In the year 1804, a very valuable memoir was written by Hisinger and Berzelius, which must be regarded as con taining the fundamental principle of those doctrines, which have since been so extensively developed by Sir Humphry Davy. By passing the galvanic influence through solu tions of the different neutral salts, they found that there was a transfer of the acid and alkali to different parts of the apparatus. They formed the general conclusion, that whenever electricity is sent across a fluid, it disposes its constituents to separate and pass to the two sides respec tively; combustible substances, alkalies, and earths, are at tracted to the negative ; acids, oxides, &cc. to the positive extremity of the pile. The force of decomposition they suppose is in the ratio of the quantity of electricity, and that the electricity is in proportion to the surface of metal which is in contact with a moist conductor. The decom position is also influenced by the affinity of the components of the substance, its power of conducting electricity, and other circumstances. See Ann. de Chim. li. 167.
Mr Cruikshanks, among his earliest discoveries, had ob served, that an acid and an alkali were generated at the two ends of the wires in the interrupted circuit, and this fact had been confirmed by other experimentalists. The sub stances produced were supposed to be nitric acid and am monia; the first originating from the union of oxygen with the azote of air dissolved in the water, the latter from hy drogen combining with the same element. But it was now announced, that muriatic acid and soda were generated by passing the electric current through pure water, and where this salt could not be suspected to be present in any part of the apparatus, or in any of the materials employed. In the spring of 1805, the following letter was published, pur porting to be written by Mr Peel of Cambridge: " I•took about a pint of distilled water, and decomposed about one half of it by means of galvanism, the other half I evapo rated, and found to remain at the bottom of the glass a small quantity of salt, which, upon examination, proved to be muriate of soda. The salt could not have been contain ed in the water before I made the experiment, because I used every precaution to have it free from impurities. I even took the trouble to repeat the experiment, though a tedious one, and I again obtained the sante result. A friend of mine has just informed me that he has tried my expe riment, and has succeeded in procuring the salt." See Tilloch's Mag. xxi. 279.
Almost at the same time that this notice was published in London, Pacchioni, professor at Pisa, gave an account of some experiments upon the action of galvanism on wa ter, in which he obtained results analogous to those sta ted above. He informs us, that when water had been for a long time subjected to the galvanic influence, and had been parting with its oxygen from the extremity of a gold wire, the fluid was found to contain a quantity of oxymu riatic acid. From this experiment he drew the following conclusions : Oxymuriatic acid is an oxide of hydrogen ; it consists of water deprived of part of its oxygen ; mu riatic acid is water in a still lower degree of oxidation ; and, of course, oxygen and hydrogen are susceptible of different degrees of oxidation. See Edinburgh Med. Journ.
i. 393.
A great degree of attention was excited by these expe riments, to which the more credit was attached, because they proceeded from sources entirely independent of each other. They were repeated by different experimentalists in this country, and in some cases with apparent success. Mr Sylvester in particular, obtained traces both of muria tic acid and soda, where proper precautions were supposed to have been taken, to exclude the muriate of soda from every part of the apparatus. But from facts which have been subsequently discovered, we may conclude, that the substances obtained in these cases were not derived from the decomposition of the water. Pacchioni's experiments are now universally admitted to have been incorrect ; and it appears that no such individual as Mr Peel could be found in Cambridge, so that the letter bearing his name is a complete fabrication. It was not, however, entirely with out its use ; for the minute examination of the effects of galvanic electricity upon water, to which it gave rise, may probably be regarded, in some measure, as the immediate cause of Sir H. Davy's most important discoveries.
An elaborate memoir was, about this time, written by Erman, on the conducting power of different bodies, which obtained the prize from the French Institute. His object was to remove some anomalies, which appeared to exist in the relation of the galvanic electricity to the different conducting substances.
He divides all bodies into five classes: 1st, Perfect non conductors ; 2d, Perfect conductors; 3d, Imperfect con ductors; 4th, Positive conductors ; and 5th, Negative con ductors. The nature of the three first classes requires no explanation ; the fourth and fifth class of bodies act as per fect conductors, when applied to either of the two poles separately, but when placed between them, insulate either the positive or negative pole respectively, and do not form a communication between them. The flame of a spirit lamp is described as a positive conductor; if it be applied to each pole separately, it conducts the electricity ; but if it be placed between the two poles, it will not form a com munication between them, in consequence of its insulating the negative electricity. Although flame is a conductor of galvanism, it does not conduct it so perfectly as metals. No effect is produced, when flame is interposed between the extremities of the pile. Flame is, however, a very dif ferent substance, according to the body from which it is procured : the above observation refers to the flame of a hydro-carbonous body. The flame of sulphur insulates both the poles ; and that of phosphorus insulates the posi tive, and conducts the negative influence. Phosphorus must therefore be placed in the fifth class of bodies; and perfectly dry soap is also a negative conductor.