198 



DR. R. ANGUS SMITH 



A in the annexed figure : connected with the ball, there is 

 a valve such as is used in air-pumps, preventing all entrance 

 of air, but allowing it to pass out. Then, again, on tube 

 B there is a valve of the same kind, preventing all egress 

 of air, but allowing it to enter. The little instrument is 

 therefore in reality an air-pump and a condenser. The air 

 passes in at B, and goes out at A. 



It is well to use always the same amount of solution, 

 which may be, as in the previous method, half an ounce. 

 If this liquid is put into an open vessel there is an escape 

 of the carbonic acid, which ought to be retained, and also 

 a collection of some from the atmosphere, which ought not 

 to be absorbed. It is better, therefore, to use a bottle as 

 at C, with a small entrance-tube. 



The bottle should have the same capacity as the ball + 

 the space required for the liquid. Previously to commencing 

 the experiment, it must be filled with the air of the place : 

 this is done by one or two pressures of the ball. The liquid 

 and cork are then put in their places, and the whole shaken 

 up. That counts for one ballful of air. The balj is then 



