TECHNIQUE FOR METABOLISM DURING WORK. 125 



ments permitted determinations of carbon dioxide up to a concentra- 

 tion of 1 per cent. This figure controlled to some extent the size of the 

 chamber and the amount of work to be performed, for too large a cham- 

 ber would give too great a dilution, while too heavy work would exceed 

 the capacity of the apparatus for the carbon-dioxide determinations. 

 Both instruments had been calibrated against the Sonden gas-analysis 

 apparatus described in an earlier publication^ and the results used in 

 the calculations are with few exceptions the average of the duplicate 

 determinations. 



While the carbon-dioxide determinations could easily be made within 

 the 10-minute divisions of the walking period, the oxygen determina- 

 tion, which involved the use of the Sonden apparatus, required 30 min- 

 utes and was obtained only at the end of the walking period. The 

 method by which the oxygen present at the beginning of the period was 

 calculated is explained on page 134. 



VOLUME OF CHAMBER. 



The total volume of the chamber was determined by allowing a known 

 weight of carbon dioxide to escape slowly from a weighed cylinder into 

 the bottom of the chamber and discarding the displaced volume of air 

 that was thereby forced into the spirometer. 



Samples of air were withdrawn for analysis both before and after the 

 addition of the carbon dioxide. A thorough stirring of the air pre- 

 ceded the withdrawal of the samples in each case and the temperature 

 and barometer readings were likewise made at the time the samples 

 were withdrawn. From the known volume of the carbon dioxide added 

 and the increase in the percentage of carbon dioxide found, the volume 

 of the chamber was computed. Four determinations gave 2,437, 2,431, 

 2,435, and 2,374 liters, with an average of 2,419 liters. An example of 

 the method of calculation of the volume follows: 



CO2 added =24.00 gms. Observed barometer =761.58 mm. Temp. =21.32° C. 



CO2 in chamber at start =0.048 per cent; after addition =0.588 per cent; increase =0.540 per cent. 



24.00 gms. CO2 =12.218 liters at 0° C. and 760 mm. 12.218 liters =0.540 per cent of chamber. 



12.218 ^^QQ =2,263 liters. 

 0.540 



This is the volume at 0° C, 760 mm., and dry. The apparent vol- 

 ume is the volume at the observed temperature and pressure and this 

 volume includes the water vapor as well as the atmospheric gases. The 

 volume of 2,263 liters must be corrected, therefore, to the observed 

 temperature and pressure readings. As this includes the water vapor, 

 no deduction for aqueous tension is made from the barometer readings. 

 The correction is made as follows : 



2,263 X ^^^ >^294^ =2,435 liters. 

 761.58 273 



1 Benedict, Carnegie Inst. Wash. Pub. No. 166, 1912, p. 75. 



