54 A MANUAL OF BACTERIOLOGY 



useful for evaporation in vacuo. They should stand on a 

 square of thick ground glass. To make an air-tight joint 

 the surface of the rim of the bell- jar, which must be quite 

 clean, should be well greased and pressed thoroughly 

 home on the ground-glass plate. A thick ridge of grease 

 should then be plastered all round the angle formed by the 

 rim of the bell-jar and the glass plate. Thick rubber 

 pressure tubing must be used for connections, and all 

 joints should be well greased. A mercurial gauge is a 



FIG. 5. Fleuss exhaust pump, arranged for filtration. 



useful addition to show the amount of exhaust and the 

 occurrence of leakage. The ordinary glass filter pumps 

 used in chemical work and actuated by a stream of water 

 are also useful for many purposes. 



Porous filter candles. The forms which are generally 

 employed are the Pasteur-Chamberland, the Doulton, and 

 the Berkefeld. These consist of " candles " composed in 

 the first two of unglazed porous porcelain, in the last of a 

 specially prepared diatomaceous earth. The filtration 

 through the Pasteur-Chamberland is much slower than 



