■I
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y
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
%%l JSor* (g&ttimovt (pvte*
BALTIMORE, MD., V. 8. 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 ex-
periments 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 asso-
ciates: Mr. W. E. Collins, mechanician of the Nutrition Laboratory, con-
structed the structural steel framework and contributed many mechanical
features to the apparatus as a whole ; Mr. J. A. Eiche, 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.
Kenshaw, 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.
iii
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 hvdrothermal 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
v
VI CONTENTS.
PAGE
General description of the respiration apparatus — Continued.
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.l. 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 calo-
rimeter 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 resist-
ance thermometers for water-circuit 38
20. Diagram of galvanometer coil, used with recording apparatus for resist-
ance 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
vii
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. 0. Atwater. Appreciating the remarkable results of Pettenkofer
and Yoit * and their associates, as early as 1892 he made plans for the
construction of a respiration apparatus accompanied by calorimetric fea-
tures. The apparatus was designed on the general ventilation plan of the
above investigators, but in the first description of this apparatus f 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 Eegnault and Eeiset. This apparatus,
thus modified, has been completely described ■ in a former publication. J
The calorimetric features likewise underwent gradual changes and, as
greater accuracy was desired, it was found impracticable to conduct calo-
rimetric 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 in-
vestigations had proceeded to such an extent that it seemed desirable to
construct a special laboratory for the purpose of carrying out the calori-
metric 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
* Pettenkofer and Voit: Ann. der Chem. u. Pharm. (1862-3), Supp. Bd. 2, p. 17.
t 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.)
JW. 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.)
1
2 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
carried on simultaneously with academic duties, it appeared absolutely
necessary to adjust the research so that the uninterrupted time of the ex-
perimenters 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 rneta-.
holism, 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 con-
struction, 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.
CALORIMETER LABORATORY. 3
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 con-
ditions 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 accessor}- 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 calorime-
ters 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 calo-
rimeter, already tested and in actual use. On the east side of the room it is
intended to place large calorimeters, one for continuous experiments extend-
ing over several days and the other large enough to take in several indi-
viduals at once and to have installed apparatus and working machinery re-
quiring 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
4 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
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 con-
veniently placed for emptying the meter. The absorption system is placed
Fig. 1. — General plan of respiration calorimeter laboratory.
on a special table conveniently situated with regard to the balance for weigh-
ing 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 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.
Fig. 5
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.
CALORIMETER LABORATORY. 5
The barometer is on the south wall of the room, to avoid temperature
fluctuations, and a special electrical recording apparatus for recording tem-
perature differences is placed on the north wall near the windows, where it
may be conveniently observed either from the observer's platform or from
any subsequent platform that may be built. Pending the construction of
other calorimeters, apparatus for gas analysis, spirometers, and special appa-
ratus for studying the respiratory exchange are placed in the east end of the
room. On the inside wall, near the double doors, are the telephone and racks
containing the extra carbon-dioxide absorbing cans.
It is thus seen that the room as arranged permits the concentration of
all the physical observations and chemical work in the center of the room,
the calorimeters lying on either side. The bed calorimeter is so placed that
the subject can easily be brought to its front end on a stretcher and slid
into the chamber easily. The subject enters the chair calorimeter from the
top. The other calorimeters will have entrances facing the center aisle, so
that the subjects and apparatus can be placed inside without difficulty. The
subjects will also be under more general observation by having the entrance
openings toward the center of the room.
A general view of the laboratory taken at the right of the main door is
shown in figure 2. In the immediate foreground is seen the balance for
weighing the absorber system. A porcelain sulphuric-acid vessel is shown
suspended on the left-hand arm of the balance. The large lead counter-
poises used for weighing are on the shelf in front of the balance at the right.
On the floor of the laboratory, in front of the door, beneath the balance, is
seen a second sulphuric-acid absorber, while inside the cupboard beneath
the balance case at the extreme right is a broken absorber which gives an
idea of the internal construction. The pneumatic elevator with its valve
is shown in the middle of the cupboard beneath the balance.
At the right of the figure is seen the absorber table with the gas-meter
used for the residual analysis on the top shelf. The two rubber pipes con-
necting the absorber table to the chair calorimeter are shown connected,
and beneath them in the rear is the bed calorimeter. At the left are the
chair calorimeter and the observer's table with the chair used by the
observer. At the extreme left, on the floor, is the balance for weighing the
water used to bring away the heat from the calorimeters, and above the
chair calorimeter is shown the large balance for weighing the subject.
In obtaining the photograph from which the figure is made, care was
taken to minimize the reflections from the glass of the balance case; hence,
the apparatus seen through this glass is substantially as actually installed
and is not distorted by reflections. The observer's table is somewhat ele-
vated and steps lead to it. The galvanometer is but imperfectly shown at
the right of the balance case, immediately above the bed calorimeter and
suspended from the ceiling.
6 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
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 sur-
rounding 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
SECTION
C-D
BRINE COILS
REHEATER BENEATH
/V >-"/ Pendant thcbmostat* \«*. Y\
&K
Fig. 6. — Plan of heating and ventilating calorimeter laboratory, showing
general plan of circulation of the special cooling system and the posi-
tion of the thermostats and radiators which they control. The two
small diagrams are cross-sections of brine and heating coils.
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
CALORIMETER LABORATORY. 7
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 * large calorim-
eter, 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
Sonden and Tigerstedtfs 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 calo-
rimeter 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 tem-
perature 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
* As this report goes to press, this calorimeter is well on the way to completion.
8 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
desired. Up to the present time it has been unnecessary to utilize this
special appliance, as the control by hand regulation has been most satis-
factory.
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 calo-
rimeter room can be held at 20° C. day in and day out, whether the tem-
perature outdoors is 40° below or 100° above 0° F.
It can be seen, also, that this system provides a very satisfactory regu-
lation 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 poten-
tial 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 assist-
ants in the room at any time is (relatively speaking) so small, seldom ex-
ceeding ten, and the humidity and temperature are so very thoroughly con-
trolled, 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
CALORIMETER LABORATORY. 9
supply and return which go through the floor to the basement. The tem-
perature 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.
10 CALOKIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
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 with-
drawal of heat by the water-current is so controlled, by varying the tem-
perature of the ingoing water, that the heat brought away from the calo-
rimeter 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 incum-
brances, so that they can be removed readily and practically all parts in-
spected 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 connec-
tions, 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 advan-
tageous. It does away with the necessity of rolling the calorimeter out of
its protecting insulating house and minimizes the delay and expense inci-
dental 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.
11
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
Fig. 7. — Horizontal cross-section of chair calorimeter, showing cross-section of
copper waU at A, zinc waU at B, hair-felt at E, and asbestos outer waU
at F; also cross-section of all upright channels in the steel construction.
At the right is the location of the ingoing and outgoing water and the
thermometers. At C is shown the food aperture, and D is a gasket sepa-
rating the two parts. The ingoing and outeoming air-pipes are shown at
the right inside the copper wall. The telephone is shown at the left, and
in the center of the drawing is the chair with its foot-rest, G. In dotted
line is shown the opening where the man enters.
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;
12 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
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
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 to
the left of this is an upright rear channel) ; M, horizontal 3-inch
channel supporting calorimeter; Zn, zinc wall; Cu, copper wall;
J, insulating asbestos.
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 accu-
rately 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,
THE CALORIMETER.
13
it was found to be very difficult to determine exactly the average tempera-
ture of so large a mass of air. The difficulties attending this measurement
and experiments upon this point are discussed in detail elsewhere.* Con-
sequently, 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
1 Meter
Fig. 9. — Vertical cross-section erf chair calorimeter from front to back,
showing structural steel supporting the calorimeter and the large
balance above for weighing the subject inside the calorimeter.
The chair, method of suspension, and apparatus for raising and
lowering are shown. Part of the heat-absorbers is shown, and
their general direction. The ingoing and outgoing air-pipes and
direction of ventilation are also indicated. The positions of the
food-aperture and wire mat and asbestos support are seen. Sur-
rounding the calorimeter are the asbestos outside and hair-felt
lining.
* W. 0. Atwater and F. G. Benedict: A respiration calorimeter with appliances
for the direct determination of oxygen. Carnegie Institution of Washington
Publication No. 42, p. 91. (1905.)
Francis G. Benedict: The influence of inanition on metabolism. Carnegie In-
stitution of Washington Publication No. 77, p. 451. (1907.)
14 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
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 prac-
tically suspended in the air, there being a large air-space of some 76 centi-
meters 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|-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
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THE CALORIMETER. 15
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.
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^-inch channel
(N, 1ST, 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^-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. 1. 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^-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 sup-
port 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 con-
sists 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
16
CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
seams for soldering, and seams are made tight only with difficulty. The cop-
per 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
ZINC,
COPPER
■
^iittuttiiitiu««tt<t
Fig. 12. — Cross-section in detail of walls of calorimeter, showing zinc and copper
walls and asbestos outside (A) ; hair-felt lining (B) ; cross-section of channel iron
(H); brass washer soldered to copper (K); asbestos insulation between channel
iron and copper (J); bolt holding the whole together (I); heating wire (W) and
insulator 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 asbestos wall with a nut on the outside;
and iron pipe (W) used as spacer between asbestos and zinc.
is the so-called 9-ounce zinc, or 0.7 pound to the square foot, or 3.5 kilo-
grams 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 com-
THE CALORIMETER. 17
monly 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 hex-
agonal nut with washer on the threaded rod E. In this manner great rig-
idity 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 appa-
ratus 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 multi-
plied 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 Eosa, 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 differ-
ence between zinc and copper and, second, to have some method for con-
trolling the temperature of the zinc. Leaving for a moment the question
of measuring the temperature differences betwen 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 posi-
tion 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
18
CALORIMETERS FOR STUDYING- RESPIRATORY EXCHANGE, ETC.
amount of wire used in any one circuit is equal to a resistance of approxi-
mately 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 remain-
ing in the pipe, provision was made to allow
water to drain out of this pipe a few mo-
ments after the valve was closed by a system
of check-valves. In building the new appa-
ratus, 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 prin-
ciple, 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 evap-
orates some of the water, thereby producing a somewhat greater cooling
effect. By adjusting the flow of water through the pipe a continuous cool-
ing 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 some-
Fig. 13. — Detail of drop-sight feed-valve
and arrangement of outside cooling
circuit. The water enters at A, and
the flow is regulated by the needle-
valve at left-hand side. Rate of flow
can be seen at end of exit tube just
above the union. The water flows
out at C and compressed air is ad-
mitted at B, regulated by the pet-
cock.
THE CALORIMETER. 19
what 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 THEKMO-ELECTBIC 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 prac-
tical as the system of iron-German-silver thermo-electric elements origi-
nally 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 construc-
tion 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-.T in fig. 25.
One ever-present difficulty with the older form of element was the ten-
dency 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,* 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
*W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances
for the direct determination of oxygen. Carnegie Institution of Washington Pub-
lication No. 42, p. 114. (1905.)
20 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
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 junc-
tions 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 per-
manently installed in the interior of the chamber. The heat-absorber con-
sists 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 milli-
meters from each other. This increases enormously the area for the absorp-
THE CALORIMETER. 21
tion 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 prac-
ticable. The total length of heat-absorbers is 5.6 meters and a rough calcu-
lation 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 stand-
ard 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 sensa-
tion of extreme dryness in the air taken in at the nostrils, nor is the absorp-
tion of water from the skin of the face, head, or neck great enough to pro-
duce 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 diffi-
culty 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 neces-
sary, however, to make a correction for the heat developed, amounting
usually to not far from 3 calories per hour.
22
CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
By means of a hand microphone and receiver, the subject can communi-
cate 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 con-
nection 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 am-
ple pressure for all pur-
poses.
The water descends
from this tank in a large
2-inch pipe to the ceiling
of the calorimeter labora-
tory, where it is subdi-
vided into three 1-inch
pipes, so as to provide
for a water-supply for
three calorimeters used
simultaneously, if neces-
sary, 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
Fig. 14. — Schematic diagram of water circuit for heat-absorbers of
calorimeter. A, constant-level tank from which water de-
scends to main pipe supplying heat-absorbers; o, valve for
controlling supply from tank A; B, section of piping passing
into cold brine; 6, valve controlling water direct from large
tank A; c, valve controlling amount of water from cooling
section B; C, thermometer at mixer; D, electric heater for
ingoing water; E, thermometer for ingoing water; d d d,
heat-absorbers inside calorimeter; F, thermometer indicating
temperature of outcoming water; G, can for collecting water
from calorimeter; f, valve for emptying G.
THE CALORIMETER- 23
cooler B, and by adjusting the valve 6 and valve c any desired mixture of
water can be obtained. A thermometer C gives a rough idea of the tem-
perature 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 calo-
rimeter, 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 / the water is conducted to the drain
after having been weighed.
Brine-tank. — The cooling system for the water-supply consists of a tank
in which there is immersed an iron coil connected by two valves to the
supply and return of the brine mains from the central power-house. These
valves are situated just ahead of the valves controlling the cooling device in
the refrigeration room and permit the passage of brine through the coil
without filling the large coils for the cooling of the air in the calorimeter
laboratory. As the brine passes through this coil, which is not shown in
the figure, it cools the water in which it is immersed and the water in turn
cools the coil through which the water-supply to the calorimeter passes.
The brass coil only is shown in the figure. The system is very efficient and
we have no difficulty in cooling the water as low as 2° C. As a matter of fact
our chief difficulty is in regulating the supply of brine so as not to freeze
the water-supply.
Water-mixer. — If the valve 6 is opened, water flows through this short
length of pipe much more rapidly than through the long coil, owing to the
greater resistance of the cooling coil. In conducting these experiments the
valve c is opened wide and by varying the amount to which the valve & is
opened, the water is evenly and readily mixed. The thermometer C is in
practice immersed in the water-mixer constructed somewhat after the prin-
ciple of the mixer inside the chamber described on page 21. All the piping,
including that under the floor, and the reheater D, are covered with hair-felt
and well insulated.
Rate-valves. — It has been found extremely difficult to secure any form of
valve which, even with a constant pressure of water, will give a constant
rate of flow. In this type of calorimeter it is highly desirable that the rate
of flow be as nearly constant as possible hour after hour, as this constant
rate of flow aids materially in maintaining the calorimeter at an even
temperature. Obviously, fluctuations in the rate of flow will produce fluc-
tuations in the temperature of the ingoing water and in the amount of
24 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
heat brought away. This disturbs greatly the temperature equilibrium,
which is ordinarily maintained fairly constant. Just before the water
enters the reheater D it is caused to pass through a rate-valve, which at
present consists of an ordinary plug-cock. At present we are experimenting
with other types of valves to secure even greater constancy, if possible.
Electric reheater. — In order to control absolutely the temperature of the
water entering at E, it is planned to cool the water leaving the water-
mixer at C somewhat below the desired temperature, so that it is necessary
to reheat it to the desired point. This is done by passing a current of
electricity through a coil inserted in the system at the point D. This
electric reheater consists of a standard " Simplex " coil, so placed in the
copper can that the water has a maximum circulation about the heater.
The whole device is thoroughly insulated with hair-felt. By connecting
the electric reheater with the rheostat on the observer's table, control of the
quantity of electricity passing through the coil is readily obtained, and
hence it is possible to regulate the temperature 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
made either by (1) increasing the rate of flow or (2) by varying the tem-
perature of the ingoing water. Usually only the second method is neces-
sary. In the older form of apparatus a third method was possible, namely,
by varying the area of the absorbing surface of the cooling system inside
of the chamber. This last method of regulation, which was used almost
exclusively in earlier experiments, called for an elaborate system of shields
which could be raised or lowered at will by the operator outside, thus
involving an opening through the chamber which was somewhat difficult
to make air-tight and also considerably complicating the mechanism inside
the chamber. The more recent method of control by regulating the tem-
perature of the ingoing water by the electric reheater has been much refined
and has given excellent service.
Insulation of water-pipes through the wall. — To insulate the water-pipes
as they pass through the metal walls of the calorimeter and to prevent any
cooling effect not measured by the thermometers presented great difficulties.
The device employed in the Middletown chamber was relatively simple, but
very inaccessible and a source of more or less trouble, namely, a large-sized
glass tube embedded in a large round wooden plug with the annular space
between the glass and wood filled with wax. An attempt was made in the
new calorimeters to secure air insulation by using a large-sized glass tube,
some 15 millimeters internal diameter, and passing it through a large rub-
ber stopper, fitting into a brass ferule soldered between the zinc and copper
walls. (See N, fig. 25.) So far as insulation was concerned, this arrange-
ment was very satisfactory, but unfortunately the glass tubes break readily
THE CALORIMETER. 25
and difficulty was constantly experienced. An attempt was next made to
substitute hard-rubber tubing for the glass tube, but this did not prove to
be an efficient insulator. More recently we have used with perfect success
a special form of vacuum-jacketed glass tube, which gives the most satis-
factory insulation. However, this system of insulation is impracticable
when electric-resistance thermometers are used for recording the water-
temperature differences and can be used only when mercurial thermometers
exclusively are employed. The electric-resistance thermometers are con-
structed in such a way, however, as to make negligible any inequalities in
the passage of heat through the hard-rubber casing. This will be seen in
the discussion of these thermometers.
Measuring the water. — As the water leaves the respiration chamber it
passes through a valve which allows it to be deflected either into the drain
during the preliminary period, or into a small can where the measure-
ments of the rate of flow can readily be made, or into a large tank (G, fig.
14) where the water is weighed. The measurement of the water is made by
weight rather than by volume, as it has been found that the weighing may
be carried out with great accuracy. The tank, a galvanized-iron ash-can,
is provided with a conical top, through an opening in which a funnel is
placed. The diagram shows the water leaving the calorimeter and entering
the meter through this funnel, but in practice it is adjusted to enter through
an opening on the side of the meter. After the valve f is tightly closed the
empty can is weighed.
When the experiment proper begins the water-current is deflected so as
to run into this can and at the end of an hour the water is deflected into
a small can used for measuring the rate of flow. While it is running into
this can, the large can G is weighed on platform scales to within 10 grams.
After weighing, the water is again deflected into the large can and that
collected in the small measuring can is poured into G through the funnel.
The can holds about 100 liters of water and consequently from 3 to 8 one-
hour periods, depending upon the rate of flow, can be continued without
emptying the meter. When it is desired to empty the meter at the end of
the period, the water is allowed to flow into the small can, and after weigh-
ing G, the valve f is opened. About 4 minutes are required to empty the
large can. After this the valve is again closed, the empty can weighed, and
the water in the small measuring-can poured into the large can G through
the funnel. The scales used are the so-called silk scales and are listed by
the manufacturers to weigh 150 kilograms. This form of scales was formerly
used in weighing the man inside the chamber.*
*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, p. 158. (1905.)
26 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
THERMOMETERS.
In connection with the calorimeter and the accessories, mercurial and
electric-resistance thermometers are employed. For measuring the tem-
perature of the water as it enters and leaves the chamber through horizontal
tubes, mercurial thermometers are used, and these are supplemented by
electric-resistance thermometers which are connected with a special form of
recording instrument for permanently recording the temperature differ-
ences. For the measurement of the temperatures inside of the calorimeter,
two sets of electric-resistance thermometers are used, one of which is a
series of open coils of wire suspended in the air of the chamber so as to
take up quickly the temperature of the air. The other set consists of resist-
ance coils encased in copper boxes soldered to the copper wall and are
designed to indicate the temperature of the copper wall rather than that
of the air.
MERCURIAL THERMOMETERS.
The mercurial thermometers used for measuring the temperature differ-
ences of the water-current are of special construction and have been cali-
brated with the greatest accuracy. As the water enters the respiration
chamber through a horizontal tube, the thermometers are so constructed
and so placed in the horizontal tubes through which the water passes that
the bulbs of the thermometers lie about in a plane with the copper wall,
thus taking the temperature of the water immediately as it enters and as it
leaves the chamber. For convenience in reading, the stem of the ther-
mometer is bent at right angles and the graduations 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 it is
possible to read accurately to the hundredth of a degree. For calibrating
these thermometers a special arrangement is necessary. The standards used
consist of well-constructed metastatic thermometers of the Beckmann type,
made by C. Eichter, of Berlin, and calibrated by the Physikalische Tech-
nische Eeichsanstalt. Furthermore, a standard thermometer, graduated
from 14° to 24° C, also made by Eichter and standardized by the Physi-
kalische Technische Eeichsanstalt, serves as a basis for securing the absolute
temperature. Since, however, on the mercurial thermometers used in the
water-current, differences in temperature are required rather than absolute
temperatures, it is unnecessary, except in an approximate way, to stand-
ardize the thermometers on the basis of absolute temperature. For cali-
brating the thermometers, an ordinary wooden water-pail is provided with
several holes in the side near the bottom. One-hole rubber stoppers are
inserted in these holes and through these are placed the bulbs and stems of
the different thermometers which are to be calibrated. The upright por-
THE CALORIMETER. 27
tion of the stem is held in a vertical position by a clamp. The pail is filled
with water, thereby insuring a large mass of water and slow temperature
fluctuations, and the water is stirred by means of an electrically driven
turbine stirrer.
The Beckmann thermometers, of which two are used, are so adjusted
that they overlap each other and thus allow a range of 8° to 14° C. without
resetting. For all temperatures above 14° C, the standard Richter ther-
mometer can be used directly. For temperatures at 8° C. or below, a large
funnel filled with cracked ice is placed with the stem dipping into the water.
As the ice melts, the cooling effect on the large mass of water is sufficient
to maintain the temperature constant and compensate the heating effect of
the surrounding room-air. The thermometers are tapped and read as nearly
simultaneously as possible. A number of readings are taken at each point
and the average readings used in the calculations. Making due allowance
for the corrections on the Beckmann thermometers, the temperature differ-
ences can be determined to less than 0.01° C. The data obtained from the
calibrations are therefore used for comparison and a table of corrections is
prepared for each set of thermometers used. It is especially important that
these thermometers be compared among themselves with great accuracy,
since as used in the calorimeter the temperature of the ingoing water is
measured on one thermometer and the temperature of the outgoing water
on another.
Thermometers of this type are extremely fragile. The long angle with
an arm some 35 centimeters in length makes it difficult to handle them
without breakage, but they are extremely sensitive and accurate and have
given great satisfaction. The construction of the bulb is such, however,
that the slightest pressure on it raises the column of mercury very percep-
tibly, and hence it is important in practical use to note the influence of the
pressure of the water upon the bulbs and make corrections therefor. The
influence of such pressure upon thermometers used in an apparatus of this
type was first pointed out by Armsby,* and with high rates of flow, amount-
ing to 1 liter or more per minute, there may be a correction on these ther-
mometers amounting to several hundredths of a degree. We have found
that, as installed at present, with a rate of flow of less than 400 cubic cen-
timeters per minute, there is no correction for water pressure.
