Chapter I: Part 1

Respiration Calorimeters for Studying the Respiratory Exchange and Energy Transformations of Man

BY

FRANCIS G. BENEDICT and THORNE M. CARPENTER

WASHINGTON, D. C. PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON 1910

CARNEGIE INSTITUTION OF WASHINGTON PUBLICATION NO. 123

The Lord Baltimore Press BALTIMORE, MD., U. S. A.

PREFACE.

The immediate development and construction of suitable apparatus for studying the complicated processes of metabolism in man was obviously the first task in equipping the Nutrition Laboratory. As several series of experiments have already been made with these respiration calorimeters, it is deemed advisable to publish the description of the apparatus as used at present. New features in the apparatus are, however, frequently introduced as opportunity to increase accuracy or facilitate manipulation is noted.

We wish here to express our sense of obligation to the following associates: Mr. W. E. Collins, mechanician of the Nutrition Laboratory, constructed the structural steel framework and contributed many mechanical features to the apparatus as a whole; Mr. J. A. Riche, formerly associated with the researches in nutrition in the chemical laboratory of Wesleyan University, added his previous experience in constructing and installing the more delicate of the heating and cooling devices. 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., Miss H. 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 75
Calculation 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 91
Balance for weighing subject 93
Pulse rate and respiration rate 95
Routine 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 AND ENERGY TRANSFORMATIONS IN MAN.

INTRODUCTION.

The establishment in Boston of an inquiry into the nutrition of man with the construction of a special laboratory for that purpose is a direct outcome of a series of investigations originally undertaken in the chemical laboratory of Wesleyan University, in Middletown, Connecticut, by the late Prof. W. O. Atwater. Appreciating the remarkable results of Pettenkofer and Voit[1] and their associates, as early as 1892 he made plans for the construction of a respiration apparatus accompanied by calorimetric features. The apparatus was designed on the general ventilation plan of the above investigators, but in the first description of this apparatus[2] it is seen that the method used for the determination of carbon dioxide and water-vapor was quite other than that used by Voit. Each succeeding year of active experimenting brought about new developments until, in 1902, the apparatus was essentially modified by changing it from the open-circuit type to the closed-circuit type of Regnault and Reiset. This apparatus, thus modified, has been completely described in a former publication.[3] The calorimetric features likewise underwent gradual changes and, as greater accuracy was desired, it was found impracticable to conduct calorimetric investigations to the best advantage in the basement of a chemical laboratory. With four sciences crowded into one building it was practically impossible to devote more space to these researches. Furthermore, the investigations had proceeded to such an extent that it seemed desirable to construct a special laboratory for the purpose of carrying out the calorimetric and allied investigations on the nutrition of man.

In designing this laboratory it was planned to overcome the difficulties experienced in Middletown with regard to control of the room-temperature and humidity, and furthermore, while the researches had heretofore been carried on simultaneously with academic duties, it appeared absolutely necessary to adjust the research so that the uninterrupted time of the experimenters could be given to work of this kind. Since these experiments frequently continued from one to ten days, their satisfactory conduct was not compatible with strenuous academic duties.

As data regarding animal physiology began to be accumulated, it was soon evident that there were great possibilities in studying abnormal metabolism, and hence the limited amount of pathological material available in Middletown necessitated the construction of the laboratory in some large center.

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

The building, a general description of which appeared in the Year Book of the Carnegie Institution of Washington for 1908, is of plain brick construction, trimmed with Bedford limestone. It consists of three stories and basement and practically all the space can be used for scientific work. Details of construction may be had by reference to the original description of the building. It is necessary here only to state that the special feature of the new building with which this report is concerned is the calorimeter laboratory, which occupies nearly half of the 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 investigations on the metabolism of nitrogen and carbon in the human organism with a respiration 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 with appliances for the direct determination of oxygen. Carnegie Institution of Washington Publication No. 42. (1905.)

CALORIMETER LABORATORY.

