Displacement of the Air by Inert Gases 229 



contain and has its stopper so replaced that the openings in 

 the neck and stopper correspond. Hydrogen gas is passed 

 through until the air is displaced. This usually takes sev- 

 eral hours, as the cotton stoppers retain the air in the test- 

 tubes and prevent rapid diffusion. When the air is all dis- 

 placed, the stopper is turned so that the tubes are closed. 

 If it be desired to expedite matters a pump can be used to 

 withdraw the air, after which the hydrogen is permitted to 

 enter. 



Botkin's apparatus is intended for cultures in Petri dishes. 



Cottonf>lug 



Fig. 53 Franker s method of 

 making anaerobic cultures. 



Fig. 54. Liborius' tube for 

 anaerobic cultures. 



It consists of three parts a deep dish of glass (6), a stand 

 to support the Petri dishes to be exposed (c), and a bell- 

 glass (a) to cover the stand and fit inside of the dish. It 

 can easily be understood by reference to figure 55. The 

 prepared dishes are stood uncovered in the rack, which is 

 then placed in the dish forming the bottom of the appara- 

 tus, and into which liquid paraffin is poured to a depth of 

 about two inches. The bell-glass cover is now stood in 

 place and hydrogen gas is conducted through previously 

 arranged rubber tubes (d, e). As soon as the air is displaced 



