certain Peroxides^ Platina, and Inactive Iron. 227 



constitute a series of substances, in which the preceding one 

 is always negative with regard to that which follows in the 

 list. 2. That any two of the four substances mentioned be- 

 ing voltaically associated with one another, and put either into 

 nitric acid or a solution of sulphate of copper, excite a con- 

 tinuous current, which is not due to oxidation or any chemical 

 change. It is hardly necessary to add, that the currents pro- 

 duced under the said circumstances are extremely feeble, being 

 only indicated by most delicate galvanometers. 



You will agree with me, that the facts spoken of are highly 

 important in a scientific point of view, as they seem to pro- 

 duce evidence in favour of that theory which asserts, that by 

 the mere contact of heterogeneous substances their electrical 

 equilibrium can be disturbed quite independently of any che- 

 mical action taking place between them. All chemists cer- 

 tainly maintain, that pure nitric acid, for instance, does not 

 chemically affect at all either platina or peroxide of lead ; 

 and inactive iron too, as we now well know, is not in the 

 least attacked by the said acid. Now, I ask, whence does the 

 current originate which is produced when we combine the 

 substances in question in such a manner as to form with them 

 a voltaic arrangement ? 



I have attempted to answer this puzzling question in a paper 

 which before long will be published in PoggendorfF's Av^. 

 nalen, as well as in the Biblioth, Univ., and in which you will 

 find besides a detailed account of all the experiments made 

 by me upon the subject spoken of. If my time' was not so 

 much taken up with a variety of business, I would have drawn 

 up a memoir in English, and sent it to the Editors of your ex- 

 cellent Philosophical Magazine, for insertion ; but those gen- 

 tlemen will, perhaps, give a translation of the paper. 



Before closing my letter allow me to communicate to you 

 in a general manner the view which I have taken of the sub- 

 ject in question. In the first place, I must tell you that I am 

 by no means inclined to consider mere contact in any case 

 as the cause of the excitement of even the most feeble current. 

 I maintain on the contrary, in accordance with the principles 

 of the chemical theory, that any current produced in a hydro- 

 electric voltaic circle is always due to some chemical action. 

 But as to the idea which I attach to the term " chemical 

 action," I go further than you and M. de la Rive seem to 

 go ; for I maintain, that any tendency of two different sub- 

 stances to unite chemically with one another must be consi- 

 dered as a chemical action, be that tendency followed up by the 

 actual combination of those substances or be it not ; and that 

 such a tendency is capable of putting electricity into circuit- 



2B2 