The laboratory room is entered from the main hall by a double door. The room is 14.2 meters long by 10.1 meters wide, and is lighted on three sides by 7 windows. Since the room faces the north, the temperature conditions are much more satisfactory than could be obtained with any other exposure. In constructing the building the use of columns in this room was avoided, as they would interfere seriously with the construction of the calorimeters and accessory apparatus. Pending the completion of the five calorimeters designed for this room a temporary wooden floor was laid, thus furnishing the greatest freedom in placing piping and electric wiring beneath the floor. As fast as the calorimeters are completed, permanent flooring with suitably covered trenches for pipes is to be laid. The room is amply lighted during the day, the windows being very high, with glass transoms above. At night a large mercury-vapor lamp in the center of the room, supplemented by a number of well-placed incandescent electric lights, gives ample illumination.

GENERAL PLAN OF CALORIMETER LABORATORY.

The general plan of the laboratory and the distribution of the calorimeters and accessory apparatus are shown in fig. 1. The double doors lead from the main hall into the room. In general, it is planned to conduct all the chemical and physical observations as near the center of the laboratory as possible, hence space has been reserved for apparatus through the center of the room from south to north. The calorimeters are on either side. In this way there is the greatest economy of space and the most advantageous arrangement of apparatus.

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

The heat insulation of the room is shown by the double windows and the heavy construction of the doors other than the double doors. On entering the room, the two calorimeters are on the left, and, as arranged at present, both calorimeters are controlled from the one platform, on which, is placed the observer's table, with electrical connections and the Wheatstone bridges for temperature measurements; above and behind the observer's table are the galvanometer and its hood. At the left of the 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 situated with regard to the balance for weighing the absorbers. The large balance used for weighing the oxygen cylinders is directly across the center aisle and the analytical balance for weighing the U-tubes for residual analysis is near by.

General view of laboratory room taken near the main door. At the extreme right is the absorber table, and back of it the bed calorimeter. In the immediate foreground is shown the balance for weighing absorbers. A sulphuric acid absorber is suspended on the left hand arm of the balance. At the left is the observer's table and back of it the chair calorimeter with a large balance above for weighing subjects. On the floor, to the left, is the water meter for weighing water used to bring away heat.]

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

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

View of laboratory taken from the entrance of the bed calorimeter, with balance for weighing oxygen cylinders at the left. The structural steel skeleton of the calorimeter for long experiments is at the right and sections of the copper lining are in the rear, resting against the wall.]

Another view of the laboratory, taken near the door leading to the refrigeration room, is shown in fig. 3. At the right is seen the balance used for weighing absorbers, and back of it, imperfectly shown, is the case surrounding the balance for weighing oxygen cylinders. On the wall, in the rear, is the recording apparatus for electric resistance thermometers 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 the right of this is shown the table for the absorption system, and at the left the chair calorimeter with the balance for weighing subjects above it. The mercury-vapor light, which is used to illuminate the room, is immediately above the balance for weighing absorbers.

The bed calorimeter and the absorbing-system table are better shown in fig. 4, a general view of the laboratory taken near the temperature recorder. In the immediate foreground is the table for the absorption system, and back of it are the observer's table and chair calorimeter. At the right, the bed calorimeter with the front removed and the rubber hose connections as carried from the absorber table to the bed calorimeter are shown. At the extreme left is the balance for weighing the absorbers. Above the chair calorimeter can be seen the balance for weighing the subject, and at its right the galvanometer suspended from the ceiling.

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

At the left the balance for weighing the oxygen cylinders is shown with its counterpoise. A reserve oxygen cylinder is standing immediately in front of it. A large calorimeter modeled somewhat after the plan of Sondén and Tigerstedt's apparatus in Stockholm and Helsingfors is planned to be built immediately back of the balance for weighing oxygen cylinders.

HEATING AND VENTILATING.

