132 



BACTERIOLOGY 



passed through the jar for two hours or more. It is well to keep 

 all flames away from the apparatus as a precaution against ex- 

 plosion of the hydrogen when mixed with air. 



Pig. 58. — Tripod and siphon flask for anaerobic culture by combined hydrogen and 



pyrogallate method. ' 



The hydrogen is generated by the action of 25 per cent sul- 

 phuric acid on granulated zinc. It should be purified by passing 

 through a wash bottle of alkaline lead acetate solution, a second 



