vicinity of large hospitals and medical schools. Advantage was taken, also, of the opportunity to secure connections witha central power-plant for obtaining heat, light, electricity, andrefrigeration, thus doing away with the necessity for privateinstallation of boilers and electrical and refrigerating machinery. Thelibrary advantages in a large city were also of importance and within afew minutes' walk of the present location are found most of the largelibraries of Boston, particularly the medical libraries and thelibraries of the medical schools. 

The building, a general description of which appeared in the Year Bookof the Carnegie Institution of Washington for 1908, is of plain brickconstruction, trimmed with Bedford limestone. It consists of threestories and basement and practically all the space can be used forscientific work. Details of construction may be had by reference to theoriginal description of the building. It is necessary here only to statethat the special feature of the new building with which this report isconcerned is the calorimeter laboratory, which occupies nearly half ofthe first floor on the northern end of the building. 

FOOTNOTES:

[1] Pettenkofer and Voit: Ann. Der Chem. U. Pharm. (1862-3), Supp. Bd. 2, p. 17. 

[2] Atwater, Woods, and Benedict: Report of preliminary investigationson the metabolism of nitrogen and carbon in the human organism with arespiration calorimeter of special construction, U. S. Dept. Of Agr. , Office of Experiment Stations Bulletin 44. (1897. )

[3] W. O. Atwater and F. G. Benedict: A respiration calorimeter withappliances for the direct determination of oxygen. Carnegie Institutionof Washington Publication No. 42. (1905. )

CALORIMETER LABORATORY. 

The laboratory room is entered from the main hall by a double door. Theroom is 14. 2 meters long by 10. 1 meters wide, and is lighted on threesides by 7 windows. Since the room faces the north, the temperatureconditions are much more satisfactory than could be obtained with anyother exposure. In constructing the building the use of columns in thisroom was avoided, as they would interfere seriously with theconstruction of the calorimeters and accessory apparatus. Pending thecompletion of the five calorimeters designed for this room a temporarywooden floor was laid, thus furnishing the greatest freedom in placingpiping and electric wiring beneath the floor. As fast as thecalorimeters are completed, permanent flooring with suitably coveredtrenches for pipes is to be laid. The room is amply lighted during theday, the windows being very high, with glass transoms above. At night alarge mercury-vapor lamp in the center of the room, supplemented by anumber of well-placed incandescent electric lights, gives ampleillumination. 

GENERAL PLAN OF CALORIMETER LABORATORY. 

The general plan of the laboratory and the distribution of thecalorimeters and accessory apparatus are shown in fig. 1. The doubledoors lead from the main hall into the room. In general, it is plannedto conduct all the chemical and physical observations as near the centerof the laboratory as possible, hence space has been reserved forapparatus through the center of the room from south to north. Thecalorimeters are on either side. In this way there is the greatesteconomy of space and the most advantageous arrangement of apparatus. 

At present two calorimeters are completed, one under construction, andtwo others are planned. The proposed calorimeters are to be placed inthe spaces inclosed by dotted lines. Of the calorimeters that arecompleted, the so-called chair calorimeter, which was the first built, is in the middle of the west side of the room, and immediately to thenorth of it is the bed calorimeter, already tested and in actual use. Onthe east side of the room it is intended to place large calorimeters, one for continuous experiments extending over several days and the otherlarge enough to take in several individuals at once and to haveinstalled apparatus and working machinery requiring larger space thanthat furnished by any of the other calorimeters. Near the chaircalorimeter a special calorimeter with treadmill is shortly to be built. 

The heat insulation of the room is shown by the double windows and theheavy construction of the doors other than the double doors. On enteringthe room, the two calorimeters are on the left, and, as arranged atpresent, both calorimeters are controlled from the one platform, onwhich, is placed the observer's table, with electrical connections andthe Wheatstone bridges for temperature measurements; above and behindthe observer's table are the galvanometer and its hood. At the left ofthe observer's platform is a platform scale supporting the water-meter, with plug valve and handle conveniently placed for emptying the meter. The absorption system is placed on a special table conveniently situatedwith regard to the balance for weighing the absorbers. The large balanceused for weighing the oxygen cylinders is directly across the centeraisle and the analytical balance for weighing the U-tubes for residualanalysis is near by. 

[Illustration: FIG. 1. --General plan of respiration calorimeterlaboratory. ]

[Illustration: FIG. 2

General view of laboratory room taken near the main door. At the extremeright is the absorber table, and back of it the bed calorimeter. In theimmediate foreground is shown the balance for weighing absorbers. Asulphuric acid absorber is suspended on the left hand arm of thebalance. At the left is the observer's table and back of it the chaircalorimeter with a large balance above for weighing subjects. On thefloor, to the left, is the water meter for weighing water used to bringaway heat. ]

[Illustration: FIG. 3

General view of laboratory taken near the refrigeration room. Theobserver's table is in the immediate foreground with water balance atthe left, and chair calorimeter with balance for weighing man at theextreme left. At the right of the observer's table is the absorptionsystem table, and on the wall in the rear the temperature recorder. Atthe right is shown the balance for weighing absorbers, and back of thatthe case surrounding the balance for weighing oxygen. ]

[Illustration: FIG. 4

General view of laboratory taken near the temperature recorder. The bedcalorimeter is at the right, the absorber table in the immediateforeground, back of it the chair calorimeter and observer's table, andat the left the balance for weighing absorbers. Near the ceiling areshown the ducts for the cold air used for temperature control. ]

[Illustration: FIG. 5

View of laboratory taken from the entrance of the bed calorimeter, withbalance for weighing oxygen cylinders at the left. The structural steelskeleton of the calorimeter for long experiments is at the right andsections of the copper lining are in the rear, resting against thewall. ]

Another view of the laboratory, taken near the door leading to therefrigeration room, is shown in fig. 3. At the right is seen the balanceused for weighing absorbers, and back of it, imperfectly shown, is thecase surrounding the balance for weighing oxygen cylinders. On the wall, in the rear, is the recording apparatus for electric resistancethermometers in the water-circuit, a detail of which is shown in fig. 23. In the foreground in the center is seen the observer's table; at theright of this is shown the table for the absorption system, and at theleft the chair calorimeter with the balance for weighing subjects aboveit. The mercury-vapor light, which is used to illuminate the room, isimmediately above the balance for weighing absorbers. 

[Illustration: FIG. 6. --Plan of heating and ventilating calorimeterlaboratory, showing general plan of circulation of the special coolingsystem and the position of the thermostats and radiators which theycontrol. The two small diagrams are cross-sections of brine and heatingcoils. ]

The bed calorimeter and the absorbing-system table are better shown infig. 4, a general view of the laboratory taken near the temperaturerecorder. In the immediate foreground is the table for the absorptionsystem, and back of it are the observer's table and chair calorimeter. At the right, the bed calorimeter with the front removed and the rubberhose connections as carried from the absorber table to the bedcalorimeter are shown. At the extreme left is the balance for weighingthe absorbers. Above the chair calorimeter can be seen the balance forweighing the subject, and at its right the galvanometer suspended fromthe ceiling. 

The west side of the laboratory at the moment of writing contains thelarger proportion of the apparatus. On the east side there exist onlythe balance for weighing oxygen cylinders and an unfinished[4] largecalorimeter, which will be used for experiments of long duration. A viewtaken near the front end of the bed calorimeter is shown in fig. 5. Atthe right, the structural skeleton of the large calorimeter is clearlyshown. Some of the copper sections to be used in constructing the liningof the calorimeter can be seen against the wall in the rear. 

At the left the balance for weighing the oxygen cylinders is shown withits counterpoise. A reserve oxygen cylinder is standing immediately infront of it. A large calorimeter modeled somewhat after the plan ofSondén and Tigerstedt's apparatus in Stockholm and Helsingfors isplanned to be built immediately back of the balance for weighing oxygencylinders. 

HEATING AND VENTILATING. 

Of special interest in connection with this calorimeter laboratory arethe plans for maintaining constant temperature and humidity (fig. 6). The room is heated by five steam radiators (each with about 47 squarefeet of radiating surface) placed about the outer wall, which arecontrolled by two pendant thermostats. A certain amount of indirectventilation is provided, as indicated by the arrows on the inner wall. The room is cooled and the humidity regulated by a system ofrefrigeration installed in an adjoining room. This apparatus is ofparticular interest and will be described in detail. 

In the small room shown at the south side of the laboratory is placed apowerful electric fan which draws the air from above the floor of thecalorimeter laboratory, draws it over brine coils, and sends it out intoa large duct suspended on the ceiling of the laboratory. This duct has anumber of openings, each of which can be controlled by a valve, and anunlimited supply of cold air can be directed to any portion of thecalorimeter room at will. To provide for more continuous operation andfor more exact temperature control, a thermostat has been placed in theduct and is so constructed as to operate some reheater coils beneath thebrine-coils in the refrigerating room. This thermostat is set at 60° F. , and when the temperature of the air in the duct falls below this point, the reheater system is automatically opened or closed. The thermostatcan be set at any point desired. Up to the present time it has beenunnecessary to utilize this special appliance, as the control by handregulation has been most satisfactory. 

Two vertical sections through the refrigerating coils are shown in fig. 6. Section A-B shows the entrance near the floor of the calorimeterroom. The air is drawn down over the coils, passes through the blower, and is forced back again to the top of the calorimeter room into thelarge duct. If outdoor air is desired, a special duct can be connectedwith the system so as to furnish outdoor air to the chamber. This hasnot as yet been used. Section C-D shows the fan and gives a sectionthrough the reheater. The brine coils, 400 meters long, are intriplicate. If one set becomes covered with moisture and is somewhatinefficient, this can be shut off and the other two used. When thefrozen moisture melts and drops off, the single coil can be used again. It has been found that the system so installed is most readilycontrolled. 

The degree of refrigeration is varied in two ways: (1) the area of brinecoils can be increased or decreased by using one, two, or all three ofthe coils; or (2) the amount of air passing over the cooling pipes maybe varied by changing the speed of the blower. In practice substantiallyall of the regulation is effected by varying the position of thecontrolling lever on the regulating rheostat. The apparatus functionatesperfectly and the calorimeter room can be held at 20° C. Day in and dayout, whether the temperature outdoors is 40° below or 100° above 0° F. 

It can be seen, also, that this system provides a very satisfactoryregulation of the humidity, for as the air passes over the brine coilsthe moisture is in large part frozen out. As yet, no hygrometric studyhas been made of the air conditions over a long period, but theapparatus is sufficiently efficient to insure thorough electricalinsulation and absence of leakage in the intricate electricalconnections on the calorimeters. 

The calorimeters employ the thermo-electric element with its lowpotential and a D'Arsonval galvanometer of high sensibility, and inclose proximity it is necessary to use the 110-volt current for heating, consequently the highest degree of insulation is necessary to preventdisturbing leakage of current. 

The respiration calorimeter laboratory is so large, the number ofassistants in the room at any time is (relatively speaking) so small, seldom exceeding ten, and the humidity and temperature are so verythoroughly controlled, that as yet it has been entirely unnecessary toutilize even the relatively small amount of indirect ventilationprovided in the original plans. 

During the greater part of the winter it is necessary to use only one ofthe thermostats and the radiators connected with the other can be shutoff, since each radiator can be independently closed by the valves onthe steam supply and return which go through the floor to the basement. The temperature control of this room is therefore very satisfactory andeconomical. 

It is not necessary here to go into the advantages of temperaturecontrol of the working rooms during the summer months. Every one seemsto be thoroughly convinced that it is necessary to heat rooms in thewinter, but our experience thus far has shown that it is no lessimportant to cool the laboratory and control the temperature andmoisture during the summer months, as by this means both the efficiencyand endurance of the assistants, to say nothing of the accuracy of thescientific measurements, are very greatly increased. Arduous scientificobservations that would be wholly impossible in a room withouttemperature control can be carried on in this room during the warmestweather. 

FOOTNOTES:

[4] As this report goes to press, this calorimeter is well on the way tocompletion. 

THE CALORIMETER. 

In describing this apparatus, for the sake of clearness, thecalorimetric features will be considered before the appliances for thedetermination of the respiratory products. 

FUNDAMENTAL PRINCIPLES OF THE APPARATUS. 

The measurements of heat eliminated by man, as made by this apparatus, are based upon the fact that the subject is inclosed in a heat-proofchamber through which a current of cold water is constantly passing. Theamount of water, the flow of which, for the sake of accuracy, is kept ata constant rate, is carefully weighed. The temperatures of the waterentering and leaving the chamber are accurately recorded at frequentintervals. The walls of the chamber are held adiabatic, thus preventinga gain or loss of heat by arbitrarily heating or cooling the outer metalwalls, and the withdrawal of heat by the water-current is so controlled, by varying the temperature of the ingoing water, that the heat broughtaway from the calorimeter is exactly equal in amount to the heateliminated by radiation and conduction by the subject, thus maintaininga constant temperature inside of the chamber. The latent heat of thewater vaporized is determined by measuring directly the water vapor inthe ventilating air-current. 

In the construction of the new calorimeters a further and fundamentalchange in construction has been made in that all the thermal junctions, heating wires, and cooling pipes have been attached directly to the zincwall of the calorimeter, leaving the outer insulating panels free fromincumbrances, so that they can be removed readily and practically allparts inspected whenever desired without necessitating completedismantling of the apparatus. This arrangement is possible except inthose instances where connections pass clear through from the interiorof the chamber to the outside, namely, the food-aperture, air-pipes, water-pipes, electrical connections, and tubes for connections withpneumograph and stethoscope; but the apparatus is so arranged as to haveall of these openings in one part of the calorimeter. It is possible, therefore, to remove all of the outer sections of the calorimeter withthe exception of panels on the east side. 

This fundamental change in construction has proven highly advantageous. It does away with the necessity of rolling the calorimeter out of itsprotecting insulating house and minimizes the delay and expenseincidental to repairs or modifications. As the calorimeter is nowconstructed, it is possible to get at all parts of it from the outside, with the exception of one small fixed panel through which the aboveconnections are passed. This panel, however, is made as narrow aspossible, so that practically all changes can be made by taking out theadjacent panels. 

THE CALORIMETER CHAMBER. 

[Illustration: FIG. 7. --Horizontal cross-section of chair calorimeter, showing cross-section of copper wall at A, zinc wall at B, hair-felt atE, and asbestos outer wall at F; also cross-section of all uprightchannels in the steel construction. At the right is the location of theingoing and outgoing water and the thermometers. At C is shown the foodaperture, and D is a gasket separating the two parts. The ingoing andoutcoming air-pipes are shown at the right inside the copper wall. Thetelephone is shown at the left, and in the center of the drawing is thechair with its foot-rest, G. In dotted line is shown the opening wherethe man enters. ]

[Illustration: FIG. 8. --Vertical cross-section of chair calorimeter, showing part of rear of calorimeter and structural-steel frame. N, cross-section of bottom horizontal channel supporting asbestos floor J;H, H, upright channels (at the right is a side upright channel and tothe left of this is an upright rear channel); M horizontal 8-inchchannel supporting calorimeter; Zn, zinc wall; Cu, copper wall; J, insulating asbestos. ]

The respiration chamber used in Middletown, Connecticut, was designed topermit of the greatest latitude in the nature of the experiments to bemade with it. As a result, it was found at the end of a number of yearsof experimenting that this particular size of chamber was somewhat toosmall for the most satisfactory experiments during muscular work and, onthe other hand, somewhat too large for the best results during so-calledrest experiments. In the earlier experiments, where no attempt was madeto determine the consumption of oxygen, these disadvantages were not soapparent, as carbon dioxide could be determined with very greataccuracy; but with the attempts to measure the oxygen it was found thatthe large volume of residual air inside the chamber, amounting to some4, 500 liters, made possible very considerable errors in thisdetermination, for, obviously, the subject could draw upon the oxygenresidual in the air of the chamber, nearly 1, 000 liters, as well as uponthe oxygen furnished from outside sources. The result was that a verycareful analysis of the residual air must be made frequently in order toinsure that the increase or decrease in the amount of oxygen residual inthe air of the chamber was known accurately at the end of each period. Analysis of this large volume of air could be made with considerableaccuracy, but in order to calculate the exact total of oxygen residualin the air it was necessary to know the total volume of air inside thechamber under standard conditions. This necessitated, therefore, acareful measurement of temperature and pressure, and while thebarometric pressure could be measured with a high degree of accuracy, it was found to be very difficult to determine exactly the averagetemperature of so large a mass of air. The difficulties attending thismeasurement and experiments upon this point are discussed in detailelsewhere. [5] Consequently, as a result of this experience, in planningthe calorimeters for the Nutrition Laboratory it was decided to designthem for special types of experiments. The first calorimeter to beconstructed was one which would have general use in experiments duringrest and, indeed, during experiments with the subject sitting quietly inthe chair. 

[Illustration: FIG. 9. --Vertical cross-section of chair calorimeter fromfront to back, showing structural steel supporting the calorimeter andthe large balance above for weighing the subject inside the calorimeter. The chair, method of suspension, and apparatus for raising and loweringare shown. Part of the heat-absorbers is shown, and their generaldirection. The ingoing and outgoing air-pipes and direction ofventilation are also indicated. The positions of the food-aperture andwire mat and asbestos support are seen. Surrounding the calorimeter arethe asbestos outside and hair-felt lining. ]

It may well be asked why the first calorimeter was not constructed ofsuch a type as to permit the subject assuming a position on a couch orsofa, such as is used by Zuntz and his collaborators in their researchon the respiratory exchange, or the position of complete muscular restintroduced by Johansson and his associates. While the body positionsmaintained by Zuntz and Johansson may be the best positions forexperiments of short duration, it was found, as a result of a largenumber of experiments, that subjects could be more comfortable and quietfor periods of from 6 to 8 hours by sitting, somewhat inclined, in acomfortable arm-chair, provided with a foot-rest. With this in mind thefirst calorimeter was constructed so as to hold an arm-chair with afoot-rest so adjusted that the air-space between the body of the subjectand the walls of the chamber could be cut down to the minimum and thusincrease the accuracy of the determination of oxygen. That the volumehas been very materially reduced may be seen from the fact that thetotal volume of the first calorimeter to be described is less than 1, 400liters, or about one-third that of the Middletown apparatus. 

GENERAL CONSTRUCTION. 

A horizontal cross-section of the apparatus is shown in fig. 7, and avertical cross-section facing the front is given in fig. 8. Otherdetails of structural steel are seen in fig. 9. 

In constructing the new chambers, the earlier wood construction, withits tendency to warp and its general non-rigidity, was avoided by theuse of structural steel, and hence in this calorimeter no use whateveris made of wood other than the wood of the chair. 

To avoid temperature fluctuations due to possible local stratificationof the air in the laboratory, the calorimeter is constructed so as to bepractically suspended in the air, there being a large air-space of some76 centimeters between the lowest point of the calorimeter and thefloor, and the top of the calorimeter is some 212 centimeters below theceiling of the room. Four upright structural-steel channels (4-inch)were bolted through the floor, so as to secure great rigidity, and weretied together at the top with structural steel. As a solid base for thecalorimeter chamber two 3-inch channels were placed parallel to eachother 70 centimeters from the floor, joined to these uprights. Uponthese two 3-inch channels the calorimeter proper was constructed. Thesteel used for the most part in the skeleton of the apparatus isstandard 2-1/2-inch channel. This steel frame and its support are shownin fig. 10, before any of the copper lining was put into position. Themain 4-inch channels upon which the calorimeter is supported, thetie-rods and turn-buckles anchoring the framework to the ceiling, theI-beam construction at the top upon which is subsequently installed thelarge balance for weighing the man, the series of small channels set onedge upon which the asbestos floor is laid, and the upright row ofchannel ribs are all clearly shown. 

[Illustration: FIG. 10

Photograph of framework of chair calorimeter. In the photograph areshown four upright channels and the channels at the top for supportingthe calorimeter. The smaller upright 2-1/2 inch channels and angles areshown inside of this frame. In the lower part of the figure is seen theasbestos board for the bottom of the calorimeter and underneath this asheet of zinc. ]

[Illustration: FIG. 11

Photograph of portion of framework and copper shell. The finished coppershell is seen in position with some of the thermal junction thimblessoldered into it. A portion of the food aperture and the four brassferrules for conducting the water pipes and air pipes are shown. Asection of the zinc outside is shown in the lower part of the figure. ]

A photograph taken subsequently, showing the inner copper lining inposition, is given in fig. 11. 

The floor of the chamber is supported by 7 pieces of 2-1/2-inch channel(N, N, N, fig. 8), laid on top and bolted to the two 3-inch channels (M, fig. 8). On top of these is placed a sheet of so-called asbestos lumber(J', fig. 8) 9. 5 millimeters thick, cut to fit exactly the bottom of thechamber. Upright 2-1/2-inch channels (H, fig. 8) are bolted to the twooutside channels on the bottom and to the ends of three of the longchannels between in such a manner as to form the skeleton of the walls. The upper ends of these channels are fastened together by pieces ofpiping (P, P, P, fig. 8) with lock-nuts on either side, thus holding thewhole framework in position. 

The I-beams and channels used to tie the four upright channels at thetop form a substantial platform upon which is mounted a large balance(fig. 9). This platform is anchored to the ceiling at four points by tierods and turn-buckles, shown in fig. 4. The whole apparatus, therefore, is extremely rigid and the balance swings freely. 

The top of the chamber is somewhat restricted near the edges (fig. 8)and two lengths of 2-1/2-inch channel support the sides of the openingthrough which the subject enters at the top (fig. 7). 

Both the front and back lower channels upon which the bottom rests areextended so as to provide for supports for the outer walls of asbestoswood, which serve to insulate the calorimeter. Between the channelsbeneath the calorimeter floor and the 3-inch channels is placed a sheetof zinc which forms the outer bottom metallic wall of the chamber. 

In order to prevent conduction of heat through the structural steel allcontact between the inner copper wall and the steel is avoided by havingstrips of asbestos lumber placed between the steel and copper. These areshown as J in fig. 8 and fig. 12. A sheet of asbestos lumber beneath thecopper bottom likewise serves this purpose and also serves to give asolid foundation for the floor. The supporting channels are placed nearenough together to reinforce fully the sheet of asbestos lumber andenable it to support solidly the weight of the man. The extra strain onthe floor due to tilting back a chair and thus throwing all the weighton two points was taken into consideration in planning the asbestos andthe reinforcement by the steel channels. The whole forms a verysatisfactory flooring. 

_Wall construction and insulation. _--The inner wall of the chamberconsists of copper, preferably tinned on both sides, thus aiding insoldering, and the tinned inner surface makes the chamber somewhatlighter. Extra large sheets are obtained from the mill, thus reducing toa minimum the number of seams for soldering, and seams are made tightonly with difficulty. The copper is of standard gage, the so-called14-ounce copper, weighing 1. 1 pounds per square foot or 5. 5 kilogramsper square meter. It has a thickness of 0. 5 millimeter. The wholeinterior of the skeleton frame of the structural steel is lined withthese sheets; fig. 11 shows the copper shell in position. 

For the outer metallic wall, zinc, as the less expensive metal, is used. One sheet of this material perforated with holes for the attachment ofbolts and other appliances is shown in position on the outside of thewall in fig. 11. The sheet zinc of the floor is obviously put inposition before the channels upon which it rests are laid. The zinc isobtained in standard size, and is the so-called 9-ounce zinc, or 0. 7pound to the square foot, or 3. 5 kilograms to the square meter. Thesheet has a thickness of 0. 5 millimeter. 

[Illustration: FIG. 12. --Cross-section in detail of walls ofcalorimeter, showing zinc and copper walls and asbestos outside (A);hair-felt lining (B); cross-section of channel iron (H); brass washersoldered to copper (K); asbestos insulation between channel iron andcopper (J); bolt holding the whole together (I); heating wire (W) andinsulator holding it (F) shown in air-space between zinc and hair-felt;section of one of the cooling pipes (C) and its brass support (G);threaded rod (E) fastened into H at one end and passing through asbestoswall with a nut on the outside; and iron pipe (D) used as spacer betweenasbestos and zinc. ]

In the cross-section, fig. 7, A represents the copper wall and B thezinc wall. Surrounding this zinc wall and providing air insulation is aseries of panels constructed of asbestos lumber, very fire-resisting, rigid, and light. The asbestos lumber used for these outer panels is 6. 4millimeters (0. 25 inch) thick. To further aid in heat insulation we haveglued to the inner face of the different panels a patented materialcomposed of two layers of sheathing-paper inclosing a half-inch ofhair-felt. This material is commonly used in the construction ofrefrigerators. This is shown as E in fig. 7, while the outer asbestospanels are shown as F. 

A detail of the construction of the walls, showing in addition theheating and cooling devices, is given in fig. 12, in which the copper isshown held firmly to the upright channel H by means of the bolt I, screwing into a brass or copper disk K soldered to the copper wall. Thebolt I serves the purpose of holding the copper to the upright channeland likewise by means of a washer under the head of the screw holds thezinc to the channel. In order to hold the asbestos-lumber panel A withthe hair-felt lining B a threaded rod E is screwed into a tapped hole inthe outer part of the upright channel H. A small piece of brass or irontubing, cut to the proper length, is slipped over this rod and theasbestos lumber held in position by a hexagonal nut with washer on thethreaded rod E. In this manner great rigidity of construction issecured, and we have two air-spaces corresponding to the dead air-spacesindicated in fig. 7, the first between the copper and zinc and thesecond between the zinc and hair-felt. 

PREVENTION OF RADIATION. 

As can be seen from these drawings the whole construction of theapparatus is more or less of the refrigerator type, _i. E. _, there islittle opportunity for radiation or conduction of heat. Such aconstruction could be multiplied a number of times, giving a greaternumber of insulating walls, and perhaps reducing radiation to theminimum, but for extreme accuracy in calorimetric investigations it isnecessary to insure the absence of radiation, and hence we have retainedthe ingenious device of Rosa, by which an attempt is made arbitrarily toalter the temperature of the zinc wall so that it always follows anyfluctuations in the temperature of the copper wall. To this end it isnecessary to know _first_ that there is a temperature difference betweenzinc and copper and, _second_, to have some method for controlling thetemperature of the zinc. Leaving for a moment the question of measuringthe temperature differences between zinc and copper, we can considerhere the methods for controlling the temperature of the zinc wall. 

