88 A RESPIRATION CALORIMETER. 



corrected volume of air in the chamber and air-pipes up to the second 

 soda-lime cylinder. The weight of carbon dioxide in the system at the 

 end of the period cited was 22.93 grams. By the use of the logarithmic 

 conversion factor .70680 this weight of carbon dioxide is found to 

 correspond to 11.67 liters. 



OXYGEN AND NITROGEN. 



The residual volume of oxygen and nitrogen together is readily de- 

 termined by deducting the volumes of water vapor and carbon dioxide 

 from the total corrected volume of air in the system, V 3 . By reference 

 to page 84 it will be seen that the carbon dioxide and water occupied 

 a volume of 47.38 liters. On deducting this volume from V 3 , i. e., 

 4,606.71 liters, the volume of the remaining gas, oxygen, and nitrogen 

 is equal to 4,559.33 liters. What portion of this volume is nitrogen 

 can be found by direct calculation. 



THE NITROGEN IN THE SYSTEM. 



The amount of nitrogen present in the system at the beginning of an 

 experiment is determined directly by an analysis of the air, from which 

 the oxygen is removed by means of potassium pyrogallate. From this 

 analysis the composition of the air free from carbon dioxide is obtained, 

 i. e. , the percentages of nitrogen and oxygen. From the apparent vol- 

 ume, the true volume of the gases in the system is calculated, and, with 

 due allowance for the volume of carbon dioxide and water vapor, the 

 initial volume of nitrogen present may be computed. This volume is 

 commonly referred to as the base line. Nitrogen may enter the system 

 in either one or both of the following ways : ( i ) With the oxygen in 

 the steel cylinders ; from 2.5 to 8 per cent of the contents of the cylin- 

 der is nitrogen. Inasmuch as each cylinder varies in composition and 

 the amount of oxygen and nitrogen must be known for each cylinder, it 

 is necessary to make an analysis before the cylinder is used. (See p. 34. ) 

 (2) In air admitted through the food aperture. 



Nitrogen may leave the system either in small quantities through 

 the food aperture by the interchange of material, through loss in 

 changing absorbers, or in the sample removed for the determinations 

 of oxygen, but more especially, however, in the large sample of air 

 rejected from time to time. 



In addition to these regular channels for the escape of nitrogen, any 

 leakage of air out of the system through defects in the couplings or 

 connections obviously carries with it a large amount of nitrogen. The 

 discussion of this point will be deferred until later. 