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

In the small room shown at the south side of the laboratory is placed a powerful electric fan which draws the air from above the floor of the calorimeter laboratory, draws it over brine coils, and sends it out into a large duct suspended on the ceiling of the laboratory. This duct has a number of openings, each of which can be controlled by a valve, and an unlimited supply of cold air can be directed to any portion of the calorimeter room at will. To provide for more continuous operation and for more exact temperature control, a thermostat has been placed in the duct and is so constructed as to operate some reheater coils beneath the brine-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 thermostat can be set at any point desired. Up to the present time it has been unnecessary to utilize this special appliance, as the control by hand regulation 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 calorimeter room. 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 the large duct. If outdoor air is desired, a special duct can be connected with the system so as to furnish outdoor air to the chamber. This has not as yet been used. Section C-D shows the fan and gives a section through the reheater. The brine coils, 400 meters long, are in triplicate. If one set becomes covered with moisture and is somewhat inefficient, this can be shut off and the other two used. When the frozen moisture melts and drops off, the single coil can be used again. It has been found that the system so installed is most readily controlled.

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

It can be seen, also, that this system provides a very satisfactory regulation of the humidity, for as the air passes over the brine coils the moisture is in large part frozen out. As yet, no hygrometric study has been made of the air conditions over a long period, but the apparatus is sufficiently efficient to insure thorough electrical insulation and absence of leakage in the intricate electrical connections on the calorimeters.

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

The respiration calorimeter laboratory is so large, the number of assistants in the room at any time is (relatively speaking) so small, seldom exceeding ten, and the humidity and temperature are so very thoroughly controlled, that as yet it has been entirely unnecessary to utilize even the relatively small amount of indirect ventilation provided in the original plans.

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

It is not necessary here to go into the advantages of temperature control of the working rooms during the summer months. Every one seems to be thoroughly convinced that it is necessary to heat rooms in the winter, but our experience thus far has shown that it is no less important to cool the laboratory and control the temperature and moisture during the summer months, as by this means both the efficiency and endurance of the assistants, to say nothing of the accuracy of the scientific measurements, are very greatly increased. Arduous scientific observations that would be wholly impossible in a room without temperature control can be carried on in this room during the warmest weather.

FOOTNOTES:

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

THE CALORIMETER.

In describing this apparatus, for the sake of clearness, the calorimetric features will be considered before the appliances for the determination 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-proof chamber through which a current of cold water is constantly passing. The amount of water, the flow of which, for the sake of accuracy, is kept at a constant rate, is carefully weighed. The temperatures of the water entering and leaving the chamber are accurately recorded at frequent intervals. The walls of the chamber are held adiabatic, thus preventing a gain or loss of heat by arbitrarily heating or cooling the outer metal walls, and the withdrawal of heat by the water-current is so controlled, by varying the temperature of the ingoing water, that the heat brought away from the calorimeter is exactly equal in amount to the heat eliminated by radiation and conduction by the subject, thus maintaining a constant temperature inside of the chamber. The latent heat of the water vaporized is determined by measuring directly the water vapor in the ventilating air-current.

In the construction of the new calorimeters a further and fundamental change in construction has been made in that all the thermal junctions, heating wires, and cooling pipes have been attached directly to the zinc wall of the calorimeter, leaving the outer insulating panels free from incumbrances, so that they can be removed readily and practically all parts inspected whenever desired without necessitating complete dismantling of the apparatus. This arrangement is possible except in those instances where connections pass clear through from the interior of the chamber to the outside, namely, the food-aperture, air-pipes, water-pipes, electrical connections, and tubes for connections with pneumograph and stethoscope; but the apparatus is so arranged as to have all of these openings in one part of the calorimeter. It is possible, therefore, to remove all of the outer sections of the calorimeter with the 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 its protecting insulating house and minimizes the delay and expense incidental to repairs or modifications. As the calorimeter is now constructed, it is possible to get at all parts of it from the outside, with the exception of one small fixed panel through which the above connections are passed. This panel, however, is made as narrow as possible, so that practically all changes can be made by taking out the adjacent panels.

THE CALORIMETER CHAMBER.

