In his treatise on chemistry Lavoisier describes more fully his proof that the calcination of a metal consists in the removal, by the metal, of dephlogisticated air (or oxygen) from the atmosphere, and that the metallic calx is simply a compound of metal and oxygen. The experiments are strictly quantitative and are thoroughly conclusive. He placed four ounces of pure mercury in a glass balloon, the neck of which dipped beneath the surface of mercury in a glass dish, and then passed a little way up into a jar containing fifty cubic inches of air, and standing in the mercury in the dish. There was thus free communication between the air in the balloon and that in the glass jar, but no communication between the air inside and that outside the whole apparatus. The mercury in the balloon was heated nearly to its boiling point for twelve days, during which time red-coloured specks gradually formed on the surface of the metal; at the end of this time it was found that the air in the glass jar measured between forty-two and forty-three cubic inches. The red specks when collected amounted to forty-five grains; they were heated in a very small retort connected with a graduated glass cylinder containing mercury. Between seven and eight cubic inches of pure dephlogisticated air (oxygen) were obtained in this cylinder, and forty-one and a half grains of metallic mercury remained when the decomposition of the red substance was completed. The conclusion drawn by Lavoisier from these experiments was that mercury, when heated nearly to boiling in contact with air, withdraws oxygen from the air and combines with this gas to form _red precipitate_, and that when the red precipitate which has been thus formed is strongly heated, it parts with the whole of its oxygen, and is changed back again into metallic mercury. Lavoisier had now (1777-78) proved that the calces of mercury, tin and lead are compounds of these metals with oxygen; and that the oxygen is obtained from the atmosphere when the metal burns. But the phlogistic chemistry was not yet overthrown. We have seen that the upholders of phlogiston believed that in the inflammable air of Cavendish they had at last succeeded in obtaining the long-sought-for phlogiston. Now they triumphantly asked, Why, when metals dissolve in diluted vitriolic or muriatic acid with evolution of inflammable air, are calces of these metals produced? And they answered as triumphantly, Because these metals lose phlogiston by this process, and we know that a calx is a metal deprived of its phlogiston.