If it is found necessary to warm the zinc wall, a current of electricityis passed through the resistance wire W, fig. 12. This wire ismaintained approximately in the middle of the air-space between the zincwall and hair-felt by winding it around an ordinary porcelain insulatorF, held in position by a threaded rod screwed into a brass disk solderedto the zinc wall. A nut on the end of the threaded rod holds theinsulator in position. Much difficulty was had in securing a resistancewire that would at the same time furnish reasonably high resistance andwould not crystallize or become brittle and would not rust. At presentthe best results have been obtained by using enameled manganin wire. Thewire used is No. 28 American wire-gage and has resistance ofapproximately 1. 54 ohms per foot. The total amount of wire used in anyone circuit is equal to a resistance of approximately 92 ohms. Thismethod of warming the air-space leaves very little to be desired. It canbe instantaneously applied and can be regulated with the greatest easeand with the greatest degree of refinement. 

If, on the other hand, it becomes necessary to cool the air-space nextto the zinc and in turn cool the zinc, we must resort to the use of coldwater, which is allowed to flow through the pipe C suspended in theair-space between the zinc and hair-felt at approximately the samedistance as is the heating wire. The support of these pipes isaccomplished by placing them in brass hangers G, soldered to the zincand provided with an opening in which the pipe rests. 

In the early experimenting, it was found impracticable to use piping ofvery small size, as otherwise stoppage as a result of sediment couldeasily occur. The pipe found best adapted to the purpose was theso-called standard one-eighth inch brass pipe with an actual internaldiameter of 7 millimeters. The opening of a valve allowed cold water toflow through this pipe and the considerable mass of water passingthrough produced a very noticeable cooling effect. In the attempt tominimize the cooling effect of the mass of water remaining in the pipe, provision was made to allow water to drain out of this pipe a fewmoments after the valve was closed by a system of check-valves. Inbuilding the new apparatus, use was made of the compressed-air servicein the laboratory to remove the large mass of cold water in the pipe. Assoon as the water-valve was closed and the air-cock opened, thecompressed air blew all of the water out of the tube. 

[Illustration: FIG. 13. --Detail of drop-eight feed-valve and arrangementof outside cooling circuit. The water enters at A, and the flow isregulated by the needle-valve at left-hand side. Rate of flow can beseen at end of exit tube just above the union. The water flows out at Cand compressed air is admitted at B, regulated by the pet-cock. ]

The best results have been obtained, however, with an entirely newprinciple, namely, a few drops of water are continually allowed to passinto the pipe, together with a steady stream of compressed air. Thiscold water is forcibly blown through the pipe, thus cooling to an amountregulated by the amount of water admitted. Furthermore, the relativelydry air evaporates some of the water, thereby producing a somewhatgreater cooling effect. By adjusting the flow of water through the pipea continuous cooling effect of mild degree may be obtained. Whileformerly the air in the space next the zinc wall was either cooled orheated alternately by opening the water-valve or by passing a currentthrough the heating coil, at present it is found much more advantageousto allow a slow flow of air and water through the pipes continuously, thus having the air-space normally somewhat cooler than is desired. Theeffect of this cooling, therefore, is then counterbalanced by passing anelectric current of varying strength through the heating wire. By thismanipulation it is unnecessary that the observer manipulate more thanone instrument, namely, the rheostat, while formerly he had tomanipulate valves, compressed-air cocks, and rheostat. The arrangementfor providing for the amount of compressed air and water is shown infig. 13, in which it is seen that a small drop-sight feed-water valve isattached to the pipe C leading into the dead air-space surrounding thecalorimeter chamber. Compressed air enters at B and the amount enteringcan be regulated by the pet-cock. The amount of water admitted isreadily observed by the sight feed-valve. When once adjusted this formof apparatus produces a relatively constant cooling effect andfacilitates greatly the manipulation of the calorimetric apparatus as awhole. 

THE THERMO-ELECTRIC ELEMENTS. 

In order to detect differences in temperature between the copper andzinc walls, some system for measuring temperature differences betweenthese walls is essential. For this purpose we have found nothing that isas practical as the system of iron-German-silver thermo-electricelements originally introduced in this type of calorimeter by E. B. Rosa, of the National Bureau of Standards, formerly professor of physicsat Wesleyan University. In these calorimeters the same principle, therefore, has been applied, and it is necessary here only to give thedetails of such changes in the construction of the elements, theirmounting, and their insulation as have been made as a result ofexperience in constructing these calorimeters. An element consisting offour pairs of junctions is shown in place as T-J in fig. 25. 

One ever-present difficulty with the older form of element was thetendency for the German-silver wires to slip out of the slots in whichthey had been vigorously crowded in the hard maple spool. In thusslipping out of the slots they came in contact with the metal thimble inthe zinc wall and thus produced a ground. In constructing the newelements four pairs of iron-German-silver thermal junctions were made onessentially the same plan as that previously described, [6] the onlymodification being made in the spool. While the ends of the junctionsnearest the copper are exposed to the air so as to take up most rapidlythe temperature of the copper, it is somewhat difficult to expose theends of the junctions nearest the zinc and at the same time avoidshort-circuiting. The best procedure is to extend the rock maple spoolwhich passes clear through the ferule in the zinc wall and cut a wideslot in the spool so as to expose the junctions to the air nearest theferule. By so doing the danger to the unprotected ends of the junctionsis much less. The two lead-wires of German silver can be carried throughthe end of the spool and thus allow the insulation to be made much moresatisfactorily. In these calorimeters free use of these thermaljunctions has been made. In the chair calorimeter there are on the top16 elements consisting of four junctions each, on the rear 18, on thefront 8, and on the bottom 13. The distribution of the elements is madewith due reference to the direction in which the heat is most directlyradiated and conducted from the surface of the body. 

While the original iron-German-silver junctions have been retained intwo of these calorimeters for the practical reason that a large numberof these elements had been constructed beforehand, we believe it will bemore advantageous to use the copper-constantin couple, which has athermo-electric force of 40 microvolts per degree as against the 25 ofthe iron-German-silver couple. It is planned to install thecopper-constantin junctions in the calorimeters now building. 

INTERIOR OF THE CALORIMETER. 

Since the experiments to be made with this chamber will rarely exceed 6to 8 hours, there is no provision made for installing a cot bed or otherconveniences which would be necessary for experiments of long duration. Aside from the arm-chair with the foot-rest suspended from the balance, there is practically no furniture inside of the chamber, and a shelf ortwo, usually attached to the chair, to support bottles for urine anddrinking-water bottles, completes the furniture equipment. Theconstruction of the calorimeter is such as to minimize the volume of airsurrounding the subject and yet secure sufficient freedom of movement tohave him comfortable. A general impression of the arrangement of thepipes, chair, telephone, etc. , inside the chamber can be obtained fromfigs. 7 and 9. The heat-absorber system is attached to rings soldered tothe ceiling at different points. The incoming air-pipe is carried to thetop of the central dome, while the air is drawn from the calorimeter ata point at the lower front near the position of the feet of the subject. From this point it is carried through a pipe along the floor and up therear wall of the calorimeter to the exit. 

With the perfect heat insulation obtaining, the heat production of theman would soon raise the temperature to an uncomfortable degree werethere no provisions for withdrawing it. It is therefore necessary tocool the chamber and, as has been pointed out, the cooling isaccomplished by passing a current of cold water through a heat-absorbingapparatus permanently installed in the interior of the chamber. Theheat-absorber consists of a continuous copper pipe of 6 millimetersinternal diameter and 10 millimeters external diameter. Along this pipethere are soldered a large number of copper disks 5 centimeters indiameter at a distance of 5 millimeters from each other. This increasesenormously the area for the absorption of heat. In order to allow theabsorber system to be removed, added to, or repaired at any time, it isnecessary to insert couplings at several points. This is usually done atcorners where the attachment of disks is not practicable. The totallength of heat-absorbers is 5. 6 meters and a rough calculation showsthat the total area of metal for the absorption of heat is 4. 7 squaremeters. The total volume of water in the absorbers is 254 cubiccentimeters. 

It has been found advantageous to place a simple apparatus to mix thewater in the water-cooling circuit at a point just before the waterleaves the chamber. This water-mixer consists of a 15-centimeter lengthof standard 1-inch pipe with a cap at each end. Through each of thesecaps there is a piece of one-eighth-inch pipe which extends nearly thewhole length of the mixer. The water thus passing into one end returnsinside the 1-inch pipe and leaves from the other. This simple deviceinsures a thorough mixing. 

The air-pipes are of thin brass, 1-inch internal diameter. One of themconducts the air from the ingoing air-pipe up into the top of thecentral dome or hood immediately above the head of the subject. The airthus enters the chamber through a pipe running longitudinally along thetop of the dome. On the upper side of this pipe a number of holes havebeen drilled so as to have the air-current directed upwards rather thandown against the head of the subject. With this arrangement nodifficulties are experienced with uncomfortable drafts and although theair enters the chamber through this pipe absolutely dry, there is nouncomfortable sensation of extreme dryness in the air taken in at thenostrils, nor is the absorption of water from the skin of the face, head, or neck great enough to produce an uncomfortable feeling of cold. The other air-pipe, as suggested, receives the air from the chamber atthe lower front and passes around the rear to the point where theoutside air-pipe leaves the chamber. 

The chamber is illuminated by a small glass door in the food aperture. This is a so-called "port" used on vessels. Sufficient light passesthrough this glass to enable the subject to see inside the calorimeterwithout difficulty and most of the subjects can read with comfort. If anelectric light is placed outside of the window, the illumination is verysatisfactory and repeated tests have shown that no measurable amount ofheat passes through the window by placing a 32 c. P. Electric lamp 0. 5meter from the food aperture outside. More recently we have arranged toproduce directly inside the chamber illumination by means of a smalltungsten electric lamp connected to the storage battery outside of thechamber. This lamp is provided with a powerful mirror and a glass shade, so that the light is very bright throughout the chamber and issatisfactory for reading. It is necessary, however, to make a correctionfor the heat developed, amounting usually to not far from 3 calories perhour. 

By means of a hand microphone and receiver, the subject can communicatewith the observers outside at will. A push-button and an electric bellmake it possible for him to call the observers whenever desired. 

HEAT-ABSORBING CIRCUIT. 

To bring away the heat produced by the subject, it is highly desirablethat a constant flow of water of even temperature be secured. Directconnection with the city supply is not practicable, owing to thevariations in pressure, and hence in constructing the laboratorybuilding provision was made to install a large tank on the top floor, fed with a supply controlled by a ball-and-cock valve. By thisarrangement the level in the tank is maintained constant and thepressure is therefore regular. As the level of the water in the tank isapproximately 9 meters above the opening in the calorimeter, there isample pressure for all purposes. 

[Illustration: FIG. 14. --Schematic diagram of water circuit forheat-absorbers of calorimeter. A, constant-level tank from which waterdescends to main pipe supplying heat-absorbers; _a_, valve forcontrolling supply from tank A; B, section of piping passing into coldbrine; _b_, valve controlling water direct from large tank A; _c_, valvecontrolling amount of water from cooling section B; C, thermometer atmixer; D, electric heater for ingoing water; E, thermometer for ingoingwater; _d d d_, heat-absorbers inside calorimeter; F, thermometerindicating temperature of outcoming water; G, can for collecting waterfrom calorimeter; _f_, valve for emptying G. ]

The water descends from this tank in a large 2-inch pipe to the ceilingof the calorimeter laboratory, where it is subdivided into three 1-inchpipes, so as to provide for a water-supply for three calorimeters usedsimultaneously, if necessary, and eliminate the influence of a variationin the rate of flow in one calorimeter upon the rate of flow in another. These pipes are brought down the inner wall of the room adjacent to therefrigeration room and part of the water circuit is passed through abrass coil immersed in a cooling-tank in the refrigeration room. Bymeans of a by-pass, water of any degree of temperature from 2° C. To 20°C. May be obtained. The water is then conducted through a pipe beneaththe floor to the calorimeter chamber, passed through the absorbers, andis finally measured in the water-meter. 

A diagrammatic sketch showing the course of the water-current is given(fig. 14), in which A is the tank on the top floor controlled by theball cock and valve, and _a_ is the main valve which controls thissupply to the cooler B, and by adjusting the valve _b_ and valve _c_any desired mixture of water can be obtained. A thermometer C gives arough idea of the temperature of the water, so as to aid in securing theproper mixture. The water then passes under the floor of the calorimeterlaboratory and ascends to the apparatus D, which is used for heating itto the desired temperature before entering the calorimeter. Thetemperature of the water as it enters the calorimeter is measured on anaccurately calibrated thermometer E, and it then passes through theabsorber system _d d d_ and leaves the calorimeter, passing thethermometer F, upon which the final temperature is read. It then passesthrough a pipe and falls into a large can G, placed upon scales. Whenthis can is filled the water is deflected for a few minutes to anothercan and by opening valve _f_ the water is conducted to the drain afterhaving been weighed. 

_Brine-tank. _--The cooling system for the water-supply consists of atank in which there is immersed an iron coil connected by two valves tothe supply and return of the brine mains from the central power-house. These valves are situated just ahead of the valves controlling thecooling device in the refrigeration room and permit the passage of brinethrough the coil without filling the large coils for the cooling of theair in the calorimeter laboratory. As the brine passes through thiscoil, which is not shown in the figure, it cools the water in which itis immersed and the water in turn cools the coil through which thewater-supply to the calorimeter passes. The brass coil only is shown inthe figure. The system is very efficient and we have no difficulty incooling the water as low as 2° C. As a matter of fact our chiefdifficulty is in regulating the supply of brine so as not to freeze thewater-supply. 

_Water-mixer. _--If the valve _b_ is opened, water flows through thisshort length of pipe much more rapidly than through the long coil, owingto the greater resistance of the cooling coil. In conducting theseexperiments the valve c is opened wide and by varying the amount towhich the valve _b_ is opened, the water is evenly and readily mixed. The thermometer C is in practice immersed in the water-mixer constructedsomewhat after the principle of the mixer inside the chamber describedon page 21. All the piping, including that under the floor, and thereheater D, are covered with hair-felt and well insulated. 

_Rate-valves. _--It has been found extremely difficult to secure any formof valve which, even with a constant pressure of water, will give aconstant rate of flow. In this type of calorimeter it is highlydesirable that the rate of flow be as nearly constant as possible hourafter hour, as this constant rate of flow aids materially in maintainingthe calorimeter at an even temperature. Obviously, fluctuations in therate of flow will produce fluctuations in the temperature of the ingoingwater and in the amount of heat brought away. This disturbs greatly thetemperature equilibrium, which is ordinarily maintained fairly constant. Just before the water enters the reheater D it is caused to pass througha rate-valve, which at present consists of an ordinary plug-cock. Atpresent we are experimenting with other types of valves to secure evengreater constancy, if possible. 

_Electric reheater. _--In order to control absolutely the temperature ofthe water entering at E, it is planned to cool the water leaving thewater-mixer at C somewhat below the desired temperature, so that it isnecessary to reheat it to the desired point. This is done by passing acurrent of electricity through a coil inserted in the system at thepoint D. This electric reheater consists of a standard "Simplex" coil, so placed in the copper can that the water has a maximum circulationabout the heater. The whole device is thoroughly insulated withhair-felt. By connecting the electric reheater with the rheostat on theobserver's table, control of the quantity of electricity passing throughthe coil is readily obtained, and hence it is possible to regulate thetemperature of the ingoing water to within a few hundredths of a degree. 

The control of the amount of heat brought away from the chamber is madeeither by (1) increasing the rate of flow or (2) by varying thetemperature of the ingoing water. Usually only the second method isnecessary. In the older form of apparatus a third method was possible, namely, by varying the area of the absorbing surface of the coolingsystem inside of the chamber. This last method of regulation, which wasused almost exclusively in earlier experiments, called for an elaboratesystem of shields which could be raised or lowered at will by theoperator outside, thus involving an opening through the chamber whichwas somewhat difficult to make air-tight and also considerablycomplicating the mechanism inside the chamber. The more recent method ofcontrol by regulating the temperature of the ingoing water by theelectric reheater has been much refined and has given excellent service. 

_Insulation of water-pipes through the wall. _--To insulate thewater-pipes as they pass through the metal walls of the calorimeter andto prevent any cooling effect not measured by the thermometers presentedgreat difficulties. The device employed in the Middletown chamber wasrelatively simple, but very inaccessible and a source of more or lesstrouble, namely, a large-sized glass tube embedded in a large roundwooden plug with the annular space between the glass and wood filledwith wax. An attempt was made in the new calorimeters to secure airinsulation by using a large-sized glass tube, some 15 millimetersinternal diameter, and passing it through a large rubber stopper, fitting into a brass ferule soldered between the zinc and copper walls. (See N, fig. 25. ) So far as insulation was concerned, this arrangementwas very satisfactory, but unfortunately the glass tubes break readilyand difficulty was constantly experienced. An attempt was next made tosubstitute hard-rubber tubing for the glass tube, but this did not proveto be an efficient insulator. More recently we have used with perfectsuccess a special form of vacuum-jacketed glass tube, which gives themost satisfactory insulation. However, this system of insulation isimpracticable when electric-resistance thermometers are used forrecording the water-temperature differences and can be used only whenmercurial thermometers exclusively are employed. The electric-resistancethermometers are constructed in such a way, however, as to makenegligible any inequalities in the passage of heat through thehard-rubber casing. This will be seen in the discussion of thesethermometers. 

_Measuring the water. _--As the water leaves the respiration chamber itpasses through a valve which allows it to be deflected either into thedrain during the preliminary period, or into a small can where themeasurements of the rate of flow can readily be made, or into a largetank (G, fig. 14) where the water is weighed. The measurement of thewater is made by weight rather than by volume, as it has been found thatthe weighing may be carried out with great accuracy. The tank, agalvanized-iron ash-can, is provided with a conical top, through anopening in which a funnel is placed. The diagram shows the water leavingthe calorimeter and entering the meter through this funnel, but inpractice it is adjusted to enter through an opening on the side of themeter. After the valve _f_ is tightly closed the empty can is weighed. 

When the experiment proper begins the water-current is deflected so asto run into this can and at the end of an hour the water is deflectedinto a small can used for measuring the rate of flow. While it isrunning into this can, the large can G is weighed on platform scales towithin 10 grams. After weighing, the water is again deflected into thelarge can and that collected in the small measuring can is poured into Gthrough the funnel. The can holds about 100 liters of water andconsequently from 3 to 8 one-hour periods, depending upon the rate offlow, can be continued without emptying the meter. When it is desired toempty the meter at the end of the period, the water is allowed to flowinto the small can, and after weighing G, the valve _f_ is opened. About4 minutes are required to empty the large can. After this the valve isagain closed, the empty can weighed, and the water in the smallmeasuring-can poured into the large can G through the funnel. The scalesused are the so-called silk scales and are listed by the manufacturersto weigh 150 kilograms. This form of scales was formerly used inweighing the man inside the chamber. [7]

THERMOMETERS. 

In connection with the calorimeter and the accessories, mercurial andelectric-resistance thermometers are employed. For measuring thetemperature of the water as it enters and leaves the chamber throughhorizontal tubes, mercurial thermometers are used, and these aresupplemented by electric-resistance thermometers which are connectedwith a special form of recording instrument for permanently recordingthe temperature differences. For the measurement of the temperaturesinside of the calorimeter, two sets of electric-resistance thermometersare used, one of which is a series of open coils of wire suspended inthe air of the chamber so as to take up quickly the temperature of theair. The other set consists of resistance coils encased in copper boxessoldered to the copper wall and are designed to indicate the temperatureof the copper wall rather than that of the air. 

MERCURIAL THERMOMETERS. 

The mercurial thermometers used for measuring the temperaturedifferences of the water-current are of special construction and havebeen calibrated with the greatest accuracy. As the water enters therespiration chamber through a horizontal tube, the thermometers are soconstructed and so placed in the horizontal tubes through which thewater passes that the bulbs of the thermometers lie about in a planewith the copper wall, thus taking the temperature of the waterimmediately as it enters and as it leaves the chamber. For conveniencein reading, the stem of the thermometer is bent at right angles and thegraduations are placed on the upright part. 

The thermometers are graduated from 0° to 12° C. Or from 8° to 20° C. And each degree is divided into fiftieths. Without the use of a lens itis possible to read accurately to the hundredth of a degree. Forcalibrating these thermometers a special arrangement is necessary. Thestandards used consist of well-constructed metastatic thermometers ofthe Beckmann type, made by C. Richter, of Berlin, and calibrated by thePhysikalische Technische Reichsanstalt. Furthermore, a standardthermometer, graduated from 14° to 24° C. , also made by Richter andstandardized by the Physikalische Technische Reichsanstalt, serves as abasis for securing the absolute temperature. Since, however, on themercurial thermometers used in the water-current, differences intemperature are required rather than absolute temperatures, it isunnecessary, except in an approximate way, to standardize thethermometers on the basis of absolute temperature. For calibrating thethermometers, an ordinary wooden water-pail is provided with severalholes in the side near the bottom. One-hole rubber stoppers are insertedin these holes and through these are placed the bulbs and stems of thedifferent thermometers which are to be calibrated. The upright portionof the stem is held in a vertical position by a clamp. The pail isfilled with water, thereby insuring a large mass of water and slowtemperature fluctuations, and the water is stirred by means of anelectrically driven turbine stirrer. 

The Beckmann thermometers, of which two are used, are so adjusted thatthey overlap each other and thus allow a range of 8° to 14° C. Withoutresetting. For all temperatures above 14° C. , the standard Richterthermometer can be used directly. For temperatures at 8° C. Or below, alarge funnel filled with cracked ice is placed with the stem dippinginto the water. As the ice melts, the cooling effect on the large massof water is sufficient to maintain the temperature constant andcompensate the heating effect of the surrounding room-air. Thethermometers are tapped and read as nearly simultaneously as possible. Anumber of readings are taken at each point and the average readings usedin the calculations. Making due allowance for the corrections on theBeckmann thermometers, the temperature differences can be determined toless than 0. 01° C. The data obtained from the calibrations are thereforeused for comparison and a table of corrections is prepared for each setof thermometers used. It is especially important that these thermometersbe compared among themselves with great accuracy, since as used in thecalorimeter the temperature of the ingoing water is measured on onethermometer and the temperature of the outgoing water on another. 

Thermometers of this type are extremely fragile. The long angle with anarm some 35 centimeters in length makes it difficult to handle themwithout breakage, but they are extremely sensitive and accurate and havegiven great satisfaction. The construction of the bulb is such, however, that the slightest pressure on it raises the column of mercury veryperceptibly, and hence it is important in practical use to note theinfluence of the pressure of the water upon the bulbs and makecorrections therefor. The influence of such pressure upon thermometersused in an apparatus of this type was first pointed out by Armsby, [8]and with high rates of flow, amounting to 1 liter or more per minute, there may be a correction on these thermometers amounting to severalhundredths of a degree. We have found that, as installed at present, with a rate of flow of less than 400 cubic centimeters per minute, thereis no correction for water pressure. 

In installing a thermometer it is of the greatest importance that therebe no pressure against the side of the tube through which thethermometer is inserted. The slightest pressure will cause considerablerise in the mercury column. Special precautions must also be taken toinsulate the tube through which the water passes, as the passage of thewater along the tube does not insure ordinarily a thorough mixing, andby moving the thermometer bulb from the center of the tube to a pointnear the edge, the water, which at the edge may be somewhat warmer thanat the center, immediately affects the thermometer. By use of the vacuumjacket mentioned above, this warming of the water has been avoided, andin electric-resistance thermometers special precautions are taken notonly with regard to the relative position of the bulb of the mercurythermometer and the resistance thermometer, but also with regard to thehard-rubber insulation, to avoid errors of this nature. 

ELECTRIC-RESISTANCE THERMOMETERS. 

Electric-resistance thermometers are used in connection with therespiration calorimeter for several purposes: first, to determine thefluctuations in the temperature of the air inside the chamber; second, to measure the fluctuations of the temperature of the copper wall of therespiration chamber; third, for determining the variations in bodytemperature; finally, for recording the differences in temperature ofthe incoming and outgoing water. While these thermometers are all builton the same principle, their installation is very different, and a wordregarding the method of using each is necessary. 

AIR THERMOMETERS. 

The air thermometers are designed with a special view to taking quicklythe temperature of the air. Five thermometers, each having a resistanceof not far from 4 ohms, are connected in series and suspended 3. 5centimeters from the wall on hooks inside the chamber. They aresurrounded for protection, first, with a perforated metal cylinder, andoutside this with a wire guard. 

[Illustration: FIG. 15. --Detail of air-resistance thermometer, showingmethod of mounting and wiring the thermometer. Parts of the wire guardand brass guard are shown, cut away so that interior structure can beseen. ]

The details of construction and method of installation are shown in fig. 15. Four strips of mica are inserted into four slots in a hard maple rod12. 5 centimeters long and 12 millimeters in diameter, and around eachstrip is wound 5 meters of double silk-covered pure copper wire(wire-gage No. 30). By means of heavy connecting wires, five of thesethermometers are connected in series, giving a total resistance of thesystem of not far from 20 ohms. The thermometer proper is suspendedbetween two hooks by rubber bands and these two hooks are in turnfastened to a wire guard which is attached to threaded rods soldered tothe inner surface of the copper wall, thus bringing the center of thethermometer 3. 4 centimeters from the copper wall. Two of thesethermometers are placed in the dome of the calorimeter immediately overthe shoulders of the subject, and the other three are distributed aroundthe sides and front of the chamber. This type of construction givesmaximum sensibility to the temperature fluctuations of the air itselfand yet insures thorough protection. The two terminals are carriedoutside of the respiration chamber to the observer's table, where thetemperature fluctuations are measured on a Wheatstone bridge. 

WALL THERMOMETERS. 

The wall thermometers are designed for the purpose of taking thetemperature of the copper wall rather than the temperature of the air. When temperature fluctuations are being experienced inside of therespiration chamber, the air obviously shows temperature fluctuationsfirst, and the copper walls are next affected. Since in makingcorrections for the hydrothermal equivalent of the apparatus and forchanges in the temperature of the apparatus as a whole it is desirableto know the temperature changes of the wall rather than the air, thesewall thermometers were installed for this special purpose. Inconstruction they are not unlike the thermometers used in the air, butinstead of being surrounded by perforated metal they are encased incopper boxes soldered directly to the wall. Five such thermometers areused in series and, though attached permanently to the wall, they areplaced in relatively the same position as the air thermometers. The twoterminals are conducted through the metal walls to the observer's table, where variations in resistance are measured. The resistance of the fivethermometers is not far from 20 ohms. 

ELECTRICAL RECTAL THERMOMETER. 

