FILTRATION 45 



the funnel ; adjust a screw clamp to the pressure tubing 

 attached to the lateral branch of the filter flask; screw 

 it up tightly, and disconnect the acid wash-bottle. 



6. Attach the air filter to the open end of the pressure 

 tubing; open the screw clamp gradually, and allow 

 filtered air to enter the flask, to abolish the negative 

 pressure. 



7. Detach the rubber tubing from the lateral branch 

 of the flask, flame the end of the branch in the Bunsen, 

 and plug its orifice with sterile cotton- wool. 



8. Remove the filter candle from the mouth of the 

 flask, flame the mouth, and plug the neck with sterile 

 cotton- wool. 



9. Disinfect the filter candle and separatory funnel 

 by boiling. 



If it is found necessary to employ pressure in addi- 

 tion to or in place of suction, insert a perforated rubber 

 stopper into the mouth of the separatory funnel and 

 secure in position with copper wire; next fit a piece of 

 glass tubing through the stopper, and connect the 

 external orifice with an air-pressure pump of some 

 kind (an ordinary foot pump such as is employed for 

 inflating bicycle tyres is one of the most generally use- 

 ful, for this purpose) or with a cylinder of compressed 

 air or other gas. 



In order to filter a large bulk of fluid very rapidly it 

 is necessary to use a higher pressure than glass would 

 stand, and in these cases the metal receptacle designed 

 by Pakes (Fig. 38, a), to hold the filter candle itself as 

 well as the fluid to be filtered, should be employed. 

 (A vacuum must also be maintained in the filter flask, 

 by means of an exhaust pump, during the entire 

 process.) 



This piece of apparatus consists of a brass cylinder, 

 capacity 2500 c.c., with two shoulders; and an opening 

 in the neck at each end, provided with screw threads. 



A nut carrying a pressure gauge fits into the top 



