FILTRATION OF CULTURES 



75 



pump. These are usually arranged on a board a, as in Fig. 26. 

 Between the tube / and the pump g, and between the tube d 

 and the filter, it is convenient to insert lengths of flexible 

 lead-tubing connected up at each end with short, stout- walled 

 rubber-tubing. 



Filters are arranged in various ways, (a) An apparatus is 

 arranged as in Fig. 27. The fluid to be filtered is placed jn 

 the cylindrical vessel a. Into this a "candle" or "bougie" 

 of porcelain dips. From the upper end of the bougie a glass 

 tube with thick rubber connections, as in Fig. 27, proceeds to 

 flask b, and passes through one of the two perforations with 

 which the rubber stopper of the flask is furnished. Through 



Fig. 28. — Chamberland's bougie 

 arranged with lamp funnel for 

 filtering a small quantity of 

 fluid. 



Fig. 29. — Bougie inserted 

 through rubber stopper 

 for same purpose as in 

 Fig. 28. 



the other opening a similar tube proceeds to the exhaust- 

 pump. When the latter is put into action the fluid is sucked 

 through the porcelain and passes over into flask b. This 

 apparatus is very good, but not suitable for small quantities of 

 fluid. 



(b) A very good apparatus can be arranged with a lamp 

 funnel and the porcelain bougie. These may be fitted up in 

 two ways. (1) An indiarubber washer is placed round the 

 bougie c at its glazed end (vide Fig. 28). On this the narrow 

 end of the funnel d, which must, of course, be of an appropriate 

 size, rests. A broad band of sheet rubber is then wrapped 

 round the lower end of the funnel and the projecting part of 

 the bougie. It is firmly wired to the funnel above and to the 