In installing a thermometer it is of the greatest importance that there
be no pressure against the side of the tube through which the thermometer
is inserted. The slightest pressure will cause considerable rise in the mer-
cury column. Special precautions must also be taken to insulate the tube
through which the water passes, as the passage of the water along the tube
does not insure ordinarily a thorough mixing, and by moving the thermom-
* Armsby: U. S. Dept. of Agr., Bureau of Animal Industry Bull. 51 p 34
(1903.)
28
CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
eter bulb from the center of the tube to a point near the edge, the water,
which at the edge may be somewhat warmer than at the center, immediately
affects the thermometer. By use of the vacuum jacket mentioned above,
this warming of the water has been avoided, and in electric-resistance ther-
mometers special precautions are taken not only with regard to the relative
position of the bulb of the mercury thermometer and the resistance ther-
mometer, but also with regard to the hard-rubber insulation, to avoid errors
of this nature.
ELECTRIC-RESISTANCE THERMOMETERS.
Electric-resistance thermometers are used in connection with the respira-
tion calorimeter for several purposes : first, to determine the fluctuations in
the temperature of the air inside the chamber; second, to measure the
fluctuations of the temperature of the copper wall of the respiration cham-
ber; third, for determining the variations in body tem-
perature ; finally, for recording the differences in tempera-
ture of the incoming and outgoing water. While these
thermometers are all built on the same principle, their
installation is very different, and a word regarding the
method of using each is necessary.
AIR THERMOMETERS.
The air thermometers are designed with a special view
to taking quickly the temperature of the air. Five ther-
mometers, each having a resistance of not far from 4 ohms,
are connected in series and suspended 3.5 centimeters from
the wall on hooks inside the chamber. They are surrounded
for protection, first, with a perforated metal cylinder, and
outside this with a wire guard.
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 rod 12.5 centimeters long and
12 millimeters in diameter, and around each strip is wound
5 meters of double silk-covered pure copper wire (wire-gage
No. 30). By means of heavy connecting wires, five of these
thermometers are connected in series, giving a total resist-
ance of the system of not far from 20 ohms. The ther-
mometer proper is suspended between two hooks by rubber
bands and these two hooks are in turn fastened to a wire
guard which is attached to threaded rods soldered to the inner surface of the
copper wall, thus bringing the center of the thermometer 3.4 centimeters
from the copper wall. Two of these thermometers are placed in the dome
of the calorimeter immediately over the shoulders of the subject, and the
other three are distributed around the sides and front of the chamber. This
Fig. 15.— Detail of
air-resistanae
thermometer,
showing method
of mounting and
wiring the ther-
mometer. Parts
of the wire guard
and brass guard
are shown, cut
away so that in-
terior structure
can be seen.
THE CALORIMETER. 29
type of construction gives maximum sensibility to the temperature fluctua-
tions of the air itself and yet insures thorough protection. The two termi-
nals are carried outside of the respiration chamber to the observer's table,
where the temperature fluctuations are measured on a Wheatstone bridge.
WALL THEBMOMETEBS.
The wall thermometers are designed for the purpose of taking the tem-
perature of the copper wall rather than the temperature of the air. When
temperature fluctuations are being experienced inside of the respiration
chamber, the air obviously shows temperature fluctuations first, and the
copper walls are next affected. Since in making corrections for the hydro-
thermal equivalent of the apparatus and for changes in the temperature
of the apparatus as a whole it is desirable to know the temperature changes
of the wall rather than the air, these wall thermometers were installed for
this special purpose. In construction they are not unlike the thermometers
used in the air, but instead of being surrounded by perforated metal they
are encased in copper boxes soldered directly to the wall. Five such ther-
mometers are used in series and, though attached permanently to the wall,
they are placed in relatively the same position as the air thermometers. The
two terminals are conducted through the metal walls to the observer's table,
where variations in resistance are measured. The resistance of the five
thermometers is not far from 20 ohms.
ELECTRICAL RECTAL THERMOMETER.
The resistance thermometer used for measuring the temperature of the
body of the man is of a somewhat different type, since it is necessary to
wind the coil in a compact form, inclose it in a pure silver tube, and con-
nect it with suitable rubber-covered connections, so that it can be inserted
deep in the rectum. The apparatus has been described in a number of
publications.* The resistance of this system is also not far from 20 ohms,
thus simplifying the use of the apparatus already installed on the observer's
table.
ELECTRIC-RESISTANCE THERMOMETERS FOR THE WATER-CURRENT.
The measurement of the temperature differences of the water-current by
the electric-resistance thermometer was tried a number of years ago by
Rosa,f but the results were not invariably satisfactory and in all the sub-
* Benedict and Snell: Eine neue Methode um Korpertemperaturen zu messen.
Archiv f. d. ges. Physiologic Bd. 88, pp. 492-500. (1901.)
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, p. 156. (1905.)
fRosa: U. S. Dept. of Agric, Office of Experiment Stations Bui. 63, p. 25.
30
CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
sequent experimenting the resistance thermometer could not be used with
satisfaction. More recently, plans were made to incorporate some of the
results of the rapidly accumulating experience in the use of resistance ther-
mometers and consequently an electric-resistance thermometer was devised
to meet the conditions of experimentation with the respiration calorimeter
by Dr. E. F. Northrup, of the Leeds & Northrup Company, of Philadelphia.
The conditions to be met were that the thermometers should take rapidly
the temperature of the ingoing and outcoming water and that the fluctua-
tions in temperature difference as measured by the resistance thermometers
should be controlled for calibration purposes by the differences in tempera-
ture of the mercurial thermometers.
For the resistance thermometer, Dr. Northrup has used, instead of copper,
pure nickel wire, which has a much higher resistance and thus enables a
J" A
Fig. 16. — Details of resistance thermometers for water-circuit. Upper part of
figure shows a sketch of the outside of the hard-rubber case. In lower part
is a section showing interior construction. Flattened lead tube wound about
central brass tube contains the resistance wire. A is enlarged part of the case
forming a chamber for the mercury bulb. Arrows indicate direction of flow
on resistance thermometer for ingoing water.
much greater total resistance to be inclosed in a given space. The insu-
lated nickel wire is wound in a flattened spiral and then passed through a
thin lead tube flattened somewhat. This lead tube is then wound around
a central core and the flattened portions attached at such an angle that the
water passing through the tubes has a tendency to be directed away from
the center and against the outer wall, thus insuring a mixing of the water.
Space is left for the insertion of the mercurial thermometer. With the
thermometer for the ingoing water, it was found necessary to extend the
bulb somewhat beyond the resistance coil, so that the water might be
thoroughly mixed before reaching the bulb and thus insure a steady tem-
perature. Thus it was found necessary to enlarge the chamber A (fig. 16)
somewhat and the tube leading out of the thermometer, so that the bulb of
the thermometer itself could be placed almost directly at the opening of the
exit tube. Under these conditions perfect mixing of water and constancy
of temperature were obtained.
THE CALORIMETER. 31
In the case of the thermometer which measured the outcoming water,
the difficulty was not so great, as the outcoming water is somewhat nearer
the temperature of the chamber, and the water as it leaves the thermometer
passes first over the mercurial thermometer and then over the resistance
thermometer. By means of a long series of tests it was found possible to
adjust these resistance thermometers so that the variations in resistance
were in direct proportion to the temperature changes noted on the mercu-
rial thermometers. Obviously, these differences in resistance of the two
thermometers can be measured directly with the Wheatstone bridge, but,
what is more satisfactory, they are measured and recorded directly on a
special type of automatic recorder described beyond.
OBSERVER'S TABLE.
The measurements of the temperature of the respiration chamber, of the
water-current, and of the body temperature of the man, as well as the heating
and cooling of the air-spaces about the calorimeter, are all under the control
of the physical assistant. The apparatus for these temperature controls
and measurements is all collected compactly on a table, the so-called " ob-
server's table." At this, the physical assistant sits throughout the experi-
ments. For convenience in observing the mercurial thermometers in the
water-current and general inspection of the whole apparatus, this table
is placed on an elevated platform, shown in fig. 3. Directly in front of the
table the galvanometer is suspended from the ceiling and a black hood
extends from the observer's table to the galvanometer itself. On the ob-
server's table proper are all the electrical connections and at the left are the
mercurial thermometers for the chair calorimeter. Formerly, when the
method of alternately cooling and heating the air-spaces was used, the
observer was able to open and close the water-valves without leaving the
chair.
The observer's table is so arranged electrically as to make possible tem-
perature control and measurement of either of the two calorimeters. It is
impossible, however, for the observer to read the mercurial thermometers
in the bed calorimeter without leaving his chair, and likewise he must
occasionally alter the cooling water flowing through the outer air-spaces
by going to the bed calorimeter itself. The installation of the electric-
resistance thermometers connected with the temperature recorder does away
with the reading of the mercurial thermometers, save for purposes of com-
parison, and hence it is unnecessary for the assistant to leave the chair at
the observer's table when the bed calorimeter is in use. Likewise the sub-
stitution of the method of continuously cooling somewhat the air-spaces
and reheating with electricity, mentioned on page 18, does away with the
necessity for alternately opening and closing the water-valves of the chair
calorimeter placed at the left of the observer's table.
32
CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
Of special interest are the electrical connections on the observer's table
itself. A diagrammatic representation of the observer's table with its con-
nections is shown in fig. 17. The heavy black outline gives in a general
way the outline of the table proper and thus shows a diagrammatic distribu-
tion of the parts. The first of the electrical measurements necessary dur-
RESISTANCE THERMOMETERS
WALL AIR RECTAL
y WVWV 1
67* s
O O O 0 o
5432)
7S7
tow
www
www
S,o
Fig. 17. — Diagram of wiring of observer's table. Wi, W2, Wheatstone bridges for resistance thermom-
eters; Ki, K2, double contact keys for controlling Wheatstone circuits; Si, S2, Ss, double-pole double-
throw switches for changing from chair to bed calorimeter; S4, double-pole double-throw switch for
changing from wall to air thermometers; G, galvanometer; R2, rheostat. 1, 2, 3, 4, 5, wires connect-
ing with resistance-coils A B D E F and a b d e f; S7, 6-point switch for connecting thermal-
junction circuits of either bed or chair calorimeter with galvanometer; Si0, 10-point double-throw
switch for changing heating circuits and thermal -junction circuits to either chair or bed calorimeter;
Ri, rheostat for controlling electric heaters in ingoing water in calorimeters; SB, double-pole single-
throw switch for connecting 110-v. current with connections on table; S9, double-pole single-throw
switch for connecting Ri with bed calorimeter.
THE CALORIMETER. 33
ing experiments is that of the thermo-electric effect of the thermal junction
systems installed on the calorimeters. To aid in indicating what parts of
the zinc wall need cooling or heating, the thermal junction systems are, as
has already been described, separated into four sections on the chair calo-
rimeter and three sections on the bed calorimeter; in the first calorimeter,
the top, 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 both calo-
rimeters at the same time, the electrical connections are so made that, by
means of electrical switches, either calorimeter can be connected to the
apparatus on the table.
The thermal-junction measurements are made by a semicircular switch
S-. The various points, I, n, in, rv, etc., are connected with the different
thermal-junction systems. Thus, by following the wiring diagram, it can
be seen that the connections with I run to the different binding-posts of the
switch S10, which as a matter of fact is placed beneath the table. This
switch S10 has three rows of binding-posts. The center row connects di-
rectly with the apparatus on the observer's table, the outer rows connect
with either the chair calorimeter or the bed calorimeter. The points marked
a, b, d, e, f, etc., connect with the bed calorimeter and A, B. D, etc., connect
with the chair calorimeter. Thus, by connecting the points g and t with
the two binding-posts opposite them on the switch S10, it can be seen that
this connection leads directly to the point I on the switch S7, and as a
matter of fact this gives direct connection with the galvanometer through
the key on S7, thus connecting the thermal- junction system on one section
of the bed calorimeter between g and t directly with the galvanometer.
Similar connections from the other points can readily be followed from
the diagram. The points on the switch S7 indicated as i, 11, m, rv, cor-
respond respectively to the thermal-junction systems on the top, rear, front,
and bottom of the chair calorimeter.
By following the wiring diagram of the point v, it will be seen that this
will include the connections with the thermal junctions connected in series
and thus give a sum total of the electromotive forces in the thermal junc-
tions. The point vi is connected with the thermal- junction system in the
air system, indicating the differences in temperature between the ingoing
and outgoing air. It will be noted that there are four sections in the chair
calorimeter, while in the bed calorimeter there are but three, and hence a
special switch S8 is installed to insure proper connections when the bed
calorimeter is in use.
This system of connecting the thermal junctions in different sections to
the galvanometer makes possible a more accurate control of the tempera-
34 CALORIMETERS FdR STUDYING RESPIRATORY EXCHANGE, ETC.
tures in the various parts, and while the algebraic sum of the temperature
differences of the parts may equal zero, it is conceivable that there may be
a condition in the calorimeter when there is a considerable amount of heat
passing out through the top, for example, compensated exactly by the heat
which passes in at the bottom, and while with the top section there would be
a large plus deflection on the galvanometer, thus indicating that the air
around the zinc wall was too cold and that heat was passing out, there
would be a corresponding minus deflection on the bottom section, indicat-
ing the reverse conditions. The two may exactly balance each other, but
it has been found advantageous to consider each section as a unit by itself
and to attempt delicate temperature control of each individual unit. This
has been made possible by the electrical connections, as shown on the
diagram.
RHEOSTAT FOR HEATING.
The rheostat for heating the air-spaces and the returning air-current
about the zinc wall is placed on the observer's table and is indicated in the
diagram as E2. There are five different sets of contact-points, marked 1, 2,
3, 4, and 5. One end of the rheostat is connected directly with the 110-
volt circuit through the main switch S5. The other side of the switch S5
connects directly with the point on the middle of switch S10, and when this
middle point is joined with either f and F, direct connection is insured
between all the various heating-circuits on the calorimeter in use. The
various numbered points on the rheostat R2 are connected with the binding
posts on S10, and each can in turn be connected with a or A, & or B, etc.
The heating of the top of the chair calorimeter is controlled by the point 5
on the rheostat E2, the rear by the point 4, the front by the point 3, and
the bottom by the point 2. Point 1 is used for heating the air entering the
calorimeter by means of an electric lamp placed in the air-pipe, as shown
in fig. 25.
The warming of the electrical reheater placed in the water-circuit just
before the water enters the calorimeter is done by an electrical current con-
trolled by the resistance Rx. This Rx is connected on one end directly with
the 110-volt circuit and the current leaving it passes through the resistance
inside the heater in the water-current. The two heaters, one for each calo-
rimeter, are indicated on the diagram above and below the switch S9. The
disposition of the switches is such as to make it possible to use alternately
the reheaters on either the bed or the chair calorimeter, and the main
resistance Ra suffices for both.
WHEATSTONE BRIDGES.
For use in measuring the temperature of the air and of the copper wall
of the calorimeters, as well as the rectal temperature of the subject, a series
/
THE CALORIMETER. 35
of resistance thermometers is employed. These are so connected on the
observers table that they may be brought into connection with two Wheat-
stone bridges, Wx and W2. Bridge W, is used for the resistance ther-
mometers indicating the temperature of the wall and the air. Bridge W2
is for the rectal thermometer. Since similar thermometers are inserted in
both calorimeters, it is necessary to introduce some switch to connect either
set at will and hence the double-throw switches S1? S2, and S3 allow the use
of either the wall, air, or rectal thermometer on either the bed or chair
calorimeter at will. Since the bridge Wx is used for measuring the tem-
perature of both the wall and the air, a fourth double-pole switch, S4, is
used to connect the air and wall thermometers alternately. The double-
contact key, K1? is connected with the bridge vv\ and is so arranged that the
battery circuit is first made and subsequently the galvanometer circuit.
A similar arrangement in K2 controls the connections for the bridge W2.
GALVANOMETER.
The galvanometer is of the Deprez-d'Arsonval type and is extremely
sensitive. The sensitiveness is so great that it is desirable to introduce a
resistance of some 500 ohms into the thermal-junction circuits. This is
indicated at the top of the diagram near the galvanometer. The maximum
sensitiveness of the galvanometer is retained when the connection is made
with the Wheatstone bridges. The galvanometer is suspended from the
ceiling of the calorimeter laboratory and is free from vibration.
RESISTANCE FOR HEATING COILS.
To vary the current passing through the manganin heating coils in the
air-spaces next the zinc wall, a series of resistances is installed connected
directly with the rheostat E2 in fig. 17. The details of these resistances
and their connection with the rheostat are shown in fig. 18. The rheostat,
which is in the right part of the figure, has five sliding contacts, each of
which can be connected with ten different points. One end of the rheostat
is connected directly with the 110-volt circuit. Beneath the observer's
table are fastened the five resistances, which consist of four lamps, each
having approximately 200 ohms resistance and then a series of resistance-
coils wound on a long strip of asbestos lumber, each section having approxi-
mately 15 ohms between the binding-posts. A fuse-wire is inserted in
each circuit to protect the chamber from excessive current. Of these re-
sistances, No. 1 is used to heat the lamp in the air-current shown in fig. 25,
and consequently it has been found advisable to place permanently a second
lamp in series with the first, but outside of the air-pipe, so as to avoid
burning out the lamp inside of the air-pipe. The other four resistances,
2, 3, 4, and 5, are connected with the different sections on the two calorim-
eters. No. 5 corresponds to the top of both calorimeters. No. 4 corre-
36
CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
sponds to the rear section of the chair calorimeter and to the sides of the
bed calorimeter. No. 3 corresponds to the front of the chair 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 be
connected at will with either the bed or the chair calorimeter and at such
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 the corresponding
resistance in series with the lamp in the air-current. The sliding contacts
I5~ PER SECTION
SLIDINC CONTACT
Fig. 18. — Diagram of rheostat and resistances in series with it. At the right are
shown the sliding contacts, and in the center places for lamps used as resist-
ances, and to left the sections of wire resistances.
at present in use are ill adapted to long-continued usage and will therefore
shortly be substituted by a more substantial instrument. The form of re-
sistance using small lamps and the resistance wires wound on asbestos lumber
has proven very satisfactory and very compact in form.
TEMPERATURE RECORDER.
The numerous electrical, thermometric, and chemical measurements neces-
sary in the full conduct of an experiment with the respiration calorimeter
has often raised the question of the desirability of making at least a por-
tion of these observations more or less automatic. This seems particularly
feasible with the observations ordinarily recorded by the physical observer.
These observations consist of the reading of the mercurial thermometers
indicating the temperatures of the ingoing and outcoming water, records
THE CALORIMETER. 37
with the electric-resistance thermometers for the temperature of the air
and the walls and the body temperatures, and the deflections of the thermo-
electric elements.
Numerous plans have been proposed for rendering automatic some of
these observations, as well as the control of the heating and cooling of the
air-circuits. Obviously, such a record of temperature measurements would
have two distinct advantages: (1) in giving an accurate graphic record
which would be permanent and in which the influence of the personal
equation would be eliminated; (2) while the physical observer at present
has much less to do than with the earlier form of apparatus, it would
materially lighten his labors and thereby tend to minimize errors in the
other observations.
The development of the thread recorder and the photographic registration
apparatus in recent years led to the belief that we could employ similar
apparatus in connection with our investigations in this laboratory. To
this end a number of accurate electrical measuring instruments were pur-
chased, and after a number of tests it was considered feasible to record
automatically the temperature differences of the ingoing and outcoming
water from the calorimeter. Based upon our preliminary tests, the Leeds &
Xorthrup Company of Philadelphia, whose experience with such problems
is very extended, were commissioned to construct an apparatus to meet
the requirements of the respiration calorimeter. The conditions to be met
by this apparatus were such as to call for a registering recorder that would
indicate the differences in temperature between the ingoing and outcoming
water to within 0.5 per cent and to record these differences 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 any one 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 of
satisfaction the conditions imposed. The thermometers themselves have
already been discussed. (See page 30.) The recording apparatus consists
of three parts: (1) the galvanometer; (2) the creeper or automatic sliding-
contact; (3) the clockwork for the forward movement of the roll of co-
ordinate paper and to control the periodic movement of the creeper.
Under ordinary conditions with rest experiments in the chair calorim-
eter or bed calorimeter, the temperature differences run not far from 2° to
4°. Thus, it is seen that if the apparatus is to meet the conditions of the
specifications it must measure differences of 2° C. to within 0.01° C. Pro-
vision has also been made to extend the measurement of temperature differ-
ences with the apparatus so that a difference of 8° can be measured with the
same percentage accuracy.
38
CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
5
FUNDAMENTAL PRINCIPLE OF THE APPARATUS.
The apparatus depends fundamentally upon the perfect balancing of the
two sides of a differential electric circuit. A conventional diagram, fig. 19,
gives a schematic outline of the connections. The two galvanometer coils,
fl and fr, are wound differentially and both coils most carefully balanced
so that the two windings have equal temperature coefficients. This is done
by inserting a small shunt y, parallel with the coil fl, and thus the tempera-
ture coefficient of fl and fr are made
absolutely equal. The two thermome-
ters are indicated as T1 and T, and are
inserted in the ingoing and outgoing
water respectively. A slide-wire resist-
ance is indicated by J, and r is the re-
sistance for the zero adjustment. Ba,
Z, and Z1 are the battery and its variable
series resistances. If Tt and T2 are
exactly of the same temperature, i. e.,
if the temperature difference of the in-
going and outeoming water is zero, the
sliding contact q stands at 0 on the
slide-wire and thus the resistance of
the system from 0 through fl, r, and Tx
back to the point C is exactly the same
as the resistance of the slide-wire J
plus the coil fr plus T2 back to the
point C. A rise in temperature of T2
gives an increase of resistance in the
circuit and the sliding contact q moves
along the slide- wire toward J maximum
until a balance is obtained.
Provision is made for automatically
moving the contact q by electrical
means and thus the complete balance
of the two differential circuits is maintained constant from second to second.
As the contact q is moved, it carries with it a stylographic pen which travels
in a straight line over a regularly moving roll of coordinate paper, thus pro-
ducing a permanently recorded curve indicating the temperature differences.
