286 



Prof. H. E. Armstrong. Electrolytic 



[Mar. 25, 



There is, however, a most significant passage in Helmholtz' paper, in 

 which it is pointed out that (in a Daniell's cell) the phenomena are 

 the same as if equivalents of positive and negative electricity were 

 attracted by different atoms, and perhaps also by the different values 

 of affinity belonging to the same atom, with different force : are we to 

 seek for an explanation in this direction ? The impression which the 

 facts make npon the mind of the chemist certainly is, 1, that no 

 two different atoms have equivalent affinities ; and, 2, that affinity is a 

 variable depending on the nature of th*e associated elements : but 

 owing to the recognised complexity of nearly all cases of chemical 

 change, it is difficult to draw any very definite conclusion on this point. 



If, however, the nature and properties of so-called molecular 

 compounds generally be considered, and if an attempt be made to 

 form any conception of their constitution, one striking fact is 

 noticeable, viz., that the metals in them apparently retain the 

 properties which they exhibited in the parent atomic compounds. 

 Every one knows the marked difference in properties of ferrous as 

 contrasted with ferric salts : they differ not only in chemical 

 behaviour, but also in their physical properties, and are readily 

 distinguishable by their colour. The properties of the ferrous 

 molecular compounds, however, are those of the simple ferrous 

 compounds : ferrous potassium chloride, for example, FeaCLt'C^E^, is 

 a green salt much like ferrous sulphate. Facts such as these have led 

 me to suggest that in such cases the formation of the molecular 

 compound is due to the attraction of the negative element of the one 

 " atomic " compound by the negative element of the other, the metal 

 having no influence except that the amount of affinity of which the 

 negative element is possessed depends on the nature of the metal with 

 which it is associated. It would in fact appear that hydrogen and the 

 metals generally may be regarded as the analogues of the CnH-zn+i 

 and C ?1 H 2K _7 hydrocarbon radicles, and that their compounds with 

 negative elements may be likened to unsaturated hydrocarbons of the 

 form CwH 2w+ i* 011*0112. We know that whenever such a compound 

 enters into combination, the C w II 2w+1 radicle takes no part in the 

 change, combination of whatever kind being effected by means of the 

 unsaturated radicle CH«CH 2 with which it is associated. I do not 



molecular charges — he uses the expression molecular in the sense that the chemist 

 uses the term atomic — may serve as a method by which we may remember a good 

 many facts about electrolysis. It is extremely improbable that when we come to 

 understand the true nature of electrolysis we shall retain in any form the theory of 

 molecular charges, for then we shall have obtained a secure basis on which to form a 

 true theory of electric currents, and so become independent of these provisional 

 theories." And later (p. 315) : "While electrolysis fully establishes the close rela- 

 tionship between electrical phenomena and those of chemical combination, the fact 

 that every chemical compound is not an electrolyte shows that chemical combination 

 is a process of a higher order of complexity than any purely electrical phenomenon." 



