62 Mr. J. En right on Electrifications due 



I now concentrated my attention on this reversal of sign. 

 I contrasted all the circumstances attending the deflexion to 

 the left with all those attending the deflexion to the right, 

 and could detect only one difference, and that was the pro- 

 duction of chloride of zinc in the generator, and I could not 

 fail to see that as the quantity of this salt increased the de- 

 flexions to the right became stronger. 



From this change of sign of the generator, when a certain 

 quantity of chloride of zinc got into solution, there suddenly 

 appeared to come a ray of light which I thought dispelled 

 the fog which hung round the earlier experiments. The 

 nature of the liquid through which the hydrogen passed 

 apparently determined the sign of the electrification. I 

 paused again to review the events of my little enterprise. 



I set out in quest of some direct evidence as to the atomic 

 charges. I had tried the four types of chemical change. 

 From double decomposition and from cases of change of 

 valency I had got no result whatever. From direct union of 

 elements — from the combination of phosphorus and iodine, 

 accompanied by a cloud of P 2 5 , and, I suppose, iodine vapour 

 — I had got an electrification. From many cases of dis- 

 placement I had got considerable electrifications ; but from 

 some, such as the displacement of iodine by chlorine, I had 

 got nothing whatever. A careful examination of these re- 

 sults disclosed the fact that no electrification was obtained 

 except when something escaped from the vessel in which the 

 reaction occurred. This circumstance I thought could not 

 fail to have some meaning. Then there were the leading 

 incidents, as I considered, of the inquiry: — (1) The escaping 

 gases or vapours came off with a charge opposite in sign but 

 equal in quantity to that on the generator. (2) The reversal 

 of the sign of both generator and escaping gas when the liquid 

 in the generator underwent a definite change. 



Such were the facts to be brought under some theory. I 

 was reluctantly compelled to conclude that they had nothing 

 to do with atomic charges, but for all that they afforded food 

 for the most delightful contemplations, often for hours at a 

 stretch, during the last two or three years. 



Reflect as I may on the reversal of sign of the electrification 

 when a certain quantity of chloride of zinc gets into solution, 

 I can find no explanation for it but the electricity of con- 

 tact. Hydrogen is positive to hydrochloric acid, but nega- 

 tive to chloride of zinc. And, indeed, looking at the whole 

 matter in this light, from my present standpoint, I can per- 

 ceive how, in the earlier experiments, the nature of the liquid 