The slide-wire J is calibrated so that any inequalities in the temperature
coefficient of the thermometer wires are equalized and also so that any unit-
length on the slide-wire taken at any point along the temperature scale rep-
resents a resistance equal to the resistance change in the thermometer for
that particular change in temperature. With the varying conditions to be
met with in this apparatus, it is necessary that varying values should be
Fig. 19. — Diagram of wiring of differential cir-
cuit with its various shunts, used in con-
nection with resistance thermometers on
water-circuit of bed calorimeter.
THE CALORIMETER. 39
assigned at times to J and to r. This necessitates the use of shunts, and the
recording range of the instrument can be easily varied by simple shunting,
i. e ., by changing the resistance value of J and r, providing these resistances
unshunted have a value which takes care of the highest obtained temperature
variations.
Fig. 19 shows the differential circuit complete with all its shunts. S is
a fixed shunt to obtain a range on J ; S' is a variable shunt to permit very
slight variations of J within the range to correct errors due to changing of
the initial temperatures of the thermometers ; y is a permanent shunt across
the galvanometer coil fl, to make the temperature coefficients of fl and fr
absolutely equal; Z is the variable resistance in the battery-circuit to keep
the current constant; r is a permanent resistance to fix the zero on varying
ranges; S" plus Sx constitutes a variable shunt to permit slight variations
of r to finally adjust 0 after S' is fixed and t is a permanent shunt across
the thermometer Tx to make the temperature coefficient of T1 equal to that
of T2.
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 is
open-circuited and the shunt S' alone used. The value of S, then, is pre-
determined so as to affect the value of the wire J and thus halve its influence
in maintaining the balance. Similarly, when the lower range, t. e., from
0° to 4°, is used, the resistance r is employed, and when the higher range is
used another value to r must be given by using a plug resistance-box, in the
use of which the resistance r is doubled.
The resistance S" and Sx are combined in a slide-wire resistance-box and
are used to change the value of the whole apparatus when there are marked
changes in the position of the thermometric scale. Thus, if the ingoing
water is at 2° C. and the outcoming water at 5° C. in one instance, and in
another instance the ingoing water is 13° and the outgoing water is 15°, a
slight alteration in the value of Sx, and also of S', is necessary in order to
have the apparatus draw a curve to represent truly the temperature differ-
ences. These slight alterations are determined beforehand by careful tests
and the exact value of the resistances in" S' and in Si are permanently
recorded for subsequent use.
THE GALVANOMETER.
The galvanometer is of the Deprez-d'Arsonval type and has a particularly
powerful magnetic field, in which a double coil swings suspended similar
to the marine galvanometer coils. This coil is protected from vibrations
by an anti-vibration tube A, fig. 20, and carries a pointer P which acts to
select the direction of movement of the recording apparatus, the movable
contact point q, fig. 19. In front of this galvanometer coil and inclosed in
the same air-tight metal case is the plunger contact PI, fig. 21. The gal-
40
CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
vanometer pointer P swings freely below the silver contacts Ss and S2, just
clearing the ivory insulator i. The magnet plunger makes a contact de-
pending upon the adjustment of a clock at intervals of 2 seconds. So
long as both galvanometer coils are influenced by exactly the same strength
of current, the pointer will stand in line with and immediately below i and
no current passes through the recording apparatus. Any disturbance of the
electrical equilibrium causes the pointer P to swing either toward St or S2,
thus completing the circuit at either the right hand or the left hand, at
A
F10. 20. — Diagram of galvanometer coil used in connection with record-
ing apparatus for resistance thermometers in the water-circuit of
bed calorimeter. A, anti-vibration tube; P, pointer.
intervals of 2 seconds. The movement of the pointer away from its normal
position exactly beneath i to either St on the left hand or S2 on the right,
results from an inequality in the current flowing through the two coils in
the galvanometer. The difference in the two currents passing through these
coils is caused by a change in temperatures of the two thermometers in the
water circuit.
THE CREEPER.
The movement of the sliding-contact q, fig. 19, along the slide- wire J, is
produced by means of a special device called a creeper, consisting of a piece
of brass carefully fitted to a threaded steel rod some 30 centimeters long.
The movement of this bar along this threaded rod accomplishes two things.
THE CALORIMETER.
41
The bar is in contact with the slide-wire J and therefore varies the position
of the point q and it also carries with it a stylographic pen. The movements
of this bar to the right or the left are produced by an auxiliary electric
current, the contact of which is made by a plunger-plate forcing the pointer
P against either St or S2. P makes the contact between PI and either St
or S, and sends a current through, solen-
oids at either the right or the left of the
creeper. At intervals of every 2 seconds
the plunger rises and forces the pointer P
against either Sx, ft, or S2 above. The
movement of this plunger is controlled by
a current from a 110- volt circuit, the con-
nections of which are shown in fig. 22. If
the contact is made at T, the current
passes through 2,600 ohms, directly across
the 110- volt circuit, and consequently
there is no effective current flowing
through the plunger PI. When the con-
tact T is open, the current flows through the plunger in series with 2,600
ohms resistance. T is opened automatically at intervals of 2 seconds by the
clock.
The movement of the contact arm along the threaded rod is produced
by the action of either one of two solenoids, each of which has a core at-
tached to a rack and pinion at either end of the rod. If the current is
passed through the contact St,
Fig. 21. — Diagram of wiring
actuating plunger and creeper.
1
IIO v
600^
ooo°[^vvw\/lM/wwli
L-^V^- 350^. 350A -WV-1
IOQOOA
Lwm
a current passes through the
left-hand solenoid, the core
moves down, the rack on the
core moves the pinion on the
rod through a definite fraction
of a complete revolution and
this movement forces the
creeper in one direction. Con-
versely, the passing of the cur-
rent through the solenoid at
the other end of the threaded
rod moves the creeper in the other direction. The distance which the iron
rack on the end of the core is moved is determined carefully, so that the
threaded rod is turned for each contact exactly the same fraction of a revolu-
tion. For actuating these solenoids, the 110-volt circuit is again used. The
wire connections are shown in part in fig. 21, in which it is seen that the
current passes through the plunger-contact and through the pointer P to
the silver plate Sx and then along the line Gx throusrh 350 ohms wound
4
Fig. 22. — Diagram of wiring of complete 110-volt circuit.
42
CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
GALVANOMETER
about the left-hand solenoid back through a 600-ohm resistance to the main
line. The use of the 110-volt current under such circumstances would nor-
mally produce a notable sparking effect on the pointer P, and to reduce this
to a minimum there is a high resistance, amounting to 10,000 ohms on each
side, shunted between the main line and the creeper connections. This
shunt is shown in diagram in fig. 22. Thus there is never a complete open
circuit and sparking is prevented.
THE CLOCK.
The clock requires winding every week and is so geared as to move the
paper forward at a rate of 3 inches per hour. The contact-point for open-
ing the circuit T on fig. 22 is likewise connected with one of the smaller
wheels of the clock. This contact is made by tripping a little lever by
means of a toothed wheel of phosphor-bronze.
INSTALLATION OF THE APPARATUS.
The whole apparatus is permanently and substantially installed on the
north wall of the calorimeter laboratory. A photograph showing the vari-
ous parts and their installation
is given in fig. 23. On the top
shelf is seen the galvanometer
and on the lower shelf the re-
corder with its glass door in
front and the coordinate paper
dropping into the box below.
The curve drawn on the co-
ordinate paper is clearly shown.
Above the recorder are the re-
sistance-boxes, three in num-
ber, the lower one at the left
being the resistance 8M the
upper one at the left being the
resistance S', and the upper
one at the right being the re-
sistance Z1# Immediately above
the resistance-box Z1 is shown
the plug resistance-box which
controls on the one hand the
resistance r and on the other hand the resistance S, both of which are sub-
stantially altered when changing the apparatus to register from the 0° to 4 c
scale to the 0° to 8° scale. A detailed wiring diagram is given in fig. 24.
IIOvDC
Fig. 24.— Detailed wiring diagram showing all parts of
recording apparatus, together with wiring to ther-
mometers complete, including all previous figures.
Fig. 23
Temperature recorder. The recorder with the co-ordinate paper
in the lower box with a glass door. A curve representing the tempera-
ture difference between the ingoing and outgoing water is directly drawn
on the co-ordinate paper. Above are three resistance boxes, and the
switches for electrical connections are at the right. On the top shelf
is the galvanometer, and immediately beneath, the plug resistance box
for altering the value of certain shunts.
THE CALORIMETER.
43
TEMPERATURE CONTROL OF THE INGOING AIR.
In passing the current of air through the calorimeter, temperature con-
ditions may easily be such that the air entering is warmer than the out-
coming 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 arbitrarily controlling the
temperature of the air as it enters the calorimeter. This temperature con-
trol is based upon the fact that the air leaving the chamber is caused to
pass over the ends of a series of thermal junctions shown as 0 in fig. 25.
Fig. 25. — Section of calorimeter walls and part of ventilating air-circuit, showing part of pipes for
ingoing air and outgoing air. On the ingoing air-pipe at the right is the lamp for heating the
ingoing air. Just above it, H is the quick-throw valve for shutting off the tension equalizer IJ. I
is the copper portion of the tension equalizer, while J is the rubber diaphragm; K, the pet -cock
for admitting oxygen; F, E, G, the lead pipe conducting the cold water for the ingoing air; and C,
the hair-felt insulation. N, N are brass ferules soldered 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 of ingoing and outgoing air and U, the
connection to the outside; QQ, exits for the air-pipes from the box in which thermal junctions are
placed; P, the dividing plate separating the ingoing and outgoing air; R, the section of piping
conducting the air inside the calorimeter; S, a section 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 the 2%-inch
angle W; B, a portion of zinc wall; C, hair-felt lining of asbestos wall D; TJ, a thermal junction
In the walls.
These thermal junctions have one terminal in the outgoing air and the
other in the ingoing air, and consequently any difference in the temperature
of the two air-currents is instantly detected by connecting the circuit with
the galvanometer. Formerly the temperature control was made a varying
one, by providing for either cooling or heating the ingoing air as the situa-
tion called for. The heating was done by passing the current through an
44 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
electric lamp placed in the cross immediately below the tension equalizer J.
Cooling was effected by means of a current of water through the lead pipe
E closely wrapped around the air-pipe, water entering at F and leaving
at G. This lead pipe is insulated by hair-felt pipe-covering, C. More
recently, we have adopted the procedure of passing a continuous current of
water, usually at a very slow rate, through the lead pipe E and always
heating the air somewhat by means of the lamp, the exact temperature con-
trol being obtained by varying the heating effect of the lamp itself. This
has been found much more satisfactory than by alternating from the cool-
ing 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 for the wall con-
trol, shown in fig. 13.
THE HEAT OF VAPORIZATION OF WATER.
During experiments with man not all the heat leaves the body by radia-
tion and conduction, since a part is required to vaporize the water from
the skin and lungs. An accurate measurement of the heat production by
man therefore required a knowledge of the amount of heat thus vaporized.
One of the great difficulties in the numerous forms of calorimeters that have
been used heretofore with man is that only that portion of heat measured
by direct radiation or conduction has been measured and the difficulties
attending the determination of water vaporized have vitiated correspond-
ingly the estimates of the heat production. Fortunately, with this apparatus
the determinations of water are very exact, and since the amount of water
vaporized inside the chamber is known it is possible to compute the heat
required to vaporize this water by knowing the heat of vaporization of water.
Since the earlier reports describing the first form of calorimeters were
written, there has appeared a research by one of our former associates, Dr.
A. W. Smith * who, recognizing the importance of knowing exactly the
heat of vaporization of water at 20°, has made this a special object of inves-
tigation. When connected with our laboratory a number of experiments
were made by Doctors Smith and Benedict in an attempt to determine
the heat of vaporization of water directly in a large calorimeter; but for
lack of time and pressure of other experimental work it was impossible to
complete the investigation. Subsequently Dr. Smith has carried out the
experiments with the accuracy of exact physical measurements and has
given us a very valuable series of observations.
Using the method of expressing the heat of vaporization in electrical
units, Smith concludes that the heat of vaporization of water between 14°
and 40° is given by the formula
L (in joules) =2502.5-2.43 T
♦Smith: Heat of evaporation of water. Physical Review, vol. 25, p. 145.
(1907.)
THE CALORIMETER. 45
and states that the " probable error " of values computed from this formula
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. of the Clark
cell at 15° C, and assuming that the mean calorie is equivalent to 4.1877
international joules,* the formula reads
L (in mean calories) =597.44-0.580 T
With this formula Smith calculates that at 15° the heat of vaporization
of water is equal to 588.73 calories; at 20°, 585.84 calories; at 25°, 582.93
calories; at 30°, 580.04 calories ;f and at 35°, 577.12 calories. In all of
the calculations in the researches herewith we have used the value found
by Smith as 586 calories at 20°. Inasmuch as all of our records are in
kilo-calories, we multiply the weight of water by the factor 0.586 to obtain
the heat of vaporization.
THE BED CALORIMETER.
The chair calorimeter was designed for experiments to last not more
than 6 to 8 hours, as a person can not remain comfortably seated in a
chair much longer than this time. For longer experiments (experiments
during the night and particularly for bed-ridden patients) a type of calo-
rimeter which permits the introduction of a couch or bed has been devised.
This calorimeter has been built, tested, and used in a number of experi-
ments with men and women. The general shape of the chamber is given
in fig. 26. The principles involved in the construction of the chair calo-
rimeter are here applied, t. e., the use of a structural-steel framework, inner
air-tight copper lining, outer zinc wall, hair-felt insulation, and outer
asbestos panels. Inside of the chamber there is a heat-absorbing system
suspended from the ceiling, and air thermometers and thermometers for the
copper wall are installed at several points. The food-aperture is of the same
general type and the furniture here consists simply of a sliding frame upon
which is placed an air-mattress. The opening is at the front end of the
calorimeter and is closed by two pieces of plate glass, each well sealed into
place by wax after the subject has been placed inside of the chamber.
Tubes through the wall opposite the food-aperture are used for the intro-
duction of electrical connections, ingoing and outgoing water, the air-pipes,
and connections for the stethoscope, pneumograph, and telephone.
The apparatus rests on four heavy iron legs. Two pieces of channel iron
are attached to these legs and the structural framework of the calorimeter
chamber rests upon these irons. The method of separating the asbestos
outer panels is shown in the diagram. In order to provide light for the
♦Philosophical Transactions, vol. 199, A, p. 149. (1902.)
t This is in agreement with the value 579.6 calories found by F. Henning, Ann.
d. Physik, vol. 21, p. 849. (1906.)
46 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
chamber, the outer wall in front of the glass windows is made of glass
rather than asbestos. The front section of the outer casing can be removed
easily for the introduction of a patient.
In this chamber it is impossible to weigh the bed and clothing, and hence
this calorimeter can not be used for the accurate determination of the
moisture vaporized from the lungs and skin of the subject, since here (as
in almost every form of respiration chamber) it is absolutely impossible to
distinguish between the amount of water vaporized from bed-clothing and
that vaporized from the lungs and skin of the subject. With the chair
calorimeter, the weighing arrangements make it possible to weigh the chair,
Meter
Fig. 26. — Cross-section of bed calorimeter, showing: part of steel construction, also copper and zinc walls,
food-aperture, and wall and air-resistance thermometers. Cross-section of opening-, cross-section of
panels of insulating; asbestos, and supports of calorimeter itself are also indicated.
clothing, etc., and thus apportion the total water vaporized between losses
from the chair, furniture, and body of the man. In view of the fact that
the water vaporized from the skin and lungs could not be determined, the
whole interior of the chamber of the bed calorimeter has been coated with
a white enamel paint, which gives it a bright appearance and makes it much
more attractive to new patients. An incandescent light placed above the
head at the front illuminates the chamber very well, and as a matter of
fact the food-aperture is so placed that one can lie on the cot and actually
look outdoors through one of the laboratory windows.
Special precaution was taken with this calorimeter to make it as com-
fortable and as attractive as possible to new and possibly apprehensive
patients. The painting of the walls unquestionably results in a condensa-
tion of more or less moisture, for the paint certainly absorbs more moisture
THE CALORIMETER. 47
than does the metallic surface of the copper. The chief value of the deter-
mination of the water vaporized inside of the chamber during an experi-
ment lies, however, not in a study of the vaporization of water as such, but
in the fact that a certain amount of heat is required to vaporize the water
and obviously an accurate measure of the heat production must involve a
measure of the amount of water vaporized. So far as the measurement of
heat is concerned, it is immaterial whether the water is vaporized from the
lungs or skin of the subject or the clothing, bedding, or walls of the cham-
ber; since for every gram of water vaporized inside of the chamber, from
whatever source, 0.586 calorie of heat must have been absorbed.
The apparatus as perfected is very sensitive. The sojourn in the chamber
is not uncomfortable; as a matter of fact, in an experiment made during
January, 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 long experi-
ments to empty the lower bowel with an enema and thus defer as long as
possible the necessity for defecation. With none of the experiments thus
far made have we experienced any difficulty in having to remove the patient
because of necessity to defecate in the cramped quarters. It is highly prob-
able that, with the majority of sick patients, experiments will not extend
for more than 8 or 10 hours, and consequently the apparatus as designed
should furnish most satisfactory results.
In testing the apparatus by the electrical-check method, it has been found
to be extremelv accurate. When the test has been made with burning alco-
hoi, as described beyond, it has been found that the large amount of mois-
ture apparently retained by the white enamel paint on the walls vitiates
the determination of water for several hours after the experiment begins,
and only after several hours of continuous ventilating is the moisture con-
tent of the air brought down to a low enough point to establish equilibrium
between the moisture condensed on the surface and the moisture in the air
and thus have the measured amount of moisture in the sulphuric acid
vessels equal the amount of moisture formed by the burning of alcohol.
Hence in practically all of the alcohol-check experiments, especially of
short duration, with this calorimeter, the values for water are invariably
somewhat too high. A comparison of the alcohol-check experiments made
with the bed and chair calorimeters gives an interesting light upon the
power of paint to absorb moisture and emphasizes again the necessity of
avoiding the use of material of a hygroscopic nature in the interior of an
apparatus in which accurate moisture determinations from the body are to
be made.
The details of the bed calorimeter are better shown in fig. 4. The open-
ing at the front is here removed and the wooden track upon which the
frame, supporting the cot, slides is clearly shown. The tension equalizer
48 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
(see page 71) partly distended is shown connected to the ingoing air-pipe,
and on the top of the calorimeter connected to the tension equalizer is a
Sonden manometer. On the floor at the right is seen the resistance coil
used for electrical tests (see page 50). A number of connections inside
the chamber at the left are made with electric wires or with rubber tubing.
Of the five connections appearing through the opening, reading from left
to right, we have, first, the rubber connection with the pneumograph, then
the tubing for connection with the stethoscope, then the electric-resistance
thermometer, the telephone, and finally a push button for bell call. The
connections for the pneumograph and stethoscope are made with the in-
struments outside on the table at the left of the bed calorimeter.
MEASUREMENTS OF BODY-TEMPERATURE.
While it is possible to control arbitrarily the temperature of the calo-
rimeter by increasing or decreasing the amount of heat brought away, and
thus compensate exactly for the heat eliminated by the subject, the hydro-
thermal equivalent of the system itself being about 20 calories — on the
other hand the body of the subject may undergo marked changes in tem-
perature and thus influence the measurement of the heat production to a
noticeable degree ; for if heat is lost from the body by a fall of body-tem-
perature or stored as indicated by a rise in temperature, obviously the heat
produced during the given period will not equal that eliminated and meas-
ured by the water-current and by the latent heat of water vaporized. In
order to make accurate measurements, therefore, of the heat-production as
distinguished from the heat elimination, we should know with great accuracy
the hydrothermal equivalent of the body and changes in body temperature.
The most satisfactory method at present known of determining the hydro-
thermal equivalent of the body is to assume the specific heat of the body
as 0.83.* This factor will of course vary considerably with the weight of
body material and the proportion of fat, water, and muscular tissue present
therein, but for general purposes nothing better can at present be employed.
From the weight of the subject and this factor the hydrothermal equivalent
of the body can be calculated. It remains to determine, then, with great
exactness the body temperature.
Recognizing early the importance of securing accurate body-temperatures
in researches of this kind, a number of investigations were made and pub-
lished elsewhere f regarding the body-temperature in connection with the
*Pembrey: Schafer's Text-book of Physiology, vol. 1, p. 838. (1898.)
f Benedict and Snell: Korpertemperatur Schwankungen mit besonderer Rtick-
sicht auf den Einfluss, welchen die Umkehrung der taglichen Lebensgewohnheit
beim Menschen ausiibt. Archiv f. d. ges. Physiologie, Bd. 90. p. 33. (1902.)
Benedict: Studies in body-temperature: I. The influence of the inversion of
the daily routine: the temperature of night-workers. American Journal of Phy-
siology, vol. 11, p. 145. (1904.)
THE CALORIMETER- 49
experiments with the respiration calorimeter. It was soon found that the
ordinary mercurial clinical thermometer was not best suited for the most
accurate observations of body-temperature and a special type of thermome-
ter employing the electrical-resistance method was used. In many of the
experiments, however, it is impracticable with new subjects to complicate
the experiment by asking them to insert the electrical rectal thermometer,
and hence we have been obliged to resort to the usual clinical thermometer
with temperatures taken in the mouth, although in a few instances they
have been taken in the axilla and the rectum. 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 period of time, it being necessary to remove
the thermometer only for defecation.
As a result of these observations it was soon found that the body tem-
perature was not constant from hour to hour, but fluctuated considerably
and underwent more or less regular rhythm with the minimum between 3
and 5 o'clock in the morning and the maximum about 5 o'clock in the
afternoon. In a number of experiments where the mercurial thermometer
was used under the tongue and observations thus taken compared with
records with the resistance thermometer, it was found that with careful
manipulation and avoiding muscular activity, mouth breathing, and the
drinking of hot or cold liquid, a fairly uniform agreement between the two
could be obtained. Such comparisons made on laboratory assistants can
not be duplicated with the ordinary subject.