The respiration chamber used in Middletown, Connecticut, was designed to permit of the greatest latitude in the nature of the experiments to be made with it. As a result, it was found at the end of a number of years of experimenting that this particular size of chamber was somewhat too small for the most satisfactory experiments during muscular work and, on the other hand, somewhat too large for the best results during so-called rest experiments. In the earlier experiments, where no attempt was made to determine the consumption of oxygen, these disadvantages were not so apparent, as carbon dioxide could be determined with very great accuracy; but with the attempts to measure the oxygen it was found that the large volume of residual air inside the chamber, amounting to some 4,500 liters, made possible very considerable errors in this determination, for, obviously, the subject could draw upon the oxygen residual in the air of the chamber, nearly 1,000 liters, as well as upon the oxygen furnished from outside sources. The result was that a very careful analysis of the residual air must be made frequently in order to insure that the increase or decrease in the amount of oxygen residual in the air of the chamber was known accurately at the end of each period. Analysis of this large volume of air could be made with considerable accuracy, but in order to calculate the exact total of oxygen residual in the air it was necessary to know the total volume of air inside the chamber under standard conditions. This necessitated, therefore, a careful measurement of temperature and pressure, and while the barometric pressure could be measured with a high degree of accuracy, it was found to be very difficult to determine exactly the average temperature of so large a mass of air. The difficulties attending this measurement and experiments upon this point are discussed in detail elsewhere.[5] Consequently, as a result of this experience, in planning the calorimeters for the Nutrition Laboratory it was decided to design them for special types of experiments. The first calorimeter to be constructed was one which would have general use in experiments during rest and, indeed, during experiments with the subject sitting quietly in the chair.

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

GENERAL CONSTRUCTION.

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

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

To avoid temperature fluctuations due to possible local stratification of the air in the laboratory, the calorimeter is constructed so as to be practically suspended in the air, there being a large air-space of some 76 centimeters between the lowest point of the calorimeter and the floor, and the top of the calorimeter is some 212 centimeters below the ceiling of the room. Four upright structural-steel channels (4-inch) were bolted through the floor, so as to secure great rigidity, and were tied together at the top with structural steel. As a solid base for the calorimeter chamber two 3-inch channels were placed parallel to each other 70 centimeters from the floor, joined to these uprights. Upon these two 3-inch channels the calorimeter proper was constructed. The steel used for the most part in the skeleton of the apparatus is standard 2-1/2-inch channel. This steel frame and its support are shown in fig. 10, before any of the copper lining was put into position. The main 4-inch channels upon which the calorimeter is supported, the tie-rods and turn-buckles anchoring the framework to the ceiling, the I-beam construction at the top upon which is subsequently installed the large balance for weighing the man, the series of small channels set on edge upon which the asbestos floor is laid, and the upright row of channel ribs are all clearly shown.

Photograph of framework of chair calorimeter. In the photograph are shown four upright channels and the channels at the top for supporting the calorimeter. The smaller upright 2-1/2 inch channels and angles are shown inside of this frame. In the lower part of the figure is seen the asbestos board for the bottom of the calorimeter and underneath this a sheet of zinc.]

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

A photograph taken subsequently, showing the inner copper lining in position, 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 the chamber. Upright 2-1/2-inch channels (H, fig. 8) are bolted to the two outside channels on the bottom and to the ends of three of the long channels between in such a manner as to form the skeleton of the walls. The upper ends of these channels are fastened together by pieces of piping (P, P, P, fig. 8) with lock-nuts on either side, thus holding the whole framework in position.

The I-beams and channels used to tie the four upright channels at the top form a substantial platform upon which is mounted a large balance (fig. 9). This platform is anchored to the ceiling at four points by tie rods 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 opening through which the subject enters at the top (fig. 7).

Both the front and back lower channels upon which the bottom rests are extended so as to provide for supports for the outer walls of asbestos wood, which serve to insulate the calorimeter. Between the channels beneath the calorimeter floor and the 3-inch channels is placed a sheet of zinc which forms the outer bottom metallic wall of the chamber.

In order to prevent conduction of heat through the structural steel all contact between the inner copper wall and the steel is avoided by having strips of asbestos lumber placed between the steel and copper. These are shown as J in fig. 8 and fig. 12. A sheet of asbestos lumber beneath the copper bottom likewise serves this purpose and also serves to give a solid foundation for the floor. The supporting channels are placed near enough together to reinforce fully the sheet of asbestos lumber and enable it to support solidly the weight of the man. The extra strain on the floor due to tilting back a chair and thus throwing all the weight on two points was taken into consideration in planning the asbestos and the reinforcement by the steel channels. The whole forms a very satisfactory flooring.

