FILTRATION 



43 



4. Water injector Sprengel (see Fig. 38, c) pump, or Geryk's 

 pump (an air pump on the hydraulic principle, sealed by means 

 of low vapor-tension oil, Fig. 35). 



If this latter is employed, a Wulff's bottle, fitted as a wash- 

 bottle and containing sulphuric acid, must be in- 

 terposed between the filter flask and the pump, in 

 order to prevent moist air reaching the oil in the 



5. Air filter (vide page 40) sterilised. 



6. Pressure tubing. 



7. Screw clamps (Fig. 36). 



METHOD. 



i. Couple the exhaust pipe of the suc- 

 tion pump with the lateral tube of the FIG. 34. Force- 

 filter flask (first removing the cotton- lainfil 

 wool plug from this latter), by means of pressure 

 tubing, interposing, if necessary, the wash-bottle of 

 sulphuric acid. 



FIG. 35. Geryk air pump. 



