Chemical Affinity in terms of Electromotive Foi 



Variation in E.M.F. due to the use of cad-"] 

 minm and zinc sulphate solutions of different 

 strengths, both solutions being of equal mole- 

 cular strengths in anv given case (strengths 

 varying from AlSO 4 50H 2 O to MS0 4 | 

 1250 H 2 0) J 



193 



Less than 

 ±•0015 



YOlt. 



Masi, Mini- Ean?e 



Are- 





rage. 



Effect of substituting for bright cadmium : — i 







Fresh electro-metal --002 -'007 



•005 



-•0045 



Amalgamated cadmium (liquid) + - 052 + '036 



016 



4--04i 



(solid, crystalline) 4- -024 



4- -009 



•015 



4-0165 



Electromotive force of combinations : — 











Amalgamated zinc — "Bright cadmium 



•367 



■361 



•006 



•364 



,, „ Electro-cadmium ... 



•362 



•358 



•004 



•360 



„ „ Amalgamated cad- 1 

 mium (hquid)... J 



•414 



•401 



•013 



•4075 



„ ,, Amalgamated cad- "I 

 mium (solid) ... j 



•38-3 



•373 



•015 



•3805 



These figures accord closely with the results deducible from 

 Julius Thomsen's thermochemical data, together with the 

 heat of solution of cadmium in mercury above quoted (§ 120); 

 thus : — 



Free metallic cadmium . 



Zn,0,S0 3 aq. . . . =106090 

 Cd,0,S0 3 aq. . . . = 89500 



Difference . . 



Difference per gramme- 1 

 equivalent ... J 

 Corresponding with volt 



16590 



8295 

 •365 



Cadmium dissolved 

 in mercury. 



106090' 



88890 

 17200 



8600 

 •379 



The observed electromotive forces* thus do not differ from 



* Regnault has shown (Ann. de Chun, et de Phys. [3] xliv. p. 453) 

 that the E.M.F. of a cell containing " concentrated " solutions of zinc and 

 cadmium sulphates and plates of these metals was 55, when that of a 

 similar cell with zinc and copper sulphates and plates was 175 (a particular 

 thermopile being employed as unit). Taking the EJMLF. of the latter 

 cell as 1-115 volt, that of the former must have been -350 volt — a value 

 differing from those observed by an amount not outside that possibly due 

 to inequality in the molecular strengths of the two metallic solutions. 

 For, by the use of more dilute cadmium-sulphate solutions (the zinc- 

 sulphate solution remaining the same) an appreciable fall in E.BLF. was 

 found to be produced, the lowest value being 42 = -268 volt with solution 

 diluted to y^-g- ; on the other hand, decreasing the strength of the zinc- 

 solphate solution produced far less effect. These and the author's some- 

 what different results on this point will be discussed in a future paper. 

 Phil Mag. S. 5. Vol. 14. No. 87. Sept. 1882. 



