470 



BACTERIOLOGY. 



provided with a globe or reservoir having a capacity of 250, 500 or 1000 

 CO. The lower end is provided with a flange (/) which is 2 cm. wide 

 and about % cm. thick. The flange is ground on the lower surface. 

 The upper surface of the flange, in the position shown in Pig. 66, 

 should be parallel with the ground surface and not sloping. This is 

 necessary in order to prevent the clamps from slipping off. The 

 ground surface of the flange must form a perfect right angle with 

 the inner wall of the cylinder (see Fig. 67). This is necessary in order 

 to give a proper support to the shoulder of the bougie. 



Fig. 67. Connections for the filter. 

 a — Flangre of cylinder; ^—Shoulder of 

 filter; i, 2 and 3— Rubber rings; 4— Metal 

 plate. 



The manner of obtaining a perfectly tight joint is shown in Fig. 

 67. Before proceeding to make the connections the cylinder should 



be inverted so that the globe rests on 

 a small ring of a retort stand, with the 

 flange uppermost. A rubber ring (Fig. 

 * 67, 1) is slipped over the bougie and 

 brought up against the shoulder. This 

 s ring should not be made of very soft 

 rubber inasmuch as it would expand 

 laterally and crush the bougie when 

 the clamps are applied. Ordinary 

 cloth-covered rubber, from which the 

 cloth has been torn will answer the 

 purpose very well. The rubber ring 

 is 2-3 mm. thick and 5 cm. in diameter. 

 The circular opening should be cut so 

 as to allow the ring to slip easily over 

 the bougie (about 2.7 cm. in diameter). The bougie provided with the 

 rubber ring is then inserted into the cylinder. 



Another rubber ring (Fig. 67, 2) is now slipped over the mouth of 

 the bougie. This ring is \%-1 mm. thick, 4 cm. in diameten and has a 

 central opening which is 1.3 cm. in diameter. The thick rubber ring 

 (Fig. 67, 3) is then placed in position. This should be 14-15 mm. thick 

 and should be 7 cm. in diameter. The central opening is cut slanting 

 so that the upper diameter is 4>^ cm., while that below is 5>^ cm. A 

 brass or iron plate about 2 mm. in thickness is then placed on top. 

 This plate has the same diameter (7 cm.) as the flange, and the central 

 opening is 2.2 cm. in diameter. 



Three clamps such as are employed in connection with the 

 author's anaerobic apparatus (p. 313), are then applied. These are 

 sufficient for vacuum filtration, but in case the liquid is to be sub- 

 jected to a positive pressure of 60 or 80 pounds, it is well to add a 

 fourth clamp. 