The resistance thermometer used for measuring the temperature of thebody of the man is of a somewhat different type, since it is necessaryto wind the coil in a compact form, inclose it in a pure silver tube, and connect it with suitable rubber-covered connections, so that it canbe inserted deep in the rectum. The apparatus has been described in anumber of publications. [9] The resistance of this system is also not farfrom 20 ohms, thus simplifying the use of the apparatus alreadyinstalled on the observer's table. 

ELECTRIC-RESISTANCE THERMOMETERS FOR THE WATER-CURRENT. 

The measurement of the temperature differences of the water-current bythe electric-resistance thermometer was tried a number of years ago byRosa, [10] but the results were not invariably satisfactory and in allthe subsequent experimenting the resistance thermometer could not beused with satisfaction. More recently, plans were made to incorporatesome of the results of the rapidly accumulating experience in the use ofresistance thermometers and consequently an electric-resistancethermometer was devised to meet the conditions of experimentation withthe respiration calorimeter by Dr. E. F. Northrup, of the Leeds &Northrup Company, of Philadelphia. The conditions to be met were thatthe thermometers should take rapidly the temperature of the ingoing andoutcoming water and that the fluctuations in temperature difference asmeasured by the resistance thermometers should be controlled forcalibration purposes by the differences in temperature of the mercurialthermometers. 

[Illustration: FIG. 16. --Details of resistance thermometers forwater-circuit. Upper part of figure shows a sketch of the outside of thehard-rubber case. In lower part is a section showing interiorconstruction. Flattened lead tube wound about central brass tubecontains the resistance wire. A is enlarged part of the case forming achamber for the mercury bulb. Arrows indicate direction of flow onresistance thermometer for ingoing water. ]

For the resistance thermometer, Dr. Northrup has used, instead ofcopper, pure nickel wire, which has a much higher resistance and thusenables a much greater total resistance to be inclosed in a given space. The insulated nickel wire is wound in a flattened spiral and then passedthrough a thin lead tube flattened somewhat. This lead tube is thenwound around a central core and the flattened portions attached at suchan angle that the water passing through the tubes has a tendency to bedirected away from the center and against the outer wall, thus insuringa mixing of the water. Space is left for the insertion of the mercurialthermometer. With the thermometer for the ingoing water, it was foundnecessary to extend the bulb somewhat beyond the resistance coil, sothat the water might be thoroughly mixed before reaching the bulb andthus insure a steady temperature. Thus it was found necessary to enlargethe chamber A (fig. 16) somewhat and the tube leading out of thethermometer, so that the bulb of the thermometer itself could be placedalmost directly at the opening of the exit tube. Under these conditionsperfect mixing of water and constancy of temperature were obtained. 

In the case of the thermometer which measured the outcoming water, thedifficulty was not so great, as the outcoming water is somewhat nearerthe temperature of the chamber, and the water as it leaves thethermometer passes first over the mercurial thermometer and then overthe resistance thermometer. By means of a long series of tests it wasfound possible to adjust these resistance thermometers so that thevariations in resistance were in direct proportion to the temperaturechanges noted on the mercurial thermometers. Obviously, thesedifferences in resistance of the two thermometers can be measureddirectly with the Wheatstone bridge, but, what is more satisfactory, they are measured and recorded directly on a special type of automaticrecorder described beyond. 

OBSERVER'S TABLE. 

The measurements of the temperature of the respiration chamber, of thewater-current, and of the body temperature of the man, as well as theheating and cooling of the air-spaces about the calorimeter, are allunder the control of the physical assistant. The apparatus for thesetemperature controls and measurements is all collected compactly on atable, the so-called "observer's table. " At this, the physical assistantsits throughout the experiments. For convenience in observing themercurial thermometers in the water-current and general inspection ofthe whole apparatus, this table is placed on an elevated platform, shownin fig. 3. Directly in front of the table the galvanometer is suspendedfrom the ceiling and a black hood extends from the observer's table tothe galvanometer itself. On the observer's table proper are all theelectrical connections and at the left are the mercurial thermometersfor the chair calorimeter. Formerly, when the method of alternatelycooling and heating the air-spaces was used, the observer was able toopen and close the water-valves without leaving the chair. 

The observer's table is so arranged electrically as to make possibletemperature control and measurement of either of the two calorimeters. It is impossible, however, for the observer to read the mercurialthermometers in the bed calorimeter without leaving his chair, andlikewise he must occasionally alter the cooling water flowing throughthe outer air-spaces by going to the bed calorimeter itself. Theinstallation of the electric-resistance thermometers connected with thetemperature recorder does away with the reading of the mercurialthermometers, save for purposes of comparison, and hence it isunnecessary for the assistant to leave the chair at the observer's tablewhen the bed calorimeter is in use. Likewise the substitution of themethod of continuously cooling somewhat the air-spaces and reheatingwith electricity, mentioned on page 18, does away with the necessity foralternately opening and closing the water-valves of the chaircalorimeter placed at the left of the observer's table. 

[Illustration: FIG. 17. --Diagram of wiring of observer's table. W_{1}, W_{2}, Wheatstone bridges for resistance thermometers; K_{1}, K_{2}, double contact keys for controlling Wheatstone circuits; S_{1}, S_{2}, S_{3}, double-pole double-throw switches for changing from chair to bedcalorimeter; S_{4}, double-pole double-throw switch for changing fromwall to air thermometers; G, galvanometer; R_{2}, rheostat. 1, 2, 3, 4, 5, wires connecting with resistance-coils A B D E F and _a b d e f_;S_{2}, 6-point switch for connecting thermal-junction circuits of eitherbed or chair calorimeter with galvanometer; S_{10}, 10-pointdouble-throw switch for changing heating circuits and thermal-junctioncircuits to either chair or bed calorimeter; R_{1}, rheostat forcontrolling electric heaters in ingoing water in calorimeters; S_{8}, double-pole single-throw switch for connecting 110-v. Current withconnections on table; S_{9}, double-pole single-throw switch forconnecting R_{1} with bed calorimeter. ]

Of special interest are the electrical connections on the observer'stable itself. A diagrammatic representation of the observer's table withits connections is shown in fig. 17. The heavy black outline gives in ageneral way the outline of the table proper and thus shows adiagrammatic distribution of the parts. The first of the electricalmeasurements necessary during experiments is that of thethermo-electric effect of the thermal junction systems installed on thecalorimeters. To aid in indicating what parts of the zinc wall needcooling or heating, the thermal junction systems are, as has alreadybeen described, separated into four sections on the chair calorimeterand three sections on the bed calorimeter; in the first calorimeter, thetop, front, rear, and bottom; in the bed calorimeter, the top, sides, and bottom. 

CONNECTIONS TO THERMAL-JUNCTION SYSTEMS. 

Since heretofore it has been deemed unwise to attempt to use bothcalorimeters at the same time, the electrical connections are so madethat, by means of electrical switches, either calorimeter can beconnected to the apparatus on the table. 

The thermal-junction measurements are made by a semicircular switchS_{7}. The various points, I, II, III, IV, etc. , are connected with thedifferent thermal-junction systems. Thus, by following the wiringdiagram, it can be seen that the connections with I run to the differentbinding-posts of the switch S_{10}, which as a matter of fact is placedbeneath the table. This switch S_{10} has three rows of binding-posts. The center row connects directly with the apparatus on the observer'stable, the outer rows connect with either the chair calorimeter or thebed calorimeter. The points marked _a_, _b_, _d_, _e_, _f_, etc. , connect with the bed calorimeter and A, B, D, etc. , connect with thechair calorimeter. Thus, by connecting the points _g_ and _i_ with thetwo binding-posts opposite them on the switch S_{10}, it can be seenthat this connection leads directly to the point I on the switch S_{7}, and as a matter of fact this gives direct connection with thegalvanometer through the key on S_{7}, thus connecting thethermal-junction system on one section of the bed calorimeter between_g_ and _i_ directly with the galvanometer. Similar connections from theother points can readily be followed from the diagram. The points on theswitch S_{7} indicated as I, II, III, IV, correspond respectively to thethermal-junction systems on the top, rear, front, and bottom of thechair calorimeter. 

By following the wiring diagram of the point V, it will be seen thatthis will include the connections with the thermal junctions connectedin series and thus give a sum total of the electromotive forces in thethermal junctions. The point VI is connected with the thermal-junctionsystem in the air system, indicating the differences in temperaturebetween the ingoing and outgoing air. It will be noted that there arefour sections in the chair calorimeter, while in the bed calorimeterthere are but three, and hence a special switch S_{3} is installed toinsure proper connections when the bed calorimeter is in use. 

This system of connecting the thermal junctions in different sections tothe galvanometer makes possible a more accurate control of thetemperatures in the various parts, and while the algebraic sum of thetemperature differences of the parts may equal zero, it is conceivablethat there may be a condition in the calorimeter when there is aconsiderable amount of heat passing out through the top, for example, compensated exactly by the heat which passes in at the bottom, and whilewith the top section there would be a large plus deflection on thegalvanometer, thus indicating that the air around the zinc wall was toocold and that heat was passing out, there would be a corresponding minusdeflection on the bottom section, indicating the reverse conditions. Thetwo may exactly balance each other, but it has been found advantageousto consider each section as a unit by itself and to attempt delicatetemperature control of each individual unit. This has been made possibleby the electrical connections, as shown on the diagram. 

RHEOSTAT FOR HEATING. 

The rheostat for heating the air-spaces and the returning air-currentabout the zinc wall is placed on the observer's table and is indicatedin the diagram as R_{2}. There are five different sets ofcontact-points, marked 1, 2, 3, 4, and 5. One end of the rheostat isconnected directly with the 110-volt circuit through the main switchS_{5}. The other side of the switch S_{5} connects directly with thepoint on the middle of switch S_{10}, and when this middle point isjoined with either _f_ and F, direct connection is insured between allthe various heating-circuits on the calorimeter in use. The variousnumbered points on the rheostat R_{2}, are connected with the bindingposts on S_{10}, and each can in turn be connected with _a_ or A, _b_ orB, etc. The heating of the top of the chair calorimeter is controlled bythe point 5 on the rheostat R_{2}, the rear by the point 4, the front bythe point 3, and the bottom by the point 2. Point 1 is used for heatingthe air entering the calorimeter by means of an electric lamp placed inthe air-pipe, as shown in fig. 25. 

The warming of the electrical reheater placed in the water-circuit justbefore the water enters the calorimeter is done by an electrical currentcontrolled by the resistance R_{1}. This R_{1} is connected on one enddirectly with the 110-volt circuit and the current leaving it passesthrough the resistance inside the heater in the water-current. The twoheaters, one for each calorimeter, are indicated on the diagram aboveand below the switch S_{9}. The disposition of the switches is such asto make it possible to use alternately the reheaters on either the bedor the chair calorimeter, and the main resistance R_{1} suffices forboth. 

WHEATSTONE BRIDGES. 

For use in measuring the temperature of the air and of the copper wallof the calorimeters, as well as the rectal temperature of the subject, aseries of resistance thermometers is employed. These are so connectedon the observer's table that they may be brought into connection withtwo Wheatstone bridges, W_{1} and W_{2}. Bridge W_{1} is used for theresistance thermometers indicating the temperature of the wall and theair. Bridge W_{2} is for the rectal thermometer. Since similarthermometers are inserted in both calorimeters, it is necessary tointroduce some switch to connect either set at will and hence thedouble-throw switches S_{1}, S_{2}, and S_{3} allow the use of eitherthe wall, air, or rectal thermometer on either the bed or chaircalorimeter at will. Since the bridge W_{1} is used for measuring thetemperature of both the wall and the air, a fourth double-pole switch, S_{4}, is used to connect the air and wall thermometers alternately. Thedouble-contact key, K_{1}, is connected with the bridge W_{1} and is soarranged that the battery circuit is first made and subsequently thegalvanometer circuit. A similar arrangement in K_{2} controls theconnections for the bridge W_{2}. 

GALVANOMETER. 

The galvanometer is of the Deprez-d'Arsonval type and is extremelysensitive. The sensitiveness is so great that it is desirable tointroduce a resistance of some 500 ohms into the thermal-junctioncircuits. This is indicated at the top of the diagram near thegalvanometer. The maximum sensitiveness of the galvanometer is retainedwhen the connection is made with the Wheatstone bridges. Thegalvanometer is suspended from the ceiling of the calorimeter laboratoryand is free from vibration. 

RESISTANCE FOR HEATING COILS. 

To vary the current passing through the manganin heating coils in theair-spaces next the zinc wall, a series of resistances is installedconnected directly with the rheostat R_{2} in fig. 17. The details ofthese resistances and their connection with the rheostat are shown infig. 18. The rheostat, which is in the right part of the figure, hasfive sliding contacts, each of which can be connected with ten differentpoints. One end of the rheostat is connected directly with the 110-voltcircuit. Beneath the observer's table are fastened the five resistances, which consist of four lamps, each having approximately 200 ohmsresistance and then a series of resistance-coils wound on a long stripof asbestos lumber, each section having approximately 15 ohms betweenthe binding-posts. A fuse-wire is inserted in each circuit to protectthe chamber from excessive current. Of these resistances, No. 1 is usedto heat the lamp in the air-current shown in fig. 25, and consequentlyit has been found advisable to place permanently a second lamp in serieswith the first, but outside of the air-pipe, so as to avoid burning outthe lamp inside of the air-pipe. The other four resistances, 2, 3, 4, and 5, are connected with the different sections on the twocalorimeters. No. 5 corresponds to the top of both calorimeters. No. 4corresponds to the rear section of the chair calorimeter and to thesides of the bed calorimeter. No. 3 corresponds to the front of thechair calorimeter and is without communication with the bed calorimeter. No. 2 connects with the bottom of both calorimeters. 

It will be seen from the diagrams that each of these resistances can beconnected at will with either the bed or the chair calorimeter and atsuch points as are indicated by the lettering below the numbers. Thus, section 1 can be connected with either the point A or point _a_ on fig. 17 and thus directly control the amount of current passing through thecorresponding resistance in series with the lamp in the air-current. Thesliding contacts at present in use are ill adapted to long-continuedusage and will therefore shortly be substituted by a more substantialinstrument. The form of resistance using small lamps and the resistancewires wound on asbestos lumber has proven very satisfactory and verycompact in form. 

[Illustration: FIG. 18. --Diagram of rheostat and resistances in serieswith it. At the right are shown the sliding contacts, and in the centerplaces for lamps used as resistances, and to left the sections of wireresistances. ]

TEMPERATURE RECORDER. 

The numerous electrical, thermometric, and chemical measurementsnecessary in the full conduct of an experiment with the respirationcalorimeter has often raised the question of the desirability of makingat least a portion of these observations more or less automatic. Thisseems particularly feasible with the observations ordinarily recorded bythe physical observer. These observations consist of the reading of themercurial thermometers indicating the temperatures of the ingoing andoutcoming water, records with the electric-resistance thermometers forthe temperature of the air and the walls and the body temperatures, andthe deflections of the thermo-electric elements. 

Numerous plans have been proposed for rendering automatic some of theseobservations, as well as the control of the heating and cooling of theair-circuits. Obviously, such a record of temperature measurements wouldhave two distinct advantages: (1) in giving an accurate graphic recordwhich would be permanent and in which the influence of the personalequation would be eliminated; (2) while the physical observer at presenthas much less to do than with the earlier form of apparatus, it wouldmaterially lighten his labors and thereby tend to minimize errors in theother observations. 

The development of the thread recorder and the photographic registrationapparatus in recent years led to the belief that we could employ similarapparatus in connection with our investigations in this laboratory. Tothis end a number of accurate electrical measuring instruments werepurchased, and after a number of tests it was considered feasible torecord automatically the temperature differences of the ingoing andoutcoming water from the calorimeter. Based upon our preliminary tests, the Leeds & Northrup Company of Philadelphia, whose experience with suchproblems is very extended, were commissioned to construct an apparatusto meet the requirements of the respiration calorimeter. The conditionsto be met by this apparatus were such as to call for a registeringrecorder that would indicate the differences in temperature between theingoing and outcoming water to within 0. 5 per cent and to record thesedifferences in a permanent ink line on coordinate paper. Furthermore, the apparatus must be installed in a fixed position in the laboratory, and connections should be such as to make it interchangeable with anyone of five calorimeters. 

After a great deal of preliminary experimenting, in which the Leeds &Northrup Company have most generously interpreted our specifications, they have furnished us with an apparatus which meets to a high degree ofsatisfaction the conditions imposed. The thermometers themselves havealready been discussed. (See page 30. ) The recording apparatus consistsof three parts: (1) the galvanometer; (2) the creeper or automaticsliding-contact; (3) the clockwork for the forward movement of the rollof coordinate paper and to control the periodic movement of the creeper. 

Under ordinary conditions with rest experiments in the chair calorimeteror bed calorimeter, the temperature differences run not far from 2° to4°. Thus, it is seen that if the apparatus is to meet the conditions ofthe specifications it must measure differences of 2° C. To within 0. 01°C. Provision has also been made to extend the measurement of temperaturedifferences with the apparatus so that a difference of 8° can bemeasured with the same percentage accuracy. 

FUNDAMENTAL PRINCIPLE OF THE APPARATUS. 

The apparatus depends fundamentally upon the perfect balancing of thetwo sides of a differential electric circuit. A conventional diagram, fig. 19, gives a schematic outline of the connections. The twogalvanometer coils, _fl_ and _fr_, are wound differentially and bothcoils most carefully balanced so that the two windings have equaltemperature coefficients. This is done by inserting a small shunt _y_, parallel with the coil _fl_, and thus the temperature coefficient of_fl_ and _fr_ are made absolutely equal. The two thermometers areindicated as T_{1} and T_{2} and are inserted in the ingoing andoutgoing water respectively. A slide-wire resistance is indicated by J, and _r_ is the resistance for the zero adjustment. Ba, Z, and Z_{1} arethe battery and its variable series resistances. If T_{1} and T_{2} areexactly of the same temperature, _i. E. _, if the temperature differenceof the ingoing and outcoming water is zero, the sliding contact _q_stands at 0 on the slide-wire and thus the resistance of the system from0 through _fl_, _r_, and T_{1} back to the point C is exactly the sameas the resistance of the slide-wire J plus the coil _fr_ plus T_{2} backto the point C. A rise in temperature of T_{2} gives an increase ofresistance in the circuit and the sliding contact _q_ moves along theslide-wire toward J maximum until a balance is obtained. 

[Illustration: FIG. 19. --Diagram of wiring of differential circuit withits various shunts, used in connection with resistance thermometers onwater-circuit of bed calorimeter. ]

Provision is made for automatically moving the contact _q_ by electricalmeans and thus the complete balance of the two differential circuits ismaintained constant from second to second. As the contact _q_ is moved, it carries with it a stylographic pen which travels in a straight lineover a regularly moving roll of coordinate paper, thus producing apermanently recorded curve indicating the temperature differences. Theslide-wire J is calibrated so that any inequalities in the temperaturecoefficient of the thermometer wires are equalized and also so that anyunit-length on the slide-wire taken at any point along the temperaturescale represents a resistance equal to the resistance change in thethermometer for that particular change in temperature. With the varyingconditions to be met with in this apparatus, it is necessary thatvarying values should be assigned at times to J and to _r_. Thisnecessitates the use of shunts, and the recording range of theinstrument can be easily varied by simple shunting, _i. E. _, by changingthe resistance value of J and _r_, providing these resistances unshuntedhave a value which takes care of the highest obtained temperaturevariations. 

Fig. 19 shows the differential circuit complete with all its shunts. Sis a fixed shunt to obtain a range on J; S' is a variable shunt topermit very slight variations of J within the range to correct errorsdue to changing of the initial temperatures of the thermometers; _y_ isa permanent shunt across the galvanometer coil _fl_, to make thetemperature coefficients of _fl_ and _fr_ absolutely equal; Z is thevariable resistance in the battery-circuit to keep the current constant;_r_ is a permanent resistance to fix the zero on varying ranges; S''plus S_{1} constitutes a variable shunt to permit slight variations of_r_ to finally adjust 0 after S' is fixed and _t_ is a permanent shuntacross the thermometer T_{1} to make the temperature coefficient ofT_{1} equal to that of T_{2}. 

The apparatus can be used for measuring temperature differences from 0°to 4° or from 0° to 8°. When on the 0° to 8° range, the shunt S isopen-circuited and the shunt S' alone used. The value of S, then, ispredetermined so as to affect the value of the wire J and thus halve itsinfluence in maintaining the balance. Similarly, when the lower range, _i. E. _, from 0° to 4°, is used, the resistance _r_ is employed, andwhen the higher range is used another value to _r_ must be given byusing a plug resistance-box, in the use of which the resistance _r_ isdoubled. 

The resistance S'' and S_{1} are combined in a slide-wire resistance-boxand are used to change the value of the whole apparatus when there aremarked changes in the position of the thermometric scale. Thus, if theingoing water is at 2° C. And the outcoming water at 5° C. In oneinstance, and in another instance the ingoing water is 13° and theoutgoing water is 15°, a slight alteration in the value of S_{1}, andalso of S', is necessary in order to have the apparatus draw a curve torepresent truly the temperature differences. These slight alterationsare determined beforehand by careful tests and the exact value of theresistances in S' and in S_{1} are permanently recorded for subsequentuse. 

THE GALVANOMETER. 

The galvanometer is of the Deprez-d'Arsonval type and has a particularlypowerful magnetic field, in which a double coil swings suspended similarto the marine galvanometer coils. This coil is protected from vibrationsby an anti-vibration tube A, fig. 20, and carries a pointer P which actsto select the direction of movement of the recording apparatus, themovable contact point _q_, fig. 19. In front of this galvanometer coiland inclosed in the same air-tight metal case is the plunger contact Pl, fig. 21. The galvanometer pointer P swings freely below the silvercontacts S_{1} and S_{2}, just clearing the ivory insulator _i_. Themagnet plunger makes a contact depending upon the adjustment of a clockat intervals of 2 seconds. So long as both galvanometer coils areinfluenced by exactly the same strength of current, the pointer willstand in line with and immediately below _i_ and no current passesthrough the recording apparatus. Any disturbance of the electricalequilibrium causes the pointer P to swing either toward S_{1} or S_{2}, thus completing the circuit at either the right hand or the left hand, at intervals of 2 seconds. The movement of the pointer away from itsnormal position exactly beneath _i_ to either S_{1} on the left hand orS_{2} on the right, results from an inequality in the current flowingthrough the two coils in the galvanometer. The difference in the twocurrents passing through these coils is caused by a change intemperatures of the two thermometers in the water circuit. 

[Illustration: FIG. 20. --Diagram of galvanometer coil used in connectionwith recording apparatus for resistance thermometers in thewater-circuit of bed calorimeter. A, anti-vibration tube; P, pointer. ]

THE CREEPER. 

The movement of the sliding-contact _q_, fig. 19, along the slide-wireJ, is produced by means of a special device called a creeper, consistingof a piece of brass carefully fitted to a threaded steel rod some 30centimeters long. The movement of this bar along this threaded rodaccomplishes two things. The bar is in contact with the slide-wire Jand therefore varies the position of the point _q_ and it also carrieswith it a stylographic pen. The movements of this bar to the right orthe left are produced by an auxiliary electric current, the contact ofwhich is made by a plunger-plate forcing the pointer P against eitherS_{1} or S_{2}. P makes the contact between Pl and either S_{1} or S_{2}and sends a current through solenoids at either the right or the left ofthe creeper. At intervals of every 2 seconds the plunger rises andforces the pointer P against either S_{1}, _i_, or S_{2} above. Themovement of this plunger is controlled by a current from a 110-voltcircuit, the connections of which are shown in fig. 22. If the contactis made at T, the current passes through 2, 600 ohms, directly across the110-volt circuit, and consequently there is no effective current flowingthrough the plunger Pl. When the contact T is open, the current flowsthrough the plunger in series with 2, 600 ohms resistance. T is openedautomatically at intervals of 2 seconds by the clock. 

[Illustration: FIG. 21. --Diagram of wiring of circuits actuating plungerand creeper. ]

[Illustration: FIG. 22. --Diagram of wiring of complete 110-voltcircuit. ]

The movement of the contact arm along the threaded rod is produced bythe action of either one of two solenoids, each of which has a coreattached to a rack and pinion at either end of the rod. If the currentis passed through the contact S_{1}, a current passes through theleft-hand solenoid, the core moves down, the rack on the core moves thepinion on the rod through a definite fraction of a complete revolutionand this movement forces the creeper in one direction. Conversely, thepassing of the current through the solenoid at the other end of thethreaded rod moves the creeper in the other direction. The distancewhich the iron rack on the end of the core is moved is determinedcarefully, so that the threaded rod is turned for each contact exactlythe same fraction of a revolution. For actuating these solenoids, the110-volt circuit is again used. The wire connections are shown in partin fig. 21, in which it is seen that the current passes through theplunger-contact and through the pointer P to the silver plate S_{1} andthen along the line G_{1} through 350 ohms wound about the left-handsolenoid back through a 600-ohm resistance to the main line. The use ofthe 110-volt current under such circumstances would normally produce anotable sparking effect on the pointer P, and to reduce this to aminimum there is a high resistance, amounting to 10, 000 ohms on eachside, shunted between the main line and the creeper connections. Thisshunt is shown in diagram in fig. 22. Thus there is never a completeopen circuit and sparking is prevented. 

THE CLOCK. 

The clock requires winding every week and is so geared as to move thepaper forward at a rate of 3 inches per hour. The contact-point foropening the circuit T on fig. 22 is likewise connected with one of thesmaller wheels of the clock. This contact is made by tripping a littlelever by means of a toothed wheel of phosphor-bronze. 

INSTALLATION OF THE APPARATUS. 

[Illustration: FIG. 23

Temperature recorder. The recorder with the coordinate paper in thelower box with a glass door. A curve representing the temperaturedifference between the ingoing and outgoing water is directly drawn onthe coordinate paper. Above are three resistance boxes, and the switchesfor electrical connections are at the right. On the top shelf is thegalvanometer, and immediately beneath, the plug resistance box foraltering the value of certain shunts. ]

[Illustration: FIG. 24. --Detailed wiring diagram showing all parts ofrecording apparatus, together with wiring to thermometers complete, including all previous figures. ]

The whole apparatus is permanently and substantially installed on thenorth wall of the calorimeter laboratory. A photograph showing thevarious parts and their installation is given in fig. 23. On the topshelf is seen the galvanometer and on the lower shelf the recorder withits glass door in front and the coordinate paper dropping into the boxbelow. The curve drawn on the coordinate paper is clearly shown. Abovethe recorder are the resistance-boxes, three in number, the lower one atthe left being the resistance S_{1}, the upper one at the left being theresistance S', and the upper one at the right being the resistanceZ_{1}. Immediately above the resistance-box Z_{1} is shown the plugresistance-box which controls on the one hand the resistance _r_ and onthe other hand the resistance S, both of which are substantially alteredwhen changing the apparatus to register from the 0° to 4° scale to the0° to 8° scale. A detailed wiring diagram is given in fig. 24. 