It is assumed that fluctuations in temperature measured by the rectal
thermometer likewise hold true for the average temperature of the whole
body, but evidence on this point is unfortunately not as complete as is
desirable. In an earlier report of investigations of this nature, a few experi-
ments on comparison of measurements of resistance thermometer deep in
the rectum and in a well-closed axilla showed a distinct tendency for the
curves to continue parallel. A research is very much needed at present on
a topographical distribution of body temperature, and particularly on the
course of the fluctuations in different parts of the body. A series of electric-
resistance thermometers placed at different points in the colon, at different
points in a stomach tube, in the well-closed axilla, possibly attached to the
surface of the body, and in women in the vagina, should give a very accurate
picture of the distribution of the body-temperature and likewise indicate
the proportionality of the fluctuations in different parts of the body. Until
such a research is completed, however, it is necessary to assume that
fluctuations in body-temperature as measured by the electric rectal ther-
mometer are a true measure of the average body-temperature of the whole
body. Indeed it is upon this assumption that it is necessary for us to make
corrections for heat lost from or stored in the body. It is our custom,
50 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
therefore, to compute the hydrothermal equivalent by multiplying the body-
weight by the specific heat of the body, commonly assumed as 0.83, and then
to make allowance for fluctuations in body-temperature.
When it is considered that with a subject having a weight of 70 kilos a
difference in temperature of 1° C. will make a difference in the measure-
ment of heat of some 60 calories, it is readily seen that the importance of
knowing the exact body-temperature can not be overestimated; indeed, the
whole problem of the comparison of the direct and indirect calorimetry
hinges more or less upon this very point, and it is strongly to be hoped that
ere long the much-needed observations on body-temperature can be made.
CONTROL EXPERIMENTS WITH THE CALORIMETER.
After providing a suitable apparatus for bringing away the heat gene-
rated inside the chamber and for preventing the loss of heat by maintaining
the walls adiabatic, it is still necessary to demonstrate the ability of the
calorimeter to measure known amounts of heat accurately. In order to do
this we pass a current of electricity of known voltage through a resistance
coil and thus develop heat inside the respiration chamber. While, un-
doubtedly, the use of a standard resistance and potentiometer is the most
accurate method for measuring currents of this nature, thus far we have
based our experiments upon the measurements made with extremely accu-
rate Weston portable voltmeter and mil-ammeters. Thanks to the kind-
ness of one of our former co-workers, Mr. S. C. Dinsmore, at present asso-
ciated with the Weston Electrical Instrument Company, we have been
able to obtain two especially exact instruments. The mil-ammeter is so
adjusted as to give a maximum current of 1.5 amperes and the voltmeter
reads from zero to 150 volts. The direct current furnished the building is
caused to pass through a variable resistance for adjusting minor variations
in voltage and then through the mil-ammeter into a manganin resistance-
coil inside the chamber, having a resistance of 84.2 ohms. Two leads from
the terminals of the manganin coil connect with the voltmeter outside the
chamber, and hence the drop in potential can be measured very accurately
and as frequently as is desired. The current furnished the building is
remarkably steady, but for the more accurate experiments a small degree of
hand regulation is necessary.
The advantage of the electrical method of controlling the apparatus is
that the measurements can be made very accurately, rapidly, and in short
periods. In making experiments of this nature it is our custom first to
place the resistance-coil in the calorimeter and make the connections. The
current is then passed through the coil, and simultaneously the water
is started flowing through the heat-absorbing system and the whole calo-
rimeter is adjusted in temperature equilibrium as soon as possible. When
the temperature of the air and walls is constant and the thermal- junction
THE CALORIMETER. 51
system in equilibrium, the exact time is noted and the water-current
deflected into the meter. At the end of one hour, the usual length of a
period, the water-current is deflected from the meter, the meter is weighed,
and the average temperature-difference of the water obtained by averaging
the results of all the temperature differences noted during the hour. Usu-
ally during an experiment of this nature, 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 means
of the formula CxExf X0.2385 = calories, in which C equals the current
in amperes, E the electromotive force, and t the time in seconds. This
gives the heat expressed in calories at 15° C. This procedure we have fol-
lowed as a result of the recommendation of Dr. E. B. Eosa, of the National
Bureau of Standards. In order to convert the values to 20°, the unit com-
monly employed in calorimetric work, it has been necessary to multiply by
the ratio of the specific heat of water at 15° to that of water at 20°. As-
suming the specific heat of water at 20° to be 1, the specific heat at 15°
is 1.001.*
Of the many electrical check-tests made with this type of apparatus, but
one need be given here, pending a special treatment of the method of con-
trol of the calorimeter in a forthcoming publication. An electrical check-
experiment with the chair calorimeter was made on January 4, 1909, and
continued 6 hours. The voltmeter and mil-ammeter were read every few
minutes, the water collected in the water-meter, carefully weighed, and the
temperature differences as measured on the two mercury thermometers
were recorded every 4 minutes.
The heat developed during the experiment may be calculated from the
data as follows: Average currents 1.293 amperes; average E. M. F.
= 109.15 volts; time = 21,600 seconds; factor used to convert watt-seconds
to calories =0.2385. (1.293x109.15x21600x0.2385) x 1.001 = 727.8 calo-
ries produced.
During the 6 hours 237.63 kilograms of water passed through the absorb-
ing system.
The average temperature rise was 3.04° C, the total heat brought away
was therefore (237.63x3.04) x 1.0024 f =724.1 calories.
Thus in 6 hours there were about 3.7 calories more heat developed inside
the apparatus than were measured by the water-current, a discrepancy of
about 0.5 per cent.
* W. O. Atwater and E. B. Rosa : Description of a new respiration calorimeter
and experiments on the conservation of energy in the human body. U. S. Dept.
of Agr., Office of Experiment Stations Bui. 63. (1899.)
f Specific heat of water at average temperature of the water in the heat-absorb-
ing system referred to the specific heat of water at 20° C.
52 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
Under ideal conditions of manipulation, the withdrawal of heat from the
calorimeter should be at just such a rate as to exactly compensate for the
heat developed by the resistance-coil. Under these conditions, then, there
would be no heat abstracted from nor stored by the calorimeter and its
temperature should remain constant throughout the whole experiment.
Practically this is very difficult to accomplish and there are minor fluctua-
tions in temperature above and below the initial temperature during a long
experiment and, indeed, during a short experimental period. If a certain
amount of heat has been stored up in the calorimeter chamber or has been
abstracted from it, there should be corrections made for the variations in
the temperature of the chamber. Such corrections are impossible unless a
proper determination of the hydrothermal equivalent has been made. A
number of experiments to determine this hydrothermal equivalent have
been made and the results are recorded beyond, together with a discussion
of the nature of the experiments. As a result of these experiments it has
been possible to make correction for the slight temperature changes in the
calorimeter.
It is interesting to note that these fluctuations are small and there may
therefore be a considerable error in the determination of the hydrothermal
equivalent without particularly affecting the corrections applied in the
ordinary electrical check-test. The greatest difficulty experienced with the
calorimeter as a means of measuring heat has been to secure the average
temperature of the ingoing water. The temperature difference between the
mass of water flowing through the pipes and the outer wall of the pipe is
at best considerable. The use of the vacuum- jacketed glass tubes has min-
imized the loss of heat through this tube considerably, but it is advisable
that the bulb of the thermometer be placed exactly in the center of the
water-tube, as otherwise too high a temperature-reading will be secured.
When the proper precautions are taken to secure the correct temperature-
reading, the results are most satisfactory.
In testing both calorimeters a large number of electrical check experi-
ments have led to the conclusion that discrepancies in results were inva-
riably due, not to the loss of heat through the walls of the calorimeter, but
to erroneous measurement of the temperature of the water-current.
DETERMINATION OF THE HYDROTHERMAL EQUIVALENT OF THE
CALORIMETER.
While the temperature control of the calorimeter is such that in general
the average temperature varies but a few hundredths of a degree between
the beginning and the end of an experimental period, in extremely accurate
work it is necessary to know the amount of heat which is absorbed with any
increase in temperature. In other words, the determination of the hydro-
thermal equivalent is essential.
THE CALORIMETER. 53
The large majority of the methods for determining the hydrothermal
equivalent of materials are at once eliminated when the nature of the calo-
rimeter here used is taken into consideration. Obviously, in warming up
the chamber there are two sources of heat : first, the heat inside of the cham-
ber; second, the heat in the outer walls. As has been previously described,
the zinc wall is arbitrarily heated so that its temperature fluctuations will
follow exactly those of the inner wall, hence it is impossible to compute from
the weight of the metal the hydrothermal equivalent. By means of the
electrical check experiments, however, a method for determining the hydro-
thermal equivalent is at hand. The general scheme is as follows.
During an electrical check experiment, when thermal equilibrium has
been thoroughly established and the heat brought away by the water-current
exactly counterbalances the heat generated in the resistance-coil inside the
chamber, the temperature of the calorimeter is allowed to rise slowly by
raising the temperature of the ingoing water and thus bringing away less
heat. At the same time the utmost pains are taken to maintain the adia-
batic condition of the metal walls. Since the temperature is rising during
this period, it is necessary to warm the air in the outer spaces by the
electric current. By this method it is possible to raise the temperature of
the calorimeter 1 degree or more in 2 hours and establish thermal equi-
librium at the higher level. The experiment is then continued for 2 hours
at this level, and the next 2 hours the temperature is gradually allowed to
fall by lowering the temperature of the ingoing water so that more heat is
brought away than is generated, care being taken likewise to keep the walls
adiabatic. Under these conditions the heat brought away by the water-
current during the period of rising temperature is considerably less than
that actually developed by the electric current and the difference repre-
sents the amount of heat absorbed by the calorimeter in the period of the
temperature rise. Conversely, during the period when the temperature is
falling, there is a considerable increase in the amount of heat brought
away by the water-current over that generated in the resistance-coil and the
difference represents exactly the amount of heat given up by the calorim-
eter during the fall in temperature. It is thus possible to measure the
capacity of the calorimeter for absorbing heat during a rise in temperature
and the amount of heat lost by it during cooling. A number of such
experiments have been made with both calorimeters and it has been found
that the hydrothermal equivalent of the bed calorimeter is not far from 21
kilograms. For the chair calorimeter a somewhat lower figure has been
found, t. e., 19.5 kilograms.
54 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
GENERAL DESCRIPTION OF RESPIRATION APPARATUS.
This apparatus is designed much after the principle of the Eegnault-
Eeiset apparatus, in that there is a confined volume of air in which the
subject lives and which is purified by its passage through vessels containing
absorbents for water and carbon dioxide. Fresh oxygen is added to this
current of air and it is then returned to the chamber to be respired. This
principle, in order to be accurate for oxygen determinations, necessitates an
absolutely air-tight system and consequently special precautions have been
taken in the construction of the chamber and accessories.
TESTING THE CHAMBER FOR TIGHTNESS.
As already suggested, the walls are constructed of the largest possible
sheets of copper with a minimum number of seams and opportunities for
leakage. In testing the apparatus for leaks, the greatest precaution is
taken. A small air-pressure is applied and the variations in height of a
delicate manometer noted. In cases of apparent leakage, all possible sources
of leak are gone over with soapsuds when there is a slight pressure on
the chamber. As a last resort, which has ultimately proven to be the best
method of testing, an assistant goes inside of the chamber, it is then her-
metically sealed, and a slight diminished pressure is produced. Ether is
then poured about the walls of the chamber and the odor of ether soon
becomes apparent inside of the chamber if there is a leakage. Many leaks
that could not be found by soapsuds can be readily detected by this method.
VENTILATION OF THE CHAMBER.
The special features of the respiration chamber are the ventilating-pipe
system and openings for supplementary apparatus for absorption of water
and carbon dioxide. The air entering the chamber is absolutely dry and is
directed into the top of the chamber immediately above the head of the
subject. The moisture given off from the lungs and skin and the expired
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 the bottom of the
chamber at the front. Under these conditions, therefore, we believe we have
a maximum intermingling of the gases. However, even with this system
of ventilation, we do not feel that there is theoretically the best mixture of
gases, and an electric fan is used inside of the chamber. In experiments
where there is considerable regularity in the carbon-dioxide production and
oxygen consumption, the system very quickly attains a state of equilibrium,
and while the analysis of the outcoming air does not necessarily represent
fairly the actual composition of the air inside of the chamber, it evidently
represents to the same degree from hour to hour the state of equilibrium
that is usually maintained through the whole of a 6-hour experiment.
GENERAL DESCRIPTION OF RESPIRATION APPARATUS. 55
The interior of the chamber and all appliances are constructed of metal
except the chair in which the subject sits. This is of hard wood, well shel-
lacked, and consequently non-porous. With this calorimeter it is desired
to make studies regarding the moisture elimination, and consequently it is
necessary to avoid the use of all material of a hygroscopic nature. Although
the chair can be weighed from time to time with great accuracy and its
changes in weight obtained, it is obviously impossible, in any type of
experiment thus far made, to differentiate between the water vaporized
from the lungs and skin of the man and that from his clothes. Subsequent
experiments with a metal chair, with minimum clothing, with cloth of
different textures, without clothing, with an oiled skin, and various other
modifications affecting the vaporization of water from the body of the man
will doubtless throw more definite light upon the question of the water
elimination through the skin. 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 in apportioning the water vaporized between the man and his
clothing and the chair.
The walls of the chamber are semi-rigid. Owing to the calorimetric fea-
tures of this apparatus, it is impracticable to use heavy boiler-plate or heavy
metal walls, as the sluggishness of the changes in temperature, the mass of
metal, and its relatively large hydrothermal equivalent would interfere
seriously with the sensitiveness of the apparatus as a calorimeter. Hence
we use copper walls, with a fair degree of rigidity, attached to a substan-
tial structural-steel support; and for all practical purposes the apparatus
can be considered as of constant volume. Particularly is this the case
when it is considered that the pressure inside of the chamber during an
experiment never varies from the atmospheric pressure by more than a few
millimeters of water. It is possible, therefore, from the measurements of
this chamber, to compute with considerable accuracy the absolute volume.
The apparent volume has been calculated to be 1,347 liters.
OPENINGS IN THE CHAMBER.
In order to communicate with the interior of the chamber, maintain a
ventilating air-current, and provide for the passage of the current of water
for the heat-absorber system and the large number of electrical connections,
a number of openings through the walls of the chamber were necessary.
The great importance of maintaining this chamber absolutely air-tight
renders it necessary to minimize the number of these openings, to reduce
their size as much as possible, and to take extra precaution in securing
their closure during an experiment. The largest opening is obviously the
trap-door at the top through which the subject enters, shown in dotted out-
line in fig. 7. While somewhat inconvenient to enter the chamber in this
way, the entrance from above possesses many advantages. It is readily
56 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
closed and sealed by hot wax and rarely is a leakage experienced. The trap-
door is constructed on precisely the same plan as the rest of the calorim-
eter, having its double walls of copper and zinc, its thermal-junction system,
its heating wires and connections, and its cooling pipes. When closed and
sealed, and the connections made with the cooling pipes and heating wires,
it presents an appearance not differing from any other portion of the
calorimeter.
The next largest opening is the food-aperture, which is a large sheet-
copper tube, somewhat flattened, thus giving a slightly oval form, closed
with a port, such as is used on vessels. The door of the port consists of
a heavy brass frame with a heavy glass window and it can be closed tightly
by means of a rubber gasket and two thumbscrews. On the outside is used
a similar port provided with a tube somewhat larger in diameter than that
connected with the inner port. The annular space between these tubes is
filled with a pneumatic gasket which can be inflated and thus a tight closure
may be maintained. When one door is closed and the other opened, articles
can be placed in and taken out of the chamber without the passage of a
material amount of air from the chamber to the room outside or into the
chamber from outside.
The air-pipes passing through the wall of the calorimeter are of standard
1-inch piping. The insulation from the copper wall is made by a rubber
stopper through which this piping is passed, the stopper being crowded
into a brass ferule which is stoutly soldered to the copper wall. This is
shown in detail in fig. 25, in which N is the brass ferule and M the rubber
stopper through which the air-pipe passes. The closure is absolutely air-
tight and a minimum amount of heat is conducted out of the chamber,
owing to the insulation of the rubber stopper M. The water-current enters
and leaves the chamber through two pipes insulated in two similar brass
ferules soldered to the copper and zinc walls. The insulation between the
water-pipe and the brass ferule has been the subject of much experimenting
and is discussed on page 24. The best insulation was secured by a vacuum-
jacketed glass tube, although the special hard-rubber tubes surrounding the
electric-resistance thermometers have proven very effective as insulators in
the bed calorimeter.
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 the manometer,
stethoscope, and pneumograph. All of these openings are tested carefully
and shown to be absolutely air-tight before being put in use.
In the dome of the calorimeter, and directly over the head of the subject,
is the opening for the weighing apparatus. This consists of a hard-rubber
tube, threaded at one end and screwed into a brass flange heavily soldered
to the copper wall (fig. 9). When not in use, a solid rubber stopper on a
GENERAL DESCRIPTION* OF RESPIRATION APPARATUS.
57
brass rod is drawn into this opening, thus producing an air-tight closure.
When in actual use during the process of weighing, a thin rubber diaphragm
prevents leakage of air through this opening. The escape of heat through
the weighing-tube is minimized by having this tube of hard rubber.
VENTILATING AIR-CURRENT.
The ventilating air-current is so adjusted that the air which leaves the
chamber is caused to pass through purifiers, where the water-vapor and
the carbon dioxide are removed, and then, after being replenished with fresh
oxygen, it is returned to the
O TENSION
EQUALIZER
T"T
r-n-
INTRODUCED
0
^
r
chamber ready for use. The
general scheme of the respi-
ration apparatus is shown in
fig. .27. The air leaving the
chamber contains carbon di-
oxide and water-vapor and
the original amount of nitro-
gen and is somewhat deficient
in oxygen. In order to pur-
ify the air it must be passed
through absorbents for car-
bonic acid and water-vapor
and hence some pressure is
necessary to force the gas
through these purifying ves-
sels. This pressure is ob-
tained by a small positive
rotary blower, which has been
described previously in de-
tail.* The air is thus forced
successively through sulphu-
ric acid, soda or potash lime,
and again sulphuric acid. Finally it is directed back to the respiration
chamber free from carbon dioxide and water and deficient in oxygen. Pure
oxygen is admitted to the chamber to make up the deficiency, and the air
thus regenerated is breathed again by the subject.
Ht0
ABSORBED
H2S 0,
n
CO,
ABSORBED
P OTA S H
LIMC
HzO
ABSORBED
L_L
HjSO.
Fig. 27. — Diagram of ventilation of respiration calorimeter.
The air ia taken out at lower right-hand corner and
forced by the blower through the apparatus for absorb-
ing water and carbon dioxide. It returns to the calo-
rimeter at the top. Oxygen can be introduced into the
chamber itself as need is shown by the tension equalizer.
The rotary blower used in these experiments for maintaining the venti-
lating current of air has given the greatest satisfaction. It is a so-called
*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, p. 18. (1905.)
5
58 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
positive blower and capable of producing at the outlet considerable pressure
and at the inlet a vacuum of several inches of mercury. At a speed of 230
revolutions per minute it delivers the air at a pressure of 43 millimeters of
mercury, forcing it through the purifying vessels at the rate of 75 liters
per minute. This rate of ventilation has been established as being satis-
factory for all experiments and is constant. Under the pressure of 43 mil-
limeters of mercury there are possibilities of leakage of air from the blower
connections and hence, to note this immediately, the blower system is
immersed in a tank filled with heavy lubricating oil. The connections are so
well made, however, that leakage rarely occurs, and, when it does, a slight
tightening of the stuffing-box on the shaft makes the apparatus tight again.
ABSORBERS FOR WATER-VAPOR.
To absorb 25 to 40 grams of water- vapor in an hour from a current of air
moving at the rate of 75 liters per minute and leaving the air essentially
dry under these conditions has been met by the apparatus herewith described.
The earlier attempts to secure this result involved the use of enameled-
iron soup-stock pots, fitted with special enameled-iron covers and closed
with rubber gaskets. For the preliminary experimenting and for a few
experiments with man these proved satisfactory, but in spite of their
resistance to the action of sulphuric acid, it was found that they were not
as desirable as they should be for continued experimenting from year to
year. Recourse was then had to a special form of chemical pottery, glazed,
and a type that usually gives excellent satisfaction in manufacturing con-
cerns was used.
This special form of absorbers presented many difficulties in construc-
tion, but the mechanical difficulties were overcome by the potter's skill and
a number of such vessels were furnished by the Charles Graham Chemical
Pottery Works. Here again these vessels served our purpose for several
months, but unfortunately the glaze used did not suffice to cover them com-
pletely and there was a slight, though persistent, leakage of sulphuric acid
through the porous walls. To overcome this difficulty the interior of the
vessels was coated with hot paraffin after a long-continued washing to remove
the acid and after they had been allowed to dry thoroughly. The paraffin-
treated absorbers continued to give satisfaction, but it was soon seen that
for permanent use something more satisfactory must be had. After innu-
merable trials with glazed vessels of different kinds of pottery and glass,
arrangements were made with the Eoyal Berlin Porcelain Works to mold
and make these absorbers out of their highly resistant porcelain. The result
thus far leaves nothing to be desired as a vessel for this purpose. A number
of such absorbers were made and have been constantly used for a year and
are absolutely without criticism.
GENERAL DESCRIPTION OF RESPIRATION APPARATUS.
59
Fig. 28 shows the nature of the interior of the apparatus. The air
enters through one opening at the top, passes down through a bent pipe,
and enters a series of roses, consisting of inverted circular saucers with
holes in the rims. The position of the holes is such that when the vessel is
one-fourth to one-third full of sulphuric acid the air must pass through
the acid three times. To prevent spattering, a small cup-shaped arrange-
ment, provided with holes, is attached to the opening through which the air
passes out of the absorber, and for filling the vessel with acid a small open-
ing is made near one edge. The speci-
fications required that the apparatus
should be made absolutely air-tight to
pressures of over 1 meter of water, and
that there is no porosity in these vessels
under these conditions is shown by the
fact that such a pressure is held indefi-
nitely. The inside and outside are both
heavily glazed. There is no apparent
action of sulphuric acid on the vessels
and the slight increase in temperature
resulting from the absorption of water-
vapor as the air passes through does not
appear to have any deleterious effect.
The vessels without filling and with-
out rubber elbows weigh 11.5 kilograms;
with the special elbows and couplings
attached so as xo enable them to be con-
nected with the ventilating air-system,
the empty absorbers weigh 13.4 kilo-
grams; and filled with sulphuric acid
they weigh 19 kilograms. Repeated
tests have shown that 5.5 kilograms of sulphuric acid will remove the water-
vapor from a current of air passing through the absorbers at the rate of 75
liters of air per minute, without letting any appreciable amount pass by
until 500 grams of water have been absorbed. At this degree of saturation
a small persistent amount of moisture escapes absorption in the acid and
consequently a second absorber will begin to gain in weight Experiments
demonstrate that the first vessel can gain 1,500 grams of water before the
second gains 5 grams. As a matter of fact, it has been found more advan-
tageous to use but one absorber and have it refilled as soon as it has gained
400 grams, thus allowing a liberal factor of safety and no danger of loss of
water.
