A METHOD OF ANAEROBIC PLATING 341 



gas, and by leading the gas from a suitable generator in through 

 one of the rubber stoppers, (allowing the air to escape by way 

 of the opposite loosely-stoppered opening) the oxygen pressure 

 inside the inclosed space may be reduced to less than 1 mm. by 

 the use of only about 200 cc. of the gas. The holes are then 

 securely closed and the plates are ready for incubation. 



Oxygen- and C02-free air has been secured by the following 

 method : Connect in series one or more of the sealed Petri dishes 

 with two wash bottles containing a 5 per cent pyrogallic acid 

 10 per cent caustic soda solution. Force air slowly through 

 this train and allow the displaced air to escape byway of the op- 

 posite outlet of the sealed Petri dish. 



When hydrogen is to be used for displacing the air, two wash 

 bottles are required: One of AgNOa solution for traces of ASH3, 

 and one of lead acetate solution for H2S. 



In general, satisfactory anaerobic conditions are obtained 

 when the volume of H2 or N2 allowed to pass through the sealed 

 plates amounts to ten times the volume of air inclosed by the 

 plates and their connections. 