TEMPERATURE CONTROL OF THE INGOING AIR. 

[Illustration: FIG. 25. --Section of calorimeter walls and part ofventilating air-circuit, showing part of pipes for ingoing air andoutgoing air. On the ingoing air-pipe at the right is the lamp forheating the ingoing air. Just above it, H is the quick-throw valve forshutting off the tension equalizer IJ. I is the copper portion of thetension equalizer, while J is the rubber diaphragm; K, the pet-cock foradmitting oxygen; F, E, G, the lead pipe conducting the cold water forthe ingoing air; and C, the hair-felt insulation. N, N are brass ferulessoldered into the copper and zinc walls through which air-pipes pass; M, a rubber stopper for insulating the air-pipe from the calorimeter; O, the thermal junctions for indicating differences of temperature ofingoing and outgoing air and U, the connection to the outside; QQ, exitsfor the air-pipes from the box in which thermal junctions are placed; P, the dividing plate separating the ingoing and outgoing air; R, thesection of piping conducting the air inside the calorimeter; S, asection of piping through which the air passes from the calorimeter; A, a section of the copper wall; Y, a bolt fastening the copper wall to the2-1/2 inch angle W; B, a portion of zinc wall; C, hair-felt lining ofasbestos wall D; T-J, a thermal junction in the walls. ]

In passing the current of air through the calorimeter, temperatureconditions may easily be such that the air entering is warmer than theoutcoming air, in which case heat will be imparted to the calorimeter, or the reverse conditions may obtain and then heat will be brought away. To avoid this difficulty, arrangements are made for arbitrarilycontrolling the temperature of the air as it enters the calorimeter. This temperature control is based upon the fact that the air leaving thechamber is caused to pass over the ends of a series of thermal junctionsshown as O in fig. 25. These thermal junctions have one terminal in theoutgoing air and the other in the ingoing air, and consequently anydifference in the temperature of the two air-currents is instantlydetected by connecting the circuit with the galvanometer. Formerly thetemperature control was made a varying one, by providing for eithercooling or heating the ingoing air as the situation called for. Theheating was done by passing the current through an electric lamp placedin the cross immediately below the tension equalizer J. Cooling waseffected by means of a current of water through the lead pipe E closelywrapped around the air-pipe, water entering at F and leaving at G. Thislead pipe is insulated by hair-felt pipe-covering, C. More recently, wehave adopted the procedure of passing a continuous current of water, usually at a very slow rate, through the lead pipe E and always heatingthe air somewhat by means of the lamp, the exact temperature controlbeing obtained by varying the heating effect of the lamp itself. Thishas been found much more satisfactory than by alternating from thecooling system to the heating system. In the case of the air-current, however, it is unnecessary to have the drop-sight feed-valve as used forthe wall control, shown in fig. 13. 

THE HEAT OF VAPORIZATION OF WATER. 

During experiments with man not all the heat leaves the body byradiation and conduction, since a part is required to vaporize the waterfrom the skin and lungs. An accurate measurement of the heat productionby man therefore required a knowledge of the amount of heat thusvaporized. One of the great difficulties in the numerous forms ofcalorimeters that have been used heretofore with man is that only thatportion of heat measured by direct radiation or conduction has beenmeasured and the difficulties attending the determination of watervaporized have vitiated correspondingly the estimates of the heatproduction. Fortunately, with this apparatus the determinations of waterare very exact, and since the amount of water vaporized inside thechamber is known it is possible to compute the heat required to vaporizethis water by knowing the heat of vaporization of water. 

Since the earlier reports describing the first form of calorimeters werewritten, there has appeared a research by one of our former associates, Dr. A. W. Smith[11] who, recognizing the importance of knowing exactlythe heat of vaporization of water at 20°, has made this a special objectof investigation. When connected with our laboratory a number ofexperiments were made by Doctors Smith and Benedict in an attempt todetermine the heat of vaporization of water directly in a largecalorimeter; but for lack of time and pressure of other experimentalwork it was impossible to complete the investigation. Subsequently Dr. Smith has carried out the experiments with the accuracy of exactphysical measurements and has given us a very valuable series ofobservations. 

Using the method of expressing the heat of vaporization in electricalunits, Smith concludes that the heat of vaporization of water between14° and 40° is given by the formula

 L (in joules) = 2502. 5 - 2. 43T

and states that the "probable error" of values computed from thisformula is 0. 5 joule. The results are expressed in international joules, that is, in terms of the international ohm and 1. 43400 for the E. M. F. Ofthe Clark cell at 15° C. , and assuming that the mean calorie isequivalent to 4. 1877 international joules, [12] the formula reads

 L (in mean calories) = 597. 44 - 0. 580T

With this formula Smith calculates that at 15° the heat of vaporizationof water is equal to 588. 73 calories; at 20°, 585. 84 calories; at 25°, 582. 93 calories; at 30°, 580. 04 calories;[13] and at 35°, 577. 12calories. In all of the calculations in the researches herewith we haveused the value found by Smith as 586 calories at 20°. Inasmuch as all ofour records are in kilo-calories, we multiply the weight of water by thefactor 0. 586 to obtain the heat of vaporization. 

THE BED CALORIMETER. 

The chair calorimeter was designed for experiments to last not more than6 to 8 hours, as a person can not remain comfortably seated in a chairmuch longer than this time. For longer experiments (experiments duringthe night and particularly for bed-ridden patients) a type ofcalorimeter which permits the introduction of a couch or bed has beendevised. This calorimeter has been built, tested, and used in a numberof experiments with men and women. The general shape of the chamber isgiven in fig. 26. The principles involved in the construction of thechair calorimeter are here applied, _i. E. _, the use of astructural-steel framework, inner air-tight copper lining, outer zincwall, hair-felt insulation, and outer asbestos panels. Inside of thechamber there is a heat-absorbing system suspended from the ceiling, andair thermometers and thermometers for the copper wall are installed atseveral points. The food-aperture is of the same general type and thefurniture here consists simply of a sliding frame upon which is placedan air-mattress. The opening is at the front end of the calorimeter andis closed by two pieces of plate glass, each well sealed into place bywax after the subject has been placed inside of the chamber. Tubesthrough the wall opposite the food-aperture are used for theintroduction of electrical connections, ingoing and outgoing water, theair-pipes, and connections for the stethoscope, pneumograph, andtelephone. 

The apparatus rests on four heavy iron legs. Two pieces of channel ironare attached to these legs and the structural framework of thecalorimeter chamber rests upon these irons. The method of separating theasbestos outer panels is shown in the diagram. In order to provide lightfor the chamber, the outer wall in front of the glass windows is madeof glass rather than asbestos. The front section of the outer casing canbe removed easily for the introduction of a patient. 

In this chamber it is impossible to weigh the bed and clothing, andhence this calorimeter can not be used for the accurate determination ofthe moisture vaporized from the lungs and skin of the subject, sincehere (as in almost every form of respiration chamber) it is absolutelyimpossible to distinguish between the amount of water vaporized frombed-clothing and that vaporized from the lungs and skin of the subject. With the chair calorimeter, the weighing arrangements make it possibleto weigh the chair, clothing, etc. , and thus apportion the total watervaporized between losses from the chair, furniture, and body of the man. In view of the fact that the water vaporized from the skin and lungscould not be determined, the whole interior of the chamber of the bedcalorimeter has been coated with a white enamel paint, which gives it abright appearance and makes it much more attractive to new patients. Anincandescent light placed above the head at the front illuminates thechamber very well, and as a matter of fact the food-aperture is soplaced that one can lie on the cot and actually look outdoors throughone of the laboratory windows. 

[Illustration: FIG. 26. --Cross-section of bed calorimeter, showing partof steel construction, also copper and zinc walls, food-aperture, andwall and air-resistance thermometers. Cross-section of opening, cross-section of panels of insulating asbestos, and supports ofcalorimeter itself are also indicated. ]

Special precaution was taken with this calorimeter to make it ascomfortable and as attractive as possible to new and possiblyapprehensive patients. The painting of the walls unquestionably resultsin a condensation of more or less moisture, for the paint certainlyabsorbs more moisture than does the metallic surface of the copper. Thechief value of the determination of the water vaporized inside of thechamber during an experiment lies, however, not in a study of thevaporization of water as such, but in the fact that a certain amount ofheat is required to vaporize the water and obviously an accurate measureof the heat production must involve a measure of the amount of watervaporized. So far as the measurement of heat is concerned, it isimmaterial whether the water is vaporized from the lungs or skin of thesubject or the clothing, bedding, or walls of the chamber; since forevery gram of water vaporized inside of the chamber, from whateversource, 0. 586 calorie of heat must have been absorbed. 

The apparatus as perfected is very sensitive. The sojourn in the chamberis not uncomfortable; as a matter of fact, in an experiment made duringJanuary, 1909, the subject remained inside of the chamber for 30 hours. With male patients no difficulty is experienced in collecting the urine. No provision is made for defecation, and hence it is our custom in longexperiments to empty the lower bowel with an enema and thus defer aslong as possible the necessity for defecation. With none of theexperiments thus far made have we experienced any difficulty in havingto remove the patient because of necessity to defecate in the crampedquarters. It is highly probable that, with the majority of sickpatients, experiments will not extend for more than 8 or 10 hours, andconsequently the apparatus as designed should furnish most satisfactoryresults. 

In testing the apparatus by the electrical-check method, it has beenfound to be extremely accurate. When the test has been made with burningalcohol, as described beyond, it has been found that the large amount ofmoisture apparently retained by the white enamel paint on the wallsvitiates the determination of water for several hours after theexperiment begins, and only after several hours of continuousventilating is the moisture content of the air brought down to a lowenough point to establish equilibrium between the moisture condensed onthe surface and the moisture in the air and thus have the measuredamount of moisture in the sulphuric acid vessels equal the amount ofmoisture formed by the burning of alcohol. Hence in practically all ofthe alcohol-check experiments, especially of short duration, with thiscalorimeter, the values for water are invariably somewhat too high. Acomparison of the alcohol-check experiments made with the bed and chaircalorimeters gives an interesting light upon the power of paint toabsorb moisture and emphasizes again the necessity of avoiding the useof material of a hygroscopic nature in the interior of an apparatus inwhich accurate moisture determinations from the body are to be made. 

The details of the bed calorimeter are better shown in fig. 4. Theopening at the front is here removed and the wooden track upon which theframe, supporting the cot, slides is clearly shown. The tensionequalizer (see page 71) partly distended is shown connected to theingoing air-pipe, and on the top of the calorimeter connected to thetension equalizer is a Sondén manometer. On the floor at the right isseen the resistance coil used for electrical tests (see page 50). Anumber of connections inside the chamber at the left are made withelectric wires or with rubber tubing. Of the five connections appearingthrough the opening, reading from left to right, we have, first, therubber connection with the pneumograph, then the tubing for connectionwith the stethoscope, then the electric-resistance thermometer, thetelephone, and finally a push button for bell call. The connections forthe pneumograph and stethoscope are made with the instruments outside onthe table at the left of the bed calorimeter. 

MEASUREMENTS OF BODY-TEMPERATURE. 

While it is possible to control arbitrarily the temperature of thecalorimeter by increasing or decreasing the amount of heat brought away, and thus compensate exactly for the heat eliminated by the subject, thehydrothermal equivalent of the system itself being about 20 calories--onthe other hand the body of the subject may undergo marked changes intemperature and thus influence the measurement of the heat production toa noticeable degree; for if heat is lost from the body by a fall ofbody-temperature or stored as indicated by a rise in temperature, obviously the heat produced during the given period will not equal thateliminated and measured by the water-current and by the latent heat ofwater vaporized. In order to make accurate measurements, therefore, ofthe heat-production as distinguished from the heat elimination, weshould know with great accuracy the hydrothermal equivalent of the bodyand changes in body temperature. The most satisfactory method at presentknown of determining the hydrothermal equivalent of the body is toassume the specific heat of the body as 0. 83. [14] This factor will ofcourse vary considerably with the weight of body material and theproportion of fat, water, and muscular tissue present therein, but forgeneral purposes nothing better can at present be employed. From theweight of the subject and this factor the hydrothermal equivalent of thebody can be calculated. It remains to determine, then, with greatexactness the body temperature. 

Recognizing early the importance of securing accurate body-temperaturesin researches of this kind, a number of investigations were made andpublished elsewhere[15] regarding the body-temperature in connectionwith the experiments with the respiration calorimeter. It was soonfound that the ordinary mercurial clinical thermometer was not bestsuited for the most accurate observations of body-temperature and aspecial type of thermometer employing the electrical-resistance methodwas used. In many of the experiments, however, it is impracticable withnew subjects to complicate the experiment by asking them to insert theelectrical rectal thermometer, and hence we have been obliged to resortto the usual clinical thermometer with temperatures taken in the mouth, although in a few instances they have been taken in the axilla and therectum. For the best results the electrical rectal thermometer is used. This apparatus permits a continuous measurement of body temperature, deep in the rectum, unknown to the subject and for an indefinite periodof time, it being necessary to remove the thermometer only fordefecation. 

As a result of these observations it was soon found that the bodytemperature was not constant from hour to hour, but fluctuatedconsiderably and underwent more or less regular rhythm with the minimumbetween 3 and 5 o'clock in the morning and the maximum about 5 o'clockin the afternoon. In a number of experiments where the mercurialthermometer was used under the tongue and observations thus takencompared with records with the resistance thermometer, it was found thatwith careful manipulation and avoiding muscular activity, mouthbreathing, and the drinking of hot or cold liquid, a fairly uniformagreement between the two could be obtained. Such comparisons made onlaboratory assistants can not be duplicated with the ordinary subject. 

It is assumed that fluctuations in temperature measured by the rectalthermometer likewise hold true for the average temperature of the wholebody, but evidence on this point is unfortunately not as complete as isdesirable. In an earlier report of investigations of this nature, a fewexperiments on comparison of measurements of resistance thermometer deepin the rectum and in a well-closed axilla showed a distinct tendency forthe curves to continue parallel. A research is very much needed atpresent on a topographical distribution of body temperature, andparticularly on the course of the fluctuations in different parts of thebody. A series of electric-resistance thermometers placed at differentpoints in the colon, at different points in a stomach tube, in thewell-closed axilla, possibly attached to the surface of the body, and inwomen in the vagina, should give a very accurate picture of thedistribution of the body-temperature and likewise indicate theproportionality of the fluctuations in different parts of the body. Until such a research is completed, however, it is necessary to assumethat fluctuations in body-temperature as measured by the electric rectalthermometer are a true measure of the average body-temperature of thewhole body. Indeed it is upon this assumption that it is necessary forus to make corrections for heat lost from or stored in the body. It isour custom, therefore, to compute the hydrothermal equivalent bymultiplying the body-weight by the specific heat of the body, commonlyassumed as 0. 83, and then to make allowance for fluctuations inbody-temperature. 

When it is considered that with a subject having a weight of 70 kilos adifference in temperature of 1° C. Will make a difference in themeasurement of heat of some 60 calories, it is readily seen that theimportance of knowing the exact body-temperature can not beoverestimated; indeed, the whole problem of the comparison of the directand indirect calorimetry hinges more or less upon this very point, andit is strongly to be hoped that ere long the much-needed observations onbody-temperature can be made. 

CONTROL EXPERIMENTS WITH THE CALORIMETER. 

After providing a suitable apparatus for bringing away the heatgenerated inside the chamber and for preventing the loss of heat bymaintaining the walls adiabatic, it is still necessary to demonstratethe ability of the calorimeter to measure known amounts of heataccurately. In order to do this we pass a current of electricity ofknown voltage through a resistance coil and thus develop heat inside therespiration chamber. While, undoubtedly, the use of a standardresistance and potentiometer is the most accurate method for measuringcurrents of this nature, thus far we have based our experiments upon themeasurements made with extremely accurate Weston portable voltmeter andmil-ammeters. Thanks to the kindness of one of our former co-workers, Mr. S. C. Dinsmore, at present associated with the Weston ElectricalInstrument Company, we have been able to obtain two especially exactinstruments. The mil-ammeter is so adjusted as to give a maximum currentof 1. 5 amperes and the voltmeter reads from zero to 150 volts. Thedirect current furnished the building is caused to pass through avariable resistance for adjusting minor variations in voltage and thenthrough the mil-ammeter into a manganin resistance-coil inside thechamber, having a resistance of 84. 2 ohms. Two leads from the terminalsof the manganin coil connect with the voltmeter outside the chamber, andhence the drop in potential can be measured very accurately and asfrequently as is desired. The current furnished the building isremarkably steady, but for the more accurate experiments a small degreeof hand regulation is necessary. 

The advantage of the electrical method of controlling the apparatus isthat the measurements can be made very accurately, rapidly, and in shortperiods. In making experiments of this nature it is our custom first toplace the resistance-coil in the calorimeter and make the connections. The current is then passed through the coil, and simultaneously thewater is started flowing through the heat-absorbing system and the wholecalorimeter is adjusted in temperature equilibrium as soon as possible. When the temperature of the air and walls is constant and thethermal-junction system in equilibrium, the exact time is noted and thewater-current deflected into the meter. At the end of one hour, theusual length of a period, the water-current is deflected from the meter, the meter is weighed, and the average temperature-difference of thewater obtained by averaging the results of all the temperaturedifferences noted during the hour. Usually during an experiment of thisnature, records of the water-temperatures are made every 4 minutes;occasionally, when the fluctuations are somewhat greater than usual, records are made every 2 minutes. 

The calculation of the heat developed in the apparatus is made by meansof the formula C × E × _t_ × 0. 2385 = calories, in which C equals thecurrent in amperes, E the electromotive force, and _t_ the time inseconds. This gives the heat expressed in calories at 15° C. Thisprocedure we have followed as a result of the recommendation of Dr. E. B. Rosa, of the National Bureau of Standards. In order to convert thevalues to 20°, the unit commonly employed in calorimetric work, it hasbeen necessary to multiply by the ratio of the specific heat of water at15° to that of water at 20°. Assuming the specific heat of water at 20°to be 1, the specific heat at 15° is 1. 001. [16]

Of the many electrical check-tests made with this type of apparatus, butone need be given here, pending a special treatment of the method ofcontrol of the calorimeter in a forthcoming publication. An electricalcheck-experiment with the chair calorimeter was made on January 4, 1909, and continued 6 hours. The voltmeter and mil-ammeter were read every fewminutes, the water collected in the water-meter, carefully weighed, andthe temperature differences as measured on the two mercury thermometerswere recorded every 4 minutes. 

The heat developed during the experiment may be calculated from the dataas follows: Average current = 1. 293 amperes; average E. M. F. = 109. 15volts; time = 21, 600 seconds; factor used to convert watt-seconds tocalories = 0. 2385. (1. 293 × 109. 15 × 21600 × 0. 2385) × 1. 001 = 727. 8calories produced. 

During the 6 hours 237. 63 kilograms of water passed through theabsorbing system. 

The average temperature rise was 3. 04° C. , the total heat brought awaywas therefore (237. 63 × 3. 04) × 1. 0024[17] = 724. 1 calories. 

Thus in 6 hours there were about 3. 7 calories more heat developed insidethe apparatus than were measured by the water-current, a discrepancy ofabout 0. 5 per cent. 

Under ideal conditions of manipulation, the withdrawal of heat from thecalorimeter should be at just such a rate as to exactly compensate forthe heat developed by the resistance-coil. Under these conditions, then, there would be no heat abstracted from nor stored by the calorimeter andits temperature should remain constant throughout the whole experiment. Practically this is very difficult to accomplish and there are minorfluctuations in temperature above and below the initial temperatureduring a long experiment and, indeed, during a short experimentalperiod. If a certain amount of heat has been stored up in thecalorimeter chamber or has been abstracted from it, there should becorrections made for the variations in the temperature of the chamber. Such corrections are impossible unless a proper determination of thehydrothermal equivalent has been made. A number of experiments todetermine this hydrothermal equivalent have been made and the resultsare recorded beyond, together with a discussion of the nature of theexperiments. As a result of these experiments it has been possible tomake correction for the slight temperature changes in the calorimeter. 

It is interesting to note that these fluctuations are small and theremay therefore be a considerable error in the determination of thehydrothermal equivalent without particularly affecting the correctionsapplied in the ordinary electrical check-test. The greatest difficultyexperienced with the calorimeter as a means of measuring heat has beento secure the average temperature of the ingoing water. The temperaturedifference between the mass of water flowing through the pipes and theouter wall of the pipe is at best considerable. The use of thevacuum-jacketed glass tubes has minimized the loss of heat through thistube considerably, but it is advisable that the bulb of the thermometerbe placed exactly in the center of the water-tube, as otherwise too higha temperature-reading will be secured. When the proper precautions aretaken to secure the correct temperature-reading, the results are mostsatisfactory. 

In testing both calorimeters a large number of electrical checkexperiments have led to the conclusion that discrepancies in resultswere invariably due, not to the loss of heat through the walls of thecalorimeter, but to erroneous measurement of the temperature of thewater-current. 

DETERMINATION OF THE HYDROTHERMAL EQUIVALENT OF THE CALORIMETER. 

While the temperature control of the calorimeter is such that in generalthe average temperature varies but a few hundredths of a degree betweenthe beginning and the end of an experimental period, in extremelyaccurate work it is necessary to know the amount of heat which isabsorbed with any increase in temperature. In other words, thedetermination of the hydrothermal equivalent is essential. 

The large majority of the methods for determining the hydrothermalequivalent of materials are at once eliminated when the nature of thecalorimeter here used is taken into consideration. Obviously, in warmingup the chamber there are two sources of heat: first, the heat inside ofthe chamber; second, the heat in the outer walls. As has been previouslydescribed, the zinc wall is arbitrarily heated so that its temperaturefluctuations will follow exactly those of the inner wall, hence it isimpossible to compute from the weight of the metal the hydrothermalequivalent. By means of the electrical check experiments, however, amethod for determining the hydrothermal equivalent is at hand. Thegeneral scheme is as follows. 

During an electrical check experiment, when thermal equilibrium has beenthoroughly established and the heat brought away by the water-currentexactly counterbalances the heat generated in the resistance-coil insidethe chamber, the temperature of the calorimeter is allowed to riseslowly by raising the temperature of the ingoing water and thus bringingaway less heat. At the same time the utmost pains are taken to maintainthe adiabatic condition of the metal walls. Since the temperature isrising during this period, it is necessary to warm the air in the outerspaces by the electric current. By this method it is possible to raisethe temperature of the calorimeter 1 degree or more in 2 hours andestablish thermal equilibrium at the higher level. The experiment isthen continued for 2 hours at this level, and the next 2 hours thetemperature is gradually allowed to fall by lowering the temperature ofthe ingoing water so that more heat is brought away than is generated, care being taken likewise to keep the walls adiabatic. Under theseconditions the heat brought away by the water-current during the periodof rising temperature is considerably less than that actually developedby the electric current and the difference represents the amount of heatabsorbed by the calorimeter in the period of the temperature rise. Conversely, during the period when the temperature is falling, there isa considerable increase in the amount of heat brought away by thewater-current over that generated in the resistance-coil and thedifference represents exactly the amount of heat given up by thecalorimeter during the fall in temperature. It is thus possible tomeasure the capacity of the calorimeter for absorbing heat during a risein temperature and the amount of heat lost by it during cooling. Anumber of such experiments have been made with both calorimeters and ithas been found that the hydrothermal equivalent of the bed calorimeteris not far from 21 kilograms. For the chair calorimeter a somewhat lowerfigure has been found, _i. E. _, 19. 5 kilograms. 

GENERAL DESCRIPTION OF RESPIRATION APPARATUS. 

This apparatus is designed much after the principle of theRegnault-Reiset apparatus, in that there is a confined volume of air inwhich the subject lives and which is purified by its passage throughvessels containing absorbents for water and carbon dioxide. Fresh oxygenis added to this current of air and it is then returned to the chamberto be respired. This principle, in order to be accurate for oxygendeterminations, necessitates an absolutely air-tight system andconsequently special precautions have been taken in the construction ofthe chamber and accessories. 

TESTING THE CHAMBER FOR TIGHTNESS. 

As already suggested, the walls are constructed of the largest possiblesheets of copper with a minimum number of seams and opportunities forleakage. In testing the apparatus for leaks, the greatest precaution istaken. A small air-pressure is applied and the variations in height of adelicate manometer noted. In cases of apparent leakage, all possiblesources of leak are gone over with soapsuds when there is a slightpressure on the chamber. As a last resort, which has ultimately provento be the best method of testing, an assistant goes inside of thechamber, it is then hermetically sealed, and a slight diminishedpressure is produced. Ether is then poured about the walls of thechamber and the odor of ether soon becomes apparent inside of thechamber if there is a leakage. Many leaks that could not be found bysoapsuds can be readily detected by this method. 

VENTILATION OF THE CHAMBER. 

The special features of the respiration chamber are the ventilating-pipesystem and openings for supplementary apparatus for absorption of waterand carbon dioxide. The air entering the chamber is absolutely dry andis directed into the top of the chamber immediately above the head ofthe subject. The moisture given off from the lungs and skin and theexpired gases all tend to mix readily with this dry air as it descends, and the final mixture of gases is withdrawn through an opening near thebottom of the chamber at the front. Under these conditions, therefore, we believe we have a maximum intermingling of the gases. However, evenwith this system of ventilation, we do not feel that there istheoretically the best mixture of gases, and an electric fan is usedinside of the chamber. In experiments where there is considerableregularity in the carbon-dioxide production and oxygen consumption, thesystem very quickly attains a state of equilibrium, and while theanalysis of the outcoming air does not necessarily represent fairly theactual composition of the air inside of the chamber, it evidentlyrepresents to the same degree from hour to hour the state of equilibriumthat is usually maintained through the whole of a 6-hour experiment. 

The interior of the chamber and all appliances are constructed of metalexcept the chair in which the subject sits. This is of hard wood, wellshellacked, and consequently non-porous. With this calorimeter it isdesired to make studies regarding the moisture elimination, andconsequently it is necessary to avoid the use of all material of ahygroscopic nature. Although the chair can be weighed from time to timewith great accuracy and its changes in weight obtained, it is obviouslyimpossible, in any type of experiment thus far made, to differentiatebetween the water vaporized from the lungs and skin of the man and thatfrom his clothes. Subsequent experiments with a metal chair, withminimum clothing, with cloth of different textures, without clothing, with an oiled skin, and various other modifications affecting thevaporization of water from the body of the man will doubtless throw moredefinite light upon the question of the water elimination through theskin. At present, however, we resort to the use of a wooden chair, relying upon its changes in weight as noted by the balance to aid us inapportioning the water vaporized between the man and his clothing andthe chair. 

