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

BY

FRANCIS G. BENEDICT and THORNE M. CARPENTER


[Illustration]

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


CARNEGIE INSTITUTION OF WASHINGTON
PUBLICATION NO. 123


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




PREFACE.


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

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

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

     BOSTON, MASSACHUSETTS,
       _August 10, 1909._




CONTENTS.


                                                                  PAGE

Introduction                                                        1

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

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

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




ILLUSTRATIONS.

                                                                      PAGE

Fig. 1. General plan of respiration calorimeter laboratory               4

     2. General view of laboratory taken near main door                  4

     3. General view of laboratory taken near refrigeration room         4

     4. General view of laboratory taken near temperature recorder       4

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

     6. Plan of heating and ventilating the calorimeter laboratory       6

     7. Horizontal cross-section of chair calorimeter                   11

     8. Vertical cross-section of chair calorimeter                     12

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

    10. Photograph of framework of chair calorimeter                    14

    11. Photograph of portion of framework and copper shell             14

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

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

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

    15. Detail of air-resistance thermometer                            28

    16. Details of resistance thermometers for water-circuit            30

    17. Diagram of wiring of observer's table                           32

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

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

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

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

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

    23. Temperature recorder                                            42

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

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

    26. Cross-section of bed calorimeter                                46

    27. Diagram of ventilation of the respiration calorimeter           57

    28. Cross-section of sulphuric acid absorber                        59

    29. Balance for weighing absorbers                                  62

    30. Diagram of absorber table                                       66

    31. Diagram of oxygen balance and cylinders                         68

    32. The oxygen cylinder and connections to tension equalizer        70




RESPIRATION CALORIMETERS FOR STUDYING THE RESPIRATORY EXCHANGE AND
ENERGY TRANSFORMATIONS IN MAN.




INTRODUCTION.


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

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

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

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

The building, a general description of which appeared in the Year Book
of the Carnegie Institution of Washington for 1908, is of plain brick
construction, trimmed with Bedford limestone. It consists of three
stories and basement and practically all the space can be used for
scientific work. Details of construction may be had by reference to the
original description of the building. It is necessary here only to state
that the special feature of the new building with which this report is
concerned is the calorimeter laboratory, which occupies nearly half of
the first floor on the northern end of the building.

FOOTNOTES:

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

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

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




CALORIMETER LABORATORY.


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


GENERAL PLAN OF CALORIMETER LABORATORY.

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

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

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

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

[Illustration: FIG. 2

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

[Illustration: FIG. 3

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

[Illustration: FIG. 4

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.]

[Illustration: 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.]

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

[Illustration: FIG. 6.--Plan of heating and ventilating calorimeter
laboratory, showing general plan of circulation of the special cooling
system and the position of the thermostats and radiators which they
control. The two small diagrams are cross-sections of brine and heating
coils.]

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

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

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


HEATING AND VENTILATING.

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

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

Two vertical sections through the refrigerating coils are shown in fig.
6. Section A-B shows the entrance near the floor of the calorimeter
room. The air is drawn down over the coils, passes through the blower,
and is forced back again to the top of the calorimeter room into the
large duct. If outdoor air is desired, a special duct can be connected
with the system so as to furnish outdoor air to the chamber. This has
not as yet been used. Section C-D shows the fan and gives a section
through the reheater. The brine coils, 400 meters long, are in
triplicate. If one set becomes covered with moisture and is somewhat
inefficient, this can be shut off and the other two used. When the
frozen moisture melts and drops off, the single coil can be used again.
It has been found that the system so installed is most readily
controlled.

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

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

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

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

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

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

FOOTNOTES:

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




THE CALORIMETER.


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


FUNDAMENTAL PRINCIPLES OF THE APPARATUS.

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

In the construction of the new calorimeters a further and fundamental
change in construction has been made in that all the thermal junctions,
heating wires, and cooling pipes have been attached directly to the zinc
wall of the calorimeter, leaving the outer insulating panels free from
incumbrances, so that they can be removed readily and practically all
parts inspected whenever desired without necessitating complete
dismantling of the apparatus. This arrangement is possible except in
those instances where connections pass clear through from the interior
of the chamber to the outside, namely, the food-aperture, air-pipes,
water-pipes, electrical connections, and tubes for connections with
pneumograph and stethoscope; but the apparatus is so arranged as to have
all of these openings in one part of the calorimeter. It is possible,
therefore, to remove all of the outer sections of the calorimeter with
the exception of panels on the east side.

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


THE CALORIMETER CHAMBER.

[Illustration: FIG. 7.--Horizontal cross-section of chair calorimeter,
showing cross-section of copper wall at A, zinc wall at B, hair-felt at
E, and asbestos outer wall 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 separating the two parts. The ingoing and
outcoming 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.]

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

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

[Illustration: FIG. 9.--Vertical cross-section of 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. Surrounding the calorimeter are
the asbestos outside and hair-felt lining.]

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


GENERAL CONSTRUCTION.

