ENERGY CHANGES INVOLVED IN THE DILUTION OF 

 ZINC AND CADMIUM AMALGAMS. 



By Theodore William Richards and George Shannon Forbes. 



INTRODUCTION. 



Nearly half a century ago a French physicist named Gaugain published a 

 note 1 on his investigation of a voltaic pile whose " negative metal " was 

 a dilute amalgam of zinc or cadmium. At first the electromotive force rose 

 very rapidly when the proportion of oxidizable metal was increased, but 

 beyond a certain point the introduction of fresh quantities of zinc caused no 

 further variation. He concluded that these phenomena were occasioned by 

 the affinity of the mercury for the amalgamated metal, an affinity which 

 varied with the proportions of the amalgam. He also found that cadmium 

 always had an electromotive force greater than its amalgams, no matter 

 whether these contained cadmium in mere traces or in sufficient quantities 

 to form a solid compound. 



Shortly after, M. E. Becquerel 2 published an exhaustive and scholarly 

 treatise on the " Disengagement of electricity in voltaic piles." His experi- 

 mental skill and his logical interpretation of results appear remarkable when 

 we consider the limitations of exact knowledge at that time. In this paper 

 he suggested the probable existence of an approximate relation between 

 the heats of combustion of different metals and their electromotive forces, 

 and pointed out the importance of further work in this direction. Among 

 the many substances examined by him were amalgams of zinc, manganese, 

 ammonium, barium, calcium, sodium, and potassium. The dependence of 

 electromotive force upon concentration was noted over a wide range, but no 

 attempt was made to explain it. Very little improvement in the experi- 

 mental or theoretical treatment of amalgams was made for thirty years 

 after the publication of this work. 



In 1863 Crova 3 concluded that amalgams containing from 1 to 5 per cent 

 of zinc could be substituted for the zinc in a Daniell cell without change of 



1 Comptes Rendus, 42, 430 (1856). 



2 Ann. Chem. Phys., 48, 266 (1856). 

 "Ibid., 68, 458 (1863). 



