Chap. V Various Experiments With the Galvanic Pile
The first experiments which we shall mention were performed by Mr. Cruickshank, with the Galvanic pile. He employed plates of zinc and silver, 1.6 inches square, and the number of plates of both metals varied from forty to a hundred, according to the power required. The lower end of the pile we shall denominate the silver end, because the plate at the bottom is of silver, and the upper end the zinc end, because the uppermost plate is of zinc. The first experiment of Mr. Cruickshank with the Galvanic pile, was upon water and silver wires. These wires were passed through corks, fitted into a glass tube filled with water, and projected about one third of the way, on both sides, into the tube; so that the space between the inner ends of the wires was one third of the length of the tube. One of the corks was made perfectly tight by cement. The tube was then placed upright in a tumbler of water, with the uncemented end downwards.
As soon as a communication was made between the extremities of the pile by the wires, small air bubbles began to ascend from the wire connected with the silver end, and a white cloud made its appearance at the wire proceeding from the zinc end.—The cloud gradually increased, assuming a darker colour, and at last it became purple, and even black. A few air bubbles were likewise observed upon this wire, which ascended from it; but when the pile acted well, a considerable stream of air could be perceived.—When this gas was examined, it was found to be a mixture of hydrogen and oxygen, in the proportion of three parts of the former to one of the latter. No great reliance, however, can be placed on the accuracy of this analysis. The wire proceeding from the zinc end, was found much corroded, and looked as if a portion of it had been dissolved.
Mr. Cruickshank supposed the cloud formed round the wire of the zinc end to be the muriate of silver, proceeding from the silver wire which had been somehow dissolved, and afterwards precipitated in this state, by the muriatic salts contained in the common water.
The next experiment was with distilled water, a tincture of litmus, and silver wires, as before. The apparatus being adjusted in the manner above described, and one wire connected with one end of the pile, while the other touched the other end, gas immediately arose from both wires, but in greater quantity from the one connected with the silver plate. In a short time the whole fluid below the point of the wire from the zinc plate, became red, and the fluid below the wire from the silver plate, looked of a deeper blue. Distilled water tinged with Brazil wood, soon became of as deep a purple as could be produced by ammonia.—From the two last experiments, Mr. Cruickshank was led to suppose, that an acid, probably the nitrous, is produced at the wire connected with the zinc plate, and an alkali, probably ammonia, at the one connected with the silver end of the pile.
As hydrogen gas, whether heated or in its natural state, reduces metallic oxyds, Mr. Cruickshank resolved to subject solutions of metallic oxyds to the hydrogen gas which was produced by the pile.—The result answered his expectation, for in a minute or two after the communication was formed, fine metallic needles or crystals, something resembling a feather, were perceived round the wire connected with the silver plate.—The oxygen too which escaped from the metal, and that generated from the fluid used in the solution, was commonly pure, when an excess of acid was added to take up the alkali.—The acetite of lead and the sulphate of copper, were among the oxyds experimented upon, but whatever the metal was, the results coincided. These experiments were made in a tube like the preceding ones.—A number of experiments were made by the same gentleman upon the earths, but we shall not detail them; we must content ourselves with some conclusions drawn from his observations.
1. Hydrogen gas, mixed with a small portion of oxygen and ammonia, is somehow disengaged at the wire communicating with the silver extremity of the pile; and this effect is equally produced, whatever the nature of the metallic wire may be, provided the fluid operated upon be water.
2. When metallic solutions are used, the same wire which separates the hydrogen gas, revives the metallic calx, and deposits it at its extremity, in its pure metallic state; in this case no hydrogen is disengaged. The wire employed for this purpose may be of any metal.
3. Of the earthy solutions, only those of magnesia and argill are decomposed by the wire: a circumstance which strongly favours the production of ammonia.