REPLACING THE AIR BY A HYDROGEN ATMOSPHERE 153 



Fia. 77 



level of the fluid in A and displaces it downward. As soon as the fluid 

 has receded from the zinc no more hydrogen is developed and an 

 equilibrium of pressure is established in the 

 apparatus. Whenever more hydrogen is 

 needed all that is necessary is to open the 

 stopcock, when the fluid from the funnel 

 falls into the lower globe, rises into the 

 upper globe, comes in contact with the 

 zinc, and hydrogen is at once developed. 

 When the zinc has all been dissolved, or 

 when the dilute acid has become exhausted, 

 it is necessary to refill the apparatus. When 

 working with hydrogen it is necessary to 

 remember that the gas is not only combus- 

 tible, but forms, when mixed with the oxygen 

 of the atmospheric air in the proportion of 

 two volumes to one volume of oxygen, a very 

 explosive gas. Hydrogen generated in the 

 Kipp apparatus from ordinary commercial 

 zinc contains, as contaminations, sulphur, 

 arsenic, and also some oxygen. These 

 bodies must all be removed before the gas 

 can be used in the anaerobic cultures. This 

 is accomplished by leading the impure 

 oxygen through three wash bottles contain- 

 ing, respectively, the following solutions: 

 No. 1, a 10 per cent, watery solution of 

 nitrate of lead; No. 2, a 10 per cent, solu- 

 tion of nitrate of silver, and No. 3, an alkaline 

 solution of pyrogallic acid. If chemically 

 pure zinc and chemically pure sulphuric 

 acid diluted with distilled water is used then 



FIG. 76 



Novy jar for anaerobic cultures. 



Buchner's anaerobic tube. 

 The fluid consists of pyro- 

 gallic acid dissolved in 10 

 per cent, soda solution. By 

 Wilson's method the tubes are 

 charged with pieces of caustic 

 potash covered with pyrogallic 

 acid. (Park.) 