Fig. 28. — Cross-section of sulphuric-acid ab-
sorber. The air enters at the top of the
right-hand opening, descends to the bot-
tom of the absorber, and then passes
through three concentric rings, which are
covered with acid, and it finally passes out
at the left-hand opening. Beneath the left-
hand opening is a cup arrangement for pre-
venting the acid being carried mechanic-
ally out through the opening. The opening
for filling and emptying the absorber is
shown midway between tie two large open-
ings.
60 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
POTASH-LIME CANS.
The problem of absorbing the water-vapor from so rapid a current of air
is second only to that of absorbing the carbon dioxide from such a current.
All experiments with potassium hydroxide in the form of sticks or in solu-
tion failed to give the desired results and the use of soda-lime has supple-
mented all other forms of carbon dioxide absorption. More recently we
have been using potash-lime, substituting caustic potash for caustic soda in
the formula, and the results thus obtained are, if anything, more satisfac-
tory than with the soda-lime.
The potash-lime is made as follows : 1 kilogram of commercial potassium
hydroxide, pulverized, is dissolved in 550 to 650 cubic centimeters of water
and 1 kilogram of pulverized quicklime added slowly. The amount of
water to be used varies with the moisture content of the potash. There is
a variation in the moisture content of different kegs of potash, so when a
keg is opened we determine experimentally the amount of water to be used.
After a batch is made up in this way it should be allowed to cool before
testing whether it has the right amount of water, and this is 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 have found that if a large
quantity is made and broken into small particles and stored in a container
it has a tendency to cake and thus interfere with its ready subsequent use.
A record was kept of the gains in weight of a can filled with potash-lime
during a series of experiments where there were three silver-plated cans
used. This can was put at the head of the system and when it began to
lose weight it was removed. The records of gains of weight when added
together amount to 400 grams. From experience with other cans where
the loss of moisture was determined, it is highly probable that at least 200
grams of water were vaporized from the reagent and thus the total amount
of carbon dioxide absorbed must have been not far from 600 grams. At
present our method is not to allow the cans 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 a new can on each side of the absorber
system (see page 66) at the beginning of every experiment. This insures
the same power of absorption on each side of the absorption system, so that
the residual amount of carbon dioxide in the chamber from period to period
does not undergo very marked changes. This has been found the best
method, because if one can is left on a day longer than the other there is
apt to be alternately a rise and fall in the amount of residual carbon dioxide
in the apparatus, owing to the unequal efficiency of the absorbers.
These cans are each day taken to the basement, where the first section *
* For a description of the apparatus and the method of filling see W. O. At-
water and F. G. Benedict: A respiration calorimeter with appliances for the
direct determination of oxygen. Carnegie Institution of Washington Publication
No. 42, p. 27. (1905.)
GENERAL DESCRIPTION OF RESPIRATION APPARATUS. 61
only is taken out and replaced with new potash-lime. Thus, three-quarters
of the contents of the can is used over and over, while the first quarter is
freshly renewed every day. Potash-lime has not been found practicable for
the U-tubes because one can not, as in the case of soda-lime, see the whiten-
ing of the reagent where the carbon dioxide is absorbed.
The importance of having the soda-lime or potash-lime somewhat moist,
to secure the highest efficiency for the absorption of the carbon dioxide,
makes it necessary to absorb the moisture taken up by the dry air in passing
through the potash-lime can. Consequently a second vessel containing
sulphuric acid is placed in the system to receive the air immediately after
it leaves the potash-lime can. Obviously the amount of water absorbed
here is very much less than in the first acid absorber and hence the same
absorber can be used for a greater number of experiments.
BALANCE FOB WEIGHING ABSOBBEBS.
The complete removal of water-vapor and carbon dioxide from a current
of air moving at the rate of 75 liters per minute calls for large and some-
what unwieldly vessels in which is placed the absorbing material. This is
particularly the case with the vessels containing the rather large amounts
of sulphuric acid required to dry the air. In the course of an hour there
is ordinarily removed from the chamber not far from 25 grams of water-
vapor and 20 to 30 grams of carbon dioxide. This necessitates weighing
the absorbers to within 0.25 gram if an accuracy of 1 per cent is desired.
The sulphuric-acid absorbers weigh about 18 kilograms when filled with
acid. In order to weigh this receptacle so as to measure accurately the
increase in weight due to the absorption of water 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 in connection with the respiration calo-
rimeter and accessory apparatus and the general type of balance leaves
nothing to be desired as a balance capable of carrying a heavy load with
remarkable sensitiveness.
The balance is rigidly mounted on a frame consisting of four upright
structural-steel angle-irons, fastened at the top to a substantial wooden bed.
Two heavy wooden pieces run the length of the table and furnish a sub-
stantial base to which the standard of the balance is bolted. The balance
is surrounded by a glass case to prevent errors due to air-currents (see
fig. 2). The pan of the balance is not large enough to permit the weigh-
ing of an absorber, hence provision is made for suspending it on a steel or
brass rod from one of the hanger arms. This rod passes through a hole in
the bottom of the balance case, and its lower end is provided with a piece
of pipe having hooks at either end. Since the increase in weight rather
than the absolute weight of the absorber is used, the greater part of the
weight is taken up by lead counterpoises suspended above the pan on the
62
CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
right-hand arm of the balance. The remainder of the weight is made up
with brass weights placed in the pan.
In order to suspend this heavy absorber, a small elevator has been con-
structed, so that the vessel may be raised by a compressed-air piston. This
Fio. 29. — Balance for weighing absorbers, showing general type of balance and
case surrounding it, with counterpoise and weights upon right-hand pan. A
sulphuric-acid absorber is suspended in position ready for weighing. Elevator
with compressed-air system is shown in lower part of case.
piston is placed in an upright position at the right of the elevator and is
connected with the compressed-air service of the building. The pressure is
about 25 pounds per square inch and the diameter of the cylinder is 2.5
inches, thus giving ample service for raising and lowering the elevator and
GENERAL DESCRIPTION OF RESPIRATION APPARATUS. 63
its load. By turning a 3-way valve at the end of the compressed-air supply-
pipe, so that the air rushes into the cylinder above the piston, the piston
is pushed to the base of the cylinder and the elevator thereby raised. The
pressure of the compressed air holds the elevator in this position while the
hooks are being adjusted on the absorber. By turning the 3-way valve so
as to open 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 the posi-
tion shown in the figure. The weighing can then be made as the absorber
is swinging freely in the air. After the weighing has been made, the ele-
vator is again lifted, the hooks are released, and by turning the valve the
elevator and load are safely lowered-
The size of the openings of the pipes into the cylinder is so adjusted that
the movement of the elevator is regular and moderate whether it is being
raised or lowered, thus avoiding any sudden jars that might cause an
accident to the absorbers. With this system it is possible to weigh these
absorbers to within 0.1 gram and, were it necessary, probably the error
could be diminished so that the weight could be taken to 0.05 gram. On
a balance of this type described elsewhere,* weighings could be obtained to
within 0.02 gram. For all practical purposes, however, we do not use the
balance for weighing the absorbers closer than to within 0.10 gram. In
attempting to secure accuracy no greater than this, it is unnecessary to
lower the glass door to the balance case or, indeed, to close the two doors to
the compartment in which the elevator is closed, as the slight air-currents
do not affect the accuracy of the weighing when only 0.1 gram sensitiveness
is required.
PURIFICATION OF THE AIB-CURRENT WITH SODIUM BICARBONATE.
As is to be expected, the passage of so large a volume of air through the
sulphuric acid in such a relatively small space results in a slight acid odor
in the air-current leaving this absorber. The amount of material thus
leaving the absorber is not weighable, as has been shown by repeated tests,
but nevertheless there is a sufficiently irritating acid odor to make the air
very uncomfortable for subsequent respiration. It has been found that this
odor can be wholly eliminated by passing the air through a can containing
cotton wool and dry sodium bicarbonate. This can is not weighed, and
indeed, after days of use, there is no appreciable change in its weight.
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 period from one
set of purifiers to the other, in order to weigh the set used and to measure
* 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, p. 56. (1905.)
64 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
the quantity of carbon dioxide and water-vapor absorbed. The conditions
under which these changes from one system to another are made, and which
call for an absolutely gas-tight closure, have been discussed in detail else-
where.* It is sufficient to state here that the very large majority of me-
chanical valves will not serve the purpose, since it is necessary to have a
pressure of some 40 millimeters of mercury on one side of the valve at
the entrance to the absorber system and on the other side atmospheric pres-
sure. A valve with an internal diameter of not less than 25 millimeters
must be used, and to secure a tight closure of this large area and permit
frequent opening and shutting is difficult. After experimenting with a
large number of valves, a valve of special construction employing a me-
chanical seal ultimately bathed in mercury was used for the earlier appa-
ratus. The possibility of contamination of the air-current by mercury
vapor was duly considered and pointed out in a description of this appa-
ratus. It was not until two years later that difficulties began to be experi-
enced and a number of men were severely poisoned while inside the cham-
ber. A discussion of this point has been presented elsewhere.f At that
time mercury valves were used both at the entrance and exit ends of the
absorber system, although as a matter of fact, when the air leaves the last
absorber and returns to the respiration chamber, the pressure is but a
little above that of the atmosphere. Consequently, mechanical valves were
substituted for mercurial valves at the exit and the toxic symptoms dis-
appeared. In constructing the new calorimeters it seemed to be desirable
to avoid all use of mercury, if possible. We were fortunate in finding a
mechanical valve which suited this condition perfectly. These valves, which
are very well constructed, have never failed to show complete tightness
under all possible tests and are used at the exit and entrance end of the
absorber system. Their workmanship is of the first order, and the valve
is somewhat higher in price than ordinary mechanical valves. They have
been in use on the apparatus for a year now and have invariably proved
to be absolutely tight. They are easy to obtain and are much easier to
manipulate and much less cumbersome than the mercury valves formerly
used.
COUPLINGS.
Throughout the construction of the respiration apparatus and its various
parts, it was constantly borne in mind that the slightest leak would be
very disastrous for accurate oxygen determinations. At any point where
there is a pressure greater or less than that of the atmosphere, special pre-
* 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, p. 20. (1905.)
fThorne M. Carpenter and Francis G. Benedict: Mercurial poisoning of men
in a respiration chamber. American Journal of Physiology, vol. 24, p. 187.
(1909.)
GENERAL DESCRIPTION OF RESPIRATION APPARATUS. 65
caution must be taken. At no point in the whole apparatus is it necessary
to be more careful than with the couplings which connect the various
absorber systems with each other and with the valves; for these couplings
are opened and closed once every hour or two and hence are subject to
considerable strain at the different points. If they are not tight the
experiment is a failure so far as the determination of oxygen is concerned.
For the various parts of the absorber system we have relied upon the ori-
ginal type of couplings used in the earlier apparatus. A rubber gasket is
placed between the male and female part of the coupling and the closure
can be made very tight. In fact, after the absorbers are coupled in place
they are invariably subjected to severe tests to prove tightness.
For connecting the piping between the calorimeter and the absorption
system we use ordinary one-inch hose-couplings, firmly set up by means
of a wrench and disturbed only when necessary to change from one calo-
rimeter chamber to another.
ABSORBER TABLE.
The purifying apparatus for the air-current is compactly and conven-
iently placed on a solidly constructed table which can be moved about the
laboratory at will. The special form of caster on the bottom of the posts
of the table permits its movement about the laboratory at will and by
screwing down the hand screws the table can be firmly fixed to the floor.
The details of the table are shown in fig. 30. (See also fig. 4, page 4.)
The air coming from the calorimeter passes in the direction of the down-
ward arrow through a J-inch pipe into the blower, which is immersed in
oil in an iron box F. The blower is driven by an electric motor fastened
to a small shelf at the left of the table. The air leaving the blower ascends
in the direction of the arrow to the valve system H, where it can be directed
into one of the two parallel sets of purifiers; after it passes through these
purifiers (sulphuric-acid vessel 2, potash-lime container K, and sulphuric-
acid vessel 1) it goes through the sodium-bicarbonate can G to a duplicate
valve system on top of the table. From there it passes through a pipe along
the top of the table and rises in the vertical pipe to the hose connection
which is coupled with the calorimeter chamber.
The electric motor is provided with a snap-switch on one of the posts of
the table and a regulating rheostat which permits variations in the speed
of the motor and consequently in the ventilation produced by the blower.
The blower is well oiled, and as oil is gradually carried in with the air, a
small pet-cock at the bottom of the T following the blower 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 arms of which connect
with two " white star " valves. The upper part of the cross is connected
66
CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
to a small rubber tubing and to the mercury manometer D, which also
serves as a valve for passing a given amount of air through a series of
U -tubes for analysis of the air from time to time. It is assumed that the
air drawn at the point H is of substantially the same composition as that
inside the chamber, an assumption that may not be strictly true, but doubt-
less the sample thus obtained is constantly proportional to the average
composition, which fluctuates but slowly. Ordinarily the piping leading
from the left-hand arm of the tube D is left open to the air and conse-
Fig. 30. — Diagram of absorber table. 1 and 2 contain sulphuric acid; K contains
potash-lime; G, sodium bicarbonate can; F, rotary blower for maintaining air-
current; H, valves for closing either side; and D, mercury manometer and
valve for diverting air to U -tubes on table. Air leaves A, passes through the
meter, and then through drying tower B and through C to ingoing air-pipe.
At the left is the regulating rheostat and motor and snap-switch. General
direction of ventilation is indicated by arrows.
quently the difference in the level of the mercury in the two arms of D
indicates the pressure on the system. This is ordinarily not far from 40 to
50 millimeters of mercury.
The absorber table, with the U -tubes and meter for residual analyses, is
shown in the foreground in fig. 2. The two white porcelain vessels with a
silver-plated can between them are on the middle shelf. The sodium bicar-
bonate can, for removing traces of acid fumes, is connected in an upright
GENERAL DESCRIPTION OF RESPIRATION APPARATUS. 67
position, while the motor, the controlling rheostat, and the blower are sup-
ported by the legs near the floor. The two rubber pipes leading from the
table can be used to connect the apparatus either with the bed or chair
calorimeter. In fig. 4 the apparatus is shown connected with the bed calo-
rimeter, but just above the lowest point of the rubber tubing can be seen in
the rear the coupling for one of the pipes leading from the chair calo-
rimeter. The other is immediately below and to the left of it.
OXYGEN SUPPLY.
The residual air inside of the chamber amounts to some 1,300 liters and
contains about 250 liters of oxygen. Consequently it can be seen that in
an 8-hour experiment the subject could easily live during the entire time
upon the amount of oxygen already present in the residual air. It has been
repeatedly shown that until the per cent of oxygen falls to about 11, or
about one-half normal, there is no disturbance in the respiratory exchange
and therefore about 125 liters of oxygen would be available for respiration
even if no oxygen were admitted. Inasmuch as the subject when at rest
uses not far from 11 to 15 liters per hour, the amount originally present
in the chamber would easily suffice for an 8-hour experiment. Moreover,
the difficulties attending an accurate gas analysis and particularly the calcu-
lation of the total amount of oxygen are such that satisfactory determina-
tions of oxygen consumption by this method would be impossible. Further-
more, from our previous experience with long-continued experiments of
from 10 days to 2 weeks, it has been found that oxygen can be supplied to
the system readily and the amount thus supplied determined accurately.
Consequently, even in these short experiments, we adhere to the original
practice of supplying oxygen to the air and noting the amount thus added.
The oxygen supply was formerly obtained from small steel cylinders of
the highly compressed gas. This gas was made by the calcium-manganate
method and represented a high degree of purity for commercial oxygen.
More recently we have been using oxygen of great purity made from liquid
air. Inasmuch as this oxygen is very pure and much less expensive than
the chemically-prepared oxygen, extensive provisions have been made for
its continued use. Instead of using small cylinders containing 10 cubic
feet and attaching thereto purifying devices in the shape of soda-lime
U -tubes and a sulphuric-acid drying- tube, we now use large cylinders and
we have found that the oxygen from liquid air is practically free from
carbon dioxide and water-vapor, the quantities present being wholly negli-
gible in experiments such as these. Consequently, no purifying attachments
are considered necessary and the oxygen is delivered directly from the
cylinder. The cylinders, containing 100 cubic feet (2,830 liters), under
a pressure of 120 atmospheres, are provided with well-closing valves and
weigh when fully charged 57 kilograms.
68
CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
It is highly desirable to determine the oxygen to within 0.1 gram, and
we are fortunate in having a balance of the type used frequently in this
Fig. 31.— Diagram of oxygen balance and cylinder. At the top is the balance
arrangement, and at the center its support. At the left is the oxygen
cylinder, with reducing valve A, rubber tube D leading from it, F the
electro-magnet which opens and closes D, K the hanger of the cylinder and
support for the magnet, R the lever which operates the supports for the
cylinder and its counterpoise S, T' a box which is raised and lowered by
R, and T its surrounding box.
laboratory which will enable us to weigh this cylinder accurately with a
sensitiveness of less than 0.1 gram. Since 1 liter of oxygen weighs 1.43
grams, it can be seen that the amount of oxygen introduced into the cham-
GENERAL DESCRIPTION OF RESPIRATION APPARATUS. 69
ber can be measured by this method within 70 cubic centimeters. Even
in experiments of but an hour's duration, where the amount of oxygen
admitted from the cylinder is but 25 to 30 grams, it can be seen that the
error in the weighing of the oxygen is much less than 1 per cent.
The earlier forms of cylinders used were provided with valves which
required some special control and a rubber bag was attached to provide
for any sudden rush of gas. The construction of the valve and valve-stem
was unfortunately such that the well-known reduction valves could not
be attached without leakage under the high pressure of 120 atmospheres.
With the type of cylinder at present in use, such leakage does not occur and
therefore we simply attach to the oxygen cylinder a reduction-valve which
reduces the pressure from 120 atmospheres to about 2 or 3 pounds to the
square inch. The cylinder, together with the reduction valve, is suspended
on one arm of the balance. The equipment of the arrangement is shown
in fig. 31. (See also fig. 5, page 4.) The cylinder is supported by a
clamp K hung from the balance arm, and the reduction-valve A is shown
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 with slightly
raised rim is attached.
In spite of the rigid construction of this balance, it would be detrimental
to allow this enormous weight to remain on the knife-edges permanently, so
provision is made for raising the cylinders on a small elevator arrangement
which consists of small boxes of wood, T, into which telescope other boxes,
T'. A lever handle, E, when pressed forward, raises T' by means of a
roller bearing U, and when the handle is raised the total weight of the
cylinders is supported on the platforms.
The balance is attached to an upright I-beam which is anchored to the
floor and ceiling of the calorimeter laboratory. Two large turnbuckle eye-
bolts give still greater rigidity at the bottom. The whole apparatus is
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 the
oxygen supply much simpler than in the apparatus formerly used. The
details of the connections somewhat schematically outlined are given in
fig. 32, in which D is the oxygen cylinder, K the supporting band, A the
reduction-valve, and J the tension-equalizer attached to one of the calo-
rimeters. Having reduced the pressure to about 2 pounds by means of
the reduction-valve, the supply of oxygen can be shut off by putting a
pinch-cock on a rubber pipe leading from the reduction-valve to the calo-
rimeters. Instead of using the ordinary screw pinch-cock, this connection
is closed by a spring clamp. The spring E draws on the rod which is con-
nected at L and pinches the rubber tube tightly. The tension at E can be
70
CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
released by an electro-magnet F, which when magnetized exercises a pull on
the iron rod, extends the spring E, and simultaneously releases the pressure
on the rubber tube at L. To make the control perfectly automatic, the
apparatus shown on the top of the tension-equalizer J is employed. A wire
ring, with a wire support, is caused to pass up through a bearing fastened
Fig. 32. — Part of the oxygen cylinder and connections to tension-equalizer. At the left is shown the
upper half of the oxygen cylinder with a detail of the electro-magnet and reducing-valve. D is the
cylinder; K, the band supporting the oxygen cylinder and electro-magnet arrangement; F, the
electro-magnet; E, the tension spring; and L, the rubber tubing at a point where it is closed by the
clamp. The tension-equalizer and the method of closing the circuit operating it are shown at the
right. C and C are two mercury cups into which the wire loop dips, thus closing the circuit. B
is a lever used for short-circuiting for filling the diaphragm J. G is a sulphuric-acid container; H,
the quick- throw valve for shutting off the tension equalizer J; M, part of the ingoing air-pipe; N, a
plug connecting the electric circuit with the electro-magnet; and O, a storage battery.
to the clamp above J. As the air inside of the whole system becomes
diminished in volume and the rubber cap J sinks, there is a point at which a
metal loop dips into two mercury cups C and C, thus closing the circuit,
which causes a current of electricity to pass through F. This releases the
pressure at L, oxygen rushes in, and the rubber bag J becomes distended.
As it is distended, it lifts the metal loop out of the cups, C and C, and
the circuit is broken. There is, therefore, an alternate opening and closing
of this circuit with a corresponding admission of oxygen. The exact posi-
tion of the rubber diaphragm can be read when desired from a pointer on a
graduated scale attached to a support holding the terminals of the electric
wires. More frequently, however, when the volume is required, instead of
GENERAL DESCRIPTION OF RESPIRATION APPARATUS. 71
filling the bag to a definite point, as shown by the pointer, a delicate man-
ometer is attached to the can by means of a pet-cock and the oxygen is
admitted by operating the switch B nntil the desired tension is reached.
In order to provide for the maximum sensitiveness for weighing D and
its appurtenances, the electric connection is broken at the cylinder by means
of the ping X and the rubber tube is connected by a glass connector which
can be disconnected during the process of weighing. Obviously, provision
is also made that there be no leakage of air out of the system during the
weighing. The current at F is obtained by means of a storage battery 0.
The apparatus has been in use for some time in the laboratory and has
proved successful in the highest degree.
TENSION-EQUALIZER.
The rigid walls of the calorimeter and piping necessitate some provision
for minor fluctuations in the absolute volume of air in the confined system.
