CALCULATION OF RESULTS. 83 



ing to Hirti, this is not strictly true. The coefficient of thermal expan- 

 sion of perfect gases is taken as 0.00367, whereas Hirn 1 states that the 

 coefficient of thermal expansion of water vapor is 0.00419 between o 

 and 119, the value seeming to diminish as the temperature rises and 

 increasing numerically for lower temperatures. Perman, 2 however, 

 concludes that the density of saturated aqueous vapor is probably only 

 very slightly (if at all) above normal at temperatures up to 90, and 

 from the data at hand it seems reasonable to assume that water vapor 

 at 20 behaves as a perfect gas, and that the weights of a liter of 

 hydrogen and water vapor are directly proportional to their molecular 



weight. 



CALCULATIONS OF RESIDUAL ANALYSIS. 



In calculating the total amounts of carbon dioxide, water, oxygen, 

 and nitrogen in the residual air of the system at the end of any given 

 period, the volumes of the sample and the apparent volume of the 

 whole air system are reduced to the same basis, i. e. , the standard con- 

 ditions at o and 760 mm. pressure, thus simplifying the calculations 

 greatly. 



Reference has already been made to the process by which the residual 

 samples are taken, and specimen data for such samples are shown in 

 the upper left-hand corner of the record sheet previously explained 

 (p. 64). There remain for consideration, first, the calculation of the 

 true volume of gas in the sample and in the system, and second, from 

 these corrected data the calculation of the amount of the various gases 

 in the system. 



These calculations are simplified as much as possible, and for con- 

 venience are recorded on a blank shown on page 84. 



VOLUME OF THE SAMPLE. 



The calculation for the samples for the residual analyses involves a 

 reduction of the gas volume as measured by the meter to standard con- 

 ditions of temperature and pressure, making a due allowance for the 

 volume of water vapor and carbon dioxide absorbed by the reagents, 

 thus giving the corrected volume of air withdrawn in the samples reduced 

 to standard conditions. The calculations for the reduction of these 

 volumes to standard conditions is made on the residual sheet (p. 84). 

 Under the head " Air sample for analysis " is first entered the apparent 

 volume of air which is passed through the meter. To the logarithm 

 of this volume must be added the logarithm of the calibration correction 



1 Hirn : Recherches sur 1'equivalent mechanique de la chaleur (1858). 



2 Proc. Roy. Soc. (1904), 72, pp. 72-83. 



