FILTRATION 



47 



4. Heat the whole apparatus in the autoclave at 

 120 C. for twenty minutes. 



METHOD. 



1. Remove the apparatus from the autoclave, and 

 allow it to cool. 



2. Screw home the box carrying the bougie. 



3. Set the apparatus up in position, with its delivery 

 tube (from which the cotton-wool wrapping has been 

 removed) passing through a perforated rubber stopper 

 in the neck of a filter flask. 



FIG. 39. Closed candle arranged for filtering. 



4. Fill the fluid to be filtered into the cylinder and 

 screw on the nut carrying the pressure gauge. (This 

 nut should be immersed in boiling water for a few 

 minutes previous to screwing on, in order to sterilise it.) 



5. Connect the horizontal arm of the entry tube 

 with a cylinder of compressed oxygen (or carbon di- 

 oxide, Fig. 38, b), by means of pressure tubing. 



6. Connect the lateral arm of the filter flask with 

 the exhaust pump (Fig. 38, c) and start the latter 

 working. 



