It is less than a century since the ancient view, that water was one of the four ele ments, has cepsed to be believed in. It is now known that it is a compound of oxygen with hydrogen in the proportion of one equivalent of each. Hence its symbol is HO, and its combining number 9. When converted into vapor, 9 grains of steam occupy the bulk of 8 grains of oxygen at the same temperature; hence the combining volume of aqueous vapor is equal to 2, if the combining volume of oxygen be taken as 1. That water is such a compound as just stated may be proved either analyti cally or synthetically; and the subject is one of so great importance in the history of chemistry, that we shall enter more fully than usual into the consideration of these two modes of proof. The following simple mode of separating water by voltaic electricity into its constituent elements is borrowed from Fownes's Manual of Chemistry: "When water is acidulated so as to render it a conductor, and a portion interposed between a pair of platinum plates connected with the extremities of a volaic apparatus of moderate power, decomposition of the liquid takes place in a very interesting manner; oxygen in a state of perfect purity is evolved from the water in contact with the plate belonging to the copper end of the battery, and hydrogen, equally pure, is disengaged at the plate connected with the zinc extremity, the middle jars of the liquid remaining appar ently unaltered. By placing small graduated ars over the platinum-plates, the gases can be collected, and their quantities determined. When this experiment has been con tinued a sufficient time, it will be found that the volume of the hydrogen is a very little above twice that of the oxygen; were it not for the circumstance of oxygen being sensi bly more soluble in water than hydrogen, the proportion of two to one by measure would come out exactly." Iu lecture-rooms, an ingenious but more complicated appa ratus, devised by Kopp, is commonly used to illustrate the electrolysis of water. It has • been shown by Mr. Grove that an extreme heat may, like electricity, be employed to decompose water into its constitutents; and it is well known that if, in the form of steam, it be passed over red-hot iron, it parts with its oxygen to the metal, while the hydrogen is given off as gas. The synthetical proof of the composition of water is afforded by passing pure hydrogen and oxygen, in the ratio of two volumes of the former to one volume of the latter, into a strong glass tube filled with mercury, and exploding the mixture by an electric spark, when the gases are replaced by a corre sponding quantity of moisture, and the mercury is forced into the tube so as to fill it. The most satisfactory form of this synthetical proof is, however, afforded by reducing pure oxide of copper at a red heat by hydrogen, and collecting and weighing the water that is thus formed. The apparatus required for this experiment, and the method of employ ing it, are given in Fownes's Manual of Chemistry, 9th ed., p. 131, and in Miller's Inor ganic Chemistry, 3d ed., p. 52.
Owing to its extremely solvent powers, the pure water which we have been hitherto considering is never found in nature. The nearest approach to a natural pure water is rain-water, after a continuance of wet weather; but even this water always contains in' 100 volumes about 2.5 volumes of atmospheric air, with a trace of ammonia; and in point of fact, it seems impossible.to obtain water which does not contain this ingredient, for, after two distillations, professor Miller found from 1.85 to 2.38 volumes of air in 100 volumes of water. In addition to rain-water, the other natural waters may be included under the heads of spring-water, mineral. waters (already considered in a special article), ricer-water (see WATER-SUPPLY), and sea-water (see below).
This article would be incomplete without a brief notice of the prolonged and acrimoni ous controversy that was for many years carried on, and is probably now hardly to be regarded as settled, regarding the respective claims of different philosophers to be the true discoverer of the nature and composition of water. In the year 1781, Cavendish made a long and careful series of experiments, which, unfortunately, were not published till Jan., 1784, when his celebrated memoir entitled Experiments on Air, was read to the royal society. ‘In the interval (June, 1783), his friend, Dr. Blagden, visited Paris, and
on the authority of Cavendish, gave an account of the experiments proving the compo sition of water to Lavoisier; and this delay between the discovery and the date of pub lication caused his claims to one of the most marvelous discoveries the world ever saw, to be contested by an English and a French rival, James Watt and Lavoisier. It may be briefly stated, that Cavendish's experiments consisted in exploding, in vari ous proportions, mixtures of hydrogen and atmospheric air, and of hydrogen and oxygen, and finding as the result a liquid which proved to be pure water. (Priest ley a-nd his friend, MrjWarltire, bad made similar experiments. and had noticed the deposition of mpiure that followed the explosion, but failed to recognize in.
it anything hut the conclerssation of aqueous vapors in the gases.) The general con clusion to which Cavendish came was, in his own words, " that water consists of dephlogisticated air united with phlogiston," and as dephlogisticated air was his term for oxygen, and phlogiston his term for hydrogen, this statement corresponds to the modern view of the nature of water introduced by Lavoisier. As Lavoisier was from the first accused by the English chemists of having acted unfairlyr toward them, and its indeed his own claim only dates back to June 25, 1783, he may be dismissed from further consideration; and during the lives of the English claimants there were eo pub lic complaints on either side, although Watt, in private letters to his friends, hinted at Cavendish's incapacity and unfairness. Hence, then—at all events, in this country— scientific men were startled when Arago, then secretary of the French academy, pub lished in 1838 the doge of Watt,' which lie had read as far hack as Dec., 1834, in which he charged Cavendish with deceit and plagiarism, inasmuch as he was said to have learned the composition of water, not by experiments of his own, but by obtaining sight of a letter from Watt to Priestley, The battle now fairly began; the first blow being struck in Aug., 1839, when the president of the British association, the rev. Vernon Harcourt, in his opening address, vindicated Cavendish, and pointed out Arago's mis .statement. At a subsequent meeting of the academy, Arago, with Dumas to back him, defended his statements. Sir David Brewster (Edin. Rev., Jan.,. 1840), then sought to net as mediator; and the controversy, as might have been expected, went on with increased acrimony; and in the summer of the same year, when the president of the British association published the report he had delivered the preceding year, he added a replying to Arago, Donuts, and lord Brougham (who had appended '• An istorical Note on the Discovery of the Theory of Water," to Arago's eloge). In 1841, Berzelius published what Dr. George Wilson terms "a conditional judgment," in favor of Watt; and in 1845, in his Lives of Men of Letters (see Life of Watt, p. 400), lord Brougham followed on the same side. Dr. Peacock (Quart. Rev., 1845, p. 105), in reviewing his book, assailed his conclusions, and asserted the claims of Cavendish. In 1846, Mr. Harcourt (Loud. and Eden. Phil. Mag., Feb., 1846), also replied to lord Brougham; and in 1847, in the second edition of Ins History of the Inductive Sciences, Dr. Whewell maintained his old conviction of the claims of Cavendish. In 1846, the pub lication of the Correspondence of the lute James Watt on his Discovery of the Theory of the Composition of Water, with an introduction by his kinsman, Mr. Muirhead, who was editor, and a letter from his son, formed a most important addition to the literature of this controversy. Finally, the question was discussed, in 1847, by sir David Brewster in the North British Review, and in 1848, by lord .Jeffrey in the Edinburgh Review, both of whom advocated the claims of Watt. As we have no space to discuss Watt's real Maims, we may here state that Dr. George Wilson, whose Life of Cavendish is in reality a strictly impartial history of the water controversy, maintains on very sound grounds that in reality Watt was informed of Cavendish's discovery through Priestley, as Lavoi sier was through Blagden.