Contact Theory of Galvanism. 373 



this the force of the circuit would only have decreased ; for 

 the platinum plate communicating metallically with the cop- 

 per, indicated itself, not only by a development of gas bub- 

 bles in the circuit, but even by a distinct experiment, the 

 circuit being made with it after some lapse of time between 

 the closings, as negative with relation to the copper. The 

 cause then of the gradually increasing action could only be 

 sought for in the decrease of opposition gradually taking place. 



The experiment with the zinc plates was performed twice, 

 that with the platinum plates three times, on different days, with 

 results exactly corresponding. Moreover De la Rive affirms 

 that platinum connected in pure nitric acid with pure gold 

 produces no current, or rather one which quickly disappears, 

 which he ascribes to accidental impurities. I have not been 

 able any more than Marianini to find this circumstance con- 

 firmed ; although I employed gold of 24 carats, and a nitric 

 acid which when properly diluted was not rendered turbid by 

 nitrate of silver. Fresh surfaces were given to the metals by 

 rubbing them with dry sand-paper (I expressly avoided treat- 

 ing them with acids to clean them, because in this case pecu- 

 liar variations of surfaces are to be feared). The divergence 

 which at the beginning was very lively, decreased, it is true, 

 considerably, very soon, but remained still constantly in 

 favour of the positive relation of the gold. A very sen- 

 sitive multiplier of several thousand coils, however, was em- 

 ployed. With the same instrument I have observed an ac- 

 tion not inconsiderable between gold and platina in rectified 

 muriatic acid, which however with a multiplier of a medium 

 number of coils but of thicker wire, was scarcely percep- 

 tible. The reasons from Ohm's theory may be sufficiently 

 well known with us to lead us to expect, that, in fact, in this 

 case, where the circuit includes in itself a considerable op- 

 position, we can expect action only from a multiplier with 

 immerous coils, even when of thin wire. 



Notwithstanding, however, that De la Rive, under the cir- 

 cumstances of his experiment, could observe no action of a 

 gold and platinum circuit, he would undoubtedly have ob- 

 served it, if he had saturated this acid with nitrate of silver 

 in excess, in which case, in fact, in all appearance opposed 

 to the chemical theory, a not less considerable divergence is 

 obtained than if gold and platinum are connected in a solu- 

 tion of nitrate of silver only. I am, however, far from giving 

 these circumstances an importance against the chemical theory, 

 equivalent to that which experiments of apparently an op- 

 posed kind are made to have in favour of it, for it is certain 

 that a solution of nitrate of silver exerts a modified influence 

 on the surfaces of gold and platinum, although this is op- 



