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ARTICLE XXI. 
On the Chemical Effects of Electric Currents of low tension, 
in producing the Crystallization of Metallic Oxides, Sul- 
phurets, Sulphates, &c.; in forms frequently closely resem- 
bling the native combinations ; by M. BecquEREL.* 
From Becquerel’s 7raité de I’ Electricité et du Magnetisme, vol. iii, p. 287. 
1. By means of long-continued electrical action proceeding from a 
single pair of plates, chemical effects more or less considerable are pro- 
duced, whether the affinity of the solution for one of the electrodes adds 
its action to these forces or opposes them. We every day observe that 
nature, having unlimited time at her disposal, produces with slender 
means immense effects. But these means frequently escape our senses, 
because they have not been studied with sufficient care, and are not in- 
cluded in the ordinary circle of our inquiries. It is only by working on 
a small scale, and closely observing every step of our processes, that we 
have a chance afforded us of discovering any of the means employed 
by nature to produce the phenomena of molecular attraction. With 
this view let us observe some of the decompositions obtained by means 
of apparently feeble electrical forces. 
At present it is not doubted that voltaic action may produce chemi- 
cal effects; but we do not know how far this action, when it is very 
feeble, influences affinities, and whether, at the very moment when 
these become sensible, particular phenomena may not be produced, 
which disappear in the general effect, when we employ a pile possessing 
a certain energy. We know, for instance, that if two wires of any 
metal are plunged into a metallic solution, each of them communi- 
cating with one of the poles of a voltaic pile of sufficient energy, we 
always obtain at the negative wire either hydrogen, reduced metal, or 
oxide. But when the tension is extremely slight, does the phenomenon 
take place in the same manner ? Do all metals possess this property 
in the same degree? In order to answer these questions, successive 
reductions must be made in the intensity of the electricity, and at the 
same time what passes in the decompositions must be observed. 
Let us put a metallic solution (for instance a solution of copper) into 
a cylindrical glass, and then with the greatest care pour over it distilled 
or acidulated water, so that the two liquids may remain separate, the 
one above the other ; and then immerse a plate of copper into it, we find 
after a few hours this plate covered with a precipitate of copper in a 
metallic state. Different metallic solutions gave similar results. Hence 
* For the selection of this Paper the Editor is indebted to H. J. Brooke, 
Esq., F.R.S. A notice of a Memoir on this subject, read by M. Becquerel to 
the Academy, is given in the Philos. Magazine and Annals for March 1830. 
