CRYSTALLIZATION PRODUCED BY VOLTAIC ACTION. 441 
the media of communication must be reversed, a! d'c! being put in the 
place of a 6c, and vice versd. In fine, if for the plate of platina there 
is substituted a plate of oxidable metal, we introduce into the interme- 
diate solution the reaction of an oxide, which being in its nascent state 
-conduces to the formation of the products. The bare inspection of the 
figure is sufficient to give an idea of the results that may be obtained 
by making the requisite variations in the solutions. 
Mode of using the Apparatus when the Positive Plate is not oxidable. 
Ist ExPERIMENT. We pour into the vessel A! an alcoholic solution 
of sulpho-carbonate of potash; into the vessel A a solution of sulphate 
of copper; and into the clay of the tube a 6c a solution of nitrate of pot~ 
ash: after 24 hours’ trial the reaction of the oxygen and the nitric acid 
on the solution of the sulpho-carbonate is now perceptible ; for we ob- 
serve on the extremity (@') of the platina plate the products already in- 
dicated (when the operation was supposed to be performed with a plate 
of lead), that is to say, crystals of sulphur, of neutral carbonate of potash, 
&e., but nocarbonate of lead, because there is no oxide of this metal. 
2nd Experiment. Crystals of Sulphur ; Sulphate and Carbonate 
of Barytes.—In the preceding apparatus we substitute for the sulpho- 
carbonate of potash a solution of sulpho-carbonate of barytes : we shall 
not have long to wait for the appearance of analogous reactions ; a pre- 
cipitation of sulphur in small erystals, and a formation of sulphate and 
carbonate of barytes in prismatic needles. We should perhaps by this 
process obtain crystals of some size, if the plate of platina was so bent as 
to form a spoon, and thus prevent the crystals formed on the surface of 
the plate from falling to the bottom of the vessel. 
3rd ExpErIMENT. Mode of ascertaining the presence of Nitric Acid 
and that of Hydrochloric Acid in any Solution, even when those two acids 
exist there in very small quantities —For the plate of platina a’ b'c! a 
plate of gold is substituted : there is then poured into the vessel A a so- 
lution of sulphate of copper ; and into the vessel A’, and the clay of the 
tube a be, a solution of the compound which is supposed to contain the 
two acids in combination with bases. As soon as the apparatus begins 
to operate, the sulphuric acid expels the two acids from their combina- 
tions, which, together with the oxygen arising from the reduction of the 
oxide of copper, are carried to the extremity (a') of the plate of gold: 
the yellow colour which immediately makes its appearance indicates the 
presence of nitric and hydrochloric acids. This reaction is also obtained 
when tubes of small dimensions are substituted for the jars. In this pro- 
cess no part of the acids is lost; for they are all transferred to the posi- 
tive pole, and contribute to the production of hydrochlorate of gold. 
4th Experiment. Sulphite of Copper.—The vessel A’ is filled with a 
solution of sulphite of potash, and for the plate of gold a'b'c! a plate of 
