22 



Mr. J. Brown on the Electrification of the 



seem improbable that the mere contact of any two substances, 

 withont anything further, could perform the work necessary 

 to produce a difference of potential of 42 volts, as found by 

 Mr. Enright, or indeed any considerable fraction of a volt. 

 The experimental evidence appears to be entirely against 

 such a supposition, and I felt that some other explanation 

 would probably be found to be the true one, more especially 

 on considering Mr. Enright's observation that the passage of 

 de-electrified gas through an acid did not electrify it, and his 

 statement on page 63 that " whatever tended to electrically 

 connect the charged liquid with the oppositely charged 

 escaping gas, also tended to lessen the charges on both." 

 If " contact " produced the charges, it is difficult to see how- 

 further " contact " could lessen them. 



2. On carefully reading Mr. Enright's paper, and before 

 making any experiments of my own, the following hypothesis 

 suggested itself to me from consideration of the typical 

 experiment, viz. zinc dissolving in hydrochloric acid, in which, 

 as Mr. Enright shows, the issuing gaseous matter is positively 

 electrified and the acid solution negatively electrified, until 

 finally, owing to the formation of a certain amount of zinc 

 chloride, a reversal of the electrifications of both gas and 

 liquid occurs. 



I use the word "gas" throughout the first part of this paper 

 for convenience. As will appear further on, it is not certain 

 ivhat the nature of the electrified matter is. 



o. Ordinary zinc is always an alloy of zinc and other 

 metals — iron, arsenic, &c. 



Fig. 1. 



Fig. 2. 



C1H 



01 



H | 



OLZn 



Cl 2 

 Ho 



H 2 C1 2 



HOI 



Suppose a b, fig. 1, to represent a portion of the surface of 

 such zinc, where a is pure zinc in contact with the foreign 

 metal at b, the whole being immersed in hydrochloric acid. 

 The solution of the metal takes place by the formation of 

 little local voltaic circuits, the chlorine combining with the 

 pure zinc at a, while the hydrogen is evolved at b } and the 

 local current flows with the arrows. 



There may of course be a larger number of HC1 molecules 

 involved than in the circuit shown, in considering which it 



