
RESPIRATION CALORIMETER AND EXPERIMENTS. 2 2h 
Ba .o1 of a degree C. In ordinary experiments the difference is generally kept 
___-within this limit and seldom reaches .o5 degrees. The differences are both 
positive and negative and are easily made to counterbalance each other during 
shorter periods and during the whole experiment. 
Measurement of the heat carried out by the water current.—The principle 
here employed is simple. The chamber neither gains nor loses heat by the air 
current nor through the walls. The current of cold water which passes through 
the heat absorbers inside the chamber is caused to enter at a temperature gen- 
"erally but little above the freezing point, and to flow out at such a rate as to 
_ absorb and carry off the heat just as fast as it is generated inside the apparatus. 
_ The temperature of the water is measured as it enters and as it comes out. The 
mercury thermometers are shown at G and H in figure 10. The electrical ther- 
“mometer indicates the difference of temperature between the incoming and 
outgoing water currents by the difference of resistance of two coils of thin 
__ copper wire, of which one is in each pipe at the place of entrance or exit from 
the calorimeter. The difference is measured by a Wheatstone’s bridge on the 
_observer’s table. The mass of water is measured automatically by the apparatus 
i shown below and at the right of the window of the respiration chamber in 
v4 ‘figure g. 

























From the mass of the water which has passed through the absorber in a given 
time, and the rise in temperature, the quantities of heat brought out are readily 
calculated. To this is to be added a certain amount of heat which is carried 
away with the water vapor produced in the apparatus. This is practically the 
difference between the water vapor in the incoming and outgoing air. From 
the amount of this vapor, and its latent heat at the temperature of exit, the 
amount of heat it carries out is easily computed. 
Meter pump for regulating, measuring and sampling the ventilating air cur- 
rent.—Three forms of apparatus have been used for maintaining the air current 
and measuring its volume. One consisted of an ordinary air pump with a meter 
made by Elster in Berlin.* With this we have been unable to make measure- 
ments as accurate as seem to us desirable. 
For taking samples of air for analysis, aspirators of 150 liters capacity were 
employed at the outset and are still used. ‘The measurements with these have 
been found quite accurate. The most satisfactory arrangement we have found, 
and one which serves the threefold purpose of maintaining the air current, 
measuring its volume and delivering aliquot samples of convenient size for 
analyses, is an apparatus designed and made by Mr. O. S. Blakeslee, and appro- 
_priately designated by him as a ‘‘meter-pump.” This is shown in figure II. 
The essential parts for maintaining the air current and measuring its volume 
are cylinders of steel. There are two pumps which work in unison. ‘Three 
steel cylinders are employed for each pump. ‘The inner and outer cylinders are 
arranged concentrically with an annular space 1.2 cm. in width between them. 
_ This space is partly filled with mercury. Between the inner and outer cylinders, 
which are stationary, plays a central cylinder, its lower portion being immersed 
-in the mercury. The central. cylinder is closed at the top and is raised and 

_ * See Report of the Storrs Station, 1896, p. 91, and Bulletin 44 of the Office of Experi- 
ment Stations of the U. S. Department of Agriculture, p. 19. 
+ See description in the Report and Bulletin just named, 
