48 METHODS OF STERILISATION 



7. Open the tap of the gas cylinder; then open the 

 tap on the entry tube of the filter cylinder and raise 

 the pressure in its interior until the desired point 

 is recorded on the manometer. Maintain this pressure, 

 usually one or one and a half atmospheres, until filtra- 

 tion is completed, by regulating the tap on the entry 

 tube. 



Some forms of filter candle are made with the open 

 end contracted into a delivery nozzle, which is glazed. 

 In this case the apparatus is fitted up in a slightly 

 different manner; the fluid to be filtered is contained 

 in an open cylinder into which the candle is plunged, 

 while its delivery nozzle is connected with the filter 

 flask by means of a piece of flexible pressure tubing 

 (previously sterilised by boiling), as in figure 39. 



