1892.] 



Voltaic Cells with Fused Electrolytes. 



III. " Voltaic Cells with Fused Electrolytes." By J. BROWN. 

 Communicated by Professor EVERETT, F.R-S. Received 

 May 27, 1892. 



In attempts to compare the observed electromotive forces of 

 voltaic combinations with the theoretical values found by Thomson's* 

 law, the discrepancies observed in many cases, and the difficulties 

 experienced in ascertaining their nature and origin, are well known. 

 It is evident that, in order to compare observations with theory, we 

 must know exactly the facts on which the theory is to be founded, 

 i.e., the true nature of the chemical reaction in the cell, and its rela- 

 tion to the electric phenomena to be observed ; and for this purpose 

 simplicity in the construction of the cell is, in the present state of 

 knowledge, almost a necessity. In many of the cells that have been 

 examined heretofore, this condition of simplicity is not realised ; and 

 the nature of the chemical action in them is not definitely ascer- 

 tainable because of the complicated nature of the substances em- 

 ployed. I have referred to this point in the introduction to a paper 

 on the " Role of the Cation in Voltaic Combinations ; "f and in a 

 foot-note OD p. 462, of that paper I have again referred to what is a 

 very frequent cause of uncertainty, viz., the action of the solvent. 

 usually of course water as distinct from the dissolved electrolys- 

 able substances. This uncertainty is still more marked in the case of 

 some of Wright and Thompson's experiments,^ where insoluble salts 

 suspended in solutions were supposed to be alone active to the 

 exclusion of both the water and the dissolved substances. The 

 solvent may act chemically on the metals, and affect the electro- 

 motive force, either directly as an electrolyte, or indirectly by the 

 formation of films insoluble in itself, which act differently from the 

 metals or protect them from chemical action. Laurie and Braun|| 

 have respectively shown that the lowering of the forces of aluminium 

 and magnesium in aqueous solutions is probably due to such pro- 

 tective films ; Julius M. Werner^" considers the cause of the com- 

 parative inaction of pure zinc in acids to be that, at the moment of 

 immersion, it becomes enclosed in a continuous film of hydrogen 

 which protects it from further action ; while with impure zinc the 

 hydrogen forms on the impurities only, leaving the zinc exposed. 



* ' Phil. Mag.,' ser. 4, vol. 2, p. 434, 1851. 

 f ' Phil. Mag.,' ser. 5, vol. 31, p. 449, 1891. 

 J ' Phil. Mag.,' ser. 5, vol. 19, p. 211, 1885. 

 ' Phil. Mag.,' ser. 5, vol. 22, p. 213, 1886. 

 || ' Phil. Mag.,' ser. 5, vol. 27, p. 209, 1889. 

 IF ' Ber. Deut. Chem. G-esell.,' vol. 21, p. 1785. 



