Chalybeate waters, it must be acknowledged, have effected very extraordinary cures in certain cases. But when so great an author as Helmont says, that such waters are fatal to all those who are afflicted with peripneumonic complaints, it is surely necessary they should be resorted to with the greatest caution; and even in complaints where they may be serviceable, it is necessary to observe whether they really possess those chalybeate qualities for which they are commended. Those who have written upon their virtues assert, and with seeming propriety, that where they deposit an ochreous sediment, they are certainly dispossessed of their steely virtues; for ochre being no other than the calx of iron, such a residue evinces the evaporation of the more eminent properties of the chalybeate, by the phlogiston of the mineral escaping by its extreme volatility. Every metal deprived of this igneous principle is immediately reduced to a calx, and thus deprived of its splendour, fusibility, and other properties, until restored again by the readmission of its phlogiston. Calcined lead having lost this inflammable quality, is reduced to a red calx or mineral earth, which, if fluxed with any igneous body, such as oil, pitch, wax, fat, wood, bone, or mineral oil or bitumen, the fiery principle is resorbed, and the lead restored to its essential qualities; from these physical observations the reader may be convinced of those mineral waters as afford such a sediment being in a state of decomposition. They are thus deprived of one of the four elements or principles of which they are all more or less composed. Every analysis of mineral waters in their perfect state has demonstrated that they possess a fixed air, a volatile alkali, a volatile vitriolic acid, and the phlogiston. If, therefore, either of these essential qualities is evaporated or corrupted, the water, being in a state of decomposition, must lose the virtues of a medicinal chalybeate.