80 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC. 



These volumes represent conditions existing inside the chamber without 

 the subject, i. e., conditions under which an alcohol check-test would be 

 conducted. In an experiment with man it would be necessary to deduct 

 the volume of the man, books, urine bottles, and all supplemental apparatus 

 and accessories. Under these circumstances the apparent volume of the 

 air in the chamber may at times be diminished by nearly 90 to 100 liters. 

 At the beginning of each experiment the apparent volume of air is calcu- 

 lated. 



RESIDUAL ANALYSES. 

 CALCULATION FROM RESIDUAL ANALYSES. 



The increment in weight of the absorbers for water and carbon dioxide 

 and the loss in weight of the oxygen cylinder give only an approximate 

 idea of the amounts of carbon dioxide and water-vapor produced and 

 oxygen absorbed during the period, and it is necessary to make correction 

 for change in the composition of the air as shown by the residual analyses 

 and for fluctuations in the actual volume. In order to compute from the 

 analyses the total carbon-dioxide content of the residual air, it is necessary 

 to know the relation of the air used for the sample to the total volume, and 

 thus we must know accurately the volume of air passing through the gas- 

 meter. 



In the earlier apparatus 10-liter samples were used, and the volume of 

 the respiration chamber was so large that it was necessary to multiply the 

 values found in the residual sample by a very large factor, 500. Hence, 

 the utmost caution was taken to procure an accurate measurement of the 

 sample, the exact amounts of carbon dioxide absorbed, and water-vapor 

 absorbed. To this end a large number of corrections were made, which 

 are not necessary with the present type of apparatus with a volume of resid- 

 ual air of but about 1,300 liters, and accordingly the manipulation and 

 calculations have been very greatly simplified. 



While formerly pains were taken to obtain the exact temperature of the 

 air leaving the gas-meter, with this apparatus it is unnecessary. When the 

 earlier type of apparatus was in use there were marked changes in the 

 temperature of the calorimeter laboratory and in the water in the meter 

 which were naturally prejudicial to the accurate measurement of the volume 

 of samples, but with the present control of temperature in this laboratory 

 it has been found by repeated tests that the temperature of the water in 

 the meter does not vary a sufficient amount to justify this painstaking 

 measurement and calculation. Obviously, this observation also pertains to 

 the corrections for the tension of aqueous vapor. It has been found pos- 

 sible to assume an average laboratory temperature and reduce the volume 

 as read on the meter by means of a constant factor. 



