OF ZINC, CADMIUM, LEAD, COPPER, AND LITHIUM 



53 



The cell was then filled, using this amalgam in cup I, diluting it in the 

 three other cups of the multiple cell, and using a solution of copper sul- 

 phate in 0.0125 normal sulphuric acid as electrolyte. As table 15 shows, 

 no constant results could be obtained. 



At first the potentials were all higher than the theoretical and later they 

 all became lower. Evidently the copper reacts with the electrolyte, form- 

 ing cuprous salt, and this reaction proceeded further in proportion in the 

 case of the more concentrated amalgam, because of its lesser volume and 

 larger proportion of exposed surface. 42 Another series of readings was 

 then tried, with additional precautions. The original amalgam was, 

 in this case, made by standing amalgamated copper wire in mercury, in an 

 atmosphere of hydrogen, for several days the mercury being frequently 

 shaken. It was drawn into the pipettes in the usual way, wholly out of 

 contact with the air. The electrolyte, again slightly acid, was also allowed 

 to stand in an atmosphere of hydrogen over a copper amalgam for several 

 days. In spite of these precautions no more constant results were obtained, 

 as table 16 shows. 



TABLE 16. 



Evidently the electrolyte was not saturated with cuprous salt, in spite 

 of its week's contact with the amalgam. Considering the small concentra- 

 tion in the amalgam and the fact that it can act upon the electrolyte only 

 at the surface in mercury, this is perhaps not surprising. 



In the light of these experiments, let us turn back for a moment to the 

 results of Meyer and Spencer. The latter's are wholly comprehensible. 

 His first cell alone was dilute enough to be beyond the limit of saturation, 

 and that gave a result like ours. The other more concentrated amalgams 

 must have contained traces of solid, and if he had waited until they reached 

 equilibrium, his cell III must have reached zero potential. His figures are 

 just what one would have expected. 



Meyer's figures are harder to explain. How he could have attained his 

 results from amalgams containing a large excess of solid phase will 



a See for example, Richards, Collins, and Heimrod, Proc. Am. Acad., 35, 125 

 (1899); Zeit. phys. Chem., 32, 324 (1900). 



