72 A RESPIRATION CALORIMETER. 



It frequently happens that other fixtures, such as the metal bed, are 

 left in the chamber when making the alcohol check experiments. 

 Under these conditions, their volumes also must be deducted. 



VOLUME IN EXPERIMENTS WITH MAN. 



In metabolism experiments with man, the alcohol lamp and iron 

 stands are removed. The food aperture is closed, and consequently its 

 volume is not added to that of the chamber. A number of additional 

 articles are, however, taken into the chamber before the experiment 

 begins. Among these may be enumerated the bed, table, chair, bed- 

 ding, weighing fixtures, books, papers, dishes, urine jars, feces cans, 

 and, in work experiments, the ergometer. By far the greatest correc- 

 tion, however, is that for the volume of the subject himself. 



The specific gravity of the body is not far from i.oo, and we have 

 been in the custom of assuming that the weight of the subject and 

 clothing represented the volume in liters displaced by the man when 

 entering the calorimeter chamber. The corrections for the furniture 

 are computed by means of the weight and specific gravity of the vari- 

 ous materials. These volumes are, in liters, as follows : Bed, 3.66 ; 

 table, 0.51 ; chair, with weighing attachments, 5.61, and ergometer, 

 when included, 14.00. 



A similar procedure is followed in the calculation of volumes of 

 books, papers, and incidental articles. 



FLUCTUATIONS IN THE AIR VOLUME. 



While the apparent volumes of air in the different sections of the 

 closed system are those given in the preceding calculations, there are 

 several fluctuating factors that must be taken into consideration. 



VOLUME IN THE PANS. 



The most noticeable and important fluctuation in volume is that 

 specially provided for in the construction of the pans. Sudden fluctua- 

 tions in temperature are not uncommon, especially in the change from 

 rest to hard work, or vice versa, and as the air in the chamber can be 

 considered as comparable to that in the bulb of an immense air ther- 

 mometer, some provision for expansion or contraction must be made 

 if the pressure is to remain constant. Furthermore, variations in baro- 

 metric pressure are accompanied by very material alterations in the 

 volume of the confined air. 



As was pointed out on page 41, fluctuations in the volume of the air 

 in the pans can be determined with considerable accuracy from readings 

 on the millimeter scale and the corresponding table of calibrations. 



