64 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC. 



the quantity of carbon dioxide and water- vapor absorbed. The conditions 

 under which these changes from one system to another are made, and which 

 call for an absolutely gas-tight closure, have been discussed in detail else- 

 where.* It is sufficient to state here that the very large majority of me- 

 chanical valves will not serve the purpose, since it is necessary to have a 

 pressure of some 40 millimeters of mercury on one side of the valve at 

 the entrance to the absorber system and on the other side atmospheric pres- 

 sure. A valve with an internal diameter of not less than 25 millimeters 

 must be used, and to secure a tight closure of this large area and permit 

 frequent opening and shutting is difficult. After experimenting with a 

 large number of valves, a valve of special construction employing a me- 

 chanical seal ultimately bathed in mercury was used for the earlier appa- 

 ratus. The possibility of contamination of the air-current by mercury 

 vapor was duly considered and pointed out in a description of this appa- 

 ratus. It was not until two years later that difficulties began to be experi- 

 enced and a number of men were severely poisoned while inside the cham- 

 ber. A discussion of this point has been presented elsewhere. f At that 

 time mercury valves were used both at the entrance and exit ends of the 

 absorber system, although as a matter of fact, when the air leaves the last 

 absorber and returns to the respiration chamber, the pressure is but a 

 little above that of the atmosphere. Consequently, mechanical valves were 

 substituted for mercurial valves at the exit and the toxic symptoms dis- 

 appeared. In constructing the new calorimeters it seemed to be desirable 

 to avoid all use of mercury, if possible. We were fortunate in finding a 

 mechanical valve which suited this condition perfectly. These valves, which 

 are very well constructed, have never failed to show complete tightness 

 under all possible tests and are used at the exit and entrance end of the 

 absorber system. Their workmanship is of the first order, and the valve 

 is somewhat higher in price than ordinary mechanical valves. They have 

 been in use on the apparatus for a year now and have invariably proved 

 to be absolutely tight. They are easy to obtain and are much easier to 

 manipulate and much less cumbersome than the mercury valves formerly 

 used. 



COUPLINGS. 



Throughout the construction of the respiration apparatus and its various 

 parts, it was constantly borne in mind that the slightest leak would be 

 very disastrous for accurate oxygen determinations. At any point where 

 there is a pressure greater or less than that of the atmosphere, special pre- 



* W. O. Atwater and F. G. Benedict: A respiration calorimeter with appliances 

 for the direct determination of oxygen. Carnegie Institution of Washington 

 Publication No. 42, p. 20. (1905.) 



f Thorne M. Carpenter and Francis G. Benedict: Mercurial poisoning of men 

 in a respiration chamber. American Journal of Physiology, vol. 24, p. 187. 

 (1909.) 



