OF ZINC, CADMIUM, LEAD, COPPER, AND LITHIUM 57 



In view of these highly unsatisfactory results, and the rapidly approach- 

 ing conclusion of the academic year, it was decided to abandon for the 

 present the attempt to obtain accurate data concerning the alkali-metals, 

 and confine the theoretical treatment to the six metals which had given 

 unimpeachable results, namely, cadmium, zinc, thallium, indium, tin, and 

 lead. The theoretical discussion of these more satisfactory data follows. 



APPLICATION OF THE EQUATION OF CADY. 



It has already been pointed out in the preceding paper" that if the 

 electromotive force of a cell as depicted by the equation of Helmholtz is 

 made equal to that demanded by the equation of Cady, the term involving 

 the heat of reaction is eliminated, and we obtain the expression : 



V F c n dT 



This equation was found as a matter of fact to hold approximately true 

 as regards thallium, indium, and tin, and it becomes a matter of interest 

 as applied also to zinc and lead. The average values for the zinc cells 



Mi-M3 and Ni-N3 are given on p. 45. The value of ^ wa s ^^c =0.15 



C n 



Thus 



R c m __ 8.316x2.214 .. nnnnne . 

 ~~r^ In ~ - ~ - ~T- " 0.0009 S4 



VF 1 C n 2X96,530 



and 



2. 



- =0.000934 



29.96 

 Difference = 0.000020 



This small difference, not much exceeding 2 per cent, seems at first 

 sight inconsistent with the wide discrepancy found by the earlier investi- 

 gation as regards cells containing zinc amalgams. There are two causes 

 for this difference of verdict: the first and most important is not a real 

 inconsistency, but appears only because of the different mode of presenta- 

 tion ; the second subordinate cause of difference is due to the doubtful 

 character of the result for the heat of dilution previously employed a 

 datum wholly eliminated from the present calculation. This latter circum- 

 stance will be considered in the subsequent heading concerning the equa- 

 tion of Helmholtz ; the former is worthy of a further word of explanation 

 here. 



In the paper by Richards and Forbes, the equation of Cady was trans- 

 posed thus : 



RT . Cl U 

 it- ~^n~ In - ~c~ 

 vr c- 2 vr 



" This monograph, p. 31. 



