CRYSTALLIZATION PRODUCED BY VOLTAIC ACTION. 4:37 
ing a greater affinity towards this base than the nitric acid has. The 
latter acid being liberated proceeded to the positive pole, where it com- 
bined itself with the oxide of lead, formed, in‘a great measure, at the 
expense of the oxygen of copper. The result was a nitrate of lead, 
which crystallized in proportion as it had saturated the aleohol. With 
a more powerful voltaic action, the sulphate of potash would have been 
decomposed. This example shows how valuable the feeble electric 
currents are in the production of combinations. In the case under 
consideration, the nitrate of potash was decomposed by the concur- 
rence of the electric forces and the chemical affinities. 
Let us now apply the foregoing principle to the decomposition of the 
sulpho-carbonate of potash, and the formation of some compounds. 
lst ExpeRIMENT.—The sulpho-carbonate of potash, whose solution 
when not very much concentrated is gradually decomposed in the air, 
is peculiarly disposed to admit of changes being produced in the state 
of combination of its molecules by the action of feeble forces. The 
following is the mode in which we operate on this substance: we take 
two glass jars, and pour into the one a solution of sulphate of copper, 
and into the other an alcoholic solution of sulpho-carbonate of potash. 
The communication between the two liquids is then established, on 
the one hand by means of a bent glass tube, filled with potter's clay 
moistened with a solution of nitrate of potash; and on the other by 
means of a metallic are formed of two plates, one copper and the 
other lead, the plate of copper being immersed in the sulphate, and 
the plate of lead in the sulpho-carbonate. According to the nature of 
the electric effects produced in the various chemical reactions, the lead 
is found to be the positive pole of a pile whose intensity is sufficient to 
decompose the sulphate; the copper is reduced ; the oxygen and the 
sulphuric acid are carried towards the lead; the acid, in its passage, 
decomposes the nitrate of potash, as in the preceding experiment, so 
that the oxygen and the nitric acid enter alone into the sulpho-carbe- 
nate. As soon as they have penetrated it, they begin to react on its 
constituent parts, and this reaction continues so long as the force of the 
current is superior to the affinities of the several bodies present: the 
transfer of the molecules is continued as far as the positive plate, 
where the last reaction takes place. The following products are suc- 
cessively formed : neutral carbonate of potash which erystallizes on the 
sides of the vessel, sulphate of potash, a sulpho-carbonate of lead and 
of potash in acicular crystals, carbonate and sulphate of lead in 
needles ; and, in fine, a portion of sulphur proceeding from the decompo- 
sition of the sulphuret of carbon and the sulphuret of potash, is depo- 
sited on the plate of lead, which is the positive pole, and there crystal- 
lized in octahedrons with a rhomboidal base. These octahedrons some- 
times attain a millimetre in length when the experiment has been con- 
tinued for a month. 
