14 NEW HAMPSHIRE EXPERIMENT STATION [Bull. 261 



cock at the base of the can, B, and one complete pumpful (about 370 

 c.c.) of the oxygenated air is withdrawn from the sj-stem. This allows 

 the bathing-cap to fall so that at the moment of combustion, when 

 there is a temporar>' increase in the volume due to the heat developed, 

 there is no undue expansion of the rubber cap. As the combustion pro- 

 ceeds, the bathing-cap, after its- initial rise, begins to sink and at the 

 end of the combustion has fallen considerably. Cold water is then 

 passed through the cooling pipe to bring the temperature of the appara- 

 tus to its initial level. When the temperature has again reached equi- 

 librium, the cold water in the cooling pipe should be removed, as other- 

 wise it would result in overcooling the apparatus. The valve, V, is, 

 therefore, turned in the proper direction so that air can enter the pipe, 

 and the cold water is rapidly siphoned out of the cooling pipe. 



When temperature equilibrium has been established, a sufficient 

 amount of moist air must be introduced into the apparatus to bring the 

 bathing-cap back to its original level. This includes the introduction of 

 the amount temporarily withdrawn to provide for the expansion of the 

 cap. Indeed, the amount withdrawn is usually replaced immediately 

 after the combustion begins, when there is no obvious tension on the 

 cap. The volume of air introduced can be measured by means of a 

 spirometer or a wet gas meter, but it is far simpler to use a pump such 

 as that employed in the Nutrition Laboratoiy, which has played an 

 important role in the development of the student and the field respira- 

 tion apparatus.' This pump is a simple hand pump which delivers al- 

 most exactly 370 c.c. of air with each complete stroke. The number of 

 whole pumpfuls introduced and the fraction of a pumpful to bring the 

 button on the bathing-cap to its original position give a measure of the 

 total apparent volume of oxygen absorbed during the combustion. 



In the original student respiration apparatus dry air was introduced 

 by the pump into the can, to note how much oxygen had been consumed 

 by the subject. More recently we have found that moist air is prefera- 

 ble and simplifies the calculations. If continued, repeated combustions 

 are to be made, the oxygen absorbed from the closed system may be 

 replaced by oxygen which has previously been stored in a football blad- 

 der. The football bladder is attached to the nozzle of an oxygen cylin- 

 der and filled with oxygen. The pump is then connected with this blad- 

 der, oxygen is drawn into the pump, and with proper turning of the 

 3-way petcock at the base of the soda-lime container as many pumpfulg 

 or fractions of a pumpful of oxygen as are necessarj' may be rapidly de- 

 livered into the apparatus. A few centimeters of water in the rubber 

 bag insure complete saturation of the oxygen. 



The calculation of the oxygen absorbed during the combustion is 

 based upon the number of full pump strokes and any fraction of a 

 stroke required to bring the bathing-cap back to its original position,' 

 the volume of a complete pumpful (about 370 c.c), the volume per 



^See footnotes 1 and 2 on p. 7 of this report. 



^Not including the pumpful withdrawn temporarily to prevent undue expan- 

 sion of the liathing-cap at the moment of comlnistion and subsequently returned 

 to the apparatus. 



