The author gives an account of a number of experiments that he performed on this latter substance, many of which are curious and original. Hard soap, when perfectly dry, if either end of the galvanic pile, conducts all the electricity from that extremity into the ground, and there appears to he no perceptible difference in its action upon the two extremities. If wires be connected with each end, and be made to terminate in a prism of hard dry soap, which is kept insulated, the circuit will not be completed; but if this soap be uninsulated, by establishing a communi cation with the ground, an electrometer connected with the positive pole, manifests a great degree of divergence, while one on the negative pole loses all signs of it. " Consequent ly," M. Erman observes, " the soap which insulates the positive effect, is a perfect conductor for the negative." As a proof and illustration of this property, the author in forms us, that "if one finger be applied to the wire of the positive pole, and another finger wetted to the soap, no shock is felt, and the electrometers do not show the least change in their respective divergencies. But if the experiment be repeated, by establishing a communication between the positive pole and the soap with both fingers wetted, a very perceptible shock will be felt, and the two electrometers will arrive at an equal, and a very weak de gree of intensity." IIe proposes the following nomencla ture for these live classes of bodies : 1st, Insulators ; 2d, Perfect conductors ; 3d, Bipolar imperfect conductors ; 4th, Positive unipolar; and 5th, Negative unipolar : (Jour. Phys. Ixiv. 121.) Although, as we shall afterwards find, Mr Brande explains the facts upon rather a different prin ciple, yet they arc highly important, and M. Erman is en titled to much commendation for the skill with which he conducted his experiments.
Guyton suggested an idea, which appears sufficiently plausible, that the action of galvanism may affect the for mation of metallic oxides, and even cause them to assume the particular forms which they occasionally exhibit : (Ann. de C'hinz, lxiii. 113.) Bucholtz detailed a series of experi ments which he performed, where a metallic oxide, held in solution by an acid, was precipitated in the metallic state by the metal itself. The metallic solution was placed in the bottom of a cylindrical jar, and a stratum of water was carefully spread over it. A slip of the same kind of metal that formed the solution was then placed perpendicularly in both the fluids. The upper part of the metal which was in the water was oxidated, while the lower part in the me tallic solution had particles of the reduced metal deposited upon it. The reduction of the oxide was always expedited by whatever promoted the oxidation of the upper part of the metal. Experiments of an analogous nature were per formed by Grotthus, on what lie calls the arborization of metals, which, like the circle of actions described by Bu choltz, he attributes to a galvanic operation. In these pro cesses, however, there are two metals concerned; and he spews that the tree is formed by successive portions of the dissolved oxide being reduced and attached to the solid metal, which, in its turn, becomes oxidated : (Ann. de C1/2im.lxiii. 5.) We have a little anticipated the chronolo gical order in the relation of these two last sets of experi ments, in order that we might not be interrupted in narrat ing the account of the decomposition of the alkalies and earths, which composes the third period of the history of galvanism.
About the conclusion of the year 1806, Sir H. Davy read
to the Royal Society of London the first of his series of pa pers, on what has been styled the electrochemical action of bodies, which have been so justly celebrated, no less for the brilliant discoveries of which they give an account, than for the acuteness and sagacity which the author dis plays in his researches into the most hidden operations of nature. He commences by some remarks on the action of galvanic electricity upon water. He notices the experi ments in which acids and alkalies appear to have been formed in water subjected to the galvanic current ; and he states, that when he employed separate portions of water, connected together by slips of bladder, and united by gold wires to the voltaic battery, he obtained nitro-muriatic acid at the positive, and soda at the negative wire. It was, how ever, conjectured, that the animal matter placed between the two portions of water might contain muriate of soda, and thus afford the substances procured in the experiment ; lie therefore, at the suggestion of Dr Wollaston, substi tuted asbestos for the slips of bladder. It was also con ceived, that when glass vessels were used, the alkali might proceed from a partial decomposition of the glass ; and af ter trying various other substances, at length conical ves sels of gold were employed : (Plate CCLXIII. Fig. 9.) With thek precautions, and when the water was very carefully prepared, no acid or alkali were obtained; and consequently the author concludes, tl.at in all those experi ments which were attended with contrary results, the acid and alkali must have proceeded from some extraneous source, not having been generated, but evolved, either from something held in solution by the water, or from some of the materials employed in the apparatus. Perfectly pure water, when subjected to the action of electricity, affords nothing except oxygen and hydrogen.
The very powerful action of the galvanic electricity, in the decomposition of various earthy and saline compounds, as experienced by Sir 11. Davy in the researches above mentioned, offered an extensive field for farther investi gation. Hisinger and Berzelius, in the valuable memoir to which we have already referred, noticed the tendency which different bodies possess, to attach themselves to one of the wires exclusively ; acids and analogous bodies being attracted to the positive, while alkalies, metals, and all in flammables, were attracted to the negative wire. , Our au thor had observed similar phenomena in his own experi ments, and was induced to make them the more immediate subject of his examination. Acids and alkalies were found uniformly to observe this order ; and it was perceived, that when substances, not supposed to he soluble in water, form ed part of the circuit, they were also decomposed, and their components carried to the positive and negative wires re spectively. In this way was effected the decomposition of sulphate of lime, sulphate of strontites, fltute of lime, and sulphate of barytes. It was also perceived, that small portions of acid and alkaline bodies ente•ed into the composition of solid earths, they might be detected by the galvanic influence, and would be transmitted `o their re spective wires. In this way, lime and soda were obtained from basalt and from zeolite, potash from lepidolite, Etc. In proportion to the solubility of a salt, its decomposition was the more readily accomplished; and when neutral salts were employed, the separation of the component parts seems to have been quite complete.