to the Contact of Gases with Liquids, 67 



no means of testing with nitric acid, because its action on 

 metals. does not give rise to hydrogen — at all events not in 

 the final stage. I therefore directed attention to the other 

 side of the question. Hydrogen was proved to be negative 

 to chloride and sulphate of zinc. Was it possible that it was 

 negative to other salts, or to salts in general ? 



I again made the old experiment with Zn + HC1, and when 

 a deflexion of 50 divisions was obtained a strong solution of 

 ferric chloride was added, with the effect of reversing the sign 

 of the electrification. I proceeded to try other salts, such as 

 NaOl, AmCl, FeS0 4 , MgS0 4 , CaCl 2 , and found that these also 

 produced reversal. I found, however, a few salts which did 

 not do so, notably Co(N0 3 ) 2 . 



A wide principle thus appeared to be foreshadowed, viz., 

 that hydrogen is positive to acids but negative to salts ; but 

 the number of cases examined does not warrant one in laying 

 it down absolutely. Moreover, I have found the hydrogen 

 passing from acetic acid, whether by the use of sodium or iron 

 filings, always comes off with a negative charge. I strongly 

 suspect, however, that the reversal of sign in these cases takes 

 place so rapidly that it escapes observation. I have had 

 several instances of the spot moving a small distance to the 

 left, suddenly turning, and moving far up on the opposite 

 side of the scale. Occurrences of this kind leave no doubt on 

 my mind that the first electrification (that due to the gas 

 passing through the acid) is often small, owing, I think, to 

 the rapidity with which the salt produced in the reaction 

 diffuses. 



Is hydrogen among gases unique in becoming charged when 

 it passes through acids ? was the question that next presented 

 itself. I considered what reactions were likely to give any 

 information with regard to the matter, and made numbers of 

 experiments in the manner already fully described. I found 

 that as a rule electrification results from any reaction giving rise 

 to an escape of any substance into the air. In many cases the 

 electrification is very trifling, and the electrometer must be in 

 a sensitive state in order to show it. Of all the reacting com- 

 binations which I have tried, HC1 -f Zn give by far the greatest 

 difference of potential between generator and expelled gas. 

 On the other hand, from H 2 S0 4 + NaCl I failed to get any 

 trace of electrification. I give in the following Table only 

 those reactions which by frequent repetition I have found to 

 give constant results. I also give the estimated difference of 

 potential, but shall postpone to a later stage a description of 

 the method of making the measurement. 



F 2 