_Wall construction and insulation._--The inner wall of the chamber consists of copper, preferably tinned on both sides, thus aiding in soldering, and the tinned inner surface makes the chamber somewhat lighter. Extra large sheets are obtained from the mill, thus reducing to a minimum the number of seams for soldering, and seams are made tight only with difficulty. The copper is of standard gage, the so-called 14-ounce copper, weighing 1.1 pounds per square foot or 5.5 kilograms per square meter. It has a thickness of 0.5 millimeter. The whole interior of the skeleton frame of the structural steel is lined with these 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 of bolts and other appliances is shown in position on the outside of the wall in fig. 11. The sheet zinc of the floor is obviously put in position before the channels upon which it rests are laid. The zinc is obtained in standard size, and is the so-called 9-ounce zinc, or 0.7 pound to the square foot, or 3.5 kilograms to the square meter. The sheet has a thickness of 0.5 millimeter.

In the cross-section, fig. 7, A represents the copper wall and B the zinc wall. Surrounding this zinc wall and providing air insulation is a series of panels constructed of asbestos lumber, very fire-resisting, rigid, and light. The asbestos lumber used for these outer panels is 6.4 millimeters (0.25 inch) thick. To further aid in heat insulation we have glued to the inner face of the different panels a patented material composed of two layers of sheathing-paper inclosing a half-inch of hair-felt. This material is commonly used in the construction of refrigerators. This is shown as E in fig. 7, while the outer asbestos panels are shown as F.

A detail of the construction of the walls, showing in addition the heating and cooling devices, is given in fig. 12, in which the copper is shown 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. The bolt I serves the purpose of holding the copper to the upright channel and likewise by means of a washer under the head of the screw holds the zinc to the channel. In order to hold the asbestos-lumber panel A with the hair-felt lining B a threaded rod E is screwed into a tapped hole in the outer part of the upright channel H. A small piece of brass or iron tubing, cut to the proper length, is slipped over this rod and the asbestos lumber held in position by a hexagonal nut with washer on the threaded rod E. In this manner great rigidity of construction is secured, and we have two air-spaces corresponding to the dead air-spaces indicated in fig. 7, the first between the copper and zinc and the second between the zinc and hair-felt.

PREVENTION OF RADIATION.

As can be seen from these drawings the whole construction of the apparatus is more or less of the refrigerator type, _i. e._, there is little opportunity for radiation or conduction of heat. Such a construction could be multiplied a number of times, giving a greater number of insulating walls, and perhaps reducing radiation to the minimum, but for extreme accuracy in calorimetric investigations it is necessary to insure the absence of radiation, and hence we have retained the ingenious device of Rosa, by which an attempt is made arbitrarily to alter the temperature of the zinc wall so that it always follows any fluctuations in the temperature of the copper wall. To this end it is necessary to know _first_ that there is a temperature difference between zinc and copper and, _second_, to have some method for controlling the temperature of the zinc. Leaving for a moment the question of measuring the temperature differences between zinc and copper, we can consider here the methods for controlling the temperature of the zinc wall.

If it is found necessary to warm the zinc wall, a current of electricity is passed through the resistance wire W, fig. 12. This wire is maintained approximately in the middle of the air-space between the zinc wall and hair-felt by winding it around an ordinary porcelain insulator F, held in position by a threaded rod screwed into a brass disk soldered to the zinc wall. A nut on the end of the threaded rod holds the insulator in position. Much difficulty was had in securing a resistance wire that would at the same time furnish reasonably high resistance and would not crystallize or become brittle and would not rust. At present the best results have been obtained by using enameled manganin wire. The wire used is No. 28 American wire-gage and has resistance of approximately 1.54 ohms per foot. The total amount of wire used in any one circuit is equal to a resistance of approximately 92 ohms. This method of warming the air-space leaves very little to be desired. It can be instantaneously applied and can be regulated with the greatest ease and with the greatest degree of refinement.

