CALCULATION OF RESULTS. 67 



pipe inclosed 11.2 liters of air, thus making a sum total of 13.7 in the 

 tension equalizing system . 



DATA FOR THE REJECTION OF AIR. 



As the amount of nitrogen in the system gradually accumulates dur- 

 ing an experiment, by reason of the fact that the admission of oxygen 

 is unavoidably accompanied by an admission of nitrogen, it becomes 

 necessary from time to time to reject a considerable volume of air, vary- 

 ing from 30 to 70 liters, by drawing it through the Elster meter, and to 

 replace it with oxygen. The calculations by which the exact amount 

 of air thus rejected is determined are made iu the lower right-hand 

 corner of this sheet. Here are recorded the time at which the air is 

 rejected, the number of liters passing through the meter, the thermom- 

 eter reading and correction for the thermometer in the meter, the water 

 manometer, with its equivalent in mercury, the tension of aqueous 

 vapor at the temperature of the meter, and the barometer reading. It 

 is thus possible to calculate the corrected volume of oxygen and nitro- 

 gen rejected. The proportions of oxygen and nitrogen in this corrected 

 volume are obtained from the analysis of air taken immediately before 

 the air is rejected. (See p. 77.) 



CORRECTIONS FOR VARIATIONS IN VOLUME AND COMPOSITION OF 



RESIDUAL AIR. 

 NECESSITY FOR RESIDUAL ANALYSES. 



The amounts of carbon dioxide and water eliminated and oxygen 

 absorbed as determined by the gains in weight of the absorbing system 

 and the loss in weight of the oxygen cylinder, with due corrections for 

 nitrogen, give, on the whole, a general approximation of the amounts of 

 carbon dioxide and water eliminated and oxygen absorbed by the sub- 

 ject ; but in this calculation, as has been pointed out, no notice is 

 taken of the alterations in composition of the residual volume of air. 

 The chief factors influencing such variations are muscular activity of 

 the subject with its consequent fluctuations in carbon-dioxide and water 

 production and oxygen absorption, rapidity of ventilation, and baro- 

 metric pressure. 



The fluctuations in the amounts of carbon dioxide and water are in 

 the main of a temporary nature. There maybe variations of over 100 

 grams of carbon dioxide and 20 grams of water vapor in the amounts 

 of these gases in the air in different periods of the day, as, for example, 

 at the beginning and cessation of hard muscular work ; but with ap- 

 proximately uniform muscular activity for the whole period the residual 

 amounts of these gases are almost invariably the same from day to day 



