FILTRATION 55 



through the Berkefeld. All give a germ-free filtrate, but 

 the last should be employed if the fluid is thick or con- 

 tains many particles ; a preliminary filtration through 

 paper is an advantage. A useful method of conducting 

 filtration is the following : The filter " candle " (B, Fig. 5) 

 is connected by a short length of pressure tubing with 

 a piece of glass tubing passing through a rubber cork 

 in the neck of an ordinary filtering flask c. The " candle " 

 is placed in a jar A, such as a glass measure or urine-jar, 

 which is filled up with the solution to be filtered. The 

 lateral branch of the filter flask is then connected with the 

 air-pump. On exhausting, the fluid passes through the 

 filter " candle " over into the filtering flask, in which it is 



FIG. 0. Platinum needles. 



collected. Before use the i( candle " should be well 

 scrubbed and some water or \ per cent, carbolic run 

 through to clean it, and the whole may be sterilised in 

 the steamer for an hour or two. After use the same 

 process should be repeated to cleanse it. 



Flasks, beakers, and test-tubes. A good supply of these 

 of various sizes is required : Erlenmeyer and ordinary 

 shapes, tall and short forms of beakers, etc. A few 

 " yeast flasks " are also useful (see Fig. 17, p. 92). 

 Enamelled iron ware, jugs, saucepans, mugs, etc., may 

 replace glass for many purposes. 



The most useful size of test-tube is 5 in. x f in. ; a few 

 larger sizes and " boiling tubes " should also be kept. 



Platinum needles (Fig. 6). Two or three platinum 

 needles are required. They consist of about 2 in. of 

 platinum wire in a handle of glass rod. One end of a 



