154 MR CONNELL ON THE VOLTAIC DECOMPOSITION OF 



the zinc, and causes the precipitation of oxide of zinc in an apparently anomalous 

 manner at the positive pole ; and when platinum is used, it unites with the hy- 

 drogen of the acid of the salt, and liberates iodine. When chlorides, as those of 

 potassium or calcium, are employed, there is in like manner a separation of oxide 

 of zinc at the positive pole ; and a portion of the oxide which is taken up by the 

 acid is sometimes carried to the negative pole, where it separates along with re- 

 duced zinc. 



I conceive that a sufficient number of cases has now been investigated to 

 warrant the general conclusion, that, " When aqueous solutions of primary com- 

 binations of elementary bodies are submitted to voltaic agency, the dissolved sub- 

 stance is not directly decomposed by the current, but only the solvent." The rule 

 of course does not embrace combinations of the second order, such as oxisalts, in 

 the solutions of which acid and base, as is well known, go to their proper poles, 

 under the direct influence of the current. 



It does not appear to me to be necessary to dwell long on the views of MAT- 

 TEUCCI and Professor DANIELL, both of whom have recently advocated the pri- 

 mary origin of metal in aqueous solution, whether of haloid or oxisalts. MAT- 

 TEUCCI* argues, because a weak pile, incapable of decomposing distilled water, 

 effects the decomposition of haloid salt solutions, the haloid salts must be more 

 readily decomposed than water, and must be the subject of direct action in their 

 solutions. It is evident, however, that the affinity of the elements of water for 

 the constituents of the salts which they find at the poles, and the inferior con- 

 ducting power of the solutions, afford the true solution of this observation. He 

 also founds on some experiments with basic acetate of lead, which, he says, both 

 in its fused state and in solution, yields less lead than the equivalent proportion ; 

 but no account is given of the exact quantity got in the former situation, nor is 

 any accurate correspondence shewn to exist between the quantities in the two 

 cases, and the whole seems explicable on the idea of such a mode of union be- 

 tween acid and base as to make the salt less susceptible of voltaic action, and of 

 the reducing agency of hydrogen ; and, at all events, I conceive that the above 

 experiments afford direct proof that the origin of the metal is not due to primary 

 decomposition. Mr DANIELL'S views are to a great extent theoretical ; the direct 

 decomposition of the haloid salts being first assumed, and an attempt then made 

 to extend the analogy to the oxisalts, on the hypothesis that the latter, in solu- 

 tion, consist of metal united to acid, plus an atom of oxygen, and to embrace, on a 

 similar analogy, the ammoniacal salts on the idea of the existence of ammonium 

 in them. All these views must assume, as their basis, that metal passes by the 

 direct action of the current to the negative pole, an assumption which is, I con- 

 ceive, directly negatived by the experiments above detailed. These views are 



* Bib. Univ. 



