from tlieir Solutions by the Galvanic Current. 435 



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 

 various. 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 di- 

 rection, the metal in the other. The first opinion was put for- 

 ward by Hisinger and Berzelius, and may be found in the 

 Annales de C/zmzV, vol. li. p. 174. "II resulte de tons ces 

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

 I'electricite, puis qu'on I'attribue au degagement de I'hydro- 

 gene, comment expliqueroit-on la reduction du fer etduzinc, 

 qui ont la propriete de decomposer I'eau sans electricite." 



A similar opinion has been advocated by Faraday 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 substances, the 

 metals, and certain metallic oxides are attracted by negatively 

 electrified metallic surfaces and repelled by positively electri- 

 fied metallic surfaces; and contrariwise, that oxygen and acid 

 substances are attracted by positively electrified metallic sur- 

 faces, and these attractive and repulsive forces are sufficiently 

 energetic to destroy or suspend the usual operation of che- 

 mical affinity." (Phil. Trans., 1807, p. 28.), 



3. The hypothesis of the direct electrolysis of metallic salts 

 lias been advanced by Prof. Daniell 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 follows: — A so- 

 lution 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 completed by a powerful bat- 

 tery, the metal is deposited on the diaphragm. From this ex- 

 periment it has been conceived that the acid and oxygen are 

 in combination, forming a proximate principle, which in sul- 

 phate of copper is called oxysulphion; and the salt of copper 

 is believed to be an oxysulphion of copper. When this salt 

 is subjected to the voltaic circuit he believes it to be directly 

 electrolysed, the oxysulphion passing one way and the copper 

 the other. 



2 F2 



