.252 



J. M. Lewis 



ferred, subsequent to its platinising, and after a thorough wash- 

 ing in distilled water. 



The second vessel is provided with a 5 per cent, solution 

 »of sulphuric acid, and when the electrodes have been connected 



~t~- 



u 



Fig. 9. 



as before, i.e., making the hydrogen electrode negative in the 

 arrangement, it is left to bubble vigorously for about ten minutes. 

 It must now receive a most careful washing, and after satura- 

 tion with hydrogen, be preserved in a beaker of distilled water. 



As Michaelis points out, the hydrogen electrode does not need 

 replatinising frequently when protein solutions only are used. 



It does not readily make small errors, but if out of order 

 will give quite impossible results. A deterioration of the elec- 

 trode is indicated when it takes a long time to obtain a con- 

 stant reading. In taking readings Michaelis recommends that 

 they should be made every ten minutes, and should not be 

 .accepted until three successive readings are identical. Before 



