444 



MERCURIAL GAS-PUMP. 



[BOOK ii. 



FIG. 87. DIAGRAMMATIC ILLUSTRATION OF LUDWIG'S MERCURIAL GAS-PUMP. 



A and B are two glass globes, connected by strong india-rubber tubes, a and 

 b, with two similar glass globes A' and B'. A is further connected by means of 

 the stopcock c with the receiver C containing the blood (or other fluid) to be 

 analyzed, and B by means of the stopcock d and the tube e with the receiver D 

 for receiving the gases. A and B are also connected with each other by means 

 of the stopcocks / and g, the latter being so arranged that B also communicates 

 with B' by the passage g'. A' and B' being full of mercury and the cocks A, /, 

 g, and d being open but c and g' closed, on raising A' by means of the pulley p 

 the mercury of A' fills A, driving out the air contained in it, into B, and so out 

 through e. When the mercury has risen above g, f is closed, and g' being opened, 

 B' is in turn raised till B is completely filled with mercury, all the air previously 

 in it being driven out through e. Upon closing d, and lowering B', the whole of 

 the mercury in B falls in B', and a vacuum consequently is established in B. 

 On closing </', but opening g, /, and k and lowering A', a vacuum is similarly 

 established in A and in the junction between A and B. If the cock c be now 

 opened the gases of the blood in C escape into the vacuum of A and B. By 

 raising A', after the closure of c, and opening of d, the gases so set free are 

 driven from A into B, and by the raising of B' from B, through e into the 

 receiver D, standing over mercury. 