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

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

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

[Illustration: FIG. 10

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

[Illustration: FIG. 11

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

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

The floor of the chamber is supported by 7 pieces of 2-1/2-inch channel
(N, N, N, fig. 8), laid on top and bolted to the two 3-inch channels (M,
fig. 8). On top of these is placed a sheet of so-called asbestos lumber
(J', fig. 8) 9.5 millimeters thick, cut to fit exactly the bottom of the
chamber. Upright 2-1/2-inch channels (H, fig. 8) are bolted to the two
outside channels on the bottom and to the ends of three of the long
channels between in such a manner as to form the skeleton of the walls.
The upper ends of these channels are fastened together by pieces of
piping (P, P, P, fig. 8) with lock-nuts on either side, thus holding the
whole framework in position.

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

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

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

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

_Wall construction and insulation._--The inner wall of the chamber
consists of copper, preferably tinned on both sides, thus aiding in
soldering, and the tinned inner surface makes the chamber somewhat
lighter. Extra large sheets are obtained from the mill, thus reducing to
a minimum the number of seams for soldering, and seams are made tight
only with difficulty. The copper is of standard gage, the so-called
14-ounce copper, weighing 1.1 pounds per square foot or 5.5 kilograms
per square meter. It has a thickness of 0.5 millimeter. The whole
interior of the skeleton frame of the structural steel is lined with
these sheets; fig. 11 shows the copper shell in position.

For the outer metallic wall, zinc, as the less expensive metal, is used.
One sheet of this material perforated with holes for the attachment of
bolts and other appliances is shown in position on the outside of the
wall in fig. 11. The sheet zinc of the floor is obviously put in
position before the channels upon which it rests are laid. The zinc is
obtained in standard size, and is the so-called 9-ounce zinc, or 0.7
pound to the square foot, or 3.5 kilograms to the square meter. The
sheet has a thickness of 0.5 millimeter.

[Illustration: 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 (D) used as spacer between
asbestos and zinc.]

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

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


PREVENTION OF RADIATION.

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

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

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

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

[Illustration: FIG. 13.--Detail of drop-eight 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 admitted at B, regulated by the pet-cock.]

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


THE THERMO-ELECTRIC ELEMENTS.

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

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

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


INTERIOR OF THE CALORIMETER.

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

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

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

The air-pipes are of thin brass, 1-inch internal diameter. One of them
conducts the air from the ingoing air-pipe up into the top of the
central dome or hood immediately above the head of the subject. The air
thus enters the chamber through a pipe running longitudinally along the
top of the dome. On the upper side of this pipe a number of holes have
been drilled so as to have the air-current directed upwards rather than
down against the head of the subject. With this arrangement no
difficulties are experienced with uncomfortable drafts and although the
air enters the chamber through this pipe absolutely dry, there is no
uncomfortable sensation of extreme dryness in the air taken in at the
nostrils, nor is the absorption of water from the skin of the face,
head, or neck great enough to produce an uncomfortable feeling of cold.
The other air-pipe, as suggested, receives the air from the chamber at
the lower front and passes around the rear to the point where the
outside air-pipe leaves the chamber.

The chamber is illuminated by a small glass door in the food aperture.
This is a so-called "port" used on vessels. Sufficient light passes
through this glass to enable the subject to see inside the calorimeter
without difficulty and most of the subjects can read with comfort. If an
electric light is placed outside of the window, the illumination is very
satisfactory and repeated tests have shown that no measurable amount of
heat passes through the window by placing a 32 c. p. electric lamp 0.5
meter from the food aperture outside. More recently we have arranged to
produce directly inside the chamber illumination by means of a small
tungsten electric lamp connected to the storage battery outside of the
chamber. This lamp is provided with a powerful mirror and a glass shade,
so that the light is very bright throughout the chamber and is
satisfactory for reading. It is necessary, however, to make a correction
for the heat developed, amounting usually to not far from 3 calories per
hour.

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


HEAT-ABSORBING CIRCUIT.

To bring away the heat produced by the subject, it is highly desirable
that a constant flow of water of even temperature be secured. Direct
connection with the city supply is not practicable, owing to the
variations in pressure, and hence in constructing the laboratory
building provision was made to install a large tank on the top floor,
fed with a supply controlled by a ball-and-cock valve. By this
arrangement the level in the tank is maintained constant and the
pressure is therefore regular. As the level of the water in the tank is
approximately 9 meters above the opening in the calorimeter, there is
ample pressure for all purposes.

[Illustration: FIG. 14.--Schematic diagram of water circuit for
heat-absorbers of calorimeter. A, constant-level tank from which water
descends to main pipe supplying heat-absorbers; _a_, valve for
controlling supply from tank A; B, section of piping passing into cold
brine; _b_, 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 water descends from this tank in a large 2-inch pipe to the ceiling
of the calorimeter laboratory, where it is subdivided into three 1-inch
pipes, so as to provide for a water-supply for three calorimeters used
simultaneously, if necessary, and eliminate the influence of a variation
in the rate of flow in one calorimeter upon the rate of flow in another.
These pipes are brought down the inner wall of the room adjacent to the
refrigeration room and part of the water circuit is passed through a
brass coil immersed in a cooling-tank in the refrigeration room. By
means of a by-pass, water of any degree of temperature from 2° C. to 20°
C. may be obtained. The water is then conducted through a pipe beneath
the floor to the calorimeter chamber, passed through the absorbers, and
is finally measured in the water-meter.

