24 



ASSIMILATION. 



[CH. II 



the access of COj while allowing other gases to pass in, 

 the boiled water will after a time become oxygenated. 



A convenient method is the following. A flask A 

 (fig. 4) is filled with spring water which has been freshly 



r^r 



Fig. 4. Exp. 34. 



boiled, and filtered from precipitated calcium carbonate; 

 it is connected with the bottle B, half filled with strong 

 KHO solution. The water in A is boiled 20 minutes, 

 with the stop-cock G left open. The flame is now 

 removed and G is closed. As the flask A cools, air is 

 sucked in by D, and in passing through the KHO in 

 the bottle B, is freed from COjj. The water so prepared 

 is now used for the culture fluid: the vessel containing 



