74 A RESPIRATION CALORIMETER. 



not been applied, since, in the very process of testing, the air in the first 

 water- absorber and the three carbon-dioxide absorbers was left in some- 

 what compressed form after the test, and obviously the true volume of 

 air in this portion of the system was the same at the beginning as at 

 the end of each period. 



CORRECTION FOR MERCURY VALVE. 



In the manipulation of the mercury valve 1 at the end of each exper- 

 imental period, a certain amount of air is rejected from the system, 

 since, by the raising of the mercury reservoir, air in the annular space 

 is forced back into the last water- absorber, and when this is uncoupled 

 escapes into the room air. The volume of air thus rejected has been 

 determined very accurately to be 0.13 liter, and this is a constant 

 correction to be applied for every period. The correction is applied 

 on the blank for the calculation of the residual amounts of nitrogen, 

 oxygen, carbon dioxide, and water vapor, as shown on page 84. 



INCREASE IN VOLUME OF THE WATER-ABSORBERS. 



As the water vapor is absorbed, the volume of the acid in the absorber 

 gradually increases, and consequently the volume of air decreases. As 

 this volume of air is practically driven into the air system, a correction 

 for it is necessary. The specific gravity of concentrated sulphuric acid 

 is 1.84, and as water is absorbed the specific gravity becomes lower. 

 There is, however, a contraction in volume which must be allowed for 

 in the calculations. It has been computed that approximately 0.7 of 

 the weight of the water absorbed when expressed in cubic centimeters 

 corresponds to the increase inside the water- absorbers, and consequently 

 it is customary to multiply the number of grams of water absorbed by 

 0.7, the product equaling the volume of air in cubic centimeters forced 

 out of the water-absorbers. This correction is always in one direction, 

 and hence a cumulative one, and, though small, is made. On the 

 blank in which the data for the weights of the absorbing system are 

 recorded, the amount of this correction is calculated by multiplying the 

 weight of water collected in the first water- absorber by 0.7, e. g., as 

 illustrated on page 64, 54.71 X 0.7 = 38.297 = 0.04 liter. That is to 

 say, 0.04 liter of air was expelled from the water- absorber during this 

 particular period. 



FLUCTUATIONS IN VOLUME OF THE CARBON-DIOXIDE ABSORBERS. 



That there is an actual difference between the volumes of the sodium 

 hydroxide and calcium hydroxide at the beginning and those of the 

 sodium carbonate and calcium carbonate at the end is highly probable, 



1 For construction of valve and diagram, see page 21. 



