to the Contact of Gases with Liquids. 69 



only difference between the two reactions is that Na 2 S0 4 is 

 very soluble compared with CaS0 4 . 



Taking a broad view of these experiments, they appeared to 

 me to indicate that, in general, gases were positive to acids, 

 bnt negative to solutions of salts. I could not, however, throw 

 off a feeling of dissatisfaction which arose from my not being 

 able to suggest a trace of any a priori reason for such a 

 thing. I fancied I saw some reason why hydrogen should be 

 positive to acids and negative to salts ; but that the generaliza- 

 tion should be so wide as to extend to all gases, seemed to me 

 most improbable. I felt disposed to question my theory of 

 contact altogether, and resolved to make experiments of a 

 different kind for the purpose of testing it. 



If hydrogen be positive to hydrochloric acid, then, why not, 

 I asked, prove it by a straightforward experiment such as 

 passing a stream of the gas through the strong acid ? Two 

 insulated plates were set up near the electrometer and con- 

 nected by a piece of copper wire. A beaker 2 inches in 

 diameter and 5 inches high containing strong HC1 was 

 placed on one, and a hydrogen generator furnished with a 

 narrow delivery-tube more than 12 inches long was set on 

 the other. The delivery-tube was suitably fixed, and a brisk 

 current of hydrogen passed through the strong hydrochloric 

 acid. The hydrogen was found to come off with a positive 

 charge, but on allowing it to get into the air direct from the 

 delivery-tube it also came off charged in the same way. Here, 

 then, I was balked. Of course the object of the long delivery- 

 tube was to neutralize the gas before it touched the strong 

 acid in the beaker. I have often remarked how firmly the 

 hydrogen held its charge, but I was quite unprepared to find 

 that it passed through more than 12 inches of wet glass 

 tubing ^ of an inch in diameter and escaped strongly elec- 

 trified. I next passed the hydrogen through a wash-bottle, 

 but it again came off charged. I passed it through all manner 

 of bent tubing, made all possible shifts in fact to de-elecfcrify 

 the gas in order to fairly carry out my experiment, but with- 

 out success. In sheer desperation I snatched up a litre-flask, 

 filled it with water, and displaced the latter at the pneumatic 

 trough by hydrogen from Zn + HC1. I then placed the flask 

 mouth upwards and open on the insulated plate which was 

 connected to the quadrants. The spot gradually moved to the 

 left, and came to rest at a distance of 180 divisions from zero. 

 This experiment yielded more food for thought. At first 

 sight the deflexion appeared to be in the wrong direction, and 

 I had to consider whether the hydrogen could, by any pos- 

 sible process, be neutralized. 





