Death in Closed Vessels 507 



Subchapter I 

 PRESSURES BELOW ONE ATMOSPHERE 



1. Experimental Set-Up. 



The apparatus with which I made my experiments on the com- 

 position of the confined air in which animals die under pressures 

 less than one atmosphere, is very simple. 



On a table four glass discs are fixed, mounted on copper plates 

 like those of pneumatic machines (Fig. 15) A, so that four experi- 

 ments can be carried on side by side. Since the four parts of the 

 apparatus are absolutely alike, only one need be described. 



The disc is pierced in the center by an orifice through which 

 passes a lead tube topped with a movable cap B, which will prevent 

 the animal from being moved by the air suction. This tube leads to 

 a cross-pipe CC, which communicates with a suction pump oper- 

 ated by a steam engine; a cock D permits or cuts off communica- 

 tion. Between the cock and the mouth B extends a long glass 

 tube with two bends EFGH, which contains mercury. It is clear 

 that when the bell-jar I is fixed on disc A and the suction pump 

 is set in motion, the mercury will rise in the closed arm of the 

 glass tube, and that the difference between the levels tin' meas- 

 ured on the divided rule K will show exactly the amount of 

 decompression; e is a bulb intended to hold the mercury which 

 a piston stroke that was too strong might suck into the lead tubes. 

 The bell- jar I ends in a neck closed with a rubber stopper through 

 which pass a thermometer L and a cock M; the lower extremity of 

 the latter has a rubber tube, so that the air, which is extracted 

 by the process I shall explain in a moment, comes from the middle 

 of the bell- jar. 



If these experiments are to give a satisfactory result, the ap- 

 paratus must be hermetically sealed and must keep exactly the 

 degree of vacuum to which it has been brought; the least opening, 

 permitting a little air to enter, may be the cause of serious errors, 

 as I found to my expense. To obtain the necessary hermetical 

 sealing, I immersed in water all the cracks through which the air 

 might enter. And therefore, the glass disc, on which the bell-jar 

 is fastened by tallow as usual, is surrounded by a projecting circle 

 of zinc N, into which water is poured; likewise, rubber capsules 

 O and P form a hydraulic seal for the adjusting of the cock M 

 and the manometric tube E; the cocks D and Q are immersed in 

 water in the receptacle R and the zinc gutter SS'. This device 

 insures that, if the closing was not perfect, water would enter 



