238 EXPERIMENTAL INVESTIGATIONS. 



galvanometer, while a strip of amalgamated zinc immersed 

 in the same liquid communicated with the other extremity ; 

 at the instant of communication an energetic current was in- 

 dicated, which however immediately diminished in intensity, 

 and at the end of a few minutes the needle returned to zero ; 

 scarcely any gas was evolved, and of the few bubbles which 

 appeared as much could be detected on the surface of the 

 zinc as of the mercury. 



3. With the same arrangement I substituted for the mer- 

 cury a strip of platinum well amalgamated. In this case, as 

 before, after a few minutes the current became null, or so 

 feeble as to require a delicate instrument to indicate its exist- 

 ence ; and if, after the cessation of the current, the zinc was 

 changed for unamalgamated platinum, this latter evolved tor- 

 rents of hydrogen, and the needle indicated a violent current 

 in a contrary direction. 



4. With things arranged as in experiment 2, I employed 

 a solution of sulphate of copper as an electrolyte instead of 

 acidulated water ; an energetic and constant current was pro- 

 duced, the mercury became amalgamated to saturation with 

 reduced copper, and the precipitation of copper upon this 

 amalgam continued as long as crystals of the sulphate were 

 added to the solution. 



By these experiments it appears that mercury, which in its 

 normal state is well known to be inefficient as the positive 

 metal of a voltaic combination, is in many cases equally in- 

 efficient as a negative metal, from its faculty of combining with 

 the cations of the electrolytes, which, by rendering it equally 

 positive with the metal with which it is voltaically associated, 

 cause the opposed forces to neutralise each other. But if, as in 

 experiment 4, the cation of the electrolyte is not of a highly 

 electro-positive character, the zinc (or other associated metal) 

 retains its superior oxidability and the voltaic current is not 

 arrested. The application of these experiments to the pheno- 

 mena presented by amalgamated zinc is evident ; all the hete- 

 rogeneous metals with which the zinc may be adulterated, and 

 which form minute negative elements, being amalgamated, 

 become by polarisation equally positive with the particles of 

 zinc, and consequently without the presence of another metal 



