CALCULATION OF RESULTS. 77 



little difficulty. It is necessary, for example, to accurately measure about 

 16 cubic centimeters of pure nitrogen, pass it into the potassium pyrogal- 

 late pipette, and then (having taken a definite sample of oxygen) gradually 

 absorb the oxygen in the potassium pyrogallate and measure subsequently 

 the accumulated nitrogen. The analysis is tedious and not particularly 

 satisfactory. Having checked the manufacturer's analysis of a number of 

 cylinders of oxygen and invariably found them to agree with our results, 

 we are at present using the manufacturer's guaranteed analysis. If there 

 was a very considerable error in the gas analysis, amounting even to 1 per 

 cent, the results during short experiments would hardly be affected. 



ADVANTAGE OF A CONSTANT-TEMPERATURE ROOM AND 

 TEMPERATURE CONTROL. 

 A careful inspection of the elaborate method of calculation required for 

 use with the calorimeter formerly at Wesleyan University shows that a 

 large proportion of it can be eliminated owing to the fact that we are here 

 able to work in a room of constant temperature. It has been pointed out 

 that the fluctuations in the temperature of the gas-meter affect not only 

 the volume of the gas passing through the meter, but likewise the tension 

 of aqueous vapor. The corrections formerly made for temperature on the 

 barometer are now unnecessary; finally (and perhaps still more important) 

 it is no longer necessary to subdivide the volume of the system into por- 

 tions of air existing under different temperatures, depending upon whether 

 they were in the upper or lower part of the laboratory. In other words, the 

 temperature of the whole ventilating circuit and chamber, with the single 

 exception of the air above the acid in the first sulphuric-acid absorber, may 

 be said to be constant. During rest experiments this assumption can be 

 made without introducing any material error, but during work experiments 

 it is highly probable that some consideration must be given to the possi- 

 bility of the development of a considerable temperature rise in the air of 

 the potash-lime absorbers, due to the reaction between the carbon dioxide 

 and the solid absorbent. It is thus apparent that the constant-temperature 

 conditions maintained in the calorimeter laboratory not only facilitate 

 calorimetric measurements, but also simplify considerably the elaborate 

 calculations of the respiratory exchange formerly required. 



VARIATIONS IN THE APPARENT VOLUME OF ALR. 



In the earlier form of apparatus the largest variation in the apparent 

 volume of air was due to the fluctuations in the height of the large rubber 

 diaphragms used on the tension equalizer. In the present form of appa- 

 ratus there is but one rubber diaphragm, and this is small, containing not 

 more than 3 to 4 liters as compared to about 30 liters in the earlier double 

 rubber diaphragms. As now arranged, all fluctuations due to the varying 



