Contact Theory of Galvanism. ^69 



takes place in the metals) passes over into the negative. The 

 taking place of the change of the metals in these fluids may 

 also be proved by various other experiments, which however 

 I here omit as they may be brought forward in connexion 

 much better in another place. 



The changes which fluids produce in metals have certainly 

 not been sufficiently attended to and studied, and I shall often 

 have occasion in this memoir to return to this point. All the 

 experiments which Pfaff^ Karsten, Becquerel, and others have 

 made on the production of electricity between fluid and solid 

 bodies are at least complicated by these changes and demand 

 in this respect a revision. It is not at all impossible that the 

 result of these experiments depends entirely on such changes. 

 Further experiments will, I hope, soon solve this part of the 

 question. 



2. Schoenbein has published in these Annalen (vol. xxxix. 

 p. 351*.) an experiment which he considers to be especially 

 decisive in favour of the chemical theory, and which chiefly 

 amounts to this, that an iron wire rendered passive by pre- 

 vious immersion in nitric acid, then connected with the circuit 

 in a solution of sulphate of copper by means of a platinum 

 wire, precipitates no copper and produces no current, but 

 that a current immediately takes place if by any cause the 

 passive condition of the wire is destroyed, i. e. if its chemical 

 state is again restored. 



With respect to this experiment we may state the fol- 

 lowing : 



By previous experiments performed by Wetzlar, and lately 

 by myself, it has been sufficiently shown that the change (as 

 little explained in the sense of the chemical theory as in that 

 of the contact theory) which iron undergoes in nitric acid 

 and in a solution of concentrated nitrate of silver, renders it 

 considerably more negative than previously. That a highly 

 negative metal neither precipitates copper, nor gives with 

 platinum any perceptible current, (especially if the metals are 

 employed in the form of wire, and a multiplier is made use of, 

 of little sensibility,) certainly cannot be regarded as incompa- 

 tible with the theory of contact, and as little, that a current 

 immediately re-appears with the precipitation of the copper, 

 if by any cause that change of surface has been destroyed. 

 Where is the proof that the precipitation of the copper is not 

 rather the consequence than the cause of the restored electri- 

 cal action ? Besides, it is possible that the peculiar change 

 which iron undergoes in nitric acid may also increase its 



[* See also L. and E. Phil. Mag., vol. x. p. 275; and also p. 167 of the 

 present volume.] 

 Phil. Mas. S. 3. Vol. 13. No. 83. Nov. 1838. 2 B 



