The explanation of the solution of metals in acids was now easy: it depended on the decomposition of water. While the oxygen united with the metal to form a calx, the hydrogen was evolved; the calx dissolved in the acid, forming a salt of the metal. And the operation of producing hydrogen by the action of steam on red-hot iron met with an equally simple explanation: the oxygen and iron united to form an oxide--the ancient _ethiops martial_--while the hydrogen escaped. The converse took place during the reduction of a calx to the metallic state by hydrogen. Here the hydrogen seized on the oxygen of the calx, removed it in the form of water, and the metal was left. These experiments were due to Cavendish; all that Lavoisier did was to show the true nature of the phenomena. The opponents of the new doctrines, Priestley chief among them, did their best to disprove the view that water was a compound of oxygen and hydrogen. But in vain. Many of Lavoisier’s opponents had to admit the justice of his views; and in 1787 De Morveau, Berthollet, and Fourcroy joined Lavoisier in reconstructing the nomenclature of chemistry on a new basis, which is substantially that in use at the present day. Black, too, was a convert, but Priestley and Cavendish remained true to their old faith, and one of Priestley’s last acts was to publish a defence of the phlogistic theory. We shall see later how Cavendish carefully considered the rival theories, and what reasons induced him to cast his vote for the older one. Among the numerous memoirs which Lavoisier communicated to the Academy during the ten years between 1772 and 1782, one still remains to be mentioned. It was published as early as 1777, but it must be remembered that many of these memoirs were antedated. It referred to the respiration of animals; and Lavoisier concluded, on the ground that the phenomena of respiration are essentially similar to those of combustion and calcination, that the only portion of the air which supports animal life is the oxygen. The azote or nitrogen is inhaled along with the oxygen, but is exhaled unaltered. The oxygen, however, is gradually converted into carbonic acid; and when a certain amount, but by no means the whole, has been thus changed, the air becomes unfit for respiration. If the carbonic acid is withdrawn by means of lime-water or caustic alkali, the residue is air poor in oxygen, and the azote is the same as that left after the calcination of metals, or the burning of a candle, in air. At the time of his impeachment, Lavoisier was engaged in experiments on perspiration, along with Séguin. He had nearly finished his experimental work, but had drawn up no account of it. His request that his life might be prolonged until he had compiled a statement of his results was refused; but Séguin, who was fortunately spared, undertook the task. The facts collected do not, however, bear directly on our subject, and shall not be further alluded to here.