of Hydrogen and some other Gases. 



341 



Another eudiometer, which is also filled with hydrogen, is 

 placed side by side ; it serves as a control for the change of 

 the atmospheric pressure and the temperature of the tank. 

 The connexion of tubes b to tube e is then made by a rubber 

 tube d. By means o£ the microscopes Q, the head of the 

 meniscus of mercury in b is observed ; the smallest division 

 of the ocular micrometer corresponds to 1/6*6 mm. 



Fisr. 9. 



t M 



nn 



B 



v 



By repeated^ blowing the air at the open end of the rubber 

 tube g, we can easily make the height of the meniscus in 

 tubes b settle to a correct position. The height of the 

 meniscus is then read with microscopes Q. When the tem- 

 perature of the tubes b becomes equal to that of the water in 

 the tank, an electric discharge is passed for 6 minutes 

 through the eudiometer with an induction coil (30 cm. 

 maximum spark distance) working at 12 volts. After an 

 hour, when the temperature of the gas becomes again equal 

 to that of the surroundings, the reading of the meniscus in 

 the tubes is again taken. If the readings of the two micro- 

 scopes undergo the same amount of change, it is to be 

 concluded that the hydrogen does not contain an amount of 

 oxygen which can be detected with the present apparatus. 

 If, however, some difference in the readings of the micro- 

 scopes be observed, another electric discharge is passed, and 