A diagrammatic sketch showing the course of the water-current is given
(fig. 14), in which A is the tank on the top floor controlled by the
ball cock and valve, and _a_ is the main valve which controls this
supply to the cooler B, and by adjusting the valve _b_ and valve _c_
any desired mixture of water can be obtained. A thermometer C gives a
rough idea of the temperature of the water, so as to aid in securing the
proper mixture. The water then passes under the floor of the calorimeter
laboratory and ascends to the apparatus D, which is used for heating it
to the desired temperature before entering the calorimeter. The
temperature of the water as it enters the calorimeter is measured on an
accurately calibrated thermometer E, and it then passes through the
absorber system _d d d_ and leaves the calorimeter, passing the
thermometer F, upon which the final temperature is read. It then passes
through a pipe and falls into a large can G, placed upon scales. When
this can is filled the water is deflected for a few minutes to another
can and by opening valve _f_ the water is conducted to the drain after
having been weighed.

_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 _b_ 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 _b_ is opened, the water is evenly and readily mixed.
The thermometer C is in practice immersed in the water-mixer constructed
somewhat after the principle 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 fluctuations in the temperature of the ingoing
water and in the amount of 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
temperature of the ingoing water. Usually only the second method is
necessary. 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 temperature 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 rubber stopper,
fitting into a brass ferule soldered between the zinc and copper walls.
(See N, fig. 25.) So far as insulation was concerned, this arrangement
was very satisfactory, but unfortunately the glass tubes break readily
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 satisfactory 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 constructed 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
measurements 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 weighing 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.[7]


THERMOMETERS.

In connection with the calorimeter and the accessories, mercurial and
electric-resistance thermometers are employed. For measuring the
temperature 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 differences. 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 resistance 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
differences of the water-current are of special construction and have
been calibrated 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 thermometer 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. Richter, of Berlin, and calibrated by the
Physikalische Technische Reichsanstalt. Furthermore, a standard
thermometer, graduated from 14° to 24° C., also made by Richter and
standardized by the Physikalische Technische Reichsanstalt, 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 standardize the
thermometers on the basis of absolute temperature. For calibrating 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 portion
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
thermometer 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 differences 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
perceptibly, 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,[8]
and with high rates of flow, amounting to 1 liter or more per minute,
there may be a correction on these thermometers amounting to several
hundredths of a degree. We have found that, as installed at present,
with a rate of flow of less than 400 cubic centimeters 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 mercury 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 thermometer 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 thermometers special precautions are taken not
only with regard to the relative position of the bulb of the mercury
thermometer and the resistance thermometer, 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
respiration 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 chamber; third, for determining the variations in body
temperature; finally, for recording the differences in temperature 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 thermometers, 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.

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

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 resistance of the
system of not far from 20 ohms. The thermometer 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 type of construction gives
maximum sensibility to the temperature fluctuations of the air itself
and yet insures thorough protection. The two terminals are carried
outside of the respiration chamber to the observer's table, where the
temperature fluctuations are measured on a Wheatstone bridge.


WALL THERMOMETERS.

The wall thermometers are designed for the purpose of taking the
temperature 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 hydrothermal 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 thermometers 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 connect 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.[9] 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,[10] but the results were not invariably satisfactory and in all
the subsequent 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 thermometers 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 fluctuations in temperature difference as
measured by the resistance thermometers should be controlled for
calibration purposes by the differences in temperature of the mercurial
thermometers.

[Illustration: 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.]

For the resistance thermometer, Dr. Northrup has used, instead of
copper, pure nickel wire, which has a much higher resistance and thus
enables a much greater total resistance to be inclosed in a given space.
The insulated 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 temperature. 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.

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 mercurial 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 "observer's table." At this, the physical assistant
sits throughout the experiments. 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 observer'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
temperature 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 comparison, 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 substitution 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.