The apparatus was not constructed to withstand great fluctuations in pres-
sure, and thin walls were used, but it is deemed inadvisable to submit it
even to minor pressures, as thus there would be danger of leakage of air
through any possible small opening. Furthermore, as the carbon dioxide
and water-vapor are absorbed out of the air-current, there is a constant
decrease in volume, which is ordinarily compensated by the admission of
oxygen. It would be very difficult to adjust the admission of oxygen so as
to exactly compensate for the contraction in volume caused by the absorp-
tion of water-vapor and carbon dioxide. Consequently it is necessary to
adjust some portion of the circulating air-current so that there may be a
contraction and expansion in the volume without producing a pressure on
the system. This was 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 a
copper can with a rubber diaphragm top. This diaphragm, which is, as a
matter of fact, a ladies' pure rubber bathing-cap, allows for an expansion or
contraction of air in the system of 2 to 3 liters. The apparatus shown
in position is to be seen in fig. 25, in which the tin can I is covered with the
rubber diaphragm J. If there is any change in volume, therefore, the rub-
ber diaphragm rises or falls with it and under ordinary conditions of an
experiment this arrangement results in a pressure in the chamber approxi-
mately that of the atmosphere. It was found, however, that even the slight
resistance of the piping from the tension-equalizer to the chamber, a pipe
some 26 millimeters in diameter and 60 centimeters long, was sufficient to
cause a slightly diminished pressure inside the calorimeter, inasmuch as the
air was sucked out by the blower with a little greater speed than it was
forced in by the pressure at the diaphragm. Accordingly the apparatus
has been modified so that at present the tension-equalizer is attached di-
rectly to the wall of the calorimeter independent of the air-pipe.
72 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
In most of the experiments made thus far it has been our custom to
conduct the supply of fresh oxygen through pet-cock K on the side of the
tension-equalizer. This is shown more in detail in fig. 32, in which, also, is
shown the interior construction of the can. Owing to the fact that the air
inside of this can is much dryer than the room air, we have followed the
custom with the earlier apparatus of placing a vessel containing sulphuric
acid inside the tension-equalizer, so that any moisture absorbed by the dry
air inside the diaphragm may be taken up by the acid and not be carried
into the chamber. The air passing through the pipe to the calorimeter is, it
must be remembered, absolutely dry and hence there are the best conditions
for the passage of moisture from the outside air through the diaphragm
to this dry air. Attaching the tension-equalizer directly to the calorimeter
obviates the necessity for this drying process and hence the sulphuric-acid
vessel has been discarded.
The valve H (fig. 25) is used to cut off the tension-equalizer completely
from the rest of the system at the exact moment of the end of the experi-
mental period. After the motor has been stopped and the slight amount of
air partly compressed in the blower has leaked back into the system, and
the whole system is momentarily at equal tension, a process occupying some
3 or 4 seconds, the gate-valve H is closed. Oxygen is then admitted from
the pet-cock K until there is a definite volume in J as measured by the
height to which the diaphragm can rise or a second pet-cock is connected
to the can I and a delicate petroleum manometer attached in such a manner
that the diaphragm can be filled to exactly the same tension each time.
Under these conditions, therefore, the apparent volume of air in the sys-
tem, exclusive of the tension-equalizer, is always the same, since it is con-
fined by the rigid walls of the calorimeter and the piping. Furthermore,
the apparent volume of air in the tension-equalizer is arbitrarily adjusted
to be the same amount at the end of each period by closing the valve and
introducing oxygen until the tension is the same.
BAROMETER.
Eecognizing the importance of measuring very accurately the barometric
pressure, or at least its fluctuations, we have installed an accurate barome-
ter of the Fortin type, made by Henry J. Green. This is attached to the
inner wall of the calorimeter laboratory, and since the calorimeter labora-
tory is held at a constant temperature, temperature corrections are unnec-
essary, for we have here to deal not so much with the accurate measure-
ment of the actual pressure as with the accurate measurement of differences
in pressure. For convenience in reading, the ivory needle at the base of the
instrument and the meniscus are well illuminated with electric lamps
behind a white screen, and a small lamp illuminates the vernier. The
barometer can be read to 0.05 millimeter.
GENERAL DESCRIPTION OF RESPIRATION APPARATUS. 73
ANALYSIS OF RESIDUAL AIR.
The carbon-dioxide production, water-vapor elimination, and oxygen
absorption of the subject during 1 or 2 hour periods are recorded in a
general way by the amounts of carbon dioxide and water-vapor absorbed
by the purifying vessels and the loss of weight of the oxygen cylinder ; but,
as a matter of fact, there may be considerable fluctuations in the amounts
of carbon dioxide and water-vapor and particularly oxygen in the large
volume of residual air inside the chamber. With carbon dioxide and water-
vapor this is not as noticeable as with oxygen, for in the 1,300 liters of air
in the chamber there are some 250 liters of oxygen, and slight changes in
the composition of this air indicate considerable changes in the amount of
oxygen. Great changes may also take place in the amounts of carbon
dioxide and water-vapor under certain conditions. In some experiments,
particularly where there are variations in muscular activity from period to
period, there may be a considerable amount of carbon dioxide in the residual
air and during the next period, when the muscular activity is decreased, for
example, the percentage composition of the air may vary so much as to
indicate a distinct fall in the amount of carbon dioxide present. Under
ordinary conditions of ventilation during rest experiments the quantity of
carbon dioxide present in the residual air is not far from 8 to 10 grams.
There are usually present in the air not far from 6 to 9 grams of water-
vapor, and hence this residual amount can undergo considerable fluctua-
tions. When it is considered that an attempt is made to measure the total
amount of carbon dioxide expired in one hour to the fraction of a gram, it
is obvious that fluctuations in the composition of residual air must be taken
into consideration.
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 carbon dioxide.
In the immediate vicinity of the entering air-tube there is air which has a
much lower percentage of carbon dioxide and water-vapor than the average,
and on the other hand close to the nose and mouth of the subject there is air
of a much higher percentage of carbon dioxide and water-vapor than the
average. It has been assumed that the composition of the air leaving the
chamber represents the average composition of the air in the chamber.
This assumption is only in part true, but in rest experiments (and by far
the largest number of experiments are rest experiments) the changes in the
composition of the residual air are so slow and so small that this assump-
tion is safe for all practical purposes.
Another difficulty presents itself in the matter of determining the amount
of carbon dioxide and water-vapor; that is, to make a satisfactory analvsis
of air without withdrawing too great a volume from the chamber. The
difficulty in analysis is almost wholly confined to the determination of
74 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
water-vapor, for while there are a large number of methods for determin-
ing small amounts of carbon dioxide with great accuracy, the method for
determining water-vapor to be accurate calls for the use of rather large
quantities of air. From preliminary experiments with a sling psychrom-
eter it was found that its use was precluded by the space required to suc-
cessfully use this instrument, the addition of an unknown amount of water
to the chamber from the wet bulb, and the difficulties of reading the in-
strument from without the chamber. Recourse was had to the determina-
tion of moisture by the absolute method, in that a definite amount of air
is caused to pass over pumice-stone saturated with sulphuric acid. It is of
interest here to record that at the moment of writing a series of experiments
are in progress in which an attempt is being made to use a hair hygrometer
for this purpose.
The method of determining the water-vapor and carbon dioxide in the
residual air is extremely simple, in that a definite volume of air is caused
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 small absorbing-
system constructed of U-tubes rather than of porcelain vessels and silver-
plated cans. Formerly a very elaborate apparatus was employed for aspi-
rating the air from the chamber through U-tubes and then returning the
aspirated air to the chamber. This involved the use of a suction-pump and
called for a special installation for maintaining the pressure of water con-
stant. More recently a much simpler device has been employed, in that
we have taken advantage of the pressure in the ventilating air-system
developed by the passage of air through the blower. After forcing a definite
quantity of air through the reagents in the U-tubes, it is then conducted
back to the system after having been measured in a gas-meter.
This procedure is best noted from fig. 30. The connected series of three
U-tubes on the rack on the table is joined on one end by well-fitting rubber
connections to the tube leading from the mercurial manometer and on the
other end to the rubber tube A leading to the gas-meter. On lowering the
mercury reservoir E, the mercury is drained out of the tube D and air
passes through both arms of the tube and then through the three U-tubes.
In the first of these it is deprived of moisture, and in the last two of
carbon dioxide. The air then enters the meter, where it is measured and
leaves the meter through the tube B, saturated with water-vapor at the
room temperature. To remove this water-vapor the air is passed through
a tower filled with pumice-stone drenched with sulphuric acid. It leaves
the tower through the tube C and enters the ventilating air-pipe on its
way to the calorimeter.
The method of manipulation is very simple. After connecting the
U-tubes the pet-cock connecting the tube C with the pipe is opened, the
mercury reservoir E is lowered, and air is allowed to pass through until
GENERAL DESCRIPTION OF RESPIRATION APPARATUS. 75
the meter registers 10 liters. By raising the reservoir E the air supply is
shut off, and after closing the stop-cock at C the tubes are disconnected, 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 portion equal to 270 millimeters
and an internal diameter of 16 millimeters. They permit the passage of
3 liters of air per minute through them without a noticeable escape of
water-vapor or carbon dioxide. The U-tubes filled with pumice-stone and
sulphuric acid weigh 90 grams. They are always weighed on the balance
with a counterpoise, but no attempt is made to weigh them closer than to
0.5 milligram.
GAS-METER.
The gas-meter is made by the Dansk Maalerfabrik in Copenhagen, and
is of the type used by Bohr in many of his investigations. It has the
advantage of showing the water-level, and the volume may be read directly.
The dial is graduated so as to be read within 50 cubic centimeters.
The Elster meter formerly used for this purpose was much smaller than
the meter of the Dansk Maalerfabrik we are now using. The volume
of water was much smaller and consequently the temperature fluctuations
much more rapid. While the residual analyses for which the meter is used
are of value in interpolating the results for the long experiments, and
consequently errors in the meter would be more or less constant, affecting
all results alike, we have nevertheless carefully calibrated the meter by
means of the method of admitting oxygen from a weighed cylinder.* The
test showed that the meter measured 1.4 per cent too much, and conse-
quently this correction must be applied to all measurements made with it.
* Francis G. Benedict: A method of calibrating gas-meters. Physical Review,
vol. 22, p. 294. (1906.)
76 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
CALCULATION OF RESULTS.
With an apparatus as elaborate as is the respiration calorimeter and its
accessories, the calculation of results presents many difficulties, but the
experience of the past few years has enabled us to lessen materially the
intricacies of the calculations formerly thought necessary.
The total amount of water-vapor leaving the chamber is determined by
noting the increase in weight of the first sulphuric-acid vessel in the
absorber system. This vessel is weighed with a counterpoise and hence
only the increment in weight is recorded. A slight correction may be
necessary here, as frequently the absorber is considerably warmer at the
end of the period than at the beginning and if weighed while warm there
may be an error of 0.1 to 0.2 gram. If the absorbers are weighed at the
same temperature at the beginning and end, this correction is avoided.
The amount of carbon dioxide absorbed from the ventilating air-current
is found by noting the changes in weight of the potash-lime can and the
last sulphuric-acid vessel. As shown by the weights of this latter vessel,
it is very rare that sufficient water is carried over from the potash-lime to
the sulphuric acid to cause a perceptible change in temperature, and no
temperature corrections are necessary. It may occasionally happen that
the amount of carbon dioxide absorbed is actually somewhat less than the
amount of water-vapor abstracted from the reagent by the dry air-current
as it passes through the can. The conditions will then be such that there
will be a loss in weight of the potash-lime can and a large gain in weight
of the sulphuric-acid vessel. Obviously, the algebraic sum of these amounts
will give the true weight of the carbon dioxide absorbed.
The amount of oxygen admitted is approximately measured by noting
the loss in weight of the oxygen cylinder. Since, however, in admitting
the oxygen from the cylinder there is a simultaneous admission of a small
amount of nitrogen, a correction is necessary. This correction can be
computed either by the elaborate formulas described in the publication of
Atwater and Benedict * or by the more abbreviated method of calculation
which has been used very successfully in all short experiments in this labora-
tory. In either case it is necessary to know the approximate percentage of
nitrogen in the oxygen.
ANALYSIS OF OXYGEN.
With the modified method of computation discussed in detail on page 88
it is seen that such exceedingly exact analyses of oxygen as were formerly
made are unnecessary, and further calculation is consequently very simple
if we know the percentage of nitrogen to within a fraction of 1 per cent.
We have used a Haldane gas-analysis apparatus for analyzing the oxygen,
although the construction of the apparatus is such that this presents some
* Atwater and Benedict: hoc cit., p. 38.
CALCULATION OF RESULTS. 77
little difficulty. It is necessary, for example, to accurately measure about
16 cubic centimeters of pure nitrogen, pass it into the potassium pyrogal-
late pipette, and then (having taken a definite sample of oxygen) gradually
absorb the oxygen in the potassium pyrogallate and measure subsequently
the accumulated nitrogen. The analysis is tedious and not particularly
satisfactory. Having checked the manufacturer's analysis of a number of
cylinders of oxygen and invariably found them to agree with our results,
we are at present using the manufacturer's guaranteed analysis. If there
was a very considerable error in the gas analysis, amounting even to 1 per
cent, 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 for
use with the calorimeter formerly at Wesleyan University shows that a
large proportion of it can be eliminated owing to the fact that we are here
able to work in a room of constant temperature. It has been pointed out
that the fluctuations in the temperature of the gas-meter affect not only
the volume of the gas passing through the meter, but likewise the tension
of aqueous vapor. The corrections formerly made for temperature on the
barometer are now unnecessary; finally (and perhaps still more important)
it is no longer necessary to subdivide the volume of the system into por-
tions of air existing under different temperatures, depending upon whether
they were in the upper or lower part of the laboratory. In other words, the
temperature of the whole ventilating circuit and chamber, with the single
exception of the air above the acid in the first sulphuric-acid absorber, may
be said to be constant. During rest experiments this assumption can be
made without introducing any material error, but during work experiments
it is highly probable that some consideration must be given to the possi-
bility of the development of a considerable temperature rise in the air of
the potash-lime absorbers, due to the reaction between the carbon dioxide
and the solid absorbent. It is thus apparent that the constant-temperature
conditions maintained in the calorimeter laboratory not only facilitate
calorimetric measurements, but also simplify considerably the elaborate
calculations of the respiratory exchange formerly required.
VARIATIONS IN THE APPARENT VOLUME OF ALR.
In the earlier form of apparatus the largest variation in the apparent
volume of air was due to the fluctuations in the height of the large rubber
diaphragms used on the tension equalizer. In the present form of appa-
ratus there is but one rubber diaphragm, and this is small, containing not
more than 3 to 4 liters as compared to about 30 liters in the earlier double
rubber diaphragms. As now arranged, all fluctuations due to the varying
78 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
positions of the tension-equalizer are eliminated as each experimental period
is ended with the diaphragm in exactly the same position, i. e., filled to a
definite tension.
In its passage through the purifiers the air is subjected to more or less
pressure, and it is obvious that if these absorbers were coupled to the venti-
lating system under atmospheric pressure, and then air caused to pass
through them, there would be compression in a portion of the purifier
system. Thus there would be a contraction in the volume, and air thus
compressed would subsequently be released into the open air when the
absorbers were uncoupled. The method of testing the system outlined on
page 100 equalizes this error, however, in that the system is tested under
the same pressure used during an actual experiment, and hence between
the surface of the sulphuric acid in the first porcelain vessel and the sul-
phuric acid in the second porcelain vessel there is a confined volume of air
which at the beginning of an experimental period is under identically the
same pressure as it is at the end. There is, then, no correction necessary
for the rejection of air with the changes in 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 slight
increase in volume of the acid. This naturally results in the diminution
of the apparent volume of air and likewise again affects the amount of
oxygen admitted to produce constant apparent volume at the end of each
experimental period. The amount of increase which thus takes place for
each experimental period is very small. It has been found that an increase
in weight of 25 grams of water- vapor results in an increase in volume of
the acid of some 15 cubic centimeters. Formerly this correction was made,
but it is now deemed unnecessary and unwise to introduce a refinement that
is hardly justified in other parts of the apparatus. Similarly, there is
theoretically at least an increase in volume of the potash-lime by reason of
the absorption of the carbon dioxide. This was formerly taken into con-
sideration, but the correction is no longer applied.
RESPIRATORY LOSS.
With experiments on man, there is a constant transformation of solid
body material into gaseous products which are carried out into the air-
current and absorbed. Particularly where no food is taken, this solid
material becomes smaller in volume and consequently additional oxygen is
required to take the place of the decrease in volume of body substance.
But this so-called respiratory loss is more theoretical than practical in
importance, and in the experiments made at present the correction is not
considered necessary.
CALCULATION OF RESULTS. 79
CALCULATION OF THE VOLUME OF AIR RESIDUAL IN THE CHAMBER.
The ventilating air-circuit may be said to consist of several portions of
air. The largest portion is that in the respiration chamber itself and con-
sists of air containing oxygen, nitrogen, carbon dioxide, and water-vapor.
This air is assumed to have the same composition up to the moment when
it begins to bubble through the sulphuric acid in the first acid-absorber.
The air in this absorber above the acid, amounting to about 14 liters, has a
different composition in that the water-vapor has been completely removed.
The same 14 liters of air may then be said to contain carbon dioxide, nitro-
gen, and oxygen. This composition is immediately disturbed the moment
the air enters the potash-lime can, when the carbon dioxide is absorbed
and the volume of air in the last sulphuric-acid absorber, in the sodium-
bicarbonate can, and in the piping back to the calorimeter may be said to
consist only of nitrogen and oxygen. The air then between the surface of
the sulphuric acid in the last porcelain absorber and the point where the
ingoing air is delivered to the calorimeter consists of air free from carbon
dioxide and free from water. Formerly this section also included the
tension-equalizer, but very recently we have in both of the calorimeters
attached the tension-equalizer directly to the respiration chamber.
In the Middletown apparatus, these portions of air of varying compo-
sition were likewise subject to considerable variations in temperature, in
that the temperature of the laboratory often differed materially from that
of the calorimeter chamber itself, especially as regards the apparatus in
the upper part of the laboratory room. It is important, however, to know
the total volume of the air inclosed in the whole system. This is obtained
by direct measurement. The cubic contents of the calorimeter has been
carefully measured and computed ; the volumes of air in the pipes, valve
systems, absorbing vessels, and tension-equalizer have been computed from
dimensions, and it has been found that the total volume in the apparatus
is, deducting the volume of the permanent fixtures in the calorimeter, 1,347
liters. The corresponding volume for the bed calorimeter is 875. These
values are altered by the subject and extra articles taken into the chamber.
From a series of careful measurements and special tests the following
apparent volumes for different parts of the system have been calculated:
Liters.
Volume of the chair calorimeter chamber (without fixtures) 1360.0
Permanent fixtures (5) ; chair and supports (8) 13.0
Apparent volume of air inside chamber 1347.0
Air in pipes, blower, and valves to surface of acid in first acid vessel 4.5
Apparent volume of air containing water-vapor 1351.5
Air above surface of acid in first sulphuric-acid vessel and potash-lime can . 16.0
Apparent volume of air containing carbon dioxide 1367.5
Air 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
80 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
These volumes represent conditions existing inside the chamber without
the subject, i. e., conditions under which an alcohol check-test would be
conducted. In an experiment with man it would be necessary to deduct
the volume of the man, books, urine bottles, and all supplemental apparatus
and accessories. Under these circumstances the apparent volume of the
air in the chamber may at times be diminished by nearly 90 to 100 liters.
At the beginning of each experiment the apparent volume of air is calcu-
lated.
RESIDUAL ANALYSES.
CALCULATION FROM RESIDUAL ANALYSES.
The increment in weight of the absorbers for water and carbon dioxide
and the loss in weight of the oxygen cylinder give only an approximate
idea of the amounts of carbon dioxide and water-vapor produced and
oxygen absorbed during the period, and it is necessary to make correction
for change in the composition of the air as shown by the residual analyses
and for fluctuations in the actual volume. In order to compute from the
analyses the total carbon-dioxide content of the residual air, it is necessary
to know the relation of the air used for the sample to the total volume, and
thus we must know accurately the volume of air passing through the gas-
meter.
In the earlier apparatus 10-liter samples were used, and the volume of
the respiration chamber was so large that it was necessary to multiply the
values found in the residual sample by a very large factor, 500. Hence,
the utmost caution was taken to procure an accurate measurement of the
sample, the exact amounts of carbon dioxide absorbed, and water-vapor
absorbed. To this end a large number of corrections were made, which
are not necessary with the present type of apparatus with a volume of resid-
ual air of but about 1,300 liters, and accordingly the manipulation and
calculations have been very greatly simplified.
While formerly pains were taken to obtain the exact temperature of the
air leaving the gas-meter, with this apparatus it is unnecessary. When the
earlier type of apparatus was in use there were marked changes in the
temperature of the calorimeter laboratory and in the water in the meter
which were naturally prejudicial to the accurate measurement of the volume
of samples, but with the present control of temperature in this laboratory
it has been found by repeated tests that the temperature of the water in
the meter does not vary a sufficient amount to justify this painstaking
measurement and calculation. Obviously, this observation also pertains to
the corrections for the tension of aqueous vapor. It has been found pos-
sible to assume an average laboratory temperature and reduce the volume
as read on the meter by means of a constant factor.
CALCULATION OF RESULTS. 81
The quantity of air passing through the meter is so adjusted that ex-
actly 10 liters as measured on the dial pass through it for one analysis.
The air as measured in the meter is, however, under markedly different
conditions from the air inside the respiration chamber. While there is the
same temperature, there is a material difference in the water-vapor present,
and hence the moisture content as expressed in terms of tension of aqueous
vapor must be considered. This obviously tends to diminish the true
volume of air in the meter.
Formerly we made accurate correction for the tension of aqueous vapor
based upon the barometer and the temperature of the meter at the end of
the period, but it has now been found that the reduction of the meter
readings to conditions inside of the chamber can be made with a sufficient
degree of accuracy by multiplying the volume of air passing through the
meter by a fraction, , in which h represents the barometer and t the
tension of aqueous vapor at the temperature of the laboratory, 20° C.
Since the tension of aqueous vapor at the laboratory temperature is not far
from 15 mm., a simple calculation will show that there may be consider-
able variations in the value of h without affecting the fraction materially,
and we have accordingly assumed a value of h as normally 760 mm., and
the correction thus obtained is 7o^~15 =0.98, and all readings on the
760
meter should be multiplied 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 hand the cor-
rection on the sample for the tension of aqueous vapor, which is —2.0 per
cent, and consequently the resultant correction is —0.6 per cent. From
the conditions under which the experiments are made, however, it is rarely
possible to read the meter closer than ±0.05 liter, as the graduations on
the meter correspond to 50 cubic centimeters. It will be seen, then, that
this final correction is really inside the limit of error of the instrument,
and consequently with this particular meter now in use no correction what-
ever is necessary for the reduction of the volume. The matter of tem-
perature corrections has been taken up in great detail in an earlier publi-
cation, and where there are noticeable differences in temperature between
the meter and the calorimeter chamber the calculation is very much more
complicated.
