The carbon dioxide in the chamber was determined in duplicate by means of two small Haldane gas-analysis apparatus.1 These instruments permitted determinations of carbon dioxide up to a concentration 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 chamber 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 publication1 and the results used in the calculations are with few exceptions the average of the duplicate determinations.

1 Haldane, Methods of air analysis, 1012, p. 62.

While the carbon-dioxide determinations could easily be made within the 10-minute divisions of the walking period, the oxygen determination, which involved the use of the Sonden apparatus, required 30 minutes 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Samples of air were withdrawn for analysis both before and after the addition of the carbon dioxide.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 preceded 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of the samples in each case and the temperature and barometer readings were likewise made at the time the samples were withdrawn.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:

C02 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.

(12.218/0.540)X100 =2,263 liters.

This is the volume at 0° C, 760 mm., and dry. The apparent volume 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(760/761.58) x (294.32/273) = 2,435 liters.

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

From a knowledge of the volume of the chamber and the percentage composition of the air at the beginning and end of the experiment, it was possible to calculate the total amount of carbon dioxide produced during the period of walking, and, from the time involved, the production per minute. In the same manner the percentage of oxygen at the beginning and end would give the amount of oxygen consumed on the per minute basis. From the gaseous exchange thus secured, the respiratory quotient was obtained and the heat produced was calculated by indirect calorimetry. The detailed method of the calculations and certain corrections required are given on page 134.