THE CALORIMETER SYSTEM .AND MEASUREMENT OF HEAT. 157 



Weighing objects inside the chamber. Aside from the variable weight 

 of the body of the subject of the respiration calorimeter experiments, 

 there is a continually fluctuating weight of the absorber system, the bed- 

 ding, furniture, and clothing, due to variations in water content. A 

 number of preliminary experiments, made several years ago in this 

 laboratory, to attempt to determine the variations in weight of sheet 

 copper exposed to different hygrometric conditions, gave negative re- 

 sults, and hence it has been assumed that any changes in the amount 

 of water condensed on the surface of the metal chamber must be very 

 slight and may be neglected ; but we have found repeatedly that wood 

 and textile fabrics absorb an appreciable amount of water which must 

 be considered in accurate work. 



There is not, however, much wood in the chamber. A wooden chair 

 is used, in which the man is weighed, and there is some woodwork on 

 the bicycle ergometer and telephone, but these are well shellacked and 

 polished, and we have no reason to believe that they alter in weight, 

 although the construction of the apparatus is such as to render actual 

 weighings somewhat difficult. 



With the clothing and bedding of the subject, we have conditions 

 under which there may readily be wide fluctuations in weight. If, 

 however, provision can be made for weighing such articles accurately, 

 the fluctuations in weight can be determined and a correction applied 

 accordingly. 



The large differences in the amount of water condensed on the ab- 

 sorbing system have been referred to on pages 23 and 126. In order 

 to know the exact amount of water in the chamber at any given time, 

 it is necessary to know the variations in weight of the absorbing 

 system. 



The variations in weight of the subject are of special significance in 

 their use as a check on the oxygen determinations, for if we have the 

 weight of the income of food and drink, the weight of the outgo, and 

 the variations in weight of the body of the subject, it is possible to cal- 

 culate arithmetically the amount of oxygen taken out of the air by the 

 man. In considering the fluctuations in the weight of the subject, 

 however, it is impossible to distinguish between the water in the body 

 of the subject and that on the surfaces of metal, or absorbed by the 

 woodwork, clothing, etc. , all of which are liable to changes in weight ; 

 and since the water on the coat of the subject can not be differentiated 

 from the same weight of water in the body of the subject, it is there- 

 fore necessary to know not only the changes in weight of the body of 

 the subject, but also the changes in weight of the bedding, absorber 

 system, etc. Only by knowing these variations in weight can the 



