78 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC. 



positions of the tension-equalizer are eliminated as each experimental period 

 is ended with the diaphragm in exactly the same position, i. e., filled to a 

 definite tension. 



In its passage through the purifiers the air is subjected to more or less 

 pressure, and it is obvious that if these absorbers were coupled to the venti- 

 lating system under atmospheric pressure, and then air caused to pass 

 through them, there would be compression in a portion of the purifier 

 system. Thus there would be a contraction in the volume, and air thus 

 compressed would subsequently be released into the open air when the 

 absorbers were uncoupled. The method of testing the system outlined on 

 page 100 equalizes this error, however, in that the system is tested under 

 the same pressure used during an actual experiment, and hence between 

 the surface of the sulphuric acid in the first porcelain vessel and the sul- 

 phuric acid in the second porcelain vessel there is a confined volume of air 

 which at the beginning of an experimental period is under identically the 

 same pressure as it is at the end. There is, then, no correction necessary 

 for the rejection of air with the changes in the absorber system. 



CHANGES IN VOLUME DUE TO THE ABSORPTION OF WATER AND 

 CARBON DIOXIDE. 



As the water-vapor is absorbed by the sulphuric acid, there is a slight 

 increase in volume of the acid. This naturally results in the diminution 

 of the apparent volume of air and likewise again affects the amount of 

 oxygen admitted to produce constant apparent volume at the end of each 

 experimental period. The amount of increase which thus takes place for 

 each experimental period is very small. It has been found that an increase 

 in weight of 25 grams of water- vapor results in an increase in volume of 

 the acid of some 15 cubic centimeters. Formerly this correction was made, 

 but it is now deemed unnecessary and unwise to introduce a refinement that 

 is hardly justified in other parts of the apparatus. Similarly, there is 

 theoretically at least an increase in volume of the potash-lime by reason of 

 the absorption of the carbon dioxide. This was formerly taken into con- 

 sideration, but the correction is no longer applied. 



RESPIRATORY LOSS. 



With experiments on man, there is a constant transformation of solid 

 body material into gaseous products which are carried out into the air- 

 current and absorbed. Particularly where no food is taken, this solid 

 material becomes smaller in volume and consequently additional oxygen is 

 required to take the place of the decrease in volume of body substance. 

 But this so-called respiratory loss is more theoretical than practical in 

 importance, and in the experiments made at present the correction is not 

 considered necessary. 



