88 CULTIVATION OF ANAEROBIC MICRO-ORGANISMS 



2. By displacing the oxygen of the atmosphere by an 



inert gas. 



The air in a liquid can be displaced by passing a current of an inert gas 

 through it. Hydrogen, carbonic oxide, nitrogen and ordinary coal gas 

 have all been suggested for the present purpose. 



A. Hydrogen. For the growth of anaerobes, hydrogen is preferable to the 

 other gases mentioned. Not only is it easily prepared, but it has no injurious 

 effect on the organisms. 



A convenient form of apparatus for readily obtaining a continuous supply 

 of hydrogen is that illustrated in fig. 75. The bottle A contains a 1 in 6 



FIG. 75. Apparatus for yielding a continuous supply of hydrogen. 



solution of pure sulphuric acid in water. The bottle B contains some pieces 

 of broken glass at the bottom, and above this a layer of granulated zinc. 

 By simply raising the bottle A and opening the tap R a stream of hydrogen 

 will issue from the tube T ; similarly, by closing the tap R and lowering A 

 to the level of B the supply is stopped. To remove impurities, especially 

 oxygen, it is desirable to wash the hydrogen as it issues from the bottle B 

 by passing it through the following solution : 



Caustic potash, 50 per cent, in water, - - 50 c.c. 



Pyrogallol, - 1 gram 



contained in a wash-bottle F. 



It is even better to have two wash-bottles, one containing a solution of potassium 

 permanganate slightly acidified with sulphuric acid, the other a solution of potas- 

 sium permanganate made slightly alkaline with caustic soda. These solutions 

 must be frequently renewed. The method is particularly useful for removing 

 traces of hydrocarbons and phosphides and arsenides of hydrogen. 



The hydrogen before being passed through the culture medium should 

 be tested by means of indigo white, to ascertain that it is quite free from 

 traces of oxygen (p. 92). 



[Hydrogen is, however, most conveniently obtained by keeping a cylinder 

 of the compressed gas in the laboratory. Cylinders of the gas can be obtained 



