In the examination of the various crystallizations that occupy us, we shall distinguish the following:  (1) Those that are produced through the direct intervention of the electric current; (2) those in which electricity is manifestly produced by small voltaic couples resulting from the presence of two different metals in the solution experimented with; (3) those in which there are no voltaic couples, but in which it is proved that electricity is one of the causes that concur in the production of the phenomenon; (4) finally, those in which it is rational, through analogy with the preceding, to infer that electricity is not absent from the phenomenon.

I. We know that, by means of voltaic electricity or induction, we can crystallize a large number of substances.

Despretz tried this means for months at a time upon carbon, either by using the electricity from a Ruhmkorff coil or the current from a weak Daniell’s battery.  In both cases, he obtained on the platinum wires a black powder, in which were found very small octohedral crystals, having the property of polishing rubies rapidly and perfectly—­a property characteristic of diamonds.

The use of voltaic apparatus of high tension has allowed Mr. Cross to form a large number of mineral substances artificially, and among these we may mention carbonate of lime, arragonite, quartz, arseniate of copper, crystalline sulphur, etc.

As regards products formed with the concurrence of electricity (oxides, sulphides, chlorides, iodides, etc.), see “Des Forces Physico-Chimiques,” by Becquerel (p. 231).

There is no doubt as to the part played by electricity in the chemical effects of electro-metallurgy, but it will not prove useless for our subject to remark that when, in this operation, the current has become too weak, the deposit of metal, instead of forming in a thin, adherent, and uniform layer, sometimes occurs under the form of protuberances and crystalline, brittle nodules.  When, on the contrary, the current is very strong, the deposit is pulverulent, that is, in a confused crystallization or in an amorphous state.

Further along, we shall find an application of this remark.  We obtain, moreover, all the intermediate effects of cohesion, form, and color of galvanic deposits.

When, into a solution of acetate of lead, we pass a current through two platinum electrodes, we observe the formation, at the negative pole, of numerous arborizations of metallic lead that grow under the observer’s eye (Fig. 1).  The phenomenon is of a most interesting character when, by means of solar or electric light, we project these brilliant vegetations on a screen.  One might believe that he was witness of the rapid growth of a plant (Fig. 2).  The same phenomenon occurs none the less brilliantly with a solution of nitrate of silver.  A large number of saline solutions are adapted to these decompositions, in which the metal is laid bare under a crystalline form.  Further along we shall see another means of producing analogous ramifications, without the direct use of the electric current.—­C.  Decharme, in La Lumiere Electrique.