In a second memoir, Mr Cruickshanks paid more par ticular attention to the nature of the gases emitted in the interrupted circuit—to the effects of different kinds of wires —and to the influence of the fluid medium upon the de composition of the water. Some of his most important conclusions are, that from the wire connected with the sil ver or copper end of the pile, whatever be its composition, if it terminate in water, the gas emitted is chiefly hydrogen ; if it terminate in a metallic solution, the metal is reduced, and is deposited at the end of the wire. When the wire connected with the zinc end is formed of a perfect metal, nearly pure oxygen is disengaged ; when of an oxidable metal, it is partly oxidated and partly dissolved, and only a small quantity of oxygen is liberated. When fluids contain no oxygen, they appear to be incapable of transmitting the galvanic influence ; while, on the contrary, it would seem that it may be transmitted by every one which contains this element, (Nicholson's Journal, 4to, iv. 258.) These views of Mr Cruickshanks respecting the action of the pile were confirmed by some experiments that were performed, about the same time, by Colo .el Haldane. He found that the apparatus ceased to act when it was immersed in water, or if it was placed in the vacuum of an air-pump. He found, on the contrary, that it acted more powerfully in ox) gen gas, than when confined in an equal bulk of at mospheric air, while azote had the same effect as a vacu um. 'I hese circumstances led him to conceive that its ac depended essentially upon the combination of oxygen, wili,;11 it derives from the atmosphere. See Nicholson's Journal 4to. iv. 242, 313.
In tin. ;:arly part of his experiments, Mr Cruickshanks invented a new manner of disposing the apparatus, which has proved scarcely less important to the interests of sci ence than its original discovery by Volta. We allude to the method of placing the metals horizontally in a frame or trough, (Plate CCLXIII. Fig. 4.) with proper intervals for containing the fluid which is intended to act upon them.
The power of the pile in decomposing chemical sub stances being now established, by the experiments of Ni cholson and Cruickshanks, a new field of investigation was opened, which was ardently entered upon, by some of the most distinguished among the English chemists. Dr Hen ry decomposed the sulphuric and nitric acids, and ammo nia, and he reduced the oxymuriatic to the state of muriatic acid ; but as gases do not conduct the galvanic influence, its decomposing power could not be applied to this last body. See Nicholson's Journal 4to. iv. 223. 245.
Sir H. Davy commenced his discoveries in galvanism at an early period of the investigation. He proposed, as a subject of experimental research, whether the ends of the wire, in the interrupted circuit, would discharge the two gases, if they were made to terminate in different portions of water. The ends of the wires were therefore placed in separate glasses, while the glasses were made to communi cate by means of the fingers, or a moist substance, and it was found that the oxygen and hydrogen were evolved as usual. He next inquired whether it was necessary for the effect that the wires should be in contact with the ends of the pile ; and in order to prove this point, slips of muscular fibre were interposed between the wires and the ends of the pile. The result of this disposition was, that the gases
were disengaged, but in a reverse order ; the hydrogen now proceeding from the wire connected with the zinc end of the pile, and the oxygen from the silver or copper wire.
These experiments, which at the time when they were performed seemed most extraordinary, and almost inex plicable, were succeeded by others equally curious, in which Sir H. Davy produced the galvanic effect, by a new combi nation of substances. He found that charcoal was capable of conducting the influenee and of decomposing water, the opper end giving out hydrogen, holding a little carbon in solution ; the zinc end did not produce any considerable quantity of gas, the carbonic acid which was produced be ing absorbed by the water in which the charcoal was im mersed. He formed a pile of zinc and charcoal, which act ed with considerable energy, and he afterwards discovered that a pile may be constructed of only one metal, with dif ferent fluids applied to its two surfaces, one of them capable of oxidating the metal, the other of preventing the effect of oxidation, the two fluids being separated from each other by water. The series which he employed was metal, diluted nitric acid, water, sulphuret of potash, and then again metal. In a subsequent train of experiments, he proceeded still farther, and composed a pile without any metal, but con sisting solely of pieces of charcoal, having their different surfaces exposed to the action of different fluids. • Sir H. Davy also made some very important observations on the nature of the fluid interposed between the plates of the pile. If the water that is employed be perfectly pure, containing no acid, salt, or gas, the apparatus is incapable of acting. He found that its energy was in proportion to the rapidity with which the oxidation of the metal advances, and consequently was most energetic when nitric acid was made use of. In pursuance of this opinion, he discovered, that the pile can act in vacuo, if an acid be interposed be tween the plates. See Nicholson's Journal, 4to. iv. 275. 326. 337. 344. ; and V. 78. 341.
About this period, Dr Wollaston began to investigate the subject of galvanism, and read a paper to the Royal Society of London, which displays great marks of sagacity and penetration. He observes that the energy of the apparatus seems to be in proportion to the tendency which one of the metals has to be acted upon by the interposed fluid. An experiment is related, not very unlike some of those which had been previously performed by Fabroni. If a plate of zinc and a plate of silver be immersed in diluted sulphuric acid, and kept asunder, the silver is not affected, but the zinc begins to decompose the water, and to evolve hydro gen. If the plates be now placed in contact, the silver dis charges hydrogen, and the zinc continues as before to be dissolved. From these, and other analogous facts, he con cludes, that whenever a metal is dissolved by an acid, elec tricity is disengaged. He extends this principle to the action of the electrical machine, which he conceives has its power increased by applying an amalgam to the cushion, into the composition of which a metal enters which is readily oxidated. As a farther illustration of the same principle, he found, that the machine will not act when immersed in carbonic acid gas.