For practical purposes, therefore, we may assume that the quantity of
air passed through the meter, as now in use, represents exactly 10 liters
measured under the conditions obtaining inside of the respiration chamber,
and in order to find the total amount of water-vapor present in the chamber
it is necessary only to multiply the weight of water found in the 10-liter
sample by one-tenth of the total volume of air containing water-vapor.
82 CALOEIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
The total volume of air which contains water-vapor is not far from 1,360
liters; consequently multiplying the weight of water in the sample by 136
gives the total amount of water in the chamber and the piping. The
volume of air containing carbon dioxide is that contained in the chamber
and piping to the first sulphuric-acid vessel plus 16 liters of air above the
sulphuric acid and connections in the first porcelain vessel, and in order
to obtain the amount of carbon dioxide from the sample it is only necessary
to multiply the weight of carbon dioxide in the sample by 137.6.
Since in the calculation of the total amount of residual oxygen volumes
rather than weights of gases are used, it is our custom to convert the
weights of carbon dioxide and water-vapor in the chamber to volumes by
multiplying by the well-known factors. The determination of oxygen
depends upon the knowledge of the true rather than the apparent volume
of air in the system, and consequently the apparent volume must be reduced
to standard conditions of temperature and pressure each time the calcula-
tion is made. To this end, the total volume of air in the inclosed circuit
(including that in the tension-equalizer, amounting to 1,400 liters in all)
is reduced to 0° and 760 millimeters by the usual methods of computation.
The total volume of air (which may be designated as V) includes the
volumes of carbon dioxide, water-vapor, oxygen, and nitrogen. From the
calculations mentioned above, the volumes of water-vapor and carbon di-
oxide have been computed, and deducting the sum of these from the reduced
volume of air gives the volume of oxygen plus nitrogen. If the volume of
nitrogen is known, obviously the volume of oxygen can be found.
At the beginning of the experiment, it is assumed that the chamber is
filled with ordinary air. By calculating the amount of nitrogen in the
chamber at the start as four-fifths of the total amount, no great error is
introduced. In many experiments actual analyses of the air have been
made at the moment of the beginning of the experiment The important
thing to bear in mind is that having once sealed the chamber and closed
it tightly, no nitrogen can enter other than that admitted with the oxygen,
and hence the residual amount of nitrogen remains unaltered save for this
single exception. If care is taken to keep an accurate record of the amount
of nitrogen admitted with the oxygen, the nitrogen residual in the chamber
at any given time is readily computed. While from an absolute mathe-
matical standpoint the accuracy of this computation can be questioned,
here again we are seeking an accurate record of differences rather than an
absolute amount, and whether we assume the volume of the air in the
chamber to contain 20.4 per cent of oxygen or 21.6 per cent is a matter of
indifference. It is of importance only to note the increases in the amount
of nitrogen, since these increases represent decrease in the residual oxygen
and it is with the changes in the residual oxygen that we particularly have
to do.
CALCULATION OF RESULTS. 83
INFLUENCE OF FLUCTUATIONS IN TEMPERATURE AND PRESSURE ON THE
APPARENT VOLUME OF ATR IN THE SYSTEM.
The air, being confined in a space with semi-rigid walls, is subjected
naturally to variations in true volume, depending upon the temperature
and barometric pressure. If the air inside of the chamber becomes con-
siderably warmer there is naturally an expansion, and were it not for the
tension-equalizer there would be pressure in the system. Also, if the ba-
rometer falls, there is an expansion of air which, again, in the absence of
the tension-equalizer, would produce pressure in the system. It is neces-
sary, therefore, in calculating the true volume of air, to take into account
not only the apparent volume, which, as is shown above, is always a con-
stant amount at the end of each period, but the changes in temperature and
barometric pressure must also be noted. Since there is a volume of about
1,400 liters, a simple calculation will show that for each degree centigrade
change in temperature there will be a change in volume of approximately
4.8 liters. In actual practice, however, this rarely occurs, as the tempera-
ture control is usually inside of 0.1° C. and for the most part within a few
hundredths. A variation in barometric pressure of 1 millimeter will affect
1,400 liters by 1.8 liters.
In actual practice, therefore, it is seen that if the barometer falls there
will be an expansion of air in the system. This will tend to increase the
volume by raising the rubber diaphragm on the tension-equalizer, the
ultimate result of which is that at the final filling with oxygen at the end
of the period less is used than would be the case had there been no change
in the barometer. In other words, for each liter expansion of air inside
of the system, there is 1 liter less oxygen required to bring the apparent
volume the same at the end of the period. Similarly, if there is an increase
in temperature of the air, there is expansion, and a smaller amount of
oxygen is required than would be the case had there been no change; and
conversely, if the barometer rises or the temperature falls, more oxygen
would be supplied than is needed for consumption. It is thus seen that the
temperature and barometer changes affect the quantity of oxygen admitted
to the chamber.
INFLUENCE OF FLUCTUATIONS IN THE AMOUNTS OF CARBON DIOXIDE AND
WATER-VAPOR UPON RESIDUAL OXYGEN.
Any variations in the residual amount of carbon dioxide or water-vapor
likewise affect the oxygen. Thus, if there is an increase of 1 gram in the
amount of residual carbon dioxide, this corresponds to 0.51 liter, and con-
sequently an equal volume of oxygen is not admitted to the chamber during
the period, since its place has been taken by the increased volume of carbon
dioxide. A similar reasoning will show that increase in the water-vapor
content will have a similar effect, for each gram of water-vapor corresponds
84 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
to 1.25 liters and therefore influences markedly the introduction of oxygen.
All four of the factors, therefore (barometric pressure, temperature, residual
carbon dioxide, and residual water- 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 to be
placed upon the analysis) unfortunately can not be directly determined
without great difficulty. Furthermore, any errors in the analysis may be
very greatly multiplied by the known errors involved in the determination
of the true volume of the air in the chamber as a result of the difficulties
in obtaining the average temperature of the air. Believing that the method
of analysis as outlined above should be controlled as far as possible by
other independent methods, we were able to compare the carbon dioxide as
determined by the soda-lime method with that obtained by the extremely
accurate method used by Sonden and Pettersson. An apparatus for the
determination of carbon dioxide and oxygen on the Pettersson principle
has been devised by Sonden and constructed 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 which connected
directly with the sampling pipette of the Sonden gas-analysis apparatus,
the other arm connecting with the U-tubes for residual analyses. By lower-
ing and raising the mercury reservoir on the gas-analysis apparatus, a
sample of air could be drawn into the apparatus for analysis. The results
of the analysis were expressed on the basis of moist air in volume per
cents rather than by weight, as is done with the soda-lime method. Hence
in comparison it was necessary to convert the weights to volume, and
during this process the errors due to not correcting for temperature and
barometer are made manifest. However, the important point to be noted
is that whatever fluctuations in composition of the residual air were noted
by the soda-lime method, similar fluctuations of a corresponding size were
recorded by the volumetric analysis with the Sonden apparatus. Under
these conditions, therefore, we believe that the gravimetric method out-
lined above is sufficiently satisfactory, so far as the carbon-dioxide content
is concerned, for ordinary work where there are no wide variations in the
composition of the air from period to period.
NITROGEN ADMITTED WITH THE OXYGEN.
It is impossible to obtain in the market absolutely chemically pure oxy-
gen. All the oxygen that we have thus far been able to purchase contains
nitrogen and, in some instances, measurable amounts of water-vapor and
carbon dioxide. The better grade of oxygen, that prepared from liquid air,
is practically free from carbon dioxide and water-vapor, but it still contains
CALCULATION OF RESULTS. 85
nitrogen, and hence with every liter of oxygen admitted there is a slight
amount of nitrogen added. This amount can readily be found from the
gasometric analysis of the oxygen and from the well-known relation between
the weight and the volume of nitrogen the weight can be accurately found.
This addition of nitrogen played a very important role in the calculation
of the oxygen consumption as formerly employed. As is seen later, a much
abbreviated form of calculation is now in use in which the nitrogen admitted
with the oxygen does not influence the calculation of the residual oxygen.
REJECTION OF AIR.
In long-continued experiments, where there is a possibility of a notice-
able diminution in the percentage of oxygen in the chamber — a diminu-
tion caused either by a marked fall in barometer, which expands the air
inside of the chamber and permits admission of less oxygen than would
otherwise be required, or by the use of oxygen containing a high percentage
of nitrogen, thus continually increasing the amount of nitrogen present
in the system — it is highly probable that there may be such an accumula-
tion of nitrogen as to render it advisable to provide for the admission of a
large amount of oxygen to restore the air to approximately normal condi-
tions. In rest experiments of short duration this is never necessary.
The procedure by which such a restoration of oxygen percentage is accom-
plished has already been discussed elsewhere.* It involves the rejection
of a definite amount of air by allowing it to pass into the room through
the gas-meter and then making proper corrections for the composition of
this air, deducting the volume of oxygen in it from the excess volume of
oxygen introduced and correcting the nitrogen residual in order to deter-
mine the oxygen absorption 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 is
approximately 5.3 liters. When the door on the inside is opened and the
material placed in the food-aperture and the outer door is subsequently
opened, there is by diffusion a passage outward of air of the composition of
the air inside of the chamber, and the food-aperture is now filled with room
air. When the inner door is again opened this room air enters the chamber
and is replaced by air of the same composition as that in the chamber. It
is seen, then, that there may theoretically be an interchange of air here
which may have an influence on the results. In severe work experiments,
where the amount of carbon dioxide in the air is enormously increased,
such interchange doubtless does take place in measurable amounts and
correction should undoubtedly be made. In ordinary rest experiments,
•Atwater and Benedict: Carnegie Institution of Washington Publication No.
42, p. 77.
86 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
where the composition of the air in the chamber is much more nearly nor-
mal, this correction is without special significance. Furthermore, in the
two forms of calorimeter now in use, the experiments being of but short
duration, provision is made to render it unnecessary to open the food-
aperture during the experiment proper. Consequently at present no cor-
rection for interchange of air in the food-aperture is made, and for the
same reason the slight alteration in volume resulting from the removal or
addition of material has also not been considered here.
USE OF THE RESIDUAL BLANK IN THE CALCULATIONS.
To facilitate the calculations and for the sake of uniformity in express-
ing the results, a special form of blank is used which permits the recording
of the principal data regarding the analyses of air in the chamber at the
end of each period. Thus at the head of the sheet are recorded the time,
the number of the period, kind of experiment, the name or initials of the
subject, and the statement as to which calorimeter is used. The barometer
recorded in millimeters is indicated in the column at the left and imme-
diately below the heading, together with the temperature of the calorimeter
as expressed in degrees centigrade. The temperature of the calorimeter as
recorded by the physical observer is usually expressed in the arbitrary
scale of the Wheatstone bridge and must be transposed into the centigrade
scale by means of a calibration table.
The apparent air-volumes in the subsections of the ventilating system
are recorded under the headings I, which represents the volume of air con-
taining water-vapor and therefore is the air in the chamber plus the air in
the piping to the surface of the acid in the first sulphuric-acid absorber;
I-II, which represents the air containing carbonic acid and includes volume
I plus the volume of the air in the first sulphuric-acid vessel and the
volume of air in the potash-lime absorber; I-II I, which includes the total
confined volume of the whole system, since this air contains both oxygen
and nitrogen. These volumes change somewhat, depending upon the size
of the body of the subject, the volume of the materials taken into the
chamber, and the type of calorimeter.
The data for the residual analyses are recorded in the lower left-hand
corner : first the weight of the water absorbed from 10 liters of air passing
through the meter ; to the logarithm of this is added the logarithm of volume
I ; the result is the logarithm of the total weight of water-vapor in the venti-
lating air-current. To convert this into liters the logarithmic factor 09462*
is added to the logarithm of the weight of water and (a) is the logarithm
of water expressed in liters. A similar treatment is accorded the weight
of carbon dioxide absorbed from the air-sample, (b) being ultimately the
logarithm of the volume of carbon dioxide.
* In the use of logarithms space is saved by not employing characteristics.
CALCULATION OF RESULTS.
87
In order to determine the total volume of air in the chamber under stan-
dard conditions of temperature and pressure, to the logarithm of volume
I-III is added, first, a logarithmic factor for the temperature recorded
for the calorimeter to correct the volume of air to standard temperature.
As the temperature fluctuations are all within 1 degree, a table has been
prepared giving the standard fluctuation represented by the formula - ,
in which t is the temperature of the calorimeter. The correction for pres-
sure has also been worked out in a series of tables and the logarithmic
factor here corresponds to the ratio x.' , in which p is the observed ba-
rometer. The logarithm of the total volume is recorded as a result of the
addition of these three logarithms enumerated, and from this logarithm
is expressed the total volume of air in liters. Deducting the sum of the
values (a) and (&) from the total volume leaves the volume of oxygen plus
nitrogen.
The calculation of the residual volume of nitrogen and the record of the
additions thereto was formerly carried out with a refinement that to-day
seems wholly unwarranted when other factors influencing this value are
taken into consideration. For the majority of experiments the residual
volume of nitrogen may be considered as constant in spite of the fact that
some nitrogen is regularly admitted with the oxygen. The significance of
this assumption is best seen after a consideration of the method of calcu-
lating the amount of oxygen admitted to the chamber.
RESIDUAL SHEET
No. 1.
Calculation of residual amounts of nitrogen, oxygen, carbon dioxide and water-rapor
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, 766.95 mm.
Temp, cal., 20.08 °C
Apparent Volume of Air
I containing H,0 716. liters
I -II " CO, 731. "
I - III " O+N 766. "
Log. wt. H,0 in residual
.0816 = 91116
Log. I = 86431
76647 = 6.83 gms. HoO
Gms. to liters. 09462
(a) 86009 = 7.26 1. H20
Log. wt. CO, in residual
0423 = 62634
Log. I-II = 86392
49026 = 3.09 gms. CO,
Gms. to liters, 70680
(b) 19706 = 1.57 1. CO,
Miscellaneous Calculations
875
164.66
710.45
4.6
48.65
25.9
•0.
164.66
716.0 I
16
731.0 I-II
24
766.0 I-III
(a)
(b)
7.26 1.
1.67 1.
8.82 =
1. CO,+H,0
Log. I-III
" temp. =
" pressure =
87795
96912
99826
Total volume 84633 =
Volume CO,+H,0 =
700.37 1.
8.82 1.
" O+N
N
-
691.66 1.
552.98 1.
= 138.67 1.
88 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
ABBREVIATED METHOD OF COMPUTATION OF OXYGEN ADMITTED TO THE
CHAMBER FOR USE DURING SHORT EXPERIMENTS.
Desiring to make the apparatus as practicable and the calculations as
simple as possible, a scheme of calculation has been devised whereby the
computations may be very much abbreviated and at the same time there
is not too great a sacrifice in accuracy. The loss in weight of the oxygen
cylinder has, in the more complicated method of computation, been con-
sidered as due to oxygen and about 3 per cent of nitrogen. The amount
of nitrogen thus admitted has been carefully computed and its volume
taken into consideration in calculating the residual oxygen. If it is con-
sidered for a moment that the admission of gas out of the steel cylinder is
made at just such a rate as to compensate for the decrease in volume of the
air in the system due to the absorption of oxygen by the subject, it can be
seen that if the exact volume of the gas leaving the cylinder were known
it would be immaterial whether this gas were pure oxygen, oxygen with
some nitrogen, or oxygen with any other inert gas not dangerous to respira-
tion or not absorbed by sulphuric acid or potash-lime. If 10 liters of
oxygen had been absorbed by the man in the course of an hour, to bring the
system back to constant apparent volume it would be necessary to admit
10 liters of such a gas or mixture of gases, assuming that during the hour
there had been no change in the temperature, the barometric pressure, or
the residual amounts of carbon dioxide or water-vapor.
Under these assumed conditions, then, it would only be necessary to
measure the amount of gas admitted in order to have a true measure of
the amount of oxygen absorbed. The measure of the volume of the gas
admitted may be used for a measure of the oxygen absorbed, even when it is
necessary to make allowances for the variations in the amount of carbon
dioxide or water-vapor in the chamber, the temperature, and barometric
pressure. From the loss in weight of the oxygen cylinder, if the cylinder
contained pure oxygen, it would be known that 10 liters would be admitted
for every 14.3 grams loss in weight.
From the difference in weight of 1 liter of oxygen and 1 liter of nitrogen,
a loss in weight of a gas containing a mixture of oxygen with a small per
cent of nitrogen would actually represent a somewhat larger volume of gas
than if pure oxygen were admitted. The differences in weight of the two
gases, however, and the amount of nitrogen present are so small that one
might almost wholly neglect the error thus arising from this admixture of
nitrogen and compute the volume of oxygen directly from the loss in weight
of the cylinder.
As a matter of fact, it has been found that by increasing the loss in
weight of the cylinder of oxygen containing 3 per cent nitrogen by 0.4 per
cent and then converting this weight to volume by multiplying by 0.7, the
volume of gas admitted is known with great accuracy. This method of
CALCULATION OF RESULTS. 89
calculation has been nsed with success in connection with the large chamber
and particularly for experiments of short duration. It has also been intro-
duced with great success in a portable type of apparatus described else-
where.* Under these conditions, therefore, it is unnecessary to make any
correction on the residual volume of nitrogen as calculated at the beginning
of the experiment. When a direct comparison of the calculated residual
amount of oxygen present is to be made upon determinations made with a
gas-analysis apparatus the earlier and much more 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 there
are constantly changing percentages of carbon dioxide, oxygen, and water-
vapor, it is important to note that the nitrogen present in the apparatus
when the apparatus is sealed remains unchanged throughout the whole
experiment, save for the small amounts added with the commercial oxygen —
amounts well known and for which definite corrections can be made. Con-
sequently, in order to find the amount of oxygen present in the residual air
at any time it is only necessary to determine the amounts of carbon dioxide
and water-vapor and, from these two factors and from the known volume of
nitrogen present, it is possible to compute the total volume of oxygen after
calculating the total absolute volume of air in the chamber at any given
time.
While the apparent volume of the air remains constant throughout the
whole experiment, by the conditions of the experiment itself the absolute
amount may change considerably, owing primarily to the fluctuations in
barometric pressure and secondarily to slight fluctuations in the tempera-
ture of the air inside of the chamber. Although the attempt is made on
the part of the observers to arbitrarily control the temperature of this air
to within a few hundredths of a degree, at times the subject may inadvert-
ently move his body about in the chair just a few moments before the end
of the period and thus temporarily cause an increased expansion of the air.
The apparatus is, in a word, a large air-thermometer, inside the bulb of
which the subject is sitting. If the whole system were inclosed in rigid
walls there would be from time to time noticeable changes in pressure on
the system due to variations in the absolute volume, but by means of the
tension-equalizer these fluctuations in pressure are avoided.
The same difficulties pertain here which were experienced with the earlier
type of apparatus in determining the average temperature of the volume of
air inside of the chamber. We have on the one hand the warm surface of
the man's body, averaging not far from 32° C. On the other hand we have
* Francis G. Benedict : An apparatus for studying the respiratory exchange.
American Journal of Physiology, vol. 24, p. 368. (1909.)
90 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
the cold water in the heat-absorbers at a temperature not far from 12° C.
Obviously, the air in the immediate neighborhood of these two localities is
considerably warmer or colder than the average temperature of the air.
The disposition of the electric-resistance thermometers about the chamber
has, after a great deal of experimenting, been made such as to permit the
measurement as nearly as possible of the average temperature in the cham-
ber. But this is at best a rough approximation, and we must rely upon the
assumption that while the temperatures which are actually measured may
not be the average temperature, the fluctuations of the average temperature
are parallel to the fluctuations in the temperatures measured. Since every
effort is made to keep these fluctuations at a minimum, it is seen that the
error of this assumption is not as great as might appear at first sight.
However, the calculation of the residual amount of oxygen in the chamber
is dependent upon this assumption and hence any errors in the assumption
will affect noticeably the calculation of the residual oxygen.
Attempts to compare the determination of the oxygen by the exceedingly
accurate Sonden apparatus with that calculated after determining the
water-vapor and carbon dioxide, temperature and pressure of the air in the
chamber have thus far led to results which indicate one of three things:
(1) that there is not a homogeneous mixture; (2) that during the time
required for making residual analyses, i. e., some three or four minutes,
there may be a variation in the oxygen content in the air of the chamber
due to the oxygen continually added from the cylinder; (3) that the oxygen
supplied from the cylinder is not thoroughly mixed with the air in the
chamber until some time has elapsed. That is to say, with the method
now in use it is necessary to fill the tension-equalizer to a definite pres-
sure immediately at the end of each experimental period. This is done by
admitting oxygen from the cylinder, and obviously this oxygen was not
present in the air when analyzed. A series of experiments with a somewhat
differently arranged system is being planned in which the oxygen will be
admitted to the respiration chamber directly and not into the tension-equal-
izer, and at the end of the experiment the tension-equalizer will be kept at
such a point that when the motor is stopped the amount of oxygen to be
added to bring the tension to a definite point will be small.
Under these conditions it is hoped to secure a more satisfactory compari-
son of the analyses as made by means of the Sonden apparatus and as calcu-
lated from the composition of the residual air by the gravimetric analysis.
It remains a fact, however, that no matter with what skill and care the gaso-
metric analysis is made, either gravimetrically or volumetrically, the calcu-
lation of the residual amount of oxygen presents the same difficulties in
both cases.
CALCULATION OF RESULTS. 91
CALCULATION OF TOTAL OUTPUT OF CARBON DIOXIDE AND WATER- VAPOR
AND OXYGEN ABSORPTION.
From the weights of the sulphuric-acid and potash-lime vessels, the
amounts of water-vapor and carbon dioxide absorbed out of the air-current
are readily obtained. The loss in weight of the oxygen cylinder increased
by 0.4 per cent (see page 88) gives the weight of oxygen admitted to the
chamber. It remains, therefore, to make proper allowance for the varia-
tions in composition of the air inside the chamber at the beginning and end
of the different periods. From the residual sheets the amounts of water-
vapor, carbonic acid, and oxygen present in the system at the beginning
and end of each period are definitely known. If there is an increase, for
example, in the amount of carbon dioxide in the chamber at the end of a
period, this increase must be added to the amount absorbed out of the air-
current in order to obtain the true value for the amount produced during
the experimental period.
