160 A RESPIRATION CALORIMETER. 



the fiber tube, which is an excellent non-conductor of heat. To pre- 

 vent the leakage of air, we at first used a thin rubber balloon with a 

 small opening in one end so that the rod could pass through it, the 

 balloon being tightly tied to the rod and attached to the tube. It was 

 thus possible to provide for not only the necessary up-and-down motion, 

 but also a slight lateral motion which would accompany the weighing 

 and at the same time prevent any loss of air from the system. Later, 

 thin- walled rubber tubing of large diameter was substituted. This thin 

 rubber diaphragm prevents the escape of air ; but it is necessary to rely 

 on this closure only during the actual period in which the weighings 

 are being made, since the flexibility of the diaphragm is such as to allow 

 the rubber stopper on the lower end of the suspension rod to be raised 

 about 1.5 cm., which is sufficient to crowd it well into the open end of 

 the fiber tube, thus completely shutting off the tube from the calorimeter 

 chamber proper. 



The rubber diaphragm is so light that the slight vertical motion pro- 

 duces no variation in weight. The extreme sensitiveness of the platform 

 balance under these conditions makes it possible to read not only the 

 graduations on the scale-beam, which are made in ic-gram divisions, but 

 also the differences in height at the end of the scale-beam itself. A 

 small metal pointer is attached to the end of the scale-arm and a milli- 

 meter scale is placed immediately behind it in such a manner that, during 

 the progress of weighing, the pointer moves over the millimeter scale. 

 A certain arbitrary point is taken on this scale as the zero point. The 

 finer weighings are made by means of a second hanger, which is very 

 much smaller, consisting practically of a stout piece of copper wire, 

 which is of such a weight that moving it through a section of the grad- 

 uated beam corresponding to 200 grams is equivalent to an alteration 

 in weight of 5 grams ; and it was found that by its use, even with a 

 weight of 90 kg. suspended from the platform balance, weighings to 

 within 2 grams or even i gram could be accurately made. 



In using this balance it is necessary only to obtain actual differences 

 in weight, and hence no correction is made for the added weight of the 

 pointer on the scale-arm, the removal of the hooks from the platform 

 balance itself, the weight of the hanger and suspension rod, or of the 

 stopper and ring at the lower end. The actual weight of the man can 

 be obtained, however, since two series of weighings are made, one in 

 which the man, bedding, clothing, etc., are weighed with the man sitting 

 in the chair, and one in which only the chair plus bedding and clothes 

 are weighed. The difference between these two weights obviously gives 

 the weight of the man himself. 



