66 Mr. J. Enright on Electrifications due 



the goblet. Almost instantly the spot moved rapidly to the 

 right, which I had expected. The generator was now with- 

 drawn. The spot slowly returned to within 5 divisions of zero. 



Now if the electrification were due to spray, the goblet 

 would retain its charge (the insulation was good) ; but being 

 due to the hydrogen, which gradually passed through the 

 perforations into the air, it very rapidly lost it. 



In the course of these experiments I had often cast about 

 for means of measuring the difference of potential arising from 

 the contact of zinc and hydrochloric acid, and on consideration 

 it appeared to me that this experiment presented a possible 

 method. Particles of matter charged with electricity, and 

 impinging on an insulated conductor, to which they give up 

 part or the whole of their charges, could not raise the conductor 

 to a higher potential than they had attained ; but they, in the 

 course of time, ought to bring it up to that level. My notion 

 was to allow the charged hydrogen to flow through the goblet, 

 fixed as described, long enough to ensure its reaching the 

 potential of the gas ; then to remove the generator, and allow 

 the gas to pass away through the perforations. The perma- 

 nent deflexion then obtained ought, I considered, to be the 

 measure of the quantity in question. I carried out with all 

 the care possible several experiments on these lines ; but on 

 account of the tenacity with which the gas holds its charge, I 

 failed to get satisfactory determinations. 



At this stage of my inquiry, I felt that I had got a few defi- 

 nite facts, that I had cleared up, at all events to my own 

 satisfaction, many points which were at first doubtful, and 

 that the theory of contact which I proposed was consistent 

 with all the observations I had made. I proceeded to devise 

 new experiments with the view of testing the truth, and de- 

 termining the scope, of this theory. 



Hydrogen passing through HC1 and H 2 S0 4 takes a positive 

 charge ; passing through the corresponding salts of zinc it 

 takes a negative charge. Then at any moment it ought to be 

 possible to reverse the electrification by introducing into the 

 vessel in which the reaction is going on acid or salt, as the 

 case may be. The old experiment was made. Hydrogen 

 was escaping from a 16-per-cent. solution of HC1, and the spot 

 had travelled 100 divisions when a strong solution of zinc 

 chloride was added. The spot went quickly back and up on 

 the other side of the scale, showing that reversal had taken 

 place. The addition of HC1 produced a second reversal. 



I had found hydrogen positive to two acids, and a question 

 as to whether this was general often floated before me. 1 had 



