1879.] Mr Shaw, On experiments with mercury electrodes. 313 



On Feb. 10, after the apparatus had been in use ten days, there 

 were small white distinct crystals scattered in the movable surface of 

 the mercury. In order to determine their nature the current was 

 allowed to pass several days longer. The crystals were then 

 collected, and their properties compared with those of known 

 mercury salts, as described in Otto's Chemistry. They were 

 in every particular identical with those of mercurous sulphate. 

 The fluid also contained a large quantity of mercury in solution. 



It will be noticed from this series of experiments that a much 

 smaller E.M.F., viz. 21 Daniell, suflticed to prevent the occurrence 

 of the current due to the diminishing surface, but that an effect 

 still remained when the mercury surface was increased. 



In order to avoid the difficulty of the passage of so large a 



Fig. 2. 



permanent current, i.e. uncompensated by the e.m.f. of polariza- 

 tion, in consequence of which the needle had to be reduced to its 



