to the Contact of Gases with Liquids. 61 



moved. This, I took it, proved that the charges on the 

 generator and evolved gas were equal in quantity, though 

 opposite in sign. 



The state of the case was now, so far, pretty clear. When 

 hydrogen was produced by zinc and hydrochloric acid the 

 hydrogen became positively, the generator negatively, charged. 

 I set this fact up before my mind and examined it as care- 

 fully as I could on every side. I turned it round and round, 

 looking for some information as to the atomic charges, but I 

 could find none. Had the charge on the escaping gas been 

 of the same sign as that on the generator, I could have set 

 up some hypothesis concerning them, but, as things were, 

 nothing of the kind was possible. 



But what is the cause of this undoubted electrification ? 

 I repeated the experiment many times. I varied the quan- 

 tities of acid and zinc, and noticed that with weaker acid 

 or a larger quantity of zinc the deflexions were not so 

 strong. During these repetitions I was in the habit of short- 

 circuiting the quadrants when the spot came to the end of 

 the scale, lest the suspending fibres of the needle should get 

 a set from being twisted too much in one direction. On one 

 occasion, however, being called away suddenly, I neglected 

 to do so, and the electrification worked its will, so to speak, 

 on the needle. On returning in about twenty minutes, I 

 found that all the zinc was dissolved, and to my very great 

 astonishment the spot was at rest at the extreme right of the 

 scale. 



Up to that time the deflexion from zinc and hydrochloric 

 acid had been to the left ; and, as I had made the experiment 

 a great many times with this unvarying result, I was much 

 perplexed. The uncertain behaviour of sodium and potassium 

 was still fresh in my memory. 



However, what to do on the occasion was quite clear: I 

 repeated the experiment in every particular, sat down, and 

 watched it. The spot went rapidly off the scale to the left as 

 usual. The reaction proceeded. In eleven minutes the spot 

 appeared again on the scale, went down 100 divisions rather 

 slowly, then more rapidly, crossed the zero, and at a good 

 pace went up the other side almost to the end of the scale. 

 This was quite a new development. Frequent repetition, 

 with the same result, proved that this behaviour, strange as 

 it was, had a definite cause. I varied the strength of the 

 acid and the quantity of zinc, and found that by either making 

 the acid weak or increasing the quantity of zinc I could 

 hasten the reversal of the sign of the electrification of the 

 generator. 