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

Of special interest are the electrical connections on the observer's
table itself. A diagrammatic representation of the observer's table with
its connections 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 distribution of the parts. The first of the electrical
measurements necessary during 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 calorimeter
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
calorimeters 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_{7}. The various points, I, II, III, IV, 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 S_{10}, which as a matter of fact is placed
beneath the table. This switch S_{10} has three rows of binding-posts.
The center row connects directly 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 _i_ with the
two binding-posts opposite them on the switch S_{10}, it can be seen
that this connection leads directly to the point I on the switch S_{7},
and as a matter of fact this gives direct connection with the
galvanometer through the key on S_{7}, thus connecting the
thermal-junction system on one section of the bed calorimeter between
_g_ and _i_ directly with the galvanometer. Similar connections from the
other points can readily be followed from the diagram. The points on the
switch S_{7} indicated as I, II, III, IV, correspond 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 junctions. 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 S_{3} 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
temperatures 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, indicating 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 R_{2}. 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
S_{5}. The other side of the switch S_{5} connects directly with the
point on the middle of switch S_{10}, 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 R_{2}, are connected with the binding
posts on S_{10}, and each can in turn be connected with _a_ or A, _b_ or
B, etc. The heating of the top of the chair calorimeter is controlled by
the point 5 on the rheostat R_{2}, 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
controlled by the resistance R_{1}. This R_{1} 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 calorimeter, are indicated on the diagram above
and below the switch S_{9}. 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 R_{1} 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 of resistance thermometers is employed. These are so connected
on the observer's table that they may be brought into connection with
two Wheatstone bridges, W_{1} and W_{2}. Bridge W_{1} is used for the
resistance thermometers indicating the temperature of the wall and the
air. Bridge W_{2} 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 S_{1}, S_{2}, and S_{3} allow the use of either
the wall, air, or rectal thermometer on either the bed or chair
calorimeter at will. Since the bridge W_{1} is used for measuring the
temperature of both the wall and the air, a fourth double-pole switch,
S_{4}, is used to connect the air and wall thermometers alternately. The
double-contact key, K_{1}, is connected with the bridge W_{1} and is so
arranged that the battery circuit is first made and subsequently the
galvanometer circuit. A similar arrangement in K_{2} controls the
connections for the bridge W_{2}.


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 R_{2} 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 approximately 15 ohms between
the binding-posts. A fuse-wire is inserted in each circuit to protect
the chamber from excessive current. Of these resistances, 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
calorimeters. No. 5 corresponds to the top of both calorimeters. No. 4
corresponds 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 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 resistance using small lamps and the resistance
wires wound on asbestos lumber has proven very satisfactory and very
compact in form.

[Illustration: 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 resistances, and to left the sections of wire
resistances.]


TEMPERATURE RECORDER.

The numerous electrical, thermometric, and chemical measurements
necessary in the full conduct of an experiment with the respiration
calorimeter has often raised the question of the desirability of making
at least a portion 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 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
purchased, 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 & Northrup 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 coordinate paper and to control the periodic movement of the creeper.

Under ordinary conditions with rest experiments in the chair calorimeter
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. Provision has also been made to extend the measurement of temperature
differences with the apparatus so that a difference of 8° can be
measured with the same percentage accuracy.


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 temperature coefficient of
_fl_ and _fr_ are made absolutely equal. The two thermometers are
indicated as T_{1} and T_{2} and are inserted in the ingoing and
outgoing water respectively. A slide-wire resistance is indicated by J,
and _r_ is the resistance for the zero adjustment. Ba, Z, and Z_{1} are
the battery and its variable series resistances. If T_{1} and T_{2} are
exactly of the same temperature, _i. e._, if the temperature difference
of the ingoing and outcoming water is zero, the sliding contact _q_
stands at 0 on the slide-wire and thus the resistance of the system from
0 through _fl_, _r_, and T_{1} back to the point C is exactly the same
as the resistance of the slide-wire J plus the coil _fr_ plus T_{2} back
to the point C. A rise in temperature of T_{2} 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.

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

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 producing 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 represents 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 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 S_{1} constitutes a variable shunt to permit slight variations of
_r_ to finally adjust 0 after S' is fixed and _t_ is a permanent shunt
across the thermometer T_{1} to make the temperature coefficient of
T_{1} equal to that of T_{2}.

The apparatus can be used for measuring temperature differences from 0°
to 4° or from 0° to 8°. When on the 0° to 8° range, the shunt S is
open-circuited and the shunt S' alone used. The value of S, then, is
predetermined so as to affect the value of the wire J and thus halve its
influence in maintaining the balance. Similarly, when the lower range,
_i. 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 S_{1} 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 S_{1}, and
also of S', is necessary in order to have the apparatus draw a curve to
represent truly the temperature differences. These slight alterations
are determined beforehand by careful tests and the exact value of the
resistances in S' and in S_{1} 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 Pl,
fig. 21. The galvanometer pointer P swings freely below the silver
contacts S_{1} and S_{2}, just clearing the ivory insulator _i_. The
magnet plunger makes a contact depending 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 S_{1} or S_{2},
thus completing the circuit at either the right hand or the left hand,
at intervals of 2 seconds. The movement of the pointer away from its
normal position exactly beneath _i_ to either S_{1} on the left hand or
S_{2} 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.

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


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 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
S_{1} or S_{2}. P makes the contact between Pl and either S_{1} or S_{2}
and sends a current through solenoids at either the right or the left of
the creeper. At intervals of every 2 seconds the plunger rises and
forces the pointer P against either S_{1}, _i_, or S_{2} above. The
movement of this plunger is controlled by a current from a 110-volt
circuit, the connections 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 Pl. When the contact 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.

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

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

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
attached to a rack and pinion at either end of the rod. If the current
is passed through the contact S_{1}, 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. Conversely, the
passing of the current 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 revolution. 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 S_{1} and
then along the line G_{1} through 350 ohms wound 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 normally 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
opening 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.

[Illustration: FIG. 23

Temperature recorder. The recorder with the coordinate paper in the
lower box with a glass door. A curve representing the temperature
difference between the ingoing and outgoing water is directly drawn on
the coordinate 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.]

