94 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC. 



sensitive. With a dead load of 100 kilograms in each pan it has shown a 

 sensitiveness of 0.1 gram, but in order to have the apparatus absolutely air- 

 tight for the oxygen and carbon-dioxide determination, the rod on which 

 the weighing-chair is suspended must pass tlirough an air-tight closure. 

 For this closure we have used a thin rubber membrane, weighing about 1.34 

 grams, one end of which is tied to a hard-rubber tube ascending from the 

 chair to the top of the calorimeter, the other end being tied to the suspen- 

 sion rod. In playing up and down this rod takes up a varying weight of the 

 rubber diaphragm, depending upon the position which it assumes, and there- 

 fore the sensitiveness noted by the balance with a dead load and swinging 

 freely is greater than that under conditions of actual use. Preliminary 

 tests with the balance lead us to believe that with a slight improvement in 

 the technique a man can be weighed to within 0.3 gram by means of this 

 balance. A series of check-experiments to test the indirect with the direct 

 determination of oxygen are in progress at the moment of writing, and it 

 is hoped that this problem can be satisfactorily solved ere long. 



During the process of weighing, the ventilating air-current is stopped 

 so as to prevent any slight tension on the rubber diaphragm and furnish 

 the best conditions for sensitive equilibrium. After the weighing has been 

 made and the time exactly recorded, the load is thrown off the knife-edges 

 of the balance, and then provision has been made to raise the rod supporting 

 the chair and simultaneously force a rubber stopper tightly into the hard- 

 rubber tube at the top of the calorimeter, thus making the closure absolutely 

 tight. It is somewhat hazardous to rely during the entire period of an 

 experiment upon the thin rubber membrane for the closure when the blower 

 is moving the air-current. 



To raise the chair and the man suspended on it in such a way as to draw 

 the cork into the hard-rubber tube, we formerly used a large hand-lever, 

 which was not particularly satisfactory. Thanks to the suggestion of Mr. 

 E. H. Metcalf, we have been able to attach a pneumatic lift (fig. 9) in 

 that the cross-bar above the calorimeter chamber, to which the suspension 

 rod is attached, rests on two oak uprights and can be raised by admitting 

 air into an air-cushion, through the central opening of which passes the 

 chair-suspending rod. As the air enters the air-cushion it expands and 

 lifts a large wooden disk which, in turn, lifts the iron cross-bar, raising 

 the chair and weight suspended upon it. At the proper height and when 

 the stopper has been thoroughly forced into place, two movable blocks are 

 slipped beneath the ends of the iron cross-bar and thus the stopper is held 

 firmly in place. The tension is then released from the air-cushion. This 

 apparatus functionates very satisfactorily, raising the man or lowering him 

 upon the knife-edges of the balance with the greatest regularity and ease. 