The walls of the chamber are semi-rigid. Owing to the calorimetricfeatures of this apparatus, it is impracticable to use heavyboiler-plate or heavy metal walls, as the sluggishness of the changes intemperature, the mass of metal, and its relatively large hydrothermalequivalent would interfere seriously with the sensitiveness of theapparatus as a calorimeter. Hence we use copper walls, with a fairdegree of rigidity, attached to a substantial structural-steel support;and for all practical purposes the apparatus can be considered as ofconstant volume. Particularly is this the case when it is consideredthat the pressure inside of the chamber during an experiment nevervaries from the atmospheric pressure by more than a few millimeters ofwater. It is possible, therefore, from the measurements of this chamber, to compute with considerable accuracy the absolute volume. The apparentvolume has been calculated to be 1, 347 liters. 

OPENINGS IN THE CHAMBER. 

In order to communicate with the interior of the chamber, maintain aventilating air-current, and provide for the passage of the current ofwater for the heat-absorber system and the large number of electricalconnections, a number of openings through the walls of the chamber werenecessary. The great importance of maintaining this chamber absolutelyair-tight renders it necessary to minimize the number of these openings, to reduce their size as much as possible, and to take extra precautionin securing their closure during an experiment. The largest opening isobviously the trap-door at the top through which the subject enters, shown in dotted outline in fig. 7. While somewhat inconvenient to enterthe chamber in this way, the entrance from above possesses manyadvantages. It is readily closed and sealed by hot wax and rarely is aleakage experienced. The trap-door is constructed on precisely the sameplan as the rest of the calorimeter, having its double walls of copperand zinc, its thermal-junction system, its heating wires andconnections, and its cooling pipes. When closed and sealed, and theconnections made with the cooling pipes and heating wires, it presentsan appearance not differing from any other portion of the calorimeter. 

The next largest opening is the food-aperture, which is a largesheet-copper tube, somewhat flattened, thus giving a slightly oval form, closed with a port, such as is used on vessels. The door of the portconsists of a heavy brass frame with a heavy glass window and it can beclosed tightly by means of a rubber gasket and two thumbscrews. On theoutside is used a similar port provided with a tube somewhat larger indiameter than that connected with the inner port. The annular spacebetween these tubes is filled with a pneumatic gasket which can beinflated and thus a tight closure may be maintained. When one door isclosed and the other opened, articles can be placed in and taken out ofthe chamber without the passage of a material amount of air from thechamber to the room outside or into the chamber from outside. 

The air-pipes passing through the wall of the calorimeter are ofstandard 1-inch piping. The insulation from the copper wall is made by arubber stopper through which this piping is passed, the stopper beingcrowded into a brass ferule which is stoutly soldered to the copperwall. This is shown in detail in fig. 25, in which N is the brass feruleand M the rubber stopper through which the air-pipe passes. The closureis absolutely air-tight and a minimum amount of heat is conducted out ofthe chamber, owing to the insulation of the rubber stopper M. Thewater-current enters and leaves the chamber through two pipes insulatedin two similar brass ferules soldered to the copper and zinc walls. Theinsulation between the water-pipe and the brass ferule has been thesubject of much experimenting and is discussed on page 24. The bestinsulation was secured by a vacuum-jacketed glass tube, although thespecial hard-rubber tubes surrounding the electric-resistancethermometers have proven very effective as insulators in the bedcalorimeter. 

A series of small brass tubes, from 10 to 15 millimeters in diameter, are soldered into the copper wall in the vicinity of the water-pipes. These are used for electrical connections and for connections with themanometer, stethoscope, and pneumograph. All of these openings aretested carefully and shown to be absolutely air-tight before being putin use. 

In the dome of the calorimeter, and directly over the head of thesubject, is the opening for the weighing apparatus. This consists of ahard-rubber tube, threaded at one end and screwed into a brass flangeheavily soldered to the copper wall (fig. 9). When not in use, a solidrubber stopper on a brass rod is drawn into this opening, thusproducing an air-tight closure. When in actual use during the process ofweighing, a thin rubber diaphragm prevents leakage of air through thisopening. The escape of heat through the weighing-tube is minimized byhaving this tube of hard rubber. 

VENTILATING AIR-CURRENT. 

[Illustration: FIG. 27. --Diagram of ventilation of respirationcalorimeter. The air is taken out at lower right-hand corner and forcedby the blower through the apparatus for absorbing water and carbondioxide. It returns to the calorimeter at the top. Oxygen can beintroduced into the chamber itself as need is shown by the tensionequalizer. ]

The ventilating air-current is so adjusted that the air which leaves thechamber is caused to pass through purifiers, where the water-vapor andthe carbon dioxide are removed, and then, after being replenished withfresh oxygen, it is returned to the chamber ready for use. The generalscheme of the respiration apparatus is shown in fig. 27. The air leavingthe chamber contains carbon dioxide and water-vapor and the originalamount of nitrogen and is somewhat deficient in oxygen. In order topurify the air it must be passed through absorbents for carbonic acidand water-vapor and hence some pressure is necessary to force the gasthrough these purifying vessels. This pressure is obtained by a smallpositive rotary blower, which has been described previously indetail. [18] The air is thus forced successively through sulphuric acid, soda or potash-lime, and again sulphuric acid. Finally it is directedback to the respiration chamber free from carbon dioxide and water anddeficient in oxygen. Pure oxygen is admitted to the chamber to make upthe deficiency, and the air thus regenerated is breathed again by thesubject. 

BLOWER. 

The rotary blower used in these experiments for maintaining theventilating current of air has given the greatest satisfaction. It is aso-called positive blower and capable of producing at the outletconsiderable pressure and at the inlet a vacuum of several inches ofmercury. At a speed of 230 revolutions per minute it delivers the air ata pressure of 43 millimeters of mercury, forcing it through thepurifying vessels at the rate of 75 liters per minute. This rate ofventilation has been established as being satisfactory for allexperiments and is constant. Under the pressure of 43 millimeters ofmercury there are possibilities of leakage of air from the blowerconnections and hence, to note this immediately, the blower system isimmersed in a tank filled with heavy lubricating oil. The connectionsare so well made, however, that leakage rarely occurs, and, when itdoes, a slight tightening of the stuffing-box on the shaft makes theapparatus tight again. 

ABSORBERS FOR WATER-VAPOR. 

To absorb 25 to 40 grams of water-vapor in an hour from a current of airmoving at the rate of 75 liters per minute and leaving the airessentially dry under these conditions has been met by the apparatusherewith described. The earlier attempts to secure this result involvedthe use of enameled-iron soup-stock pots, fitted with specialenameled-iron covers and closed with rubber gaskets. For the preliminaryexperimenting and for a few experiments with man these provedsatisfactory, but in spite of their resistance to the action ofsulphuric acid, it was found that they were not as desirable as theyshould be for continued experimenting from year to year. Recourse wasthen had to a special form of chemical pottery, glazed, and a type thatusually gives excellent satisfaction in manufacturing concerns was used. 

This special form of absorbers presented many difficulties inconstruction, but the mechanical difficulties were overcome by thepotter's skill and a number of such vessels were furnished by theCharles Graham Chemical Pottery Works. Here again these vessels servedour purpose for several months, but unfortunately the glaze used did notsuffice to cover them completely and there was a slight, thoughpersistent, leakage of sulphuric acid through the porous walls. Toovercome this difficulty the interior of the vessels was coated with hotparaffin after a long-continued washing to remove the acid and afterthey had been allowed to dry thoroughly. The paraffin-treated absorberscontinued to give satisfaction, but it was soon seen that for permanentuse something more satisfactory must be had. After innumerable trialswith glazed vessels of different kinds of pottery and glass, arrangements were made with the Royal Berlin Porcelain Works to mold andmake these absorbers out of their highly resistant porcelain. The resultthus far leaves nothing to be desired as a vessel for this purpose. Anumber of such absorbers were made and have been constantly used for ayear and are absolutely without criticism. 

Fig. 28 shows the nature of the interior of the apparatus. The airenters through one opening at the top, passes down through a bent pipe, and enters a series of roses, consisting of inverted circular saucerswith holes in the rims. The position of the holes is such that when thevessel is one-fourth to one-third full of sulphuric acid the air mustpass through the acid three times. To prevent spattering, a smallcup-shaped arrangement, provided with holes, is attached to the openingthrough which the air passes out of the absorber, and for filling thevessel with acid a small opening is made near one edge. Thespecifications required that the apparatus should be made absolutelyair-tight to pressures of over 1 meter of water, and that there is noporosity in these vessels under these conditions is shown by the factthat such a pressure is held indefinitely. The inside and outside areboth heavily glazed. There is no apparent action of sulphuric acid onthe vessels and the slight increase in temperature resulting from theabsorption of water-vapor as the air passes through does not appear tohave any deleterious effect. 

[Illustration: FIG. 28. --Cross-section of sulphuric-acid absorber. Theair enters at the top of the right-hand opening, descends to the bottomof the absorber, and then passes through three concentric rings, whichare covered with acid, and it finally passes out at the left-handopening. Beneath the left-hand opening is a cup arrangement forpreventing the acid being carried mechanically out through the opening. The opening for filling and emptying the absorber is shown midwaybetween the two large openings. ]

The vessels without filling and without rubber elbows weigh 11. 5kilograms; with the special elbows and couplings attached so as toenable them to be connected with the ventilating air-system, the emptyabsorbers weigh 13. 4 kilograms; and filled with sulphuric acid theyweigh 19 kilograms. Repeated tests have shown that 5. 5 kilograms ofsulphuric acid will remove the water-vapor from a current of air passingthrough the absorbers at the rate of 75 liters of air per minute, without letting any appreciable amount pass by until 500 grams of waterhave been absorbed. At this degree of saturation a small persistentamount of moisture escapes absorption in the acid and consequently asecond absorber will begin to gain in weight. Experiments demonstratethat the first vessel can gain 1, 500 grams of water before the secondgains 5 grams. As a matter of fact, it has been found more advantageousto use but one absorber and have it refilled as soon as it has gained400 grams, thus allowing a liberal factor of safety and no danger ofloss of water. 

POTASH-LIME CANS. 

The problem of absorbing the water-vapor from so rapid a current of airis second only to that of absorbing the carbon dioxide from such acurrent. All experiments with potassium hydroxide in the form of sticksor in solution failed to give the desired results and the use ofsoda-lime has supplemented all other forms of carbon dioxide absorption. More recently we have been using potash-lime, substituting causticpotash for caustic soda in the formula, and the results thus obtainedare, if anything, more satisfactory than with the soda-lime. 

The potash-lime is made as follows: 1 kilogram of commercial potassiumhydroxide, pulverized, is dissolved in 550 to 650 cubic centimeters ofwater and 1 kilogram of pulverized quicklime added slowly. The amount ofwater to be used varies with the moisture content of the potash. Thereis a variation in the moisture content of different kegs of potash, sowhen a keg is opened we determine experimentally the amount of water tobe used. After a batch is made up in this way it should be allowed tocool before testing whether it has the right amount of water, and thisis determined by feeling of it and noting how it pulverizes in the hand. It is not advisable to make a great quantity at once, because we havefound that if a large quantity is made and broken into small particlesand stored in a container it has a tendency to cake and thus interferewith its ready subsequent use. 

A record was kept of the gains in weight of a can filled withpotash-lime during a series of experiments where there were threesilver-plated cans used. This can was put at the head of the system andwhen it began to lose weight it was removed. The records of gains ofweight when added together amount to 400 grams. From experience withother cans where the loss of moisture was determined, it is highlyprobable that at least 200 grams of water were vaporized from thereagent and thus the total amount of carbon dioxide absorbed must havebeen not far from 600 grams. At present our method is not to allow thecans to gain a certain weight, but during 4-hour or 5-hour experiments, in which each can may be used 2 or 3 hours, it is the practice to put anew can on each side of the absorber system (see page 66) at thebeginning of every experiment. This insures the same power of absorptionon each side of the absorption system so that the residual amount ofcarbon dioxide in the chamber from period to period does not undergovery marked changes. This has been found the best method, because if onecan is left on a day longer than the other there is apt to bealternately a rise and fall in the amount of residual carbon dioxide inthe apparatus, owing to the unequal efficiency of the absorbers. 

These cans are each day taken to the basement, where the firstsection[19] only is taken out and replaced with new potash-lime. Thus, three-quarters of the contents of the can is used over and over, whilethe first quarter is freshly renewed every day. Potash-lime has not beenfound practicable for the U-tubes because one can not, as in the case ofsoda-lime, see the whitening of the reagent where the carbon dioxide isabsorbed. 

The importance of having the soda-lime or potash-lime somewhat moist, tosecure the highest efficiency for the absorption of the carbon dioxide, makes it necessary to absorb the moisture taken up by the dry air inpassing through the potash-lime can. Consequently a second vesselcontaining sulphuric acid is placed in the system to receive the airimmediately after it leaves the potash-lime can. Obviously the amount ofwater absorbed here is very much less than in the first acid absorberand hence the same absorber can be used for a greater number ofexperiments. 

BALANCE FOR WEIGHING ABSORBERS. 

The complete removal of water-vapor and carbon dioxide from a current ofair moving at the rate of 75 liters per minute calls for large andsomewhat unwieldy vessels in which is placed the absorbing material. This is particularly the case with the vessels containing the ratherlarge amounts of sulphuric acid required to dry the air. In the courseof an hour there is ordinarily removed from the chamber not far from 25grams of water-vapor and 20 to 30 grams of carbon dioxide. Thisnecessitates weighing the absorbers to within 0. 25 gram if an accuracyof 1 per cent is desired. The sulphuric-acid absorbers weigh about 18kilograms when filled with acid. In order to weigh this receptacle so asto measure accurately the increase in weight due to the absorption ofwater to within less than 1 per cent, we use the balance shown in fig. 29. This balance has been employed in a number of other manipulations inconnection with the respiration calorimeter and accessory apparatus andthe general type of balance leaves nothing to be desired as a balancecapable of carrying a heavy load with remarkable sensitiveness. 

The balance is rigidly mounted on a frame consisting of four uprightstructural-steel angle-irons, fastened at the top to a substantialwooden bed. Two heavy wooden pieces run the length of the table andfurnish a substantial base to which the standard of the balance isbolted. The balance is surrounded by a glass case to prevent errors dueto air-currents (see fig. 2). The pan of the balance is not large enoughto permit the weighing of an absorber, hence provision is made forsuspending it on a steel or brass rod from one of the hanger arms. Thisrod passes through a hole in the bottom of the balance case, and itslower end is provided with a piece of pipe having hooks at either end. Since the increase in weight rather than the absolute weight of theabsorber is used, the greater part of the weight is taken up by leadcounterpoises suspended above the pan on the right-hand arm of thebalance. The remainder of the weight is made up with brass weightsplaced in the pan. 

[Illustration: FIG. 29. --Balance for weighing absorbers, showing generaltype of balance and case surrounding it, with counterpoise and weightsupon right-hand pan. A sulphuric-acid absorber is suspended in positionready for weighing. Elevator with compressed-air system is shown inlower part of case. ]

In order to suspend this heavy absorber, a small elevator has beenconstructed, so that the vessel may be raised by a compressed-airpiston. This piston is placed in an upright position at the right of theelevator and is connected with the compressed-air service of thebuilding. The pressure is about 25 pounds per square inch and thediameter of the cylinder is 2. 5 inches, thus giving ample service forraising and lowering the elevator and its load. By turning a 3-wayvalve at the end of the compressed-air supply-pipe, so that the airrushes into the cylinder above the piston, the piston is pushed to thebase of the cylinder and the elevator thereby raised. The pressure ofthe compressed air holds the elevator in this position while the hooksare being adjusted on the absorber. By turning the 3-way valve so as toopen the exhaust leading to the upper part of the cylinder to the air, the weight of the elevator expels the air, and it soon settles into theposition shown in the figure. The weighing can then be made as theabsorber is swinging freely in the air. After the weighing has beenmade, the elevator is again lifted, the hooks are released, and byturning the valve the elevator and load are safely lowered. 

The size of the openings of the pipes into the cylinder is so adjustedthat the movement of the elevator is regular and moderate whether it isbeing raised or lowered, thus avoiding any sudden jars that might causean accident to the absorbers. With this system it is possible to weighthese absorbers to within 0. 1 gram and, were it necessary, probably theerror could be diminished so that the weight could be taken to 0. 05gram. On a balance of this type described elsewhere, [20] weighings couldbe obtained to within 0. 02 gram. For all practical purposes, however, wedo not use the balance for weighing the absorbers closer than to within0. 10 gram. In attempting to secure accuracy no greater than this, it isunnecessary to lower the glass door to the balance case or, indeed, toclose the two doors to the compartment in which the elevator is closed, as the slight air-currents do not affect the accuracy of the weighingwhen only 0. 1 gram sensitiveness is required. 

PURIFICATION OF THE AIR-CURRENT WITH SODIUM BICARBONATE. 

As is to be expected, the passage of so large a volume of air throughthe sulphuric acid in such a relatively small space results in a slightacid odor in the air-current leaving this absorber. The amount ofmaterial thus leaving the absorber is not weighable, as has been shownby repeated tests, but nevertheless there is a sufficiently irritatingacid odor to make the air very uncomfortable for subsequent respiration. It has been found that this odor can be wholly eliminated by passing theair through a can containing cotton wool and dry sodium bicarbonate. This can is not weighed, and indeed, after days of use, there is noappreciable change in its weight. 

VALVES. 

In order to subdivide experiments into periods as short as 1 or 2 hours, it is necessary to deflect the air-current at the end of each periodfrom one set of purifiers to the other, in order to weigh the set usedand to measure the quantity of carbon dioxide and water-vapor absorbed. The conditions under which these changes from one system to another aremade, and which call for an absolutely gas-tight closure, have beendiscussed in detail elsewhere. [21] It is sufficient to state here thatthe very large majority of mechanical valves will not serve the purpose, since it is necessary to have a pressure of some 40 millimeters ofmercury on one side of the valve at the entrance to the absorber systemand on the other side atmospheric pressure. A valve with an internaldiameter of not less than 25 millimeters must be used, and to secure atight closure of this large area and permit frequent opening andshutting is difficult. After experimenting with a large number ofvalves, a valve of special construction employing a mechanical sealultimately bathed in mercury was used for the earlier apparatus. Thepossibility of contamination of the air-current by mercury vapor wasduly considered and pointed out in a description of this apparatus. Itwas not until two years later that difficulties began to be experiencedand a number of men were severely poisoned while inside the chamber. Adiscussion of this point has been presented elsewhere. [22] At that timemercury valves were used both at the entrance and exit ends of theabsorber system, although as a matter of fact, when the air leaves thelast absorber and returns to the respiration chamber, the pressure isbut a little above that of the atmosphere. Consequently, mechanicalvalves were substituted for mercurial valves at the exit and the toxicsymptoms disappeared. In constructing the new calorimeters it seemed tobe desirable to avoid all use of mercury, if possible. We were fortunatein finding a mechanical valve which suited this condition perfectly. These valves, which are very well constructed, have never failed to showcomplete tightness under all possible tests and are used at the exit andentrance end of the absorber system. Their workmanship is of the firstorder, and the valve is somewhat higher in price than ordinarymechanical valves. They have been in use on the apparatus for a year nowand have invariably proved to be absolutely tight. They are easy toobtain and are much easier to manipulate and much less cumbersome thanthe mercury valves formerly used. 

COUPLINGS. 

Throughout the construction of the respiration apparatus and its variousparts, it was constantly borne in mind that the slightest leak would bevery disastrous for accurate oxygen determinations. At any point wherethere is a pressure greater or less than that of the atmosphere, specialprecaution must be taken. At no point in the whole apparatus is itnecessary to be more careful than with the couplings which connect thevarious absorber systems with each other and with the valves; for thesecouplings are opened and closed once every hour or two and hence aresubject to considerable strain at the different points. If they are nottight the experiment is a failure so far as the determination of oxygenis concerned. For the various parts of the absorber system we haverelied upon the original type of couplings used in the earlierapparatus. A rubber gasket is placed between the male and female part ofthe coupling and the closure can be made very tight. In fact, after theabsorbers are coupled in place they are invariably subjected to severetests to prove tightness. 

For connecting the piping between the calorimeter and the absorptionsystem we use ordinary one-inch hose-couplings, firmly set up by meansof a wrench and disturbed only when necessary to change from onecalorimeter chamber to another. 

ABSORBER TABLE. 

The purifying apparatus for the air-current is compactly andconveniently placed on a solidly constructed table which can be movedabout the laboratory at will. The special form of caster on the bottomof the posts of the table permits its movement about the laboratory atwill and by screwing down the hand screws the table can be firmly fixedto the floor. 

The details of the table are shown in fig. 30. (See also fig. 4, page4. ) The air coming from the calorimeter passes in the direction of thedownward arrow through a 3/4-inch pipe into the blower, which isimmersed in oil in an iron box F. The blower is driven by an electricmotor fastened to a small shelf at the left of the table. The airleaving the blower ascends in the direction of the arrow to the valvesystem H, where it can be directed into one of the two parallel sets ofpurifiers; after it passes through these purifiers (sulphuric-acidvessel 2, potash-lime container K, and sulphuric-acid vessel 1) it goesthrough the sodium-bicarbonate can G to a duplicate valve system on topof the table. From there it passes through a pipe along the top of thetable and rises in the vertical pipe to the hose connection which iscoupled with the calorimeter chamber. 

The electric motor is provided with a snap-switch on one of the posts ofthe table and a regulating rheostat which permits variations in thespeed of the motor and consequently in the ventilation produced by theblower. The blower is well oiled, and as oil is gradually carried inwith the air, a small pet-cock at the bottom of the T following theblower allows any accumulated oil to be drawn away from time to time. The air entering the valve system at H enters through a cross, two armsof which connect with two "white star" valves. The upper part of thecross is connected to a small rubber tubing and to the mercurymanometer D, which also serves as a valve for passing a given amount ofair through a series of U-tubes for analysis of the air from time totime. It is assumed that the air drawn at the point H is ofsubstantially the same composition as that inside the chamber, anassumption that may not be strictly true, but doubtless the sample thusobtained is constantly proportional to the average composition, whichfluctuates but slowly. Ordinarily the piping leading from the left-handarm of the tube D is left open to the air and consequently thedifference in the level of the mercury in the two arms of D indicatesthe pressure on the system. This is ordinarily not far from 40 to 50millimeters of mercury. 

[Illustration: FIG. 30. --Diagram of absorber table. 1 and 2 containsulphuric acid; K contains potash-lime; G, sodium bicarbonate can; F, rotary blower for maintaining air-current; H, valves for closing eitherside; and D, mercury manometer and valve for diverting air to U-tubes ontable. Air leaves A, passes through the meter, and then through dryingtower B and through C to ingoing air-pipe. At the left is the regulatingrheostat and motor and snap-switch. General direction of ventilation isindicated by arrows. ]

The absorber table, with the U-tubes and meter for residual analyses, isshown in the foreground in fig. 2. The two white porcelain vessels witha silver-plated can between them are on the middle shelf. The sodiumbicarbonate can, for removing traces of acid fumes, is connected in anupright position, while the motor, the controlling rheostat, and theblower are supported by the legs near the floor. The two rubber pipesleading from the table can be used to connect the apparatus either withthe bed or chair calorimeter. In fig. 4 the apparatus is shown connectedwith the bed calorimeter, but just above the lowest point of the rubbertubing can be seen in the rear the coupling for one of the pipes leadingfrom the chair calorimeter. The other is immediately below and to theleft of it. 

OXYGEN SUPPLY. 

The residual air inside of the chamber amounts to some 1, 300 liters andcontains about 250 liters of oxygen. Consequently it can be seen that inan 8-hour experiment the subject could easily live during the entiretime upon the amount of oxygen already present in the residual air. Ithas been repeatedly shown that until the per cent of oxygen falls toabout 11, or about one-half normal, there is no disturbance in therespiratory exchange and therefore about 125 liters of oxygen would beavailable for respiration even if no oxygen were admitted. Inasmuch asthe subject when at rest uses not far from 14 to 15 liters per hour, theamount originally present in the chamber would easily suffice for an8-hour experiment. Moreover, the difficulties attending an accurate gasanalysis and particularly the calculation of the total amount of oxygenare such that satisfactory determinations of oxygen consumption by thismethod would be impossible. Furthermore, from our previous experiencewith long-continued experiments of from 10 days to 2 weeks, it has beenfound that oxygen can be supplied to the system readily and the amountthus supplied determined accurately. Consequently, even in these shortexperiments, we adhere to the original practice of supplying oxygen tothe air and noting the amount thus added. 

The oxygen supply was formerly obtained from small steel cylinders ofthe highly compressed gas. This gas was made by the calcium-manganatemethod and represented a high degree of purity for commercial oxygen. More recently we have been using oxygen of great purity made from liquidair. Inasmuch as this oxygen is very pure and much less expensive thanthe chemically-prepared oxygen, extensive provisions have been made forits continued use. Instead of using small cylinders containing 10 cubicfeet and attaching thereto purifying devices in the shape of soda-limeU-tubes and a sulphuric-acid drying-tube, we now use large cylinders andwe have found that the oxygen from liquid air is practically free fromcarbon dioxide and water-vapor, the quantities present being whollynegligible in experiments such as these. Consequently, no purifyingattachments are considered necessary and the oxygen is delivereddirectly from the cylinder. The cylinders, containing 100 cubic feet(2, 830 liters), under a pressure of 120 atmospheres, are provided withwell-closing valves and weigh when fully charged 57 kilograms. 

[Illustration: FIG. 31. --Diagram of oxygen balance and cylinder. At thetop is the balance arrangement, and at the center its support. At theleft is the oxygen cylinder, with reducing valve A, rubber tube Dleading from it, F the electro-magnet which opens and closes D, K thehanger of the cylinder and support for the magnet, R the lever whichoperates the supports for the cylinder and its counterpoise S, T' a boxwhich is raised and lowered by R, and T its surrounding box. ]

It is highly desirable to determine the oxygen to within 0. 1 gram, andwe are fortunate in having a balance of the type used frequently in thislaboratory which will enable us to weigh this cylinder accurately with asensitiveness of less than 0. 1 gram. Since 1 liter of oxygen weighs 1. 43grams, it can be seen that the amount of oxygen introduced into thechamber can be measured by this method within 70 cubic centimeters. Even in experiments of but an hour's duration, where the amount ofoxygen admitted from the cylinder is but 25 to 30 grams, it can be seenthat the error in the weighing of the oxygen is much less than 1 percent. 

