236 EXPERIMENTAL INVESTIGATIONS. 



ON THE INACTION OF AMALGAMATED ZINC IN 

 ACIDULATED WATER.* 



Phil. Mag., August 1839. 



IT is a well-known fact that the common zinc of commerce, 

 when immersed in water acidulated by sulphuric, phosphoric, 

 or muriatic acid, is rapidly dissolved, evolving torrents of 

 hydrogen gas, while zinc with the surface amalgamated 

 remains inactive under similar circumstances, unless touched 

 by another metal placed in the same solution, in which case 

 hydrogen, amounting to the equivalent of the oxygen which 

 unites with the zinc, is evolved from the surface of the 

 associated metal, and the zinc is tranquilly dissolved. 



M. De la Rive observed that pure zinc is much less vigor- 

 ously attacked by diluted acid than commerical zinc, and has 

 thence, after a careful experimental investigation, concluded 

 that the evolution of gas by common zinc arises from the 

 circumstance of its adulteration by other metals ; thus an 

 infinity of minute voltaic circles is established, the particles 

 of zinc being oxidated, while those of the more negative 

 metals evolve hydrogen ('Bib. Univ./ 1830). This explana- 

 tion does not apply to the inactivity of amalgamated zinc, 

 for, as M. Becquerel asks (' Traite,' vol. v. p. 8), ' Why does 

 not mercury, which by its contact with zinc and acidulated 

 water must also form a voltaic combination, produce a similar 

 effect ? ' 



An accidental circumstance led me to some experiments 

 which I think give a satisfactory answer to this question. The 

 circumstance to which I allude, and which has in all proba- 

 bility been observed by many others, was this : in decom- 

 posing by a voltaic battery water acidulated with sulphuric 

 acid, there happened to be a few globules of mercury at the 

 bottom of the operating cell or glass containing the electrodes 

 of platinum. I remarked that whenever the negative electrode 

 touched the mercury it became amalgamated ; at first I attri- 



* Read before the Royal Academy of Sciences of Paris, on June 24, 1839. 



