6 ENERGY CHANGES INVOLVED IN DILUTION OF AMALGAMS. 



a calculation of h, the heats of amalgamation of zinc and cadmium, from 

 the temperature coefficient of cells of the type 



Electrolytic zinc, Zinc sulphate, Zinc amalgam. 



If the equation of Helmholtz is thrown into the form E = T^S, + h, 

 h can be found by assuming that -j= and h are nearly constant at all tem- 

 peratures. The result for zinc agreed so well with Favre's " calorimetric 

 determination that confidence was placed in the value proposed for cadmium. 



Another significant paper was published by Cady 18 in December of the 

 same year. Working with sodium and calcium amalgams (the former more 

 concentrated than Meyer's), he obtained molecular weights for the two 

 metals in striking agreement with Ramsay's results. He now measured Q, 

 the heat of dilution of sodium amalgam, and found that its conversion into 

 electrical energy would account for the abnormally high potential of the 

 corresponding cell. In other words, Meyer's expression must be replaced, 

 in such a case, by the formula 



vEF Q + RT In *U 



Ramsay's value for sodium could be made normal upon the application of 

 similar treatment. Cady also showed that the electromotive force between 

 tin amalgams in potassic stannate, where tin is quadrivalent, is half that 

 observed in stannous chloride. Lewis, in a paper published in the Proceed- 

 ings of the American Academy (volume 35, 1899), independently arrived 

 at the same equation by thermodynamic reasoning. 



Cady's work prompted Trevor 19 to work out a complicated treatment of 

 the temperature coefficient of amalgam cells. This paper is valuable from 

 the standpoint of pure mathematics, but the experimental facts necessary to 

 verify his assumptions are not within reach at present. 



The next theoretical contribution was made by Haber, 20 who showed the 

 necessity of applying a new correction to the calculated potential of sodium 

 amalgam cells. If sodium dissolves in mercury with the formation of 

 NaHg 6 , the reversible cycle described by Meyer must be amplified by a 

 fourth step the reversible squeezing out of six mols of mercury from the 



17 Jahn. Grundriss der Elektrochemie, p. 8. 



18 Journ. Phys. Chem., 2, 551 (1898). Attention should be called to a correction after- 

 wards made in Cady's paper, without which it is incomplete and erroneous in one 

 feature. Journ. Phys. Chem., 3, 107 (1899). 



10 Journ. Phys. Chem., 3, 95 (1899). 

 20 Zeit. Phys. Chem., 41, 399 (1902). 



