OF THALLIUM, INDIUM, AND TIN 3 



VALUES OF CONSTANTS. 



In the discussion which follows, all the experimental work is viewed in 

 the light of three mathematical expressions : 



T r J_ 



(0 



'=::-/ 7 (2) 



In these expressions, 



TT = electromotive force. c = concentration of more concen- 



F= Faraday's equivalent 96,530 trated amalgam. 



coulombs. c 2 = concentration of less concen- 



R = the gas constant. trated amalgam. 



T=the absolute temperature. U = the change of total energy in- 



v = valence. volved in the dilution of the 



In natural logarithm to the base e. amalgam. 



The first of the numbered equations is the well-known expression of 

 Helmholtz (sometimes called the Gibbs-Helmholtz equation) ; the second 

 contains the substance of the proposal of von Turin and G. Meyer ; and 

 the third is the suggestion of Cady and Lewis. Both of the last two may 

 be said to be the outcome of other work of Helmholtz, and to be covered by 

 the equation of Nernst. Before defining the quantities whose symbols are 

 given in the foregoing list, it may be well to say a word about these funda- 

 mental equations themselves. 



Equation (i) needs no comment. Equation (2) has been reached in 

 somewhat different ways by a number of thinkers ; it is based essentially 

 upon the epoch-making discussion by Helmholtz of the concentration cell. 2 

 The forms in which the several investigators have expressed their results 

 appear to be different, although they express essentially the same idea; 

 the equation, as given here, is not exactly like that of any of them. 

 Nernst, 3 who did not himself at first apply his equation to cells of the type 

 under consideration, used the ratio of pressures instead of the ratio of 

 concentrations, and would have expressed the result thus 



RTl, P 



P'\ 



J I 



2 Helmholtz, Monatsberichte d. kgl. pr. Akad., Berlin, 1877, p. 713. Helmholtz's 

 other well-known paper on the thermodynamic equation numbered (i) above was 

 published in the Sitzungsberichte der kgl. pr. Akad., Berlin, in February, 1882, p. 22. 



3 Nernst, Zeitschr. phys. Chem., 4, 129 (1889). 