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

In the early experimenting, it was found impracticable to use piping of very small size, as otherwise stoppage as a result of sediment could easily occur. The pipe found best adapted to the purpose was the so-called standard one-eighth inch brass pipe with an actual internal diameter of 7 millimeters. The opening of a valve allowed cold water to flow through this pipe and the considerable mass of water passing through produced a very noticeable cooling effect. In the attempt to minimize 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 few moments after the valve was closed by a system of check-valves. In building the new apparatus, use was made of the compressed-air service in the laboratory to remove the large mass of cold water in the pipe. As soon as the water-valve was closed and the air-cock opened, the compressed air blew all of the water out of the tube.

The best results have been obtained, however, with an entirely new principle, namely, a few drops of water are continually allowed to pass into the pipe, together with a steady stream of compressed air. This cold water is forcibly blown through the pipe, thus cooling to an amount regulated by the amount of water admitted. Furthermore, the relatively dry air evaporates some of the water, thereby producing a somewhat greater cooling effect. By adjusting the flow of water through the pipe a continuous cooling effect of mild degree may be obtained. While formerly the air in the space next the zinc wall was either cooled or heated alternately by opening the water-valve or by passing a current through the heating coil, at present it is found much more advantageous to allow a slow flow of air and water through the pipes continuously, thus having the air-space normally somewhat cooler than is desired. The effect of this cooling, therefore, is then counterbalanced by passing an electric current of varying strength through the heating wire. By this manipulation it is unnecessary that the observer manipulate more than one instrument, namely, the rheostat, while formerly he had to manipulate valves, compressed-air cocks, and rheostat. The arrangement for providing for the amount of compressed air and water is shown in fig. 13, in which it is seen that a small drop-sight feed-water valve is attached to the pipe C leading into the dead air-space surrounding the calorimeter chamber. Compressed air enters at B and the amount entering can be regulated by the pet-cock. The amount of water admitted is readily observed by the sight feed-valve. When once adjusted this form of apparatus produces a relatively constant cooling effect and facilitates greatly the manipulation of the calorimetric apparatus as a whole.

THE THERMO-ELECTRIC ELEMENTS.

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

One ever-present difficulty with the older form of element was the tendency for the German-silver wires to slip out of the slots in which they had been vigorously crowded in the hard maple spool. In thus slipping out of the slots they came in contact with the metal thimble in the zinc wall and thus produced a ground. In constructing the new elements four pairs of iron-German-silver thermal junctions were made on essentially the same plan as that previously described,[6] the only modification being made in the spool. While the ends of the junctions nearest the copper are exposed to the air so as to take up most rapidly the temperature of the copper, it is somewhat difficult to expose the ends of the junctions nearest the zinc and at the same time avoid short-circuiting. The best procedure is to extend the rock maple spool which passes clear through the ferule in the zinc wall and cut a wide slot in the spool so as to expose the junctions to the air nearest the ferule. By so doing the danger to the unprotected ends of the junctions is much less. The two lead-wires of German silver can be carried through the end of the spool and thus allow the insulation to be made much more satisfactorily. In these calorimeters free use of these thermal junctions has been made. In the chair calorimeter there are on the top 16 elements consisting of four junctions each, on the rear 18, on the front 8, and on the bottom 13. The distribution of the elements is made with due reference to the direction in which the heat is most directly radiated and conducted from the surface of the body.

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

INTERIOR OF THE CALORIMETER.

Since the experiments to be made with this chamber will rarely exceed 6 to 8 hours, there is no provision made for installing a cot bed or other conveniences 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 or two, usually attached to the chair, to support bottles for urine and drinking-water bottles, completes the furniture equipment. The construction of the calorimeter is such as to minimize the volume of air surrounding the subject and yet secure sufficient freedom of movement to have him comfortable. A general impression of the arrangement of the pipes, chair, telephone, etc., inside the chamber can be obtained from figs. 7 and 9. The heat-absorber system is attached to rings soldered to the ceiling at different points. The incoming air-pipe is carried to the top of the central dome, while the air is drawn from the calorimeter at a 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 the rear wall of the calorimeter to the exit.

