FILTRATION OF BACTERIAL LIQUIDS. 



471 



The mouth of the sterile bougie is now flamed and connected 

 with the sterile glass tube which passes through the rubber stopper. 

 A glass globe similar to that of Martin can be used in place of an 

 Erlenmeyer flask to receive the filtrate (Fig. 68 B). The cylinder is 

 now inverted and connected with the receiver (Fig. 66 e). 



Ordinary liquids can be filtered by the aid of a Chapman aspira- 

 tor. If the liquid under these conditions filters slowly, the neck of 

 the globe (Fig. 66 h) should be connected 

 with a tank containing compressed air. 

 When pressure is applied care must be 

 taken to prevent the stopper or the glass 

 tube from being blown -out of place. 

 The end of the glass tube after it has 

 been slipped through the rubber stopper 

 is softened in the flame and then flanged 

 by means of a piece of charcoal or a nail. 

 The stopper, when inserted, should be 

 wired securely in place. A brass ring 

 (ft), placed on the upper side of the stop- 

 per, will prevent it from being cut by 

 the wires. 



The compressed air is contained in 

 a small steel cylinder such as is used by 

 physicians for atomizing purposes. A 

 cheap substitute can be made by con- 

 necting a domestic, hot-water tank with 

 a pressure gauge and a bicycle pump. 



The Berkef eld filter can be attached F IG 58 A Berkefeld filter showing 

 to the glass cylinder in a somewhat simi- yS^SSfSf^^.^Kf. 

 lar manner. An iron plate (Fig. 68 6) 5-6 



mm. thick and 7 cm. in diameter is provided with a central opening 

 (1.2 cm. diameter) just sufficient to allow the nozzle of the filter to pass 

 through. A rubber ring (Fig. 68 a), 7 cm. in diameter and 2 mm. thick, 

 with a central opening 3 cm. in diameter, is placed between the glass 

 flange and the iron plate. The whole is then clamped securely. . 



In place of the Erlenmeyer vacuum flask (Fig. 66 e), a glass globe 

 like that shown in Fig. 68 B can be employed to advantage. The three 

 tubes (d, e, /) are plugged with cotton and the globe is then sterilized 

 in the dry-heat oven. The tube d, after removal of the plug, is con- 

 nected with the bougie by means of the sterile rubber tube c. The 

 tube / is connected in like manner with a rubber tube to the drawn- 



