FILTRATION OF CULTURES 



79 



bougie below. The extreme point of the latter is left exposed, 

 and the whole apparatus, being supported on a stand, is con- 

 nected by a glass tube with the lateral tube of the flask b ; the 

 tube a is connected with the exhaust-pump. The fluid to be 

 filtered is placed between the funnel and the bougie in the 

 space e, and is sucked through into the flask b. The efficiency 

 of such a filter, especially when small amounts of fluid are being 

 dealt with, is much increased if when the level of the fluid falls 

 below the upper end of the candle a closely fitting test-tube is 

 slipped over the latter. By this device the leakage of air 

 through the exposed part of the candle is prevented. There 

 are now in the market candles with glass sheaths cemented into 

 a nickle-plated fitting from the lower part of which a metal 

 tube emerges; the latter 

 can be passed through a 

 rubber stopper into a filter 

 flask. (2) This modifica- 

 tion is shown in Fig. 33. 

 Into the narrow part of 

 the funnel an indiarubber 

 bung is fitted, with a per- 

 foration in it sufficiently 

 large to receive the candle, 

 which it should grasp 

 tightly. 



(c) Muencke's modifica- 

 tion of the Chamberland 

 filter is seen in Fig. 34. 

 It consists of a thick- 

 walled flask a, the lower 



part conical, the upper cylindrical, with a strong flange on the 

 lip. There are two lateral tubes, one horizontal to connect with 

 exhaust- pipe, and one sloping, by which the contents may be 

 poured out. Passing into the upper cylindrical part of the 

 flask is a hollow porcelain cylinder b, of less diameter than the 

 cylindrical part of flask a. It is closed below, open above, and 

 rests by a projecting rim on the flange of the flask, an asbestos 

 washer, c, being interposed. The fluid to be filtered is placed 

 in the porcelain cylinder, and the whole top covered, as shown 

 at /, with an indiarubber cap with a central perforation ; the 

 tube d is connected with the exhaust-pump, and the tube e 

 plugged with a rubber stopper. For filtering small quantities 

 of fluid the apparatus shown in Fig. 35 may be used. It 

 consists of a small Chamberland bougie fitted by a rubber tube 



FIG. 34. Muencke's modification of 

 Chamber-laud's filter. 



