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.