THE FILTRATION OF CULTURES. 



Si 



it with rubber solution strips of the rubbered canvas used 



for mending punctures in the outer case of a bicycle tyre. 



A manometer tube 



(b) and a receptacle 



(f) (the latter to 



catch any back flow 



of water from the 



pump if the filter 



accidentally breaks) 



are intercepted be- 



tween the filter and 



the pump. These 



are usually arranged 



on a board a, as in 



Fig. 29. Between 



the tube / and the 



pump g, and be- 



tween the tube d 



and the filter, it is 



convenient to insert 



lengths of flexible 



FIG. 29. Geissler's vacuum pump arranged 

 w ' 1 ^ manometer for filtering cultures. (The tap 



Hi hi no- rnn and pump are intentionall y drawn to a lar S er 

 " scale than the manometer board to show details.) 

 nected up at each 



end with short, stout-walled rubber-tubing. 



Various modifications of the 

 filter are used, (a) An ap- 

 paratus is arranged as in Fig. 

 30. The fluid to be filtered 

 is placed in the cylindrical ves- 

 sel a. Into this a " candle " or 

 "bougie" of porcelain dips. 

 From the upper end of the 

 bougie a glass tube with thick 

 FIG. 30. Chamber-land's rubber connections, as in Fig. 



candle and flask arranged for proceeds to flask b and 



filtration. . , 



passes through one of the two 



perforations with which the rubber stopper of the flask 

 is furnished. Through the other opening a similar tube 

 6 



