188 APPENDIX. [No. X. 



No. X. 



ON THE CAUSE OF THE REDUCTION OP METALS WHEN 

 SOLUTIONS OP THEIR SALTS ARE SUBJECTED TO THE 

 GALVANIC CURRENT. By Alpeed Smeb, Esq., P.R.S., Surgeon 

 to the Bank of England, &o.* ('London, Edinburgh, and Dublin 

 Philosophical Magazine, and Journal of Science,' December 1844.) 



1. At the present time, when the new science of electro-metallurgy is 

 improving and multiplying the arts of this already extensive manufactur- 

 ing empire, there cannot be a subject more fit for the consideration of the 

 Pellows of the Royal Society than the cause of metals being reduced when 

 solutions of their salts are subjected to the voltaic circuit. 



2. The opinions of philosophers upon this point, from the period when 

 electricity first lent its mighty aid to chemists, are Tarious. Some have 

 supposed that hydrogen evolved by the decomposition of water reduces the 

 metals, others that the poles directly attract the metals to their surfaces, 

 and lately a paper has been printed in the Transactions of this Society 

 whereby a new constitution of the salts is inferred ; the acid and oxygen 

 being supposed by electrolysis to pass in one direction, the metal in the 

 other. The first opinion was put forward by Hisinger and BerzeHus, and 

 may be found in the ' Annales de Chimie,' vol. K. p. 174 : " II resulte de 

 tous ces faits, que Ton a une idee fausse de la reduction operee par 

 relectricite, puis qu'on I'attribue au degagement de I'hydrogene, comment 

 expliqueroit-on la reduction du fer et du zinc, qui ont la propriete de de- 

 composer I'eau sans I'electricite." 



A similar opinion has been advocated by Paraday in the ' Philosophical 

 Transactions,' and he applied a new name to this kind of action, giving it 

 the term electro-chemical action. The second hypothesis was promulgated 

 by Sir Humphry Davy, who states, "that hydrogen, the alkaline sub- 

 stances, the metals, and certain metaUic oxides are attracted by negatively 

 electrified metallic surfaces, and repelled by positively electrified metaUic 

 surfaces ; and contrariwise, that oxygen and acid substances are attracted 

 by positively electrified metaUic surfaces, and these attractive and repxd-, 

 sive forces are sufficiently energetic to destroy or suspend the usual 

 operation of chemical affinity." (Phil. Ti-ans. 1807, p. 28.) 



3. The hypothesis of the direct electrolysis of metallic salts has been 

 advanced by Prof. DanieU in consequence of some ingenious experiments 

 which have been detailed before this Society, and in which it is supposed 

 that he directly stopped the metal in its passage to the negative pole. The 

 mode in which the experiments were performed is as f oUows : — A solution 

 of the metallic salt is placed on the positive side of a diaphragm apparatus 

 and a solution of potassa on the other side, when, on the circuit being com- 



* Communicated by the Author ; having been read before the Eoyal Society, 

 March 9, 1843, as recorded in Phil. Mag. a. 3, vol. xxiii. p. 51. This paper 

 was also published in the 4th vol. of the ' Archives de I'filectr.' in 1844 ; in 

 Majocchj, 'Ann. Fis. Chim.' vol. xv. 1844; in the 'Philosophical Magazine,' 

 vol. XXV. 1844 ; in the ' Proceedings of the Royal Society,' vol. iv. ; in the 

 ' I'oggend. Atmal.' Ixv. 1845. 



