554 



MERCURIAL GAS-PUMP. 



[BOOK ii. 



FIG. 73. 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 analysed, 

 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 k, f, 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 g', 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. 



