Death in Closed Vessels 553 



confinement, at 7.2 atmospheres only 0.5 per cent, and so on. We 

 shall see how far this hypothesis is from the truth. 



In the experiments which I shall report, I used sparrows almost 

 exclusively. Their small size allowed me to use glass apparatuses 

 whose advantages are evident, but whose dangers, when highly 

 compressed air is used, are no less evident. In fact, glass has this 

 serious disadvantage, that one is never sure that an apparatus 

 which withstood a certain pressure at a certain moment, will be 

 able to withstand it again. Furthermore, under the influence of 

 atmospheric changes, the metallic pieces in which it must be held 

 expand or contract in lengthy experiments, following a law dif- 

 ferent from that of the glass, which is thus subjected to pulls in 

 opposite directions which threaten its solidity and may even crack 

 it without the application of any pressure, since these glasses are 

 very thick. At any rate, thanks to the precautions we used, the 

 accidents which occurred never had serious consequences. 



One of the apparatuses which I used most frequently and which 

 allows me to compress air up to 25 atmospheres, consists of a glass 

 cylinder, of a capacity of 650 cc. and a thickness of 18 millimeters, 

 protected by a large-mesh jacket. This reservoir is topped with a 

 bronze part, which exactly fits its orifice, or rather fits another 

 fixed bjonze plate which is fastened to the stand on which the 

 reservoir rests by four steel columns which pass through both the 

 fixed part and the movable part. These two parts are solidly held 

 by four movable nuts which screw on the steel columns. All of 

 this is plainly visible in Figure 20. 



A Bourdon manometer, which indicates the pressure of the air 

 in the reservoir, is fixed on the immovable plate. A screw cock 

 with a very small opening at the right of the cylinder permits one 

 to take a sample of this air whenever he wishes. To do so, one fits 

 to this cock a rubber tube which dips into a mercury basin below 

 a graduated tube; if then this cock is opened carefully, the com- 

 pressed air escapes from the apparatus and enters the graduated 

 tube; I always took care, of course, to let out a certain quantity 

 before taking what I intended to analyze. 



The air is compressed in the reservoir by means of a small force- 

 pump; I had this pump enclosed in a metal jacket through which 

 a constant stream of water passes; the operation of it is then less 

 painful and — which is more important — no hot air is pumped to 

 the animal. I can thus reach a pressure of 25 atmospheres in about 

 20 minutes. Finally, a large cock fastened to the movable part 

 topping the cylinder opens or closes the apparatus hermetically. 