A similar calculation holds true with regard to the water-vapor and
oxygen. For convenience in calculating, the amounts of water-vapor and
carbon dioxide residual in the chamber are usually expressed in grams,
while the oxygen is expressed in liters. Hence, before making the additions
or subtractions from the amount of oxygen admitted, the variations in the
amount of oxygen residual in the system should be converted 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 the
apparatus for determining carbon dioxide, water, and oxygen, it becomes
necessary to submit the apparatus to a severe test and thus demonstrate
its ability to give satisfactory results under conditions that can be accu-
rately controlled. The liberation of a definite amount of carbon dioxide
from a carbonate by means of acid has frequently been employed for con-
trolling an apparatus used for researches in gaseous exchange, but this only
furnishes a definite amount of carbon dioxide and throws no light what-
ever upon the ability of the apparatus to determine the other two factors,
water-vapor and oxygen. Some of the earlier experimenters have used burn-
ing candles, but these we have found to be extremely unsatisfactory. The
necessity for an accurate elementary analysis, the high carbon content of
the stearin and paraffin, and the possibility of a change in the chemical
composition of the material all render this method unfit for the most
accurate testing. As a result of a large number of experiments with dif-
ferent materials, we still rely upon the use of ethyl alcohol of known water-
content. The experiments with absolute alcohol and with alcohol con-
taining varying amounts of water showed no differences in the results, and
92
CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
hence it is now our custom to obtain the highest grade commercial alcohol,
determine the specific gravity accurately, and burn this material. We use
the Squibb pyknometer * and thereby can determine the specific gravity of
the alcohol to the fifth or sixth decimal plaee with a high degree of accuracy.
Using the alcoholometric tables of Squibb f or Morley,$ the percentage of
alcohol by weight is readily found, and from the chemical composition of
the alcohol can be computed not only the amount of carbon dioxide and
water-vapor formed and oxygen absorbed by the combustion of 1 gram of
ethyl hydroxide containing a definite known amount of water, but also
the heat developed during its combustion.
With the construction of this apparatus it was found impracticable to
employ the type of alcohol lamp formerly used with success in the Wesleyan
University respiration chamber. Inability to illuminate the gage on the
side of the lamp and the small windows on the side of the calorimeter
precluded its use. It was necessary to resort to the use of an 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, made with 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 ven-
tilation 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.
Water-vapor ... "
252.9
273.5
165.8
829.0
251.4
274.3
165.6
834.5
Thus does the apparatus prove accurate for the determination of all four
factors.
♦Squibb: Journal of American Chemical Society, vol. 19, p. 111. (1897.)
f Squibb: Ephemeris, 1884 to 1885, part 2, pp. 562-577.
JMorley: Journal of American Chemical Society, vol. 26, p. 1185. (1904.)
BALANCE FOR WEIGHING SUBJECT. 93
BALANCE FOR WEIGHING SUBJECT.
The loss or gain in body-weight has always been taken as indicating the
nature of body condition, a loss usually indicating that there is a loss of
body substance and a gain the reverse. In experiments in which a delicate
balance between the income and outgo is maintained, as in these experi-
ments, it is of special interest to compare the losses in weight as determined
by the balance with the calculated metabolism of material and thus obtain
a check on the computation of the whole process of metabolism. Since the
days of Sanctorius the loss of weight of the body from period to period has
been of special interest. The most recent contribution to these investiga-
tions is that of the balance described by Lombard,* in which the body-
weight is recorded graphically from moment to moment with an extra-
ordinarily sensitive balance.
In connection with the experiments here described, however, the weighing
with the balance has a special significance, in that it is possible to have an
indirect determination of the oxygen consumption. As pointed out by
Pettenkofer and Yoit, if the weight of the excretions and the loss in body-
weight are taken into consideration, the difference between the weight of the
excretions and the loss in body-weight should be the weight of the oxygen
absorbed. With this apparatus we are able to determine the water-vapor,
the carbon-dioxide excretion, and the weight of the urine and feces when
passed. If there is an accurate determination of the body-weight from
hour to hour, this should give the data for computing exactly the oxygen
consumption. Moreover, we have the direct determination of oxygen with
which the indirect method can be compared.
In the earlier apparatus this comparison was by no means as satisfactory
as was desired. The balance there used was sensitive only to 2 grams, the
experiments were long (24 hours or more), and it seemed to be absolutely
impossible, even by exerting the utmost precaution, to secure the body-
weight of the subject each day with exactly the same clothing and acces-
sories. Furthermore, where there is a constant change in body-weight
amounting to 0.5 gram or more per minute, it is obvious that the weighing
should be done at exactly the same moment from day to day. It is seen,
therefore, that the comparison with the direct oxygen determination is in
reality an investigation by itself, involving the most accurate measurements
and the most painstaking development of routine.
With the hope of contributing materially to our knowledge regarding the
indirect determination of oxygen, the special form of balance shown in
fig. 9 was installed above the chair calorimeter. This balance is extremely
* W. P. Lombard : A method of recording changes in body- weight which occur
within short intervals of time. The Journal of the American Medical Associa-
tion, vol. 47, p. 1790. (1906.)
94 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
sensitive. With a dead load of 100 kilograms in each pan it has shown a
sensitiveness of 0.1 gram, but in order to have the apparatus absolutely air-
tight for the oxygen and carbon-dioxide determination, the rod on which
the weighing-chair is suspended must pass through an air-tight closure.
For this closure we have used a thin rubber membrane, weighing about 1.34
grams, one end of which is tied to a hard-rubber tube ascending from the
chair to the top of the calorimeter, the other end being tied to the suspen-
sion rod. In playing up and down this rod takes up a varying weight of the
rubber diaphragm, depending upon the position which it assumes, and there-
fore the sensitiveness noted by the balance with a dead load and swinging
freely is greater than that under conditions of actual use. Preliminary
tests with the balance lead us to believe that with a slight improvement in
the technique a man can be weighed to within 0.3 gram by means of this
balance. A series of check-experiments to test the indirect with the direct
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 stopped
so as to prevent any slight tension on the rubber diaphragm and furnish
the best conditions for sensitive equilibrium. After the weighing has been
made and the time exactly recorded, the load is thrown off the knife-edges
of the balance, and then provision has been made to raise the rod supporting
the chair and simultaneously force a rubber stopper tightly into the hard-
rubber tube at the top of the calorimeter, thus making the closure absolutely
tight. It is somewhat hazardous to rely during the entire period of an
experiment upon the thin rubber membrane for 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 draw
the 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) in
that the cross-bar above the calorimeter chamber, to which the suspension
rod is attached, rests on two oak uprights and can be raised by admitting
air into an air-cushion, through the central opening of which passes the
chair-suspending rod. As the air enters the air-cushion it expands and
lifts a large wooden disk which, in turn, lifts the iron cross-bar, raising
the chair and weight suspended upon it. At the proper height and when
the stopper has been thoroughly forced into place, two movable blocks are
slipped beneath the ends of the iron cross-bar and thus the stopper is held
firmly in place. The tension is then released from the air-cushion. This
apparatus functionates very satisfactorily, raising the man or lowering him
upon the knife-edges of the balance with the greatest regularity and ease.
PULSE RATE AND RESPIRATION BATE. 95
PULSE RATE AND RESPIRATION RATE.
The striking relationship existing betwen pulse rate and general metab-
olism, noted in the fasting experiments made with the earlier apparatus,
has impressed upon us the desirability of obtaining records of the pulse
rate as frequently as possible during an experiment. Records of the res-
piration rate also have an interest, though not of as great importance. In
order to obtain the pulse rate, we attach a Bowles stethoscope over the
apex beat of the heart and hold it in place with a light canvas harness.
Through a long transmission-tube passing through an air-tight closure in
the walls of the calorimeter it is possible to count the beats of the heart
without difficulty. The respiration rate is determined by attaching a Fitz
pneumograph about the trunk, midway between the nipples and the umbili-
cus. The excursions of the tambour pointer as recorded on the smoked
paper of the kymograph give a true picture of the respiration rate.
Of still more importance, however, is the fact that the expansion and
contraction of the pneumograph afford an excellent means for noting the
minor muscular activity of a subject, otherwise considered at complete rest.
The slightest movement of the arm or the contraction or relaxation of any
of the muscles of the body-trunk results in a movement of the tambour
quite distinct from the respiratory movements of the thorax or abdomen.
These movements form a very true picture of the muscular movements of
the subject, and these graphic records have been of very great value in
interpreting the results of many of the experiments.
96 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
ROUTINE OF AN EXPERIMENT WITH MAN.
In the numerous previously published reports which describe the con-
struction of and experiments with the respiration calorimeter, but little
attention has been devoted to a statement of the routine. Since, with the
increasing interest in this form of apparatus and the possible construction
of others of similar form, a detailed description of the routine would be of
advantage, it is here included.
PREPARATION OF SUBJECT.
Prior to an experiment, the subject is usually given either a stipulated
diet 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 food for at
least 12 hours preceding. Occasionally it has been deemed advisable to
administer a cup of black coffee without sugar or cream, and by this means
we have succeeded in studying the early stages of starvation without making
it too uncomfortable for the subject. The stimulating effect of the small
amount of black coffee on metabolism is hardly noticeable and for most
experiments it does not introduce any error.
The urine is collected usually for 24 hours before, in either 6 or 12 hour
periods. During the experiment proper urine is voided if possible at the
end of each period. This offers an opportunity for studying the periodic
elimination of nitrogen and helps frequently to throw light upon any pecu-
liarities of metabolism.
Even with the use of a long-continued preceding diet of constant com-
position, it is impossible to rely upon any regular time for defecation or for
any definite separation of feces. For many experiments it is impracticable
and highly undesirable to have the subject attempt to defecate inside the
chamber, and for experiments of short duration the desire to defecate is
avoided by emptying the lower bowel with a warm-water enema just before
the subject enters the chamber. Emphasis should be laid upon the fact
that a moderate amount of water only should be used and only the lower
bowel emptied, so as not to increase the desire for defecation.
The clothing is usually that of a normal subject, although occasionally
experiments have been made to study the influence of various amounts of
clothing upon the person. There should be opportunity for a comfortable
adjustment of the stethoscope and pneumograph, etc., and the clothing
should be warm enough to enable the subject to remain comfortable and
quiet 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, and
inserted while warm in the rectum to the depth of 10 to 12 centimeters.
The lead wires are brought out through the clothing in a convenient position.
ROUTINE OF AX EXPERIMENT WITH MAN. 97
The stethoscope is attached as nearly as possible over the apex beat of
the heart by means of a light harness of canvas. In the use of the Bowles
stethoscope, it has been found that the heart-beats can easily be counted if
there is but one layer of clothing between the stethoscope and the skin.
Usually it is placed directly upon the undershirt of the subject.
The pneumograph is placed about the body midway between the nipple
and the umbilicus and sufficient traction is put upon the chain or strap
which holds it in place to secure a good and clear movement of the tambour
for each respiration.
The subject is then ready to enter the chamber and, after climbing the
stepladder, he descends into the opening of the chair calorimeter, sits in
the chair, and is then ready to take care of the material to be handed in to
him and adjust himself and his apparatus for the experiment. Usually
several bottles of drinking-water are deposited in the calorimeter in a
convenient position, as well as some urine bottles, reading matter, clinical
thermometer, note-book, etc. Before the cover is finally put in place, the
pneumograph is tested, stethoscope connections are tested to see if the
pulse can be heard, the rectal thermometer connections are tested, and the
telephone, call-bell, and electric light are all put in good working order.
When the subject has been weighed in the chair, the balance is tested to see
that it swings freely and has the maximum sensibility. All the adjustments
are so made that only the minimum exertion will be necessary on the part
of the subject after the experiment has once begun.
SEALING IN THE COVER.
The cover is put in place and wax is well crowded in between it and the
rim of the opening. The wax is preferably prepared in long rolls about the
size of a lead-pencil and 25 to 30 centimeters long. This is crowded into
place, a flat knife being used if necessary. An ordinary soldering-iron,
which has previously been moderately heated in a gas flame, is then used to
melt the wax into place. This process must be carried out with the utmost
care and caution, as the slightest pinhole through the wax will vitiate the
results. The sealing is examined carefully with an electric light and
preferably by two persons independently. After the sealing is assured, the
plugs connecting the thermal junctions and heating wires of the cover with
those of the remainder of the chamber are connected, the water-pipe is
put in place, and the unions well screwed together. After seeing that the
electrical connections can not in any way become short-circuited on either
the metal 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
16 to 24 candle-power (depending upon the size of the subject) is placed
inside of the chamber as a substitute for the man, and the cooling water-
98 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
current is started and the whole apparatus is adjusted to bring away the
heat prior to the entrance of the man. The rate of flow with the chair
calorimeter is not far from 350 cubic centimeters per minute with a resting
man. The proper mixture of cold and warm water is made, so that the
electric reheater can be controlled readily by the resistance in series with it.
Care is taken not to allow the water to enter the chamber below the dew-
point and thus avoid the condensation of moisture on the absorbers. The
thermal junctions indicate the temperature differences in the walls and the
different sections are heated or cooled as is necessary until the whole system
is brought as near thermal equilibrium as possible.
After the man enters, the lamp is removed and the water-current is so
varied, if necessary, and the heating and cooling of the various parts so
adjusted as to again secure temperature equilibrium of all parts. When the
amount of heat brought away by the water-current exactly compensates
that generated by the subject, when the thermal-junction elements in the
walls indicate a 0 or very small deflection, when the resistance thermometers
indicate a constant temperature of the air inside the chamber and the walls
of the chamber, the experiment proper is ready to begin.
The physical observer keeps the chemical assistant thoroughly informed
as to the probable time for the beginning of the experiment, so that there
will be ample time for making the residual analyses of the air. After these
analyses have been made and the experiment is about to begin, the observer
at the table calls the time on the exact minute, at which time the blower is
stopped and the purifying system changed. The physical observer takes
the temperatures of the wall and air by the electric-resistance thermometers,
reads the mercury thermometers, records the rectal thermometer, and at the
exact moment of beginning the experiment the current of water which has
previously been running into the drain is deflected into the water-meter.
At the end of the period this routine is varied only in that the water-cur-
rent is deflected from the water-meter into a small can holding about 4
liters, into which the water flows while the meter is being weighed.
MANIPULATION OF THE WATER-METER.
The rate of flow of water through the apparatus is determined before the
experiment begins. This is done by deflecting the water for a certain
number of seconds into a graduate or by deflecting it into the small can and
weighing the water thus collected. The water is then directed into the
drain during the preliminary period. Meanwhile the main valve at the
bottom of the water-meter is opened, such water as has accumulated from
tests in preceding experiments is allowed to run out, and the valve is closed
after the can is empty. The meter is then carefully balanced on the scales
and the weight is recorded. At the beginning of the experiment the water
is deflected from the drain into the meter. At the end of the period,
ROUTINE OF AN EXPERIMENT WITH MAN. 99
while the water is running into the small can, the water-meter is again
carefully weighed and the weight recorded. Having recorded the weight,
the water is again deflected into the large meter and what has accumulated
in the small can is carefully poured into the large meter through a funnel.
If the meter is nearly full, so that during the next period water will accu-
mulate and overflow the meter, it is emptied immediately after weighing
and while the small can is filling up. About 4 minutes is required to empty
the can completely.
After it is emptied, it is again weighed, the water-current deflected from
the small can to the meter, and the water which has accumulated in the
small can carefully poured into the meter. All weights on the water-meter,
both of the empty can and the can at the end of each period, are checked
by two observers.
ABSORBER TABLE.
Shortly after the subject has entered the chamber and in many instances
before the sealing-in process has begun, the ventilating air-current is started
by starting the blower. The air passes through one set of purifiers during
this preliminary period, and as no measurements are made for this period
it is not necessary that the weights of the absorbers be previously known.
All precautions are taken, however, so far as securing tightness in coup-
ling and installing them on the absorber system are concerned. During this
period the other set of absorbers is carefully weighed and made ready to
be put in place and tested and about 10 minutes before the experiment
proper begins the residual analyses are begun. The series of U-tubes, which
have previously been carefully weighed, are placed on small inclined racks
and are connected with the meter and also with the tube leading to the
mercury valve. The pet-cock which connects the return air-pipe with the
drying-tower and the gas-meter is then opened and the mercury reservoir
is lowered. The rate of flow of air through the U-tubes is regulated by a
screw pinch-cock on the rubber tube leading to the first U-tube. This rate
is so adjusted by means of the pinch-cock that about 3 liters of air per
minute will flow through the U-tubes, and as the pointer on the gas-meter
approaches 10 liters the mercury reservoir is raised at just such a point,
gained by experience, as will shut off the air-current when the total volume
registers 10 liters on the meter. The pet-cock in the pipe behind the meter
is then closed, the U-tubes disconnected, and a new set put in place. A
duplicate and sometimes a triplicate analysis is made.
When the physical observer calls the time for the end of the period, the
switch which controls the motor is opened and the chemical assistant then
opens the rear valve of the new set of absorbers and closes the rear valve
of the old set, and likewise opens the front valve of the new set and closes
the front valve of the old set. As soon as the signal is given that the oxygen
100 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
connections have been properly made and that the oxygen has been admitted
to the chamber in proper amount, the blower is again started. It is then
necessary to weigh the U -tubes and disconnect the old set of absorbers and
weigh them. If the sulphuric-acid absorbers have not exceeded the limit of
gain in weight they are used again ; if they have, new ones are put in their
place.
The first sulphuric-acid absorber is connected to the front valve, then
the potash-lime can, and then the last sulphuric-acid absorber; but before
connecting the last sulphuric-acid absorber with the sodium-bicarbonate
can, a test is made of the whole system from the front valve to the end of
the second sulphuric-acid absorber. This is made by putting a solid-rubber
stopper in the exit end of the second sulphuric-acid absorber and, by means
of a bicycle pump, forcing compressed air in through a pipe tapped into
the pipe from the valve at the front end until a pressure of about 2 feet
of water is developed in this part of the system. This scheme for testing
and the method of connecting the extra pipe have been discussed in detail
in an earlier publication.* Eepeated tests have shown that this method of
testing the apparatus for tightness is very successful, as the minutest leak
is quickly shown.
After the system has been thoroughly tested, the rubber stopper in the
exit end of the second sulphuric-acid absorber is first removed, then the
tube connected with the pump and manometer is disconnected and its end
placed in the reservoir of mercury. Occasionally, through oversight, the
pressure is released at the testing-tube with the result that the air com-
pressed in the system expands, forcing sulphuric acid into the valves and
down into the blower, thus spoiling completely the experiment. After the
testing, the last sulphuric-acid absorber is coupled to the sodium-bicarbo-
nate can. It is seen that this last connection is the only one not tested, and
it has been found that care must be taken to use only the best gaskets at
this point, as frequently leaks occur; in fact, it is our custom to moisten
this connection with soapsuds. If new rubber gaskets are used a leak is
never found.
SUPPLEMENTAL APPARATUS.
To maintain the apparent volume of air through the whole system con-
stant, oxygen is admitted into the tension-equalizer until the same tension
is exerted on this part of the system at the end as at the beginning. This
is done by closing the valve connecting the tension-equalizer with the sys-
tem and admitting oxygen to the tension-equalizer until the petroleum
manometer shows a definite tension. After the motor is stopped, at the
end of the experimental period, there is a small amount of air compressed
in the blower which almost instantly leaks back through the blower and the
whole system comes under atmospheric pressure, save that portion which
* Atwater and Benedict: hoc. cit., p. 21.
ROUTINE OF AN EXPERIMENT WITH MAN. 101
is sealed off between the two levels of the sulphuric acid in the two absorb-
ing vessels. A few seconds after the motor is stopped the valve cutting off
the tension-equalizer from the rest of the system is closed, the pet-cock con-
necting this with the petroleum manometer is opened, and oxygen is
admitted by short-circuiting the electrical connections at the two mercury
cups. This is done by the hands of the observer and must be performed
very gently and carefully, as otherwise oxygen will rush in so rapidly as to
cause excessive tension. As the bag fills with gas, the index on the petro-
leum manometer moves along the arc of a circle and gradually reaches the
desired point. At this point, the supply of oxygen is cut off, the valve con-
necting the tension-equalizer with the main system is opened, and simul-
taneously the needle-valve on the reduction-valve of the oxygen cylinder is
tightly closed, preliminary to weighing the cylinder. At this point the
motor can be started and the experiment continued.
It is necessary, then, that the oxygen cylinder be weighed. This is done
after first closing the pet-cock on the end of the pipe conducting the gas
beneath the floor of the calorimeter room, slipping the glass joint in the
rubber pipe leading from the reduction valve to the pet-cock, and breaking
the connections between the two rubber pipes, the one from the pet-cock
and the other to the reduction valve, also breaking the electrical connection
leading to the magnet on the cylinder. The cylinder is then ready to swing
freely without any connections to either oxygen pipe or electrical wires.
It is then weighed, the loss in weight being noted by removing the brass
weights on the shelf attached to the counterpoise. It is important to see
that there is a sufficient number of brass weights always on the shelf to
allow for a maximum loss of weight of oxygen from the cylinder during
a given period. Since the cylinders contain not far from 4 to 5 kilograms
of oxygen, in balancing the cylinders at the start it is customary to place
at least 4 kilograms of brass weights on the shelf and then adjust the
counterpoise so as to allow for the gradual removal of these weights as the
oxygen is withdrawn.
As soon after the beginning of the period as possible, the U- tubes are
weighed on the analytical balance, and if they have not gained too much
they are connected ready for the next analysis. If they have already ab-
sorbed too much water or carbon dioxide, they are replaced by freshly filled
tubes.
Immediately at the end of the experimental period the barometer is
carefully set and read, and the reading is verified by another assistant.
Throughout the whole experiment an assistant counts the pulse of the sub-
ject frequently, by means of the stethoscope, and records the respiration
rate by noting the lesser fluctuations of the tambour pointer on the smoked
paper. These observations are recorded every few minutes in a book kept
especially for this purpose.
102 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC.
A most excellent preservation of the record of the minor muscular move-
ments is obtained by dipping the smoked paper on the kymograph drum in
a solution of resin and alcohol. The lesser movements on the paper indi-
cate the respiration rate, but every minor muscular movement, such as
moving the arm or shifting the body in any way, is shown by a large deflec-
tion of the pointer out of the regular zone of vibration. These records of
the minor muscular activity are of great importance in interpreting the
results of the chemical and physical determinations.
(*(*-
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QP Benedict, Francis Gano
171 Respiration calorimeters
B472
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