With the perfect heat insulation obtaining, the heat production of the man would soon raise the temperature to an uncomfortable degree were there no provisions for withdrawing it. It is therefore necessary to cool the chamber and, as has been pointed out, the cooling is accomplished by passing a current of cold water through a heat-absorbing apparatus permanently installed in the interior of the chamber. The heat-absorber consists of a continuous copper pipe of 6 millimeters internal diameter and 10 millimeters external diameter. Along this pipe there are soldered a large number of copper disks 5 centimeters in diameter at a distance of 5 millimeters from each other. This increases enormously the area for the absorption of heat. In order to allow the absorber system to be removed, added to, or repaired at any time, it is necessary to insert couplings at several points. This is usually done at corners where the attachment of disks is not practicable. The total length of heat-absorbers is 5.6 meters and a rough calculation shows that the total area of metal for the absorption of heat is 4.7 square meters. The total volume of water in the absorbers is 254 cubic centimeters.

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

The air-pipes are of thin brass, 1-inch internal diameter. One of them conducts the air from the ingoing air-pipe up into the top of the central dome or hood immediately above the head of the subject. The air thus enters the chamber through a pipe running longitudinally along the top of the dome. On the upper side of this pipe a number of holes have been drilled so as to have the air-current directed upwards rather than down against the head of the subject. With this arrangement no difficulties are experienced with uncomfortable drafts and although the air enters the chamber through this pipe absolutely dry, there is no uncomfortable sensation of extreme dryness in the air taken in at the nostrils, 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 at the lower front and passes around the rear to the point where the outside 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 passes through this glass to enable the subject to see inside the calorimeter without difficulty and most of the subjects can read with comfort. If an electric light is placed outside of the window, the illumination is very satisfactory and repeated tests have shown that no measurable amount of heat passes through the window by placing a 32 c. p. electric lamp 0.5 meter from the food aperture outside. More recently we have arranged to produce directly inside the chamber illumination by means of a small tungsten electric lamp connected to the storage battery outside of the chamber. This lamp is provided with a powerful mirror and a glass shade, so that the light is very bright throughout the chamber and is satisfactory for reading. It is necessary, however, to make a correction for the heat developed, amounting usually to not far from 3 calories per hour.

By means of a hand microphone and receiver, the subject can communicate with the observers outside at will. A push-button and an electric bell make 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 desirable that a constant flow of water of even temperature be secured. Direct connection with the city supply is not practicable, owing to the variations in pressure, and hence in constructing the laboratory building provision was made to install a large tank on the top floor, fed with a supply controlled by a ball-and-cock valve. By this arrangement the level in the tank is maintained constant and the pressure is therefore regular. As the level of the water in the tank is approximately 9 meters above the opening in the calorimeter, there is ample pressure for all purposes.

The water descends from this tank in a large 2-inch pipe to the ceiling of the calorimeter laboratory, where it is subdivided into three 1-inch pipes, so as to provide for a water-supply for three calorimeters used simultaneously, if necessary, and eliminate the influence of a variation in 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 the refrigeration room and part of the water circuit is passed through a brass coil immersed in a cooling-tank in the refrigeration room. By means 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 beneath the floor to the calorimeter chamber, passed through the absorbers, and is 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 the ball cock and valve, and _a_ is the main valve which controls this supply 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 a rough idea of the temperature of the water, so as to aid in securing the proper mixture. The water then passes under the floor of the calorimeter laboratory and ascends to the apparatus D, which is used for heating it to the desired temperature before entering the calorimeter. The temperature of the water as it enters the calorimeter is measured on an accurately calibrated thermometer E, and it then passes through the absorber system _d d d_ and leaves the calorimeter, passing the thermometer F, upon which the final temperature is read. It then passes through a pipe and falls into a large can G, placed upon scales. When this can is filled the water is deflected for a few minutes to another can and by opening valve _f_ the water is conducted to the drain after having been weighed.