The earlier forms of cylinders used were provided with valves whichrequired some special control and a rubber bag was attached to providefor any sudden rush of gas. The construction of the valve and valve-stemwas unfortunately such that the well-known reduction valves could not beattached without leakage under the high pressure of 120 atmospheres. With the type of cylinder at present in use, such leakage does not occurand therefore we simply attach to the oxygen cylinder a reduction-valvewhich reduces the pressure from 120 atmospheres to about 2 or 3 poundsto the square inch. The cylinder, together with the reduction valve, issuspended on one arm of the balance. The equipment of the arrangement isshown in fig. 31. (See also fig. 5, page 4. ) The cylinder is supportedby a clamp K hung from the balance arm, and the reduction-valve A isshown at the top. The counterpoise S consists of a piece of 7-inch pipe, with caps at each end. At a convenient height a wooden shelf withslightly raised rim is attached. 

In spite of the rigid construction of this balance, it would bedetrimental to allow this enormous weight to remain on the knife-edgespermanently, so provision is made for raising the cylinders on a smallelevator arrangement which consists of small boxes of wood, T, intowhich telescope other boxes, T'. A lever handle, R, when pressedforward, raises T' by means of a roller bearing U, and when the handleis raised the total weight of the cylinders is supported on theplatforms. 

The balance is attached to an upright I-beam which is anchored to thefloor and ceiling of the calorimeter laboratory. Two large turnbuckleeye-bolts give still greater rigidity at the bottom. The whole apparatusis inclosed in a glass case, shown in fig. 5. 

AUTOMATIC CONTROL OF OXYGEN SUPPLY. 

The use of the reduction-valve has made the automatic control of theoxygen supply much simpler than in the apparatus formerly used. Thedetails of the connections somewhat schematically outlined are given infig. 32, in which D is the oxygen cylinder, K the supporting band, A thereduction-valve, and J the tension-equalizer attached to one of thecalorimeters. Having reduced the pressure to about 2 pounds by means ofthe reduction-valve, the supply of oxygen can be shut off by putting apinch-cock on a rubber pipe leading from the reduction-valve to thecalorimeters. Instead of using the ordinary screw pinch-cock, thisconnection is closed by a spring clamp. The spring E draws on the rodwhich is connected at L and pinches the rubber tube tightly. The tensionat E can be released by an electro-magnet F, which when magnetizedexercises a pull on the iron rod, extends the spring E, andsimultaneously releases the pressure on the rubber tube at L. To makethe control perfectly automatic, the apparatus shown on the top of thetension-equalizer J is employed. A wire ring, with a wire support, iscaused to pass up through a bearing fastened to the clamp above J. Asthe air inside of the whole system becomes diminished in volume and therubber cap J sinks, there is a point at which a metal loop dips into twomercury cups C and C', thus closing the circuit, which causes a currentof electricity to pass through F. This releases the pressure at L, oxygen rushes in, and the rubber bag J becomes distended. As it isdistended, it lifts the metal loop out of the cups, C and C', and thecircuit is broken. There is, therefore, an alternate opening and closingof this circuit with a corresponding admission of oxygen. The exactposition of the rubber diaphragm can be read when desired from a pointeron a graduated scale attached to a support holding the terminals of theelectric wires. More frequently, however, when the volume is required, instead of filling the bag to a definite point, as shown by thepointer, a delicate manometer is attached to the can by means of apet-cock and the oxygen is admitted by operating the switch B until thedesired tension is reached. 

[Illustration: FIG. 32. --Part of the oxygen cylinder and connections totension-equalizer. At the left is shown the upper half of the oxygencylinder with a detail of the electro-magnet and reducing-valve. D isthe cylinder; K, the band supporting the oxygen cylinder andelectro-magnet arrangement; F, the electro-magnet; E, the tensionspring; and L, the rubber tubing at a point where it is closed by theclamp. The tension-equalizer and the method of closing the circuitoperating it are shown at the right. C and C' are two mercury cups intowhich the wire loop dips, thus closing the circuit. B is a lever usedfor short-circuiting for filling the diaphragm J. G is a sulphuric-acidcontainer; H, the quick-throw valve for shutting off the tensionequalizer J; M, part of the ingoing air-pipe; N, a plug connecting theelectric circuit with the electro-magnet; and O, a storage battery. ]

In order to provide for the maximum sensitiveness for weighing D and itsappurtenances, the electric connection is broken at the cylinder bymeans of the plug N and the rubber tube is connected by a glassconnector which can be disconnected during the process of weighing. Obviously, provision is also made that there be no leakage of air out ofthe system during the weighing. The current at F is obtained by means ofa storage battery O. The apparatus has been in use for some time in thelaboratory and has proved successful in the highest degree. 

TENSION-EQUALIZER. 

The rigid walls of the calorimeter and piping necessitate some provisionfor minor fluctuations in the absolute volume of air in the confinedsystem. The apparatus was not constructed to withstand greatfluctuations in pressure, and thin walls were used, but it is deemedinadvisable to submit it even to minor pressures, as thus there would bedanger of leakage of air through any possible small opening. Furthermore, as the carbon dioxide and water-vapor are absorbed out ofthe air-current, there is a constant decrease in volume, which isordinarily compensated by the admission of oxygen. It would be verydifficult to adjust the admission of oxygen so as to exactly compensatefor the contraction in volume caused by the absorption of water-vaporand carbon dioxide. Consequently it is necessary to adjust some portionof the circulating air-current so that there may be a contraction andexpansion in the volume without producing a pressure on the system. Thiswas done in a manner similar to that described in the earlier apparatus, but on a much simpler plan. 

To the air-pipe just before it entered the calorimeter was attached acopper can with a rubber diaphragm top. This diaphragm, which is, as amatter of fact, a ladies' pure rubber bathing-cap, allows for anexpansion or contraction of air in the system of 2 to 3 liters. Theapparatus shown in position is to be seen in fig. 25, in which the tincan I is covered with the rubber diaphragm J. If there is any change involume, therefore, the rubber diaphragm rises or falls with it and underordinary conditions of an experiment this arrangement results in apressure in the chamber approximately that of the atmosphere. It wasfound, however, that even the slight resistance of the piping from thetension-equalizer to the chamber, a pipe some 26 millimeters in diameterand 60 centimeters long, was sufficient to cause a slightly diminishedpressure inside the calorimeter, inasmuch as the air was sucked out bythe blower with a little greater speed than it was forced in by thepressure at the diaphragm. Accordingly the apparatus has been modifiedso that at present the tension-equalizer is attached directly to thewall of the calorimeter independent of the air-pipe. 

In most of the experiments made thus far it has been our custom toconduct the supply of fresh oxygen through pet-cock K on the side of thetension-equalizer. This is shown more in detail in fig. 32, in which, also, is shown the interior construction of the can. Owing to the factthat the air inside of this can is much dryer than the room air, we havefollowed the custom with the earlier apparatus of placing a vesselcontaining sulphuric acid inside the tension-equalizer, so that anymoisture absorbed by the dry air inside the diaphragm may be taken up bythe acid and not be carried into the chamber. The air passing throughthe pipe to the calorimeter is, it must be remembered, absolutely dryand hence there are the best conditions for the passage of moisture fromthe outside air through the diaphragm to this dry air. Attaching thetension-equalizer directly to the calorimeter obviates the necessity forthis drying process and hence the sulphuric-acid vessel has beendiscarded. 

The valve H (fig. 25) is used to cut off the tension-equalizercompletely from the rest of the system at the exact moment of the end ofthe experimental period. After the motor has been stopped and the slightamount of air partly compressed in the blower has leaked back into thesystem, and the whole system is momentarily at equal tension, a processoccupying some 3 or 4 seconds, the gate-valve H is closed. Oxygen isthen admitted from the pet-cock K until there is a definite volume in Jas measured by the height to which the diaphragm can rise or a secondpet-cock is connected to the can I and a delicate petroleum manometerattached in such a manner that the diaphragm can be filled to exactlythe same tension each time. Under these conditions, therefore, the apparent volume of air in the system, exclusive of thetension-equalizer, is always the same, since it is confined by the rigidwalls of the calorimeter and the piping. Furthermore, the apparentvolume of air in the tension-equalizer is arbitrarily adjusted to be thesame amount at the end of each period by closing the valve andintroducing oxygen until the tension is the same. 

BAROMETER. 

Recognizing the importance of measuring very accurately the barometricpressure, or at least its fluctuations, we have installed an accuratebarometer of the Fortin type, made by Henry J. Green. This is attachedto the inner wall of the calorimeter laboratory, and since thecalorimeter laboratory is held at a constant temperature, temperaturecorrections are unnecessary, for we have here to deal not so much withthe accurate measurement of the actual pressure as with the accuratemeasurement of differences in pressure. For convenience in reading, theivory needle at the base of the instrument and the meniscus are wellilluminated with electric lamps behind a white screen, and a small lampilluminates the vernier. The barometer can be read to 0. 05 millimeter. 

ANALYSIS OF RESIDUAL AIR. 

The carbon-dioxide production, water-vapor elimination, and oxygenabsorption of the subject during 1 or 2 hour periods are recorded in ageneral way by the amounts of carbon dioxide and water-vapor absorbed bythe purifying vessels and the loss of weight of the oxygen cylinder;but, as a matter of fact, there may be considerable fluctuations in theamounts of carbon dioxide and water-vapor and particularly oxygen in thelarge volume of residual air inside the chamber. With carbon dioxide andwater-vapor this is not as noticeable as with oxygen, for in the 1, 300liters of air in the chamber there are some 250 liters of oxygen, andslight changes in the composition of this air indicate considerablechanges in the amount of oxygen. Great changes may also take place inthe amounts of carbon dioxide and water-vapor under certain conditions. In some experiments, particularly where there are variations in muscularactivity from period to period, there may be a considerable amount ofcarbon dioxide in the residual air and during the next period, when themuscular activity is decreased, for example, the percentage compositionof the air may vary so much as to indicate a distinct fall in the amountof carbon dioxide present. Under ordinary conditions of ventilationduring rest experiments the quantity of carbon dioxide present in theresidual air is not far from 8 to 10 grams. There are usually present inthe air not far from 6 to 9 grams of water-vapor, and hence thisresidual amount can undergo considerable fluctuations. When it isconsidered that an attempt is made to measure the total amount of carbondioxide expired in one hour to the fraction of a gram, it is obviousthat fluctuations in the composition of residual air must be taken intoconsideration. 

It is extremely difficult to get a fair sample of air from the chamber. The air entering the chamber is free from water-vapor and carbondioxide. In the immediate vicinity of the entering air-tube there is airwhich has a much lower percentage of carbon dioxide and water-vapor thanthe average, and on the other hand close to the nose and mouth of thesubject there is air of a much higher percentage of carbon dioxide andwater-vapor than the average. It has been assumed that the compositionof the air leaving the chamber represents the average composition of theair in the chamber. This assumption is only in part true, but in restexperiments (and by far the largest number of experiments are restexperiments) the changes in the composition of the residual air are soslow and so small that this assumption is safe for all practicalpurposes. 

Another difficulty presents itself in the matter of determining theamount of carbon dioxide and water-vapor; that is, to make asatisfactory analysis of air without withdrawing too great a volume fromthe chamber. The difficulty in analysis is almost wholly confined to thedetermination of water-vapor, for while there are a large number ofmethods for determining small amounts of carbon dioxide with greataccuracy, the method for determining water-vapor to be accurate callsfor the use of rather large quantities of air. From preliminaryexperiments with a sling psychrometer it was found that its use wasprecluded by the space required to successfully use this instrument, theaddition of an unknown amount of water to the chamber from the wet bulb, and the difficulties of reading the instrument from without the chamber. Recourse was had to the determination of moisture by the absolutemethod, in that a definite amount of air is caused to pass overpumice-stone saturated with sulphuric acid. It is of interest here torecord that at the moment of writing a series of experiments are inprogress in which an attempt is being made to use a hair hygrometer forthis purpose. 

The method of determining the water-vapor and carbon dioxide in theresidual air is extremely simple, in that a definite volume of air iscaused to pass over sulphuric acid and soda-lime contained in U-tubes. In other words, a small amount of air is caused to pass through a smallabsorbing-system constructed of U-tubes rather than of porcelain vesselsand silver-plated cans. Formerly a very elaborate apparatus was employedfor aspirating the air from the chamber through U-tubes and thenreturning the aspirated air to the chamber. This involved the use of asuction-pump and called for a special installation for maintaining thepressure of water constant. More recently a much simpler device has beenemployed, in that we have taken advantage of the pressure in theventilating air-system developed by the passage of air through theblower. After forcing a definite quantity of air through the reagents inthe U-tubes, it is then conducted back to the system after having beenmeasured in a gas-meter. 

This procedure is best noted from fig. 30. The connected series of threeU-tubes on the rack on the table is joined on one end by well-fittingrubber connections to the tube leading from the mercurial manometer andon the other end to the rubber tube A leading to the gas-meter. Onlowering the mercury reservoir E, the mercury is drained out of the tubeD and air passes through both arms of the tube and then through thethree U-tubes. In the first of these it is deprived of moisture, and inthe last two of carbon dioxide. The air then enters the meter, where itis measured and leaves the meter through the tube B, saturated withwater-vapor at the room temperature. To remove this water-vapor the airis passed through a tower filled with pumice-stone drenched withsulphuric acid. It leaves the tower through the tube C and enters theventilating air-pipe on its way to the calorimeter. 

The method of manipulation is very simple. After connecting the U-tubesthe pet-cock connecting the tube C with the pipe is opened, the mercuryreservoir E is lowered, and air is allowed to pass through until themeter registers 10 liters. By raising the reservoir E the air supply isshut off, and after closing the stop-cock at C the tubes aredisconnected, a second set is put in place, and the operation repeated. The U-tubes are of a size having a total length of the glass portionequal to 270 millimeters and an internal diameter of 16 millimeters. They permit the passage of 3 liters of air per minute through themwithout a noticeable escape of water-vapor or carbon dioxide. TheU-tubes filled with pumice-stone and sulphuric acid weigh 90 grams. Theyare always weighed on the balance with a counterpoise, but no attempt ismade to weigh them closer than to 0. 5 milligram. 

GAS-METER. 

The gas-meter is made by the Dansk Maalerfabrik in Copenhagen, and is ofthe type used by Bohr in many of his investigations. It has theadvantage of showing the water-level, and the volume may be readdirectly. The dial is graduated so as to be read within 50 cubiccentimeters. 

The Elster meter formerly used for this purpose was much smaller thanthe meter of the Dansk Maalerfabrik we are now using. The volume ofwater was much smaller and consequently the temperature fluctuationsmuch more rapid. While the residual analyses for which the meter is usedare of value in interpolating the results for the long experiments, andconsequently errors in the meter would be more or less constant, affecting all results alike, we have nevertheless carefully calibratedthe meter by means of the method of admitting oxygen from a weighedcylinder. [23] The test showed that the meter measured 1. 4 per cent toomuch, and consequently this correction must be applied to allmeasurements made with it. 

CALCULATION OF RESULTS. 

With an apparatus as elaborate as is the respiration calorimeter and itsaccessories, the calculation of results presents many difficulties, butthe experience of the past few years has enabled us to lessen materiallythe intricacies of the calculations formerly thought necessary. 

The total amount of water-vapor leaving the chamber is determined bynoting the increase in weight of the first sulphuric-acid vessel in theabsorber system. This vessel is weighed with a counterpoise and henceonly the increment in weight is recorded. A slight correction may benecessary here, as frequently the absorber is considerably warmer at theend of the period than at the beginning and if weighed while warm theremay be an error of 0. 1 to 0. 2 gram. If the absorbers are weighed at thesame temperature at the beginning and end, this correction is avoided. 

The amount of carbon dioxide absorbed from the ventilating air-currentis found by noting the changes in weight of the potash-lime can and thelast sulphuric-acid vessel. As shown by the weights of this lattervessel, it is very rare that sufficient water is carried over from thepotash-lime to the sulphuric acid to cause a perceptible change intemperature, and no temperature corrections are necessary. It mayoccasionally happen that the amount of carbon dioxide absorbed isactually somewhat less than the amount of water-vapor abstracted fromthe reagent by the dry air-current as it passes through the can. Theconditions will then be such that there will be a loss in weight of thepotash-lime can and a large gain in weight of the sulphuric-acid vessel. Obviously, the algebraic sum of these amounts will give the true weightof the carbon dioxide absorbed. 

The amount of oxygen admitted is approximately measured by noting theloss in weight of the oxygen cylinder. Since, however, in admitting theoxygen from the cylinder there is a simultaneous admission of a smallamount of nitrogen, a correction is necessary. This correction can becomputed either by the elaborate formulas described in the publicationof Atwater and Benedict[24] or by the more abbreviated method ofcalculation which has been used very successfully in all shortexperiments in this laboratory. In either case it is necessary to knowthe approximate percentage of nitrogen in the oxygen. 

ANALYSIS OF OXYGEN. 

With the modified method of computation discussed in detail on page 88it is seen that such exceedingly exact analyses of oxygen as wereformerly made are unnecessary, and further calculation is consequentlyvery simple if we know the percentage of nitrogen to within a fractionof 1 per cent. We have used a Haldane gas-analysis apparatus foranalyzing the oxygen, although the construction of the apparatus is suchthat this presents some little difficulty. It is necessary, forexample, to accurately measure about 16 cubic centimeters of purenitrogen, pass it into the potassium pyrogallate pipette, and then(having taken a definite sample of oxygen) gradually absorb the oxygenin the potassium pyrogallate and measure subsequently the accumulatednitrogen. The analysis is tedious and not particularly satisfactory. Having checked the manufacturer's analysis of a number of cylinders ofoxygen and invariably found them to agree with our results, we are atpresent using the manufacturer's guaranteed analysis. If there was avery considerable error in the gas analysis, amounting even to 1 percent, the results during short experiments would hardly be affected. 

ADVANTAGE OF A CONSTANT-TEMPERATURE ROOM AND TEMPERATURE CONTROL. 

A careful inspection of the elaborate method of calculation required foruse with the calorimeter formerly at Wesleyan University shows that alarge proportion of it can be eliminated owing to the fact that we arehere able to work in a room of constant temperature. It has been pointedout that the fluctuations in the temperature of the gas-meter affect notonly the volume of the gas passing through the meter, but likewise thetension of aqueous vapor. The corrections formerly made for temperatureon the barometer are now unnecessary; finally (and perhaps still moreimportant) it is no longer necessary to subdivide the volume of thesystem into portions of air existing under different temperatures, depending upon whether they were in the upper or lower part of thelaboratory. In other words, the temperature of the whole ventilatingcircuit and chamber, with the single exception of the air above the acidin the first sulphuric-acid absorber, may be said to be constant. Duringrest experiments this assumption can be made without introducing anymaterial error, but during work experiments it is highly probable thatsome consideration must be given to the possibility of the developmentof a considerable temperature rise in the air of the potash-limeabsorbers, due to the reaction between the carbon dioxide and the solidabsorbent. It is thus apparent that the constant-temperature conditionsmaintained in the calorimeter laboratory not only facilitatecalorimetric measurements, but also simplify considerably the elaboratecalculations of the respiratory exchange formerly required. 

VARIATIONS IN THE APPARENT VOLUME OF AIR. 

In the earlier form of apparatus the largest variation in the apparentvolume of air was due to the fluctuations in the height of the largerubber diaphragms used on the tension equalizer. In the present form ofapparatus there is but one rubber diaphragm, and this is small, containing not more than 3 to 4 liters as compared to about 30 liters inthe earlier double rubber diaphragms. As now arranged, all fluctuationsdue to the varying positions of the tension-equalizer are eliminated aseach experimental period is ended with the diaphragm in exactly the sameposition, _i. E. _, filled to a definite tension. 

In its passage through the purifiers the air is subjected to more orless pressure, and it is obvious that if these absorbers were coupled tothe ventilating system under atmospheric pressure, and then air causedto pass through them, there would be compression in a portion of thepurifier system. Thus there would be a contraction in the volume, andair thus compressed would subsequently be released into the open airwhen the absorbers were uncoupled. The method of testing the systemoutlined on page 100 equalizes this error, however, in that the systemis tested under the same pressure used during an actual experiment, andhence between the surface of the sulphuric acid in the first porcelainvessel and the sulphuric acid in the second porcelain vessel there is aconfined volume of air which at the beginning of an experimental periodis under identically the same pressure as it is at the end. There is, then, no correction necessary for the rejection of air with the changesin the absorber system. 

CHANGES IN VOLUME DUE TO THE ABSORPTION OF WATER AND CARBON DIOXIDE. 

As the water-vapor is absorbed by the sulphuric acid, there is a slightincrease in volume of the acid. This naturally results in the diminutionof the apparent volume of air and likewise again affects the amount ofoxygen admitted to produce constant apparent volume at the end of eachexperimental period. The amount of increase which thus takes place foreach experimental period is very small. It has been found that anincrease in weight of 25 grams of water-vapor results in an increase involume of the acid of some 15 cubic centimeters. Formerly thiscorrection was made, but it is now deemed unnecessary and unwise tointroduce a refinement that is hardly justified in other parts of theapparatus. Similarly, there is theoretically at least an increase involume of the potash-lime by reason of the absorption of the carbondioxide. This was formerly taken into consideration, but the correctionis no longer applied. 

RESPIRATORY LOSS. 

With experiments on man, there is a constant transformation of solidbody material into gaseous products which are carried out into theair-current and absorbed. Particularly where no food is taken, thissolid material becomes smaller in volume and consequently additionaloxygen is required to take the place of the decrease in volume of bodysubstance. But this so-called respiratory loss is more theoretical thanpractical in importance, and in the experiments made at present thecorrection is not considered necessary. 

CALCULATION OF THE VOLUME OF AIR RESIDUAL IN THE CHAMBER. 

The ventilating air-circuit may be said to consist of several portionsof air. The largest portion is that in the respiration chamber itselfand consists of air containing oxygen, nitrogen, carbon dioxide, andwater-vapor. This air is assumed to have the same composition up to themoment when it begins to bubble through the sulphuric acid in the firstacid-absorber. The air in this absorber above the acid, amounting toabout 14 liters, has a different composition in that the water-vapor hasbeen completely removed. The same 14 liters of air may then be said tocontain carbon dioxide, nitrogen, and oxygen. This composition isimmediately disturbed the moment the air enters the potash-lime can, when the carbon dioxide is absorbed and the volume of air in the lastsulphuric-acid absorber, in the sodium-bicarbonate can, and in thepiping back to the calorimeter may be said to consist only of nitrogenand oxygen. The air then between the surface of the sulphuric acid inthe last porcelain absorber and the point where the ingoing air isdelivered to the calorimeter consists of air free from carbon dioxideand free from water. Formerly this section also included thetension-equalizer, but very recently we have in both of the calorimetersattached the tension-equalizer directly to the respiration chamber. 

In the Middletown apparatus, these portions of air of varyingcomposition were likewise subject to considerable variations intemperature, in that the temperature of the laboratory often differedmaterially from that of the calorimeter chamber itself, especially asregards the apparatus in the upper part of the laboratory room. It isimportant, however, to know the total volume of the air inclosed in thewhole system. This is obtained by direct measurement. The cubic contentsof the calorimeter has been carefully measured and computed; the volumesof air in the pipes, valve systems, absorbing vessels, andtension-equalizer have been computed from dimensions, and it has beenfound that the total volume in the apparatus is, deducting the volume ofthe permanent fixtures in the calorimeter, 1, 347 liters. Thecorresponding volume for the bed calorimeter is 875. These values arealtered by the subject and extra articles taken into the chamber. 

From a series of careful measurements and special tests the followingapparent volumes for different parts of the system have been calculated:

 Liters. Volume of the chair calorimeter chamber (without fixtures) 1360. 0Permanent fixtures (5); chair and supports (8) 13. 0 ------ Apparent volume of air inside chamber 1347. 0Air in pipes, blower, and valves to surface of acid in first acid vessel 4. 5 ------ Apparent volume of air containing water-vapor 1351. 5Air above surface of acid in first sulphuric-acid vessel and potash-lime can 16. 0 ------ Apparent volume of air containing carbon dioxide 1367. 5Air in potash-lime can, second sulphuric-acid vessel and connections, sodium-bicarbonate cans, and pipes to calorimeter chamber 23. 5 ------ Apparent volume of air containing carbon dioxide, water, oxygen, and nitrogen 1391. 0

These volumes represent conditions existing inside the chamber withoutthe subject, _i. E. _, conditions under which an alcohol check-test wouldbe conducted. In an experiment with man it would be necessary to deductthe volume of the man, books, urine bottles, and all supplementalapparatus and accessories. Under these circumstances the apparent volumeof the air in the chamber may at times be diminished by nearly 90 to 100liters. At the beginning of each experiment the apparent volume of airis calculated. 

RESIDUAL ANALYSES. 

CALCULATION FROM RESIDUAL ANALYSES. 

The increment in weight of the absorbers for water and carbon dioxideand the loss in weight of the oxygen cylinder give only an approximateidea of the amounts of carbon dioxide and water-vapor produced andoxygen absorbed during the period, and it is necessary to makecorrection for change in the composition of the air as shown by theresidual analyses and for fluctuations in the actual volume. In order tocompute from the analyses the total carbon-dioxide content of theresidual air, it is necessary to know the relation of the air used forthe sample to the total volume, and thus we must know accurately thevolume of air passing through the gas-meter. 

In the earlier apparatus 10-liter samples were used, and the volume ofthe respiration chamber was so large that it was necessary to multiplythe values found in the residual sample by a very large factor, 500. Hence, the utmost caution was taken to procure an accurate measurementof the sample, the exact amounts of carbon dioxide absorbed, andwater-vapor absorbed. To this end a large number of corrections weremade, which are not necessary with the present type of apparatus with avolume of residual air of but about 1, 300 liters, and accordingly themanipulation and calculations have been very greatly simplified. 

