88 PROCEEDINGS OP THE AMERICAN ACADEMY. 



amalgams follow rigidly the laws of dilute solutions, oa account of wide 

 deviations in the observed values. 



It has been the object of the present research to determine the electro- 

 motive forces of cells of the above type at varying temperatures, and 

 with amalgams of all degrees of concentration, and also of similar cells 

 in which one amalgam is replaced by the pure metal. Zinc and cad- 

 mium as metals, and normal solutions of their sulphates as electrolytes, 

 were chosen as best adapted to the purpose. The experimental results 

 were studied in relation to the two following equations: — 



£= — Tin — = .0000^0 T log -^. (2) 



dE _E Q 



Equation (2) is the simpler form that (1) assumes when the atomic 

 weight is substituted for M. E is the observed electromotive force ; R 

 is the gas constant ; n, the valence of the metal in question (« = 2 in the 

 case of zinc and cadmium) ; e^ is the quantity of electricity in coulombs 



which is carried by one gram-equivalent; In — is the natural logarithm 



of the concentration ratio. A comparison of this formula with the 

 experimental results shows the extent of applicability of the laws of 

 dilute solutions to amalgams (assuming the molecule of the metal to be 

 monatomic when amalgamated). 



Equation (3) is the Ilelmholtz equation for the temperature coefficient 

 of a cell, where Q is the heat given off by the cell during a transfer of 

 n gram-equivalents. In the cells under consideration the only change 

 produced by the current is the transfer of metal from the solid electrode 

 to the amalgam, or from one amalgam to another more dilute. Q then 

 represents either the heat of amalgamation of w gram-ecjuivalents (one 

 gram-atom) of the metal, or the heat of dilution of an amalgam contain- 

 ing one gram-atom. The use of this equation permits the calculation of 

 these quantities from the temperature coefficient of the cell.* 



Since the heat capacity of the amalgam is approximately the sum 

 of the heat capacities of its constituents, the heat of amalgamation is 



Q 



practically constant. If we place a constant, h, in place of — , equation 

 (3) becomes 



* Compare the interesting paper by Bugarszky, Zeit. anorg. Chem., XIV. 145. 



