Chemical Science. 377 



tube containing chloride of silver was found to contain reduced silver: 

 and when potassa had been submitted to the electric current, then 

 the potassium was seen to take fire as it was produced*. 



3. ON THE DECOMPOSITION OP METALLIC SALTS BY THE VOLTAIC 



PiLE, AND ON THE STATE OF CHLORIDES, IODIDES, &C. IN 

 SOLUTION. 



Whilst experimenting with a voltaic pile of thirty pairs of plates, 

 M. Carlo Matteuci observed, that when the poles were plunged into 

 solution of common salt, they both evolved gas ; but that when in- 

 troduced into solution of sulphate of copper, although oxygen was 

 evolved as before from the positive pole, hydrogen ceased to be dis- 

 engaged at the negative pole, but metallic copper was there deposited. 

 Using various other metallic solutions, he found that those of lead 

 and silver, with some others, produced the same effect, 2. e. evolved 

 no hydrogen, but had the metals deposited in the metallic state, 

 whilst others evolved gas at the negative pole, and had their bases 

 deposited as oxides. Reasoning on the effect, he was induced to 

 conclude, that in the cases in question, the hydrogen separated at 

 the negative pole was employed in reducing the oxides of the metals ; 

 and hence its disappearance, and the deposition of the base in a 

 metallic state. To assure himself of the truth of this view, lie con- 

 structed a weak pile composed of only two elements, and incapable 

 of decomposing a weak solution of salt. A solution of nitrate of 

 silver is far more easily decomposed than water, as M. Becquerel has 

 shown, and such a solution was readily decomposed by this weak pile 

 of two elements ; and at the same time it was observed, that the 

 usual deposit of metallic silver did not occur, but an olive-coloured 

 layer of oxide of silver was produced. It is, therefore, sufficiently 

 proved, that the disengagement of hydrogen at the negative pole of 

 the pile ceases, only because that element is employed in reducing 

 the metallic oxides already separated from these acids by the action 

 of the pile. It is a striking case of the powers of nascent hydrogen 

 at common temperatures. 



Having explained this appearance, M. Matteuci proceeded to 

 decompose the chlorides and iodides by means of the pile, with the 

 expectation of being able to deduce the nature of these compounds 

 when dissolved in water. If it were possible to decompose these 

 combinations by means of electric currents, incapable of decomposing 

 water, one might then justly conclude that their composition was not 

 changed by solution in that liquid. He, therefore, took a pile com- 

 posed of two elements only, charged with water rendered slightly 

 saline, and which had no power of decomposing water even a little 

 acidulated. The platina conductors were then dipped in a solution 

 of muriate of copper, and after some time, the negative conductor 



Bib, Univ. 1830, p, 213. 



