76 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC. 



CALCULATION OF RESULTS. 



With an apparatus as elaborate as is the respiration calorimeter and its 

 accessories, the calculation of results presents many difficulties, but the 

 experience of the past few years has enabled us to lessen materially the 

 intricacies of the calculations formerly thought necessary. 



The total amount of water-vapor leaving the chamber is determined by 

 noting the increase in weight of the first sulphuric-acid vessel in the 

 absorber system. This vessel is weighed with a counterpoise and hence 

 only the increment in weight is recorded. A slight correction may be 

 necessary here, as frequently the absorber is considerably warmer at the 

 end of the period than at the beginning and if weighed while warm there 

 may be an error of 0.1 to 0.2 gram. If the absorbers are weighed at the 

 same temperature at the beginning and end, this correction is avoided. 



The amount of carbon dioxide absorbed from the ventilating air-current 

 is found by noting the changes in weight of the potash-lime can and the 

 last sulphuric-acid vessel. As shown by the weights of this latter vessel, 

 it is very rare that sufficient water is carried over from the potash-lime to 

 the sulphuric acid to cause a perceptible change in temperature, and no 

 temperature corrections are necessary. It may occasionally happen that 

 the amount of carbon dioxide absorbed is actually somewhat less than the 

 amount of water-vapor abstracted from the reagent by the dry air-current 

 as it passes through the can. The conditions will then be such that there 

 will be a loss in weight of the potash-lime can and a large gain in weight 

 of the sulphuric-acid vessel. Obviously, the algebraic sum of these amounts 

 will give the true weight of the carbon dioxide absorbed. 



The amount of oxygen admitted is approximately measured by noting 

 the loss in weight of the oxygen cylinder. Since, however, in admitting 

 the oxygen from the cylinder there is a simultaneous admission of a small 

 amount of nitrogen, a correction is necessary. This correction can be 

 computed either by the elaborate formulas described in the publication of 

 Atwater and Benedict * or by the more abbreviated method of calculation 

 which has been used very successfully in all short experiments in this labora- 

 tory. In either case it is necessary to know the approximate percentage of 

 nitrogen in the oxygen. 



ANALYSIS OF OXYGEN. 



With the modified method of computation discussed in detail on page 88 

 it is seen that such exceedingly exact analyses of oxygen as were formerly 

 made are unnecessary, and further calculation is consequently very simple 

 if we know the percentage of nitrogen to within a fraction of 1 per cent. 

 We have used a Haldane gas-analysis apparatus for analyzing the oxygen, 

 although the construction of the apparatus is such that this presents some 



* Atwater and Benedict: hoc cit., p. 38. 