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

The whole apparatus is permanently and substantially installed on the
north wall of the calorimeter laboratory. A photograph showing the
various parts and their installation is given in fig. 23. On the top
shelf is seen the galvanometer and on the lower shelf the recorder with
its glass door in front and the coordinate paper dropping into the box
below. The curve drawn on the coordinate paper is clearly shown. Above
the recorder are the resistance-boxes, three in number, the lower one at
the left being the resistance S_{1}, the upper one at the left being the
resistance S', and the upper one at the right being the resistance
Z_{1}. Immediately above the resistance-box Z_{1} 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 substantially altered
when changing the apparatus to register from the 0° to 4° scale to the
0° to 8° scale. A detailed wiring diagram is given in fig. 24.


TEMPERATURE CONTROL OF THE INGOING AIR.

[Illustration: FIG. 25.--Section of calorimeter walls and part 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
2-1/2 inch angle W; B, a portion of zinc wall; C, hair-felt lining of
asbestos wall D; T-J, a thermal junction in the walls.]

In passing the current of air through the calorimeter, temperature
conditions may easily be such that the air entering is warmer than the
outcoming 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 control 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 O in fig. 25. 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 situation called for. The
heating was done by passing the current through an 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 control
being obtained by varying the heating effect of the lamp itself. This
has been found much more satisfactory than by alternating from the
cooling 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 control, shown in fig. 13.


THE HEAT OF VAPORIZATION OF WATER.

During experiments with man not all the heat leaves the body by
radiation 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 correspondingly 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[11] who, recognizing the importance of knowing exactly
the heat of vaporization of water at 20°, has made this a special object
of investigation. 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 - 2.43T

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,[12] the formula reads

     L (in mean calories) = 597.44 - 0.580T

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;[13] 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
calorimeter which permits the introduction of a couch or bed has been
devised. This calorimeter has been built, tested, and used in a number
of experiments with men and women. The general shape of the chamber is
given in fig. 26. The principles involved in the construction of the
chair calorimeter are here applied, _i. 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
introduction 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 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, 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.

[Illustration: 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.]

Special precaution was taken with this calorimeter to make it as
comfortable and as attractive as possible to new and possibly
apprehensive patients. The painting of the walls unquestionably results
in a condensation of more or less moisture, for the paint certainly
absorbs more moisture than does the metallic surface of the copper. The
chief value of the determination of the water vaporized inside of the
chamber during an experiment 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 chamber; 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
experiments 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 probable 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 extremely accurate. When the test has been made with burning
alcohol, as described beyond, it has been found that the large amount of
moisture 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 content 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
opening at the front is here removed and the wooden track upon which the
frame, supporting the cot, slides is clearly shown. The tension
equalizer (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 Sondén 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 instruments 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
calorimeter by increasing or decreasing the amount of heat brought away,
and thus compensate exactly for the heat eliminated by the subject, the
hydrothermal equivalent of the system itself being about 20 calories--on
the other hand the body of the subject may undergo marked changes in
temperature 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-temperature or stored as indicated by a rise in temperature,
obviously the heat produced during the given period will not equal that
eliminated and measured 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 hydrothermal equivalent of the body is to
assume the specific heat of the body as 0.83.[14] 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
published elsewhere[15] regarding the body-temperature in connection
with the 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 thermometer 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
temperature 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
experiments 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
thermometer 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, 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
measurement 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
generated 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, undoubtedly, 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 accurate Weston portable voltmeter and
mil-ammeters. Thanks to the kindness of one of our former co-workers,
Mr. S. C. Dinsmore, at present associated 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
calorimeter is adjusted in temperature equilibrium as soon as possible.
When the temperature of the air and walls is constant and the
thermal-junction 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. Usually 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 C × E × _t_ × 0.2385 = 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 followed as a result of the recommendation of Dr. E.
B. Rosa, of the National Bureau of Standards. In order to convert the
values to 20°, the unit commonly 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°. Assuming the specific heat of water at 20°
to be 1, the specific heat at 15° is 1.001.[16]

Of the many electrical check-tests made with this type of apparatus, but
one need be given here, pending a special treatment of the method of
control 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 current = 1.293 amperes; average E. M. F. = 109.15
volts; time = 21,600 seconds; factor used to convert watt-seconds to
calories = 0.2385. (1.293 × 109.15 × 21600 × 0.2385) × 1.001 = 727.8
calories produced.

During the 6 hours 237.63 kilograms of water passed through the
absorbing system.

The average temperature rise was 3.04° C., the total heat brought away
was therefore (237.63 × 3.04) × 1.0024[17] = 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.

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
fluctuations 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 minimized 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
experiments have led to the conclusion that discrepancies in results
were invariably 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 hydrothermal equivalent is essential.

The large majority of the methods for determining the hydrothermal
equivalent of materials are at once eliminated when the nature of the
calorimeter here used is taken into consideration. Obviously, in warming
up the chamber there are two sources of heat: first, the heat inside of
the chamber; 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 hydrothermal 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 adiabatic 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 equilibrium 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 represents 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
calorimeter 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, _i. e._, 19.5 kilograms.