While formerly pains were taken to obtain the exact temperature of theair leaving the gas-meter, with this apparatus it is unnecessary. Whenthe earlier type of apparatus was in use there were marked changes inthe temperature of the calorimeter laboratory and in the water in themeter which were naturally prejudicial to the accurate measurement ofthe volume of samples, but with the present control of temperature inthis laboratory it has been found by repeated tests that the temperatureof the water in the meter does not vary a sufficient amount to justifythis painstaking measurement and calculation. Obviously, thisobservation also pertains to the corrections for the tension of aqueousvapor. It has been found possible to assume an average laboratorytemperature and reduce the volume as read on the meter by means of aconstant factor. 

The quantity of air passing through the meter is so adjusted thatexactly 10 liters as measured on the dial pass through it for oneanalysis. The air as measured in the meter is, however, under markedlydifferent conditions from the air inside the respiration chamber. Whilethere is the same temperature, there is a material difference in thewater-vapor present, and hence the moisture content as expressed interms of tension of aqueous vapor must be considered. This obviouslytends to diminish the true volume of air in the meter. 

Formerly we made accurate correction for the tension of aqueous vaporbased upon the barometer and the temperature of the meter at the end ofthe period, but it has now been found that the reduction of the meterreadings to conditions inside of the chamber can be made with asufficient degree of accuracy by multiplying the volume of air passingthrough the meter by a fraction, _(h-t)/h_, in which _h_ represents thebarometer and _t_ the tension of aqueous vapor at the temperature of thelaboratory, 20° C. Since the tension of aqueous vapor at the laboratorytemperature is not far from 15 mm. , a simple calculation will show thatthere may be considerable variations in the value of _h_ withoutaffecting the fraction materially, and we have accordingly assumed avalue of _h_ as normally 760 mm. , and the correction thus obtained is(760 - 15)/760 = 0. 98, and all readings on the meter should bemultiplied by this fraction. 

On the one hand, then, there is the correction on the meter itself, which correction is +1. 4 per cent (see page 75); and on the other handthe correction on the sample for the tension of aqueous vapor, which is-2. 0 per cent, and consequently the resultant correction is -0. 6 percent. From the conditions under which the experiments are made, however, it is rarely possible to read the meter closer than ±0. 05 liter, as thegraduations on the meter correspond to 50 cubic centimeters. It will beseen, then, that this final correction is really inside the limit oferror of the instrument, and consequently with this particular meter nowin use no correction whatever is necessary for the reduction of thevolume. The matter of temperature corrections has been taken up in greatdetail in an earlier publication, and where there are noticeabledifferences in temperature between the meter and the calorimeter chamberthe calculation is very much more complicated. 

For practical purposes, therefore, we may assume that the quantity ofair passed through the meter, as now in use, represents exactly 10liters measured under the conditions obtaining inside of the respirationchamber, and in order to find the total amount of water-vapor present inthe chamber it is necessary only to multiply the weight of water foundin the 10-liter sample by one-tenth of the total volume of aircontaining water-vapor. 

The total volume of air which contains water-vapor is not far from 1, 360liters; consequently multiplying the weight of water in the sample by136 gives the total amount of water in the chamber and the piping. Thevolume of air containing carbon dioxide is that contained in the chamberand piping to the first sulphuric-acid vessel plus 16 liters of airabove the sulphuric acid and connections in the first porcelain vessel, and in order to obtain the amount of carbon dioxide from the sample itis only necessary to multiply the weight of carbon dioxide in the sampleby 137. 6. 

Since in the calculation of the total amount of residual oxygen volumesrather than weights of gases are used, it is our custom to convert theweights of carbon dioxide and water-vapor in the chamber to volumes bymultiplying by the well-known factors. The determination of oxygendepends upon the knowledge of the true rather than the apparent volumeof air in the system, and consequently the apparent volume must bereduced to standard conditions of temperature and pressure each time thecalculation is made. To this end, the total volume of air in theinclosed circuit (including that in the tension-equalizer, amounting to1, 400 liters in all) is reduced to 0° and 760 millimeters by the usualmethods of computation. The total volume of air (which may be designatedas _V_) includes the volumes of carbon dioxide, water-vapor, oxygen, andnitrogen. From the calculations mentioned above, the volumes ofwater-vapor and carbon dioxide have been computed, and deducting the sumof these from the reduced volume of air gives the volume of oxygen plusnitrogen. If the volume of nitrogen is known, obviously the volume ofoxygen can be found. 

At the beginning of the experiment, it is assumed that the chamber isfilled with ordinary air. By calculating the amount of nitrogen in thechamber at the start as four-fifths of the total amount, no great erroris introduced. In many experiments actual analyses of the air have beenmade at the moment of the beginning of the experiment. The importantthing to bear in mind is that having once sealed the chamber and closedit tightly, no nitrogen can enter other than that admitted with theoxygen, and hence the residual amount of nitrogen remains unaltered savefor this single exception. If care is taken to keep an accurate recordof the amount of nitrogen admitted with the oxygen, the nitrogenresidual in the chamber at any given time is readily computed. Whilefrom an absolute mathematical standpoint the accuracy of thiscomputation can be questioned, here again we are seeking an accuraterecord of differences rather than an absolute amount, and whether weassume the volume of the air in the chamber to contain 20. 4 per cent ofoxygen or 21. 6 per cent is a matter of indifference. It is of importanceonly to note the increases in the amount of nitrogen, since theseincreases represent decrease in the residual oxygen and it is with thechanges in the residual oxygen that we particularly have to do. 

INFLUENCE OF FLUCTUATIONS IN TEMPERATURE AND PRESSURE ON THE APPARENTVOLUME OF AIR IN THE SYSTEM. 

The air, being confined in a space with semi-rigid walls, is subjectednaturally to variations in true volume, depending upon the temperatureand barometric pressure. If the air inside of the chamber becomesconsiderably warmer there is naturally an expansion, and were it not forthe tension-equalizer there would be pressure in the system. Also, ifthe barometer falls, there is an expansion of air which, again, in theabsence of the tension-equalizer, would produce pressure in the system. It is necessary, therefore, in calculating the true volume of air, totake into account not only the apparent volume, which, as is shownabove, is always a constant amount at the end of each period, but thechanges in temperature and barometric pressure must also be noted. Sincethere is a volume of about 1, 400 liters, a simple calculation will showthat for each degree centigrade change in temperature there will be achange in volume of approximately 4. 8 liters. In actual practice, however, this rarely occurs, as the temperature control is usuallyinside of 0. 1° C. And for the most part within a few hundredths. Avariation in barometric pressure of 1 millimeter will affect 1, 400liters by 1. 8 liters. 

In actual practice, therefore, it is seen that if the barometer fallsthere will be an expansion of air in the system. This will tend toincrease the volume by raising the rubber diaphragm on thetension-equalizer, the ultimate result of which is that at the finalfilling with oxygen at the end of the period less is used than would bethe case had there been no change in the barometer. In other words, foreach liter expansion of air inside of the system, there is 1 liter lessoxygen required to bring the apparent volume the same at the end of theperiod. Similarly, if there is an increase in temperature of the air, there is expansion, and a smaller amount of oxygen is required thanwould be the case had there been no change; and conversely, if thebarometer rises or the temperature falls, more oxygen would be suppliedthan is needed for consumption. It is thus seen that the temperature andbarometer changes affect the quantity of oxygen admitted to the chamber. 

INFLUENCE OF FLUCTUATIONS IN THE AMOUNTS OF CARBON DIOXIDE ANDWATER-VAPOR UPON RESIDUAL OXYGEN. 

Any variations in the residual amount of carbon dioxide or water-vaporlikewise affect the oxygen. Thus, if there is an increase of 1 gram inthe amount of residual carbon dioxide, this corresponds to 0. 51 liter, and consequently an equal volume of oxygen is not admitted to thechamber during the period, since its place has been taken by theincreased volume of carbon dioxide. A similar reasoning will show thatincrease in the water-vapor content will have a similar effect, for eachgram of water-vapor corresponds to 1. 25 liters and therefore influencesmarkedly the introduction of oxygen. All four of the factors, therefore(barometric pressure, temperature, residual carbon dioxide, and residualwater-vapor), affect noticeably the oxygen determination. 

CONTROL OF RESIDUAL ANALYSES. 

Of the three factors to be determined in the residual air, the oxygen(which is most important from the standpoint of the relative weight tobe placed upon the analysis) unfortunately can not be directlydetermined without great difficulty. Furthermore, any errors in theanalysis may be very greatly multiplied by the known errors involved inthe determination of the true volume of the air in the chamber as aresult of the difficulties in obtaining the average temperature of theair. Believing that the method of analysis as outlined above should becontrolled as far as possible by other independent methods, we were ableto compare the carbon dioxide as determined by the soda-lime method withthat obtained by the extremely accurate method used by Sondén andPettersson. An apparatus for the determination of carbon dioxide andoxygen on the Pettersson principle has been devised by Sondén andconstructed for us by Grave, of Stockholm. 

In the control experiments, the air leaving the mercury valve D (fig. 30, page 66) was caused to pass through a T-tube, one arm of whichconnected directly with the sampling pipette of the Sondén gas-analysisapparatus, the other arm connecting with the U-tubes for residualanalyses. By lowering and raising the mercury reservoir on thegas-analysis apparatus, a sample of air could be drawn into theapparatus for analysis. The results of the analysis were expressed onthe basis of moist air in volume per cents rather than by weight, as isdone with the soda-lime method. Hence in comparison it was necessary toconvert the weights to volume, and during this process the errors due tonot correcting for temperature and barometer are made manifest. However, the important point to be noted is that whatever fluctuations incomposition of the residual air were noted by the soda-lime method, similar fluctuations of a corresponding size were recorded by thevolumetric analysis with the Sondén apparatus. Under these conditions, therefore, we believe that the gravimetric method outlined above issufficiently satisfactory, so far as the carbon-dioxide content isconcerned, for ordinary work where there are no wide variations in thecomposition of the air from period to period. 

NITROGEN ADMITTED WITH THE OXYGEN. 

It is impossible to obtain in the market absolutely chemically pureoxygen. All the oxygen that we have thus far been able to purchasecontains nitrogen and, in some instances, measurable amounts ofwater-vapor and carbon dioxide. The better grade of oxygen, thatprepared from liquid air, is practically free from carbon dioxide andwater-vapor, but it still contains nitrogen, and hence with every literof oxygen admitted there is a slight amount of nitrogen added. Thisamount can readily be found from the gasometric analysis of the oxygenand from the well-known relation between the weight and the volume ofnitrogen the weight can be accurately found. This addition of nitrogenplayed a very important rôle in the calculation of the oxygenconsumption as formerly employed. As is seen later, a much abbreviatedform of calculation is now in use in which the nitrogen admitted withthe oxygen does not influence the calculation of the residual oxygen. 

REJECTION OF AIR. 

In long-continued experiments, where there is a possibility of anoticeable diminution in the percentage of oxygen in the chamber--adiminution caused either by a marked fall in barometer, which expandsthe air inside of the chamber and permits admission of less oxygen thanwould otherwise be required, or by the use of oxygen containing a highpercentage of nitrogen, thus continually increasing the amount ofnitrogen present in the system--it is highly probable that there may besuch an accumulation of nitrogen as to render it advisable to providefor the admission of a large amount of oxygen to restore the air toapproximately normal conditions. In rest experiments of short durationthis is never necessary. The procedure by which such a restoration ofoxygen percentage is accomplished has already been discussedelsewhere. [25] It involves the rejection of a definite amount of air byallowing it to pass into the room through the gas-meter and then makingproper corrections for the composition of this air, deducting the volumeof oxygen in it from the excess volume of oxygen introduced andcorrecting the nitrogen residual in order to determine the oxygenabsorption during the period in which the air has been rejected. 

INTERCHANGE OF AIR IN THE FOOD-APERTURE. 

The volume of air in the food-aperture between the two glass doors isapproximately 5. 3 liters. When the door on the inside is opened and thematerial placed in the food-aperture and the outer door is subsequentlyopened, there is by diffusion a passage outward of air of thecomposition of the air inside of the chamber, and the food-aperture isnow filled with room air. When the inner door is again opened this roomair enters the chamber and is replaced by air of the same composition asthat in the chamber. It is seen, then, that there may theoretically bean interchange of air here which may have an influence on the results. In severe work experiments, where the amount of carbon dioxide in theair is enormously increased, such interchange doubtless does take placein measurable amounts and correction should undoubtedly be made. Inordinary rest experiments, where the composition of the air in thechamber is much more nearly normal, this correction is without specialsignificance. Furthermore, in the two forms of calorimeter now in use, the experiments being of but short duration, provision is made to renderit unnecessary to open the food-aperture during the experiment proper. Consequently at present no correction for interchange of air in thefood-aperture is made, and for the same reason the slight alteration involume resulting from the removal or addition of material has also notbeen considered here. 

USE OF THE RESIDUAL BLANK IN THE CALCULATIONS. 

To facilitate the calculations and for the sake of uniformity inexpressing the results, a special form of blank is used which permitsthe recording of the principal data regarding the analyses of air in thechamber at the end of each period. Thus at the head of the sheet arerecorded the time, the number of the period, kind of experiment, thename or initials of the subject, and the statement as to whichcalorimeter is used. The barometer recorded in millimeters is indicatedin the column at the left and immediately below the heading, togetherwith the temperature of the calorimeter as expressed in degreescentigrade. The temperature of the calorimeter as recorded by thephysical observer is usually expressed in the arbitrary scale of theWheatstone bridge and must be transposed into the centigrade scale bymeans of a calibration table. 

The apparent air-volumes in the subsections of the ventilating systemare recorded under the headings I, which represents the volume of aircontaining water-vapor and therefore is the air in the chamber plus theair in the piping to the surface of the acid in the first sulphuric-acidabsorber; I-II, which represents the air containing carbonic acid andincludes volume I plus the volume of the air in the first sulphuric-acidvessel and the volume of air in the potash-lime absorber; I-III, whichincludes the total confined volume of the whole system, since this aircontains both oxygen and nitrogen. These volumes change somewhat, depending upon the size of the body of the subject, the volume of thematerials taken into the chamber, and the type of calorimeter. 

The data for the residual analyses are recorded in the lower left-handcorner: first the weight of the water absorbed from 10 liters of airpassing through the meter; to the logarithm of this is added thelogarithm of volume I; the result is the logarithm of the total weightof water-vapor in the ventilating air-current. To convert this intoliters the logarithmic factor 09462[26] is added to the logarithm of theweight of water and (_a_) is the logarithm of water expressed in liters. A similar treatment is accorded the weight of carbon dioxide absorbedfrom the air-sample, (_b_) being ultimately the logarithm of the volumeof carbon dioxide. 

In order to determine the total volume of air in the chamber understandard conditions of temperature and pressure, to the logarithm ofvolume I-III is added, first, a logarithmic factor for the temperaturerecorded for the calorimeter to correct the volume of air to standardtemperature. As the temperature fluctuations are all within 1 degree, atable has been prepared giving the standard fluctuation represented bythe formula

 1 ----- 1 + _at_

in which _t_ is the temperature of the calorimeter. The correction forpressure has also been worked out in a series of tables and thelogarithmic factor here corresponds to the ratio _p_/760, in which _p_is the observed barometer. The logarithm of the total volume is recordedas a result of the addition of these three logarithms enumerated, andfrom this logarithm is expressed the total volume of air in liters. Deducting the sum of the values (_a_) and (_b_) from the total volumeleaves the volume of oxygen plus nitrogen. 

The calculation of the residual volume of nitrogen and the record of theadditions thereto was formerly carried out with a refinement that to-dayseems wholly unwarranted when other factors influencing this value aretaken into consideration. For the majority of experiments the residualvolume of nitrogen may be considered as constant in spite of the factthat some nitrogen is regularly admitted with the oxygen. Thesignificance of this assumption is best seen after a consideration ofthe method of calculating the amount of oxygen admitted to the chamber. 

RESIDUAL SHEET No. 1. 

Calculation of residual amounts of nitrogen, oxygen, carbon dioxide andwater-vapor remaining in chamber at 8. 10 A. M. , June 24, 1909. 

Residual at end of Prelim. Period. Exp. : Parturition. No. .. .. .. .. Subject: Mrs. Whelan. Calorimeter: Bed. 

-------------------------------------------+------------------------------- Barometer, 756. 95 mm. | Miscellaneous Calculations Temp. Cal. , 20. 08 °C | 875 48. 65-------------------------------------------+ 164. 55 25. 9 | ------ 90. Apparent Volume of Air | 710. 46 ------ | 4. 6 164. 55I containing H_{2}O 715. Liters | ------I-II " CO_{2} 781. " | 715. 0 II-III " O+N 755. " | 14-------------------------------------------+ ------Log. Wt. H_{2}O to residual | 781. 0 I-II. 0815 = 91116 | 24Log. I = 85431 | ------ ----- | 755. 0 I-III 76547 = 5. 88 gms. H_{2}O +-----------------------------Gms. To liters, 09462 | (a) 7. 26 l. ----- | (b) 1. 57 l. (a) 86909 = 7. 25 l. H_{2}O | ----- | 8. 82 = l. CO_{2} + H_{2}O |Log. Wt. CO_{2} in residual | Log. I-III = 87796. 0438 = 62634 | " temp. = 96912Log. I-II = 84392 | " pressure = 99856 ----- | ------ 49026 = 3. 09 gms. CO_{2} | Total volume 84588 = 700. 37 l. Gms. To liters, 70680 | Volume CO_{2} + H_{2}O = 8. 82 l. ----- | ------ (b) 19706 = 1. 57 l. CO_{2} | " O + N = 691. 56 l. | " N = 552. 96 l. | ------ | " O = 186. 57 l. |

ABBREVIATED METHOD OF COMPUTATION OF OXYGEN ADMITTED TO THE CHAMBER FORUSE DURING SHORT EXPERIMENTS. 

Desiring to make the apparatus as practicable and the calculations assimple as possible, a scheme of calculation has been devised whereby thecomputations may be very much abbreviated and at the same time there isnot too great a sacrifice in accuracy. The loss in weight of the oxygencylinder has, in the more complicated method of computation, beenconsidered as due to oxygen and about 3 per cent of nitrogen. The amountof nitrogen thus admitted has been carefully computed and its volumetaken into consideration in calculating the residual oxygen. If it isconsidered for a moment that the admission of gas out of the steelcylinder is made at just such a rate as to compensate for the decreasein volume of the air in the system due to the absorption of oxygen bythe subject, it can be seen that if the exact volume of the gas leavingthe cylinder were known it would be immaterial whether this gas werepure oxygen, oxygen with some nitrogen, or oxygen with any other inertgas not dangerous to respiration or not absorbed by sulphuric acid orpotash-lime. If 10 liters of oxygen had been absorbed by the man in thecourse of an hour, to bring the system back to constant apparent volumeit would be necessary to admit 10 liters of such a gas or mixture ofgases, assuming that during the hour there had been no change in thetemperature, the barometric pressure, or the residual amounts of carbondioxide or water-vapor. 

Under these assumed conditions, then, it would only be necessary tomeasure the amount of gas admitted in order to have a true measure ofthe amount of oxygen absorbed. The measure of the volume of the gasadmitted may be used for a measure of the oxygen absorbed, even when itis necessary to make allowances for the variations in the amount ofcarbon dioxide or water-vapor in the chamber, the temperature, andbarometric pressure. From the loss in weight of the oxygen cylinder, ifthe cylinder contained pure oxygen, it would be known that 10 literswould be admitted for every 14. 3 grams loss in weight. 

From the difference in weight of 1 liter of oxygen and 1 liter ofnitrogen, a loss in weight of a gas containing a mixture of oxygen witha small per cent of nitrogen would actually represent a somewhat largervolume of gas than if pure oxygen were admitted. The differences inweight of the two gases, however, and the amount of nitrogen present areso small that one might almost wholly neglect the error thus arisingfrom this admixture of nitrogen and compute the volume of oxygendirectly from the loss in weight of the cylinder. 

As a matter of fact, it has been found that by increasing the loss inweight of the cylinder of oxygen containing 3 per cent nitrogen by 0. 4per cent and then converting this weight to volume by multiplying by0. 7, the volume of gas admitted is known with great accuracy. Thismethod of calculation has been used with success in connection with thelarge chamber and particularly for experiments of short duration. It hasalso been introduced with great success in a portable type of apparatusdescribed elsewhere. [27] Under these conditions, therefore, it isunnecessary to make any correction on the residual volume of nitrogen ascalculated at the beginning of the experiment. When a direct comparisonof the calculated residual amount of oxygen present is to be made upondeterminations made with a gas-analysis apparatus the earlier and muchmore complicated method of calculation must be employed. 

CRITICISM OF THE METHOD OF CALCULATING THE VOLUME OF OXYGEN. 

Since the ventilating air-current has a confined volume, in which thereare constantly changing percentages of carbon dioxide, oxygen, andwater-vapor, it is important to note that the nitrogen present in theapparatus when the apparatus is sealed remains unchanged throughout thewhole experiment, save for the small amounts added with the commercialoxygen--amounts well known and for which definite corrections can bemade. Consequently, in order to find the amount of oxygen present in theresidual air at any time it is only necessary to determine the amountsof carbon dioxide and water-vapor and, from these two factors and fromthe known volume of nitrogen present, it is possible to compute thetotal volume of oxygen after calculating the total absolute volume ofair in the chamber at any given time. 

While the apparent volume of the air remains constant throughout thewhole experiment, by the conditions of the experiment itself theabsolute amount may change considerably, owing primarily to thefluctuations in barometric pressure and secondarily to slightfluctuations in the temperature of the air inside of the chamber. Although the attempt is made on the part of the observers to arbitrarilycontrol the temperature of this air to within a few hundredths of adegree, at times the subject may inadvertently move his body about inthe chair just a few moments before the end of the period and thustemporarily cause an increased expansion of the air. The apparatus is, in a word, a large air-thermometer, inside the bulb of which the subjectis sitting. If the whole system were inclosed in rigid walls there wouldbe from time to time noticeable changes in pressure on the system due tovariations in the absolute volume, but by means of the tension-equalizerthese fluctuations in pressure are avoided. 

The same difficulties pertain here which were experienced with theearlier type of apparatus in determining the average temperature of thevolume of air inside of the chamber. We have on the one hand the warmsurface of the man's body, averaging not far from 32° C. On the otherhand we have the cold water in the heat-absorbers at a temperature notfar from 12° C. Obviously, the air in the immediate neighborhood ofthese two localities is considerably warmer or colder than the averagetemperature of the air. The disposition of the electric-resistancethermometers about the chamber has, after a great deal of experimenting, been made such as to permit the measurement as nearly as possible of theaverage temperature in the chamber. But this is at best a roughapproximation, and we must rely upon the assumption that while thetemperatures which are actually measured may not be the averagetemperature, the fluctuations of the average temperature are parallel tothe fluctuations in the temperatures measured. Since every effort ismade to keep these fluctuations at a minimum, it is seen that the errorof this assumption is not as great as might appear at first sight. However, the calculation of the residual amount of oxygen in the chamberis dependent upon this assumption and hence any errors in the assumptionwill affect noticeably the calculation of the residual oxygen. 

Attempts to compare the determination of the oxygen by the exceedinglyaccurate Sondén apparatus with that calculated after determining thewater-vapor and carbon dioxide, temperature and pressure of the air inthe chamber have thus far led to results which indicate one of threethings: (1) that there is not a homogeneous mixture; (2) that during thetime required for making residual analyses, _i. E. _, some three or fourminutes, there may be a variation in the oxygen content in the air ofthe chamber due to the oxygen continually added from the cylinder; (3)that the oxygen supplied from the cylinder is not thoroughly mixed withthe air in the chamber until some time has elapsed. That is to say, withthe method now in use it is necessary to fill the tension-equalizer to adefinite pressure immediately at the end of each experimental period. This is done by admitting oxygen from the cylinder, and obviously thisoxygen was not present in the air when analyzed. A series of experimentswith a somewhat differently arranged system is being planned in whichthe oxygen will be admitted to the respiration chamber directly and notinto the tension-equalizer, and at the end of the experiment thetension-equalizer will be kept at such a point that when the motor isstopped the amount of oxygen to be added to bring the tension to adefinite point will be small. 

Under these conditions it is hoped to secure a more satisfactorycomparison of the analyses as made by means of the Sondén apparatus andas calculated from the composition of the residual air by thegravimetric analysis. It remains a fact, however, that no matter withwhat skill and care the gasometric analysis is made, eithergravimetrically or volumetrically, the calculation of the residualamount of oxygen presents the same difficulties in both cases. 

CALCULATION OF TOTAL OUTPUT OF CARBON DIOXIDE AND WATER-VAPOR AND OXYGENABSORPTION. 

From the weights of the sulphuric-acid and potash-lime vessels, theamounts of water-vapor and carbon dioxide absorbed out of theair-current are readily obtained. The loss in weight of the oxygencylinder increased by 0. 4 per cent (see page 88) gives the weight ofoxygen admitted to the chamber. It remains, therefore, to make properallowance for the variations in composition of the air inside thechamber at the beginning and end of the different periods. From theresidual sheets the amounts of water-vapor, carbonic acid, and oxygenpresent in the system at the beginning and end of each period aredefinitely known. If there is an increase, for example, in the amount ofcarbon dioxide in the chamber at the end of a period, this increase mustbe added to the amount absorbed out of the air-current in order toobtain the true value for the amount produced during the experimentalperiod. 

A similar calculation holds true with regard to the water-vapor andoxygen. For convenience in calculating, the amounts of water-vapor andcarbon dioxide residual in the chamber are usually expressed in grams, while the oxygen is expressed in liters. Hence, before making theadditions or subtractions from the amount of oxygen admitted, thevariations in the amount of oxygen residual in the system should beconverted from liters to grams. This is done by dividing by 0. 7. 

CONTROL EXPERIMENTS WITH BURNING ALCOHOL. 

After having brought to as high a degree of perfection as possible theapparatus for determining carbon dioxide, water, and oxygen, it becomesnecessary to submit the apparatus to a severe test and thus demonstrateits ability to give satisfactory results under conditions that can beaccurately controlled. The liberation of a definite amount of carbondioxide from a carbonate by means of acid has frequently been employedfor controlling an apparatus used for researches in gaseous exchange, but this only furnishes a definite amount of carbon dioxide and throwsno light whatever upon the ability of the apparatus to determine theother two factors, water-vapor and oxygen. Some of the earlierexperimenters have used burning candles, but these we have found to beextremely unsatisfactory. The necessity for an accurate elementaryanalysis, the high carbon content of the stearin and paraffin, and thepossibility of a change in the chemical composition of the material allrender this method unfit for the most accurate testing. As a result of alarge number of experiments with different materials, we still rely uponthe use of ethyl alcohol of known water-content. The experiments withabsolute alcohol and with alcohol containing varying amounts of watershowed no differences in the results, and hence it is now our custom toobtain the highest grade commercial alcohol, determine the specificgravity accurately, and burn this material. We use the Squibbpyknometer[28] and thereby can determine the specific gravity of thealcohol to the fifth or sixth decimal place with a high degree ofaccuracy. Using the alcoholometric tables of Squibb[29] or Morley, [30]the percentage of alcohol by weight is readily found, and from thechemical composition of the alcohol can be computed not only the amountof carbon dioxide and water-vapor formed and oxygen absorbed by thecombustion of 1 gram of ethyl hydroxide containing a definite knownamount of water, but also the heat developed during its combustion. 

