56 A RESPIRATION CALORIMETER. 



80.856 per cent of nitrogen. A duplicate analysis gave 80.854 P er cent 

 of nitrogen. It is only fair to state that such an agreement is excep- 

 tional rather than the rule. In general, however, the agreement is 

 within 0.03 to 0.05 per cent. 



During the process of each analysis a small quantity of water is un- 

 avoidably forced into the pipette, and consequently, while 155 cc. of 

 reagent will absorb nearly 500 cc. of oxygen in oxygen analyses, it 

 will absorb only 150 cc. of oxygen in the air analyses. It seems reason- 

 able to suppose that this diminished efficiency is due, in part at least, to 

 the gradual dilution of the reagent by the introduction of water. Expe- 

 rience has led to the renewing of the solution after eight analyses of air. 



It can be readily seen that this method of analysis, depending as it 

 does on so many readings of burettes, thermometers, barometer, etc., 

 is open to serious objections when used for the most accurate work. 1 

 However, a series of analyses of samples of outdoor air taken on suc- 

 cessive days indicated extremely close agreement, such as to lead us to 

 believe that the method is as accurate as we can expect, in the absence 

 of a constant-temperature room and the services of an expert gas ana- 

 lyst, whose whole time can be devoted to this kind of work. 



ACCESSORY APPARATUS. 



Aside from the elaborate respiration apparatus proper, certain inci- 

 dental apparatus is necessary, such as balances for obtaining the weights 

 of gases absorbed by the residual U tubes, of the carbon dioxide and 

 water in the absorbers, and of the oxygen, a barometer, and thermom- 

 eters for determining the temperature of the air, both in the respiration 

 chamber and in the exterior portions of the air-circuit. Other incidental 

 apparatus, which has, however, more to do with the measurements of 

 heat than of the respiratory products, will be described hereafter in 

 connection with the discussion of heat measurements. 



BALANCES. 



Analytical. For weighing the residual U tubes and all general ana- 

 lytical work in the laboratory, in connection with experiments with 

 the respiration calorimeter, short-beam analytical balances of standard 

 types are used. 



Balance for weighing the carbon-dioxide and water absorbers and oxygen 

 cylinders. The quantitative determination of the total carbon dioxide, 

 water, and oxygen in the air current necessitates the use of a balance at 



the moment of writing there is being installed in this laboratory the form of 

 air-analysis apparatus used by Zuntz in his work on the respiratory exchange. 