GENERAL DESCRIPTION OF RESPIRATION APPARATUS.

This apparatus is designed much after the principle of the
Regnault-Reiset 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 hermetically 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.

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
shellacked, 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
features 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 substantial 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 outline in fig. 7. While somewhat inconvenient to enter
the chamber in this way, the entrance from above possesses many
advantages. It is readily 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 calorimeter, 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 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.

[Illustration: FIG. 27.--Diagram of ventilation of respiration
calorimeter. The air is taken out at lower right-hand corner and forced
by the blower through the apparatus for absorbing water and carbon
dioxide. It returns to the calorimeter at the top. Oxygen can be
introduced into the chamber itself as need is shown by the tension
equalizer.]

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 chamber ready for use. The general
scheme of the respiration apparatus is shown in fig. 27. The air leaving
the chamber contains carbon dioxide and water-vapor and the original
amount of nitrogen and is somewhat deficient in oxygen. In order to
purify the air it must be passed through absorbents for carbonic acid
and water-vapor and hence some pressure is necessary to force the gas
through these purifying vessels. This pressure is obtained by a small
positive rotary blower, which has been described previously in
detail.[18] The air is thus forced successively through sulphuric 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.


BLOWER.

The rotary blower used in these experiments for maintaining the
ventilating current of air has given the greatest satisfaction. It is a
so-called 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 satisfactory for all
experiments and is constant. Under the pressure of 43 millimeters 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 concerns was used.

This special form of absorbers presented many difficulties in
construction, 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 completely 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 innumerable trials
with glazed vessels of different kinds of pottery and glass,
arrangements were made with the Royal 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.

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 arrangement, 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 opening is made near one edge. The
specifications 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 indefinitely. 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.

[Illustration: FIG. 28.--Cross-section of sulphuric-acid absorber. The
air enters at the top of the right-hand opening, descends to the bottom
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
preventing the acid being carried mechanically out through the opening.
The opening for filling and emptying the absorber is shown midway
between the two large openings.]

The vessels without filling and without rubber elbows weigh 11.5
kilograms; with the special elbows and couplings attached so as to
enable them to be connected with the ventilating air-system, the empty
absorbers weigh 13.4 kilograms; 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 advantageous
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.


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 solution failed to give the desired results and the use of
soda-lime has supplemented 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 satisfactory 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[19] only is taken out and replaced with new potash-lime. Thus,
three-quarters of the contents of the can is used over and over, 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 whitening 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 FOR WEIGHING ABSORBERS.

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
somewhat unwieldy 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 calorimeter 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 substantial 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 weighing 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 right-hand arm of the
balance. The remainder of the weight is made up with brass weights
placed in the pan.

[Illustration: FIG. 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.]

In order to suspend this heavy absorber, a small elevator has been
constructed, so that the vessel may be raised by a compressed-air
piston. This 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 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
position 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 elevator 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,[20] 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 AIR-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.


VALVES.

In order to subdivide experiments into periods as short as 1 or 2 hours,
it is necessary to deflect the air-current at the end of each period
from one set of purifiers to the other, in order to weigh the set used
and to measure 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 elsewhere.[21] It is sufficient to state here that
the very large majority of mechanical 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 pressure. 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 mechanical seal
ultimately bathed in mercury was used for the earlier apparatus. The
possibility of contamination of the air-current by mercury vapor was
duly considered and pointed out in a description of this apparatus. It
was not until two years later that difficulties began to be experienced
and a number of men were severely poisoned while inside the chamber. A
discussion of this point has been presented elsewhere.[22] 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 disappeared. 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
precaution 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 original 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
calorimeter chamber to another.


ABSORBER TABLE.

The purifying apparatus for the air-current is compactly and
conveniently 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
downward arrow through a 3/4-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 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 doubtless 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 consequently 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.

[Illustration: 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.]

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
bicarbonate can, for removing traces of acid fumes, is connected in an
upright position, while the motor, the controlling rheostat, and the
blower are supported 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 calorimeter, 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 calorimeter. 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 14 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 calculation of the total amount of oxygen
are such that satisfactory determinations of oxygen consumption by this
method would be impossible. Furthermore, 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
negligible 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.

[Illustration: 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.]

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
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
chamber 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, R, 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
calorimeters. 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
calorimeters. 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 connected at L and pinches the rubber tube tightly. The tension
at E can be 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 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
position 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 filling the bag to a definite point, as shown by the
pointer, a delicate manometer is attached to the can by means of a
pet-cock and the oxygen is admitted by operating the switch B until the
desired tension is reached.

[Illustration: 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.]

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 plug N 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 O. 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 pressure, 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 absorption 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 rubber diaphragm rises or falls with it and under
ordinary conditions of an experiment this arrangement results in a
pressure in the chamber approximately 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 directly to the
wall of the calorimeter independent of the air-pipe.

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 experimental 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 system, exclusive of the
tension-equalizer, is always the same, since it is confined 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.