With the construction of this apparatus it was found impracticable toemploy the type of alcohol lamp formerly used with success in theWesleyan University respiration chamber. Inability to illuminate thegage on the side of the lamp and the small windows on the side of thecalorimeter precluded its use. It was necessary to resort to the use ofan ordinary kerosene lamp with a large glass font and an Argand burner. Of the many check-tests made we quote one of December 31, 1908, madewith the bed calorimeter:

 Several preliminary weights of the rates of burning were made before the lamp was introduced into the chamber. The lamp was then put in place and the ventilation started without sealing the cover. The lamp burned for about one hour and a quarter and was then weighed again. Then the window was sealed in and the experiment started as soon as possible. At the end of the experiment the window was taken out immediately and the lamp blown out and then weighed. The amount burned between the time of weighing the alcohol and the beginning of the experiment was calculated from the rate of burning before the experiment and this amount subtracted from the total burned from the time that the lamp was weighed before being sealed in until the end, when it was weighed the second time. For the minute which elapsed between the end of the experiment and the last weighing, the rate for the length of the experiment itself was used. 

 During the experiment there were burned 142. 7 grams of 92. 20 per cent alcohol of a specific gravity of 0. 8163. 

A tabular summary of results is given below:

 +----------------------+--------+-----------+ | | Found. | Required. | +----------------------+--------+-----------+ | Carbon dioxide gms. | 259. 9 | 251. 4 | | Oxygen " | 278. 5 | 274. 8 | | Water-vapor " | 165. 8 | 165. 6 | | Heat cals. | 829. 0 | 834. 5 | +----------------------+--------+-----------+

Thus does the apparatus prove accurate for the determination of all fourfactors. 

BALANCE FOR WEIGHING SUBJECT. 

The loss or gain in body-weight has always been taken as indicating thenature of body condition, a loss usually indicating that there is a lossof body substance and a gain the reverse. In experiments in which adelicate balance between the income and outgo is maintained, as in theseexperiments, it is of special interest to compare the losses in weightas determined by the balance with the calculated metabolism of materialand thus obtain a check on the computation of the whole process ofmetabolism. Since the days of Sanctorius the loss of weight of the bodyfrom period to period has been of special interest. The most recentcontribution to these investigations is that of the balance described byLombard, [31] in which the body-weight is recorded graphically frommoment to moment with an extraordinarily sensitive balance. 

In connection with the experiments here described, however, the weighingwith the balance has a special significance, in that it is possible tohave an indirect determination of the oxygen consumption. As pointed outby Pettenkofer and Voit, if the weight of the excretions and the loss inbody-weight are taken into consideration, the difference between theweight of the excretions and the loss in body-weight should be theweight of the oxygen absorbed. With this apparatus we are able todetermine the water-vapor, the carbon-dioxide excretion, and the weightof the urine and feces when passed. If there is an accuratedetermination of the body-weight from hour to hour, this should give thedata for computing exactly the oxygen consumption. Moreover, we have thedirect determination of oxygen with which the indirect method can becompared. 

In the earlier apparatus this comparison was by no means as satisfactoryas was desired. The balance there used was sensitive only to 2 grams, the experiments were long (24 hours or more), and it seemed to beabsolutely impossible, even by exerting the utmost precaution, to securethe body-weight of the subject each day with exactly the same clothingand accessories. Furthermore, where there is a constant change inbody-weight amounting to 0. 5 gram or more per minute, it is obvious thatthe weighing should be done at exactly the same moment from day to day. It is seen, therefore, that the comparison with the direct oxygendetermination is in reality an investigation by itself, involving themost accurate measurements and the most painstaking development ofroutine. 

With the hope of contributing materially to our knowledge regarding theindirect determination of oxygen, the special form of balance shown infig. 9 was installed above the chair calorimeter. This balance isextremely sensitive. With a dead load of 100 kilograms in each pan ithas shown a sensitiveness of 0. 1 gram, but in order to have theapparatus absolutely air-tight for the oxygen and carbon-dioxidedetermination, the rod on which the weighing-chair is suspended mustpass through an air-tight closure. For this closure we have used a thinrubber membrane, weighing about 1. 34 grams, one end of which is tied toa hard-rubber tube ascending from the chair to the top of thecalorimeter, the other end being tied to the suspension rod. In playingup and down this rod takes up a varying weight of the rubber diaphragm, depending upon the position which it assumes, and therefore thesensitiveness noted by the balance with a dead load and swinging freelyis greater than that under conditions of actual use. Preliminary testswith the balance lead us to believe that with a slight improvement inthe technique a man can be weighed to within 0. 3 gram by means of thisbalance. A series of check-experiments to test the indirect with thedirect determination of oxygen are in progress at the moment of writing, and it is hoped that this problem can be satisfactorily solved ere long. 

During the process of weighing, the ventilating air-current is stoppedso as to prevent any slight tension on the rubber diaphragm and furnishthe best conditions for sensitive equilibrium. After the weighing hasbeen made and the time exactly recorded, the load is thrown off theknife-edges of the balance, and then provision has been made to raisethe rod supporting the chair and simultaneously force a rubber stoppertightly into the hard rubber tube at the top of the calorimeter, thusmaking the closure absolutely tight. It is somewhat hazardous to relyduring the entire period of an experiment upon the thin rubber membranefor the closure when the blower is moving the air-current. 

To raise the chair and the man suspended on it in such a way as to drawthe cork into the hard-rubber tube, we formerly used a large hand-lever, which was not particularly satisfactory. Thanks to the suggestion of Mr. E. H. Metcalf, we have been able to attach a pneumatic lift (fig. 9) inthat the cross-bar above the calorimeter chamber, to which thesuspension rod is attached, rests on two oak uprights and can be raisedby admitting air into an air-cushion, through the central opening ofwhich passes the chair-suspending rod. As the air enters the air-cushionit expands and lifts a large wooden disk which, in turn, lifts the ironcross-bar, raising the chair and weight suspended upon it. At the properheight and when the stopper has been thoroughly forced into place, twomovable blocks are slipped beneath the ends of the iron cross-bar andthus the stopper is held firmly in place. The tension is then releasedfrom the air-cushion. This apparatus functionates very satisfactorily, raising the man or lowering him upon the knife-edges of the balance withthe greatest regularity and ease. 

PULSE RATE AND RESPIRATION RATE. 

The striking relationship existing between pulse rate and generalmetabolism, noted in the fasting experiments made with the earlierapparatus, has impressed upon us the desirability of obtaining recordsof the pulse rate as frequently as possible during an experiment. Records of the respiration rate also have an interest, though not of asgreat importance. In order to obtain the pulse rate, we attach a Bowlesstethoscope over the apex beat of the heart and hold it in place with alight canvas harness. Through a long transmission-tube passing throughan air-tight closure in the walls of the calorimeter it is possible tocount the beats of the heart without difficulty. The respiration rate isdetermined by attaching a Fitz pneumograph about the trunk, midwaybetween the nipples and the umbilicus. The excursions of the tambourpointer as recorded on the smoked paper of the kymograph give a truepicture of the respiration rate. 

Of still more importance, however, is the fact that the expansion andcontraction of the pneumograph afford an excellent means for noting theminor muscular activity of a subject, otherwise considered at completerest. The slightest movement of the arm or the contraction or relaxationof any of the muscles of the body-trunk results in a movement of thetambour quite distinct from the respiratory movements of the thorax orabdomen. These movements form a very true picture of the muscularmovements of the subject, and these graphic records have been of verygreat value in interpreting the results of many of the experiments. 

ROUTINE OF AN EXPERIMENT WITH MAN. 

In the numerous previously published reports which describe theconstruction of and experiments with the respiration calorimeter, butlittle attention has been devoted to a statement of the routine. Since, with the increasing interest in this form of apparatus and the possibleconstruction of others of similar form, a detailed description of theroutine would be of advantage, it is here included. 

PREPARATION OF SUBJECT. 

Prior to an experiment, the subject is usually given either a stipulateddiet for a period of time varying with the nature of the experiment or, as in the case of some experiments, he is required to go without foodfor at least 12 hours preceding. Occasionally it has been deemedadvisable to administer a cup of black coffee without sugar or cream, and by this means we have succeeded in studying the early stages ofstarvation without making it too uncomfortable for the subject. Thestimulating effect of the small amount of black coffee on metabolism ishardly noticeable and for most experiments it does not introduce anyerror. 

The urine is collected usually for 24 hours before, in either 6 or 12hour periods. During the experiment proper urine is voided if possibleat the end of each period. This offers an opportunity for studying theperiodic elimination of nitrogen and helps frequently to throw lightupon any peculiarities of metabolism. 

Even with the use of a long-continued preceding diet of constantcomposition, it is impossible to rely upon any regular time fordefecation or for any definite separation of feces. For many experimentsit is impracticable and highly undesirable to have the subject attemptto defecate inside the chamber, and for experiments of short durationthe desire to defecate is avoided by emptying the lower bowel with awarm-water enema just before the subject enters the chamber. Emphasisshould be laid upon the fact that a moderate amount of water only shouldbe used and only the lower bowel emptied, so as not to increase thedesire for defecation. 

The clothing is usually that of a normal subject, although occasionallyexperiments have been made to study the influence of various amounts ofclothing upon the person. There should be opportunity for a comfortableadjustment of the stethoscope and pneumograph, etc. , and the clothingshould be warm enough to enable the subject to remain comfortable andquiet during his sojourn inside the chamber. 

The rectal thermometer, which has previously been carefully calibrated, is removed from a vessel of lukewarm water, smeared with vaseline, andinserted while warm in the rectum to the depth of 10 to 12 centimeters. The lead wires are brought out through the clothing in a convenientposition. 

The stethoscope is attached as nearly as possible over the apex beat ofthe heart by means of a light harness of canvas. In the use of theBowles stethoscope, it has been found that the heart-beats can easily becounted if there is but one layer of clothing between the stethoscopeand the skin. Usually it is placed directly upon the undershirt of thesubject. 

The pneumograph is placed about the body midway between the nipple andthe umbilicus and sufficient traction is put upon the chain or strapwhich holds it in place to secure a good and clear movement of thetambour for each respiration. 

The subject is then ready to enter the chamber and, after climbing thestepladder, he descends into the opening of the chair calorimeter, sitsin the chair, and is then ready to take care of the material to behanded in to him and adjust himself and his apparatus for theexperiment. Usually several bottles of drinking-water are deposited inthe calorimeter in a convenient position, as well as some urine bottles, reading matter, clinical thermometer, note-book, etc. Before the coveris finally put in place, the pneumograph is tested, stethoscopeconnections are tested to see if the pulse can be heard, the rectalthermometer connections are tested, and the telephone, call-bell, andelectric light are all put in good working order. When the subject hasbeen weighed in the chair, the balance is tested to see that it swingsfreely and has the maximum sensibility. All the adjustments are so madethat only the minimum exertion will be necessary on the part of thesubject after the experiment has once began. 

SEALING IN THE COVER. 

The cover is put in place and wax is well crowded in between it and therim of the opening. The wax is preferably prepared in long rolls aboutthe size of a lead-pencil and 25 to 30 centimeters long. This is crowdedinto place, a flat knife being used if necessary. An ordinarysoldering-iron, which has previously been moderately heated in a gasflame, is then used to melt the wax into place. This process must becarried out with the utmost care and caution, as the slightest pinholethrough the wax will vitiate the results. The sealing is examinedcarefully with an electric light and preferably by two personsindependently. After the sealing is assured, the plugs connecting thethermal junctions and heating wires of the cover with those of theremainder of the chamber are connected, the water-pipe is put in place, and the unions well screwed together. After seeing that the electricalconnections can not in any way become short-circuited on either themetal chamber or metal pipes, the asbestos cover is put in place. 

ROUTINE AT OBSERVER'S TABLE. 

Some time before the man enters the chamber, an electric lamp of from 16to 24 candle-power (depending upon the size of the subject) is placedinside of the chamber as a substitute for the man, and the coolingwater-current is started and the whole apparatus is adjusted to bringaway the heat prior to the entrance of the man. The rate of flow withthe chair calorimeter is not far from 350 cubic centimeters per minutewith a resting man. The proper mixture of cold and warm water is made, so that the electric reheater can be controlled readily by theresistance in series with it. Care is taken not to allow the water toenter the chamber below the dew-point and thus avoid the condensation ofmoisture on the absorbers. The thermal junctions indicate thetemperature differences in the walls and the different sections areheated or cooled as is necessary until the whole system is brought asnear thermal equilibrium as possible. 

After the man enters, the lamp is removed and the water-current is sovaried, if necessary, and the heating and cooling of the various partsso adjusted as to again secure temperature equilibrium of all parts. When the amount of heat brought away by the water-current exactlycompensates that generated by the subject, when the thermal-junctionelements in the walls indicate a 0 or very small deflection, when theresistance thermometers indicate a constant temperature of the airinside the chamber and the walls of the chamber, the experiment properis ready to begin. 

The physical observer keeps the chemical assistant thoroughly informedas to the probable time for the beginning of the experiment, so thatthere will be ample time for making the residual analyses of the air. After these analyses have been made and the experiment is about tobegin, the observer at the table calls the time on the exact minute, atwhich time the blower is stopped and the purifying system changed. Thephysical observer takes the temperatures of the wall and air by theelectric-resistance thermometers, reads the mercury thermometers, records the rectal thermometer, and at the exact moment of beginning theexperiment the current of water which has previously been running intothe drain is deflected into the water-meter. At the end of the periodthis routine is varied only in that the water-current is deflected fromthe water-meter into a small can holding about 4 liters, into which thewater flows while the meter is being weighed. 

MANIPULATION OF THE WATER-METER. 

The rate of flow of water through the apparatus is determined before theexperiment begins. This is done by deflecting the water for a certainnumber of seconds into a graduate or by deflecting it into the small canand weighing the water thus collected. The water is then directed intothe drain during the preliminary period. Meanwhile the main valve at thebottom of the water-meter is opened, such water as has accumulated fromtests in preceding experiments is allowed to run out, and the valve isclosed after the can is empty. The meter is then carefully balanced onthe scales and the weight is recorded. At the beginning of theexperiment the water is deflected from the drain into the meter. At theend of the period, while the water is running into the small can, thewater-meter is again carefully weighed and the weight recorded. Havingrecorded the weight, the water is again deflected into the large meterand what has accumulated in the small can is carefully poured into thelarge meter through a funnel. If the meter is nearly full, so thatduring the next period water will accumulate and overflow the meter, itis emptied immediately after weighing and while the small can is fillingup. About 4 minutes is required to empty the can completely. 

After it is emptied, it is again weighed, the water-current deflectedfrom the small can to the meter, and the water which has accumulated inthe small can carefully poured into the meter. All weights on thewater-meter, both of the empty can and the can at the end of eachperiod, are checked by two observers. 

ABSORBER TABLE. 

Shortly after the subject has entered the chamber and in many instancesbefore the sealing-in process has begun, the ventilating air-current isstarted by starting the blower. The air passes through one set ofpurifiers during this preliminary period, and as no measurements aremade for this period it is not necessary that the weights of theabsorbers be previously known. 

All precautions are taken, however, so far as securing tightness incoupling and installing them on the absorber system are concerned. During this period the other set of absorbers is carefully weighed andmade ready to be put in place and tested and about 10 minutes before theexperiment proper begins the residual analyses are begun. The series ofU-tubes, which have previously been carefully weighed, are placed onsmall inclined racks and are connected with the meter and also with thetube leading to the mercury valve. The pet-cock which connects thereturn air-pipe with the drying-tower and the gas-meter is then openedand the mercury reservoir is lowered. The rate of flow of air throughthe U-tubes is regulated by a screw pinch-cock on the rubber tubeleading to the first U-tube. This rate is so adjusted by means of thepinch-cock that about 3 liters of air per minute will flow through theU-tubes, and as the pointer on the gas-meter approaches 10 liters themercury reservoir is raised at just such a point, gained by experience, as will shut off the air-current when the total volume registers 10liters on the meter. The pet-cock in the pipe behind the meter is thenclosed, the U-tubes disconnected, and a new set put in place. Aduplicate and sometimes a triplicate analysis is made. 

When the physical observer calls the time for the end of the period, theswitch which controls the motor is opened and the chemical assistantthen opens the rear valve of the new set of absorbers and closes therear valve of the old set, and likewise opens the front valve of the newset and closes the front valve of the old set. As soon as the signal isgiven that the oxygen connections have been properly made and that theoxygen has been admitted to the chamber in proper amount, the blower isagain started. It is then necessary to weigh the U-tubes and disconnectthe old set of absorbers and weigh them. If the sulphuric-acid absorbershave not exceeded the limit of gain in weight they are used again; ifthey have, new ones are put in their place. 

The first sulphuric-acid absorber is connected to the front valve, thenthe potash-lime can, and then the last sulphuric-acid absorber; butbefore connecting the last sulphuric-acid absorber with thesodium-bicarbonate can, a test is made of the whole system from thefront valve to the end of the second sulphuric-acid absorber. This ismade by putting a solid-rubber stopper in the exit end of the secondsulphuric-acid absorber and, by means of a bicycle pump, forcingcompressed air in through a pipe tapped into the pipe from the valve atthe front end until a pressure of about 2 feet of water is developed inthis part of the system. This scheme for testing and the method ofconnecting the extra pipe have been discussed in detail in an earlierpublication. [32] Repeated tests have shown that this method of testingthe apparatus for tightness is very successful, as the minutest leak isquickly shown. 

After the system has been thoroughly tested, the rubber stopper in theexit end of the second sulphuric-acid absorber is first removed, thenthe tube connected with the pump and manometer is disconnected and itsend placed in the reservoir of mercury. Occasionally, through oversight, the pressure is released at the testing-tube with the result that theair compressed in the system expands, forcing sulphuric acid into thevalves and down into the blower, thus spoiling completely theexperiment. After the testing, the last sulphuric-acid absorber iscoupled to the sodium-bicarbonate can. It is seen that this lastconnection is the only one not tested, and it has been found that caremust be taken to use only the best gaskets at this point, as frequentlyleaks occur; in fact, it is our custom to moisten this connection withsoapsuds. If new rubber gaskets are used a leak is never found. 

SUPPLEMENTAL APPARATUS. 

To maintain the apparent volume of air through the whole systemconstant, oxygen is admitted into the tension-equalizer until the sametension is exerted on this part of the system at the end as at thebeginning. This is done by closing the valve connecting thetension-equalizer with the system and admitting oxygen to thetension-equalizer until the petroleum manometer shows a definitetension. After the motor is stopped, at the end of the experimentalperiod, there is a small amount of air compressed in the blower whichalmost instantly leaks back through the blower and the whole systemcomes under atmospheric pressure, save that portion which is sealed offbetween the two levels of the sulphuric acid in the two absorbingvessels. A few seconds after the motor is stopped the valve cutting offthe tension-equalizer from the rest of the system is closed, thepet-cock connecting this with the petroleum manometer is opened, andoxygen is admitted by short-circuiting the electrical connections at thetwo mercury cups. This is done by the hands of the observer and must beperformed very gently and carefully, as otherwise oxygen will rush in sorapidly as to cause excessive tension. As the bag fills with gas, theindex on the petroleum manometer moves along the arc of a circle andgradually reaches the desired point. At this point, the supply of oxygenis cut off, the valve connecting the tension-equalizer with the mainsystem is opened, and simultaneously the needle-valve on thereduction-valve of the oxygen cylinder is tightly closed, preliminary toweighing the cylinder. At this point the motor can be started and theexperiment continued. 

It is necessary, then, that the oxygen cylinder be weighed. This is doneafter first closing the pet-cock on the end of the pipe conducting thegas beneath the floor of the calorimeter room, slipping the glass jointin the rubber pipe leading from the reduction valve to the pet-cock, andbreaking the connections between the two rubber pipes, the one from thepet-cock and the other to the reduction valve, also breaking theelectrical connection leading to the magnet on the cylinder. Thecylinder is then ready to swing freely without any connections to eitheroxygen pipe or electrical wires. It is then weighed, the loss in weightbeing noted by removing the brass weights on the shelf attached to thecounterpoise. It is important to see that there is a sufficient numberof brass weights always on the shelf to allow for a maximum loss ofweight of oxygen from the cylinder during a given period. Since thecylinders contain not far from 4 to 5 kilograms of oxygen, in balancingthe cylinders at the start it is customary to place at least 4 kilogramsof brass weights on the shelf and then adjust the counterpoise so as toallow for the gradual removal of these weights as the oxygen iswithdrawn. 

As soon after the beginning of the period as possible, the U-tubes areweighed on the analytical balance, and if they have not gained too muchthey are connected ready for the next analysis. If they have alreadyabsorbed too much water or carbon dioxide, they are replaced by freshlyfilled tubes. 

Immediately at the end of the experimental period the barometer iscarefully set and read, and the reading is verified by anotherassistant. Throughout the whole experiment an assistant counts the pulseof the subject frequently, by means of the stethoscope, and records therespiration rate by noting the lesser fluctuations of the tambourpointer on the smoked paper. These observations are recorded every fewminutes in a book kept especially for this purpose. 

A most excellent preservation of the record of the minor muscularmovements is obtained by dipping the smoked paper on the kymograph drumin a solution of resin and alcohol. The lesser movements on the paperindicate the respiration rate, but every minor muscular movement, suchas moving the arm or shifting the body in any way, is shown by a largedeflection of the pointer out of the regular zone of vibration. Theserecords of the minor muscular activity are of great importance ininterpreting the results of the chemical and physical determinations. 

FOOTNOTES:

[5] W. O. Atwater and F. G. Benedict: A respiration calorimeter withappliances for the direct determination of oxygen. Carnegie Institutionof Washington Publication No. 42, p. 91. (1905. )

Francis G. Benedict: The influence of inanition on metabolism. CarnegieInstitution of Washington Publication No. 77, p. 451. (1907. )

[6] W. O. Atwater and F. G. Benedict: A respiration calorimeter withappliances for the direct determination of oxygen. Carnegie Institutionof Washington Publication No. 42, p. 114. (1905. )

[7] W. O. Atwater and F. G. Benedict: A respiration calorimeter withappliances for the direct determination of oxygen. Carnegie Institutionof Washington Publication No. 42, p. 158. (1905. )

[8] Armsby: U. S. Dept. Of Agr. , Bureau of Animal Industry Bull. 51, p. 34. (1903. )

[9] Benedict and Snell: Eine neue Methode um Körpertemperaturen zumessen. Archiv f. D. Ges. Physiologie, Bd. 88, pp. 492-500. (1901. )

W. O. Atwater and F. G. Benedict: A respiration calorimeter withappliances for the direct determination of oxygen. Carnegie Institutionof Washington Publication No. 42, p. 156. (1905. )

[10] Rosa: U. S. Dept. Of Agric. , Office of Experiment Stations Bul. 63, p. 25. 

[11] Smith: Heat of evaporation of water. Physical Review, vol. 25, p. 145. (1907. )

[12] Philosophical Transactions, vol. 199, A, p. 149. (1902. )

[13] This is in agreement with the value 579. 6 calories found by F. Henning, Ann. D. Physik, vol. 21, p. 849. (1906. )

[14] Pembrey: Schäfer's Text-book of Physiology, vol. 1, p. 838. (1898. )

[15] Benedict and Snell: Körpertemperatur Schwankungen mit besondererRücksicht auf den Einfluss, welchen die Umkehrung der täglichenLebensgewöhnheit beim Menschen ausübt. Archiv f. D. Ges. Physiologie, Bd. 90. P. 33. (1902. )

Benedict: Studies in body-temperature: I. The influence of the inversionof the daily routine: the temperature of night-workers. American Journalof Physiology, vol. 11, p. 145. (1904. )

[16] W. O. Atwater and E. B. Rosa: Description of a new respirationcalorimeter and experiments on the conservation of energy in the humanbody. U. S. Dept. Of Agr. , Office of Experiment Stations Bul. 63. (1899. )

[17] Specific heat of water at average temperature of the water in theheat-absorbing system referred to the specific heat of water at 20° C. 

[18] W. O. Atwater and F. G. Benedict: A respiration calorimeter withappliances for the direct determination of oxygen. Carnegie Institutionof Washington Publication No. 42, p. 18. (1905. )

[19] For a description of the apparatus and the method of filling see W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliancesfor the direct determination of oxygen. Carnegie Institution ofWashington Publication No. 43, p. 27. (1905. )

[20] W. O. Atwater and F. G. Benedict: A respiration calorimeter withappliances for the direct determination of oxygen. Carnegie Institutionof Washington Publication No. 42, p. 56. (1905. )

[21] W. O. Atwater and F. G. Benedict: A respiration calorimeter withappliances for the direct determination of oxygen. Carnegie Institutionof Washington Publication No. 42, p. 20. (1905. )

[22] Thorne M. Carpenter and Francis G. Benedict: Mercurial poisoning ofmen in a respiration chamber. American Journal of Physiology, vol. 24, p. 187. (1909. )

[23] Francis G. Benedict: A method of calibrating gas-meters. PhysicalReview, vol. 22, p. 294. (1906. )

[24] Atwater and Benedict: _Loc. Cit. _, p. 38. 

[25] Atwater and Benedict: Carnegie Institution of WashingtonPublication No. 42, p. 77. 

[26] In the use of logarithms space is saved by not employingcharacteristics. 

[27] Francis G. Benedict: An apparatus for studying the respiratoryexchange. American Journal of Physiology, vol. 24, p. 368. (1909. )

[28] Squibb: Journal of American Chemical Society, vol. 19, p. 111. (1897. )

[29] Squibb: Ephemeris, 1884 to 1885, part 2, pp. 562-577. 

[30] Morley: Journal of American Chemical Society, vol. 26, p. 1185. (1904. )

[31] W. P. Lombard: A method of recording changes in body-weight whichoccur within short intervals of time. The Journal of the AmericanMedical Association, vol. 47, p. 1790. (1906. )

[32] Atwater and Benedict: _Loc. Cit. _, p. 21.