Recognizing the importance of measuring very accurately the barometric
pressure, or at least its fluctuations, we have installed an accurate
barometer of the Fortin type, made by Henry J. Green. This is attached
to the inner wall of the calorimeter laboratory, and since the
calorimeter laboratory is held at a constant temperature, temperature
corrections are unnecessary, for we have here to deal not so much with
the accurate measurement 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.


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 fluctuations. 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 assumption 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 analysis of air without withdrawing too great a volume from
the chamber. The difficulty in analysis is almost wholly confined to the
determination of water-vapor, for while there are a large number of
methods for determining 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 psychrometer it was found that its use was
precluded by the space required to successfully use this instrument, the
addition of an unknown amount of water to the chamber from the wet bulb,
and the difficulties of reading the instrument from without the chamber.
Recourse was had to the determination of moisture by the 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 aspirating 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 constant. 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 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.[23] The test showed that the meter measured 1.4 per cent too
much, and consequently this correction must be applied to all
measurements made with it.


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[24] or by the more abbreviated method of
calculation which has been used very successfully in all short
experiments in this laboratory. 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 little difficulty. It is necessary, for
example, to accurately measure about 16 cubic centimeters of pure
nitrogen, pass it into the potassium pyrogallate 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 portions 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 possibility 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 AIR.

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
apparatus 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 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 ventilating 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 sulphuric 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 consideration, 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 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 consists 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, nitrogen, 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
composition 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

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 calculated.


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 residual 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 possible to assume an average laboratory
temperature and reduce the volume as read on the meter by means of a
constant factor.

The quantity of air passing through the meter is so adjusted that
exactly 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, _(h-t)/h_, 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 considerable 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
(760 - 15)/760 = 0.98, and all readings on the 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 correction 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 whatever is necessary for the reduction of the
volume. The matter of temperature corrections has been taken up in great
detail in an earlier publication, 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.

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
calculation 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 dioxide 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 mathematical 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.


INFLUENCE OF FLUCTUATIONS IN TEMPERATURE AND PRESSURE ON THE APPARENT
VOLUME OF AIR 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
considerably warmer there is naturally an expansion, and were it not for
the tension-equalizer there would be pressure in the system. Also, if
the barometer falls, there is an expansion of air which, again, in the
absence of the tension-equalizer, would produce pressure in the system.
It is necessary, 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 constant 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 temperature 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 consequently 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 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 Sondén and
Pettersson. An apparatus for the determination of carbon dioxide and
oxygen on the Pettersson principle has been devised by Sondén 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 Sondén gas-analysis
apparatus, the other arm connecting with the U-tubes for residual
analyses. By lowering 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 Sondén apparatus. Under these conditions,
therefore, we believe that the gravimetric method outlined 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
oxygen. 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 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 rôle 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
noticeable diminution in the percentage of oxygen in the chamber--a
diminution 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 accumulation 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 conditions. In rest experiments of short duration
this is never necessary. The procedure by which such a restoration of
oxygen percentage is accomplished has already been discussed
elsewhere.[25] 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 determine 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, where the composition of the air in the
chamber is much more nearly normal, 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 correction 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
expressing 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 immediately 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
containing 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-III, 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 ventilating air-current. To convert this into
liters the logarithmic factor 09462[26] 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 order to determine the total volume of air in the chamber under
standard 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

       1
     -----
     1 + _at_

in which _t_ is the temperature of the calorimeter. The correction for
pressure has also been worked out in a series of tables and the
logarithmic factor here corresponds to the ratio _p_/760, in which _p_
is the observed barometer. 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 (_b_) 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 calculating the amount of oxygen admitted to the chamber.

RESIDUAL SHEET  No. 1.

Calculation of residual amounts of nitrogen, oxygen, carbon dioxide and
water-vapor remaining in chamber at 8.10 A. M., June 24, 1909.

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

-------------------------------------------+-------------------------------
    Barometer, 756.95 mm.                  |     Miscellaneous Calculations
    Temp. cal., 20.08 °C                   |      875            48.65
-------------------------------------------+      164.55         25.9
                                           |      ------         90.
Apparent Volume of Air                     |      710.46        ------
                                           |         4.6        164.55
I    containing H_{2}O 715. liters         |      ------
I-II     "      CO_{2} 781.   "            |       715.0 I
I-III    "      O+N    755.   "            |        14
-------------------------------------------+      ------
Log. wt. H_{2}O to residual                |       781.0  I-II
.0815           = 91116                    |        24
Log. I          = 85431                    |      ------
                  -----                    |       755.0  I-III
                  76547 = 5.88 gms. H_{2}O +-----------------------------
Gms. to liters,   09462                    |    (a) 7.26 l.
                  -----                    |    (b) 1.57 l.
            (a)   86909 = 7.25 l. H_{2}O   |        -----
                                           |        8.82  = l. CO_{2} + H_{2}O
                                           |
Log. wt. CO_{2} in residual                | Log. I-III    = 87796
.0438           = 62634                    | "    temp.    = 96912
Log. I-II       = 84392                    | "    pressure = 99856
                  -----                    |                ------
                  49026 = 3.09 gms. CO_{2} | Total volume    84588  = 700.37 l.
Gms. to liters,        70680               | Volume CO_{2} + H_{2}O =   8.82 l.
                       -----               |                          ------
            (b)   19706 = 1.57 l. CO_{2}   |    "   O + N           = 691.56 l.
                                           |    "     N             = 552.96 l.
                                           |                           ------
                                           |    "     O             = 186.57 l.
                                           |


ABBREVIATED METHOD OF COMPUTATION OF OXYGEN ADMITTED TO THE CHAMBER 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
considered 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
considered 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 respiration 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 has been used with success in connection with the
large chamber and particularly for experiments of short duration. It has
also been introduced with great success in a portable type of apparatus
described elsewhere.[27] 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. Consequently, 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 temperature 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 inadvertently 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 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 chamber. 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 Sondén 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 pressure 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-equalizer, 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
comparison of the analyses as made by means of the Sondén apparatus and
as calculated 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 gasometric analysis is made, either
gravimetrically or volumetrically, the calculation of the residual
amount of oxygen presents the same difficulties in both cases.


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 variations 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
accurately controlled. The liberation of a definite amount of carbon
dioxide from a carbonate by means of acid has frequently been employed
for controlling an apparatus used for researches in gaseous exchange,
but this only furnishes a definite amount of carbon dioxide and throws
no light whatever upon the ability of the apparatus to determine the
other two factors, water-vapor and oxygen. Some of the earlier
experimenters have used burning 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 different materials, we still rely upon
the use of ethyl alcohol of known water-content. The experiments with
absolute alcohol and with alcohol containing varying amounts of water
showed no differences in the results, and 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[28] and thereby can determine the specific gravity of the
alcohol to the fifth or sixth decimal place with a high degree of
accuracy. Using the alcoholometric tables of Squibb[29] or Morley,[30]
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 ventilation started without sealing
     the cover. The lamp burned for about one hour and a quarter and
     was then weighed again. Then the window was sealed in and the
     experiment started as soon as possible. At the end of the
     experiment the window was taken out immediately and the lamp
     blown out and then weighed. The amount burned between the time
     of weighing the alcohol and the beginning of the experiment was
     calculated from the rate of burning before the experiment and
     this amount subtracted from the total burned from the time that
     the lamp was weighed before being sealed in until the end, when
     it was weighed the second time. For the minute which elapsed
     between the end of the experiment and the last weighing, the
     rate for the length of the experiment itself was used.

     During the experiment there were burned 142.7 grams of 92.20
     per cent alcohol of a specific gravity of 0.8163.

A tabular summary of results is given below:

  +----------------------+--------+-----------+
  |                      | Found. | Required. |
  +----------------------+--------+-----------+
  | Carbon dioxide  gms. | 259.9  |  251.4    |
  | Oxygen           "   | 278.5  |  274.8    |
  | Water-vapor      "   | 165.8  |  165.6    |
  | Heat           cals. | 829.0  |  834.5    |
  +----------------------+--------+-----------+

Thus does the apparatus prove accurate for the determination of all four
factors.


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
experiments, 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 investigations is that of the balance described by
Lombard,[31] in which the body-weight is recorded graphically from
moment to moment with an extraordinarily 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 Voit, 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 accessories. 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 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 suspension 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 therefore 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 RATE.

The striking relationship existing between pulse rate and general
metabolism, 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 respiration 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 umbilicus. 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.


ROUTINE OF AN EXPERIMENT WITH MAN.

In the numerous previously published reports which describe the
construction 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 peculiarities of metabolism.

Even with the use of a long-continued preceding diet of constant
composition, 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.

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 began.


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-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-current 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, 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 accumulate 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
coupling 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 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.[32] Repeated 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 compressed 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-bicarbonate 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
constant, 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 system 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 is sealed off
between the two levels of the sulphuric acid in the two absorbing
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 connecting 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 petroleum 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 connecting the tension-equalizer with the main
system is opened, and simultaneously 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
absorbed 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 subject 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.

A most excellent preservation of the record of the minor muscular
movements is obtained by dipping the smoked paper on the kymograph drum
in a solution of resin and alcohol. The lesser movements on the paper
indicate 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
deflection 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.

FOOTNOTES:

[5] 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. 91. (1905.)

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

[6] 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. 114. (1905.)

[7] 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.)

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

[9] Benedict and Snell: Eine neue Methode um Körpertemperaturen zu
messen. Archiv f. d. ges. Physiologie, 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.)

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

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

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

[13] This is in agreement with the value 579.6 calories found by F.
Henning, Ann. d. Physik, vol. 21, p. 849. (1906.)

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

[15] Benedict and Snell: Körpertemperatur Schwankungen mit besonderer
Rücksicht auf den Einfluss, welchen die Umkehrung der täglichen
Lebensgewöhnheit beim Menschen ausübt. 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 Physiology, vol. 11, p. 145. (1904.)

[16] 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 Bul. 63.
(1899.)

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

[18] 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.)

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

[20] 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.)

[21] 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.)

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

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

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

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

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

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

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

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

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

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

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