probably the substance. The alchemists sometimes mention a magnesia, but the name seems to have been a very elastic one with them. The Historical English Dictionary quotes the following reference to the word from "Norton Ord. Alch.," 1477:—"Another stone you must have . . . a stone glittering with perspicuitie . . . the price of an ounce conveniently is Twenty Shillings. Her name is Magnetia. Few people her knows."
Paracelsus uses the term in the sense of an amalgam. He writes of the Magnesia of Gold. In Pomet's "History of Drugs," 1712, magnesia meant manganese. Hoffmann, 1722, first applied the name to oxide of magnesia, adapting it from the medical Latin term, magnes carneus, flesh magnet, because it adheres so strongly to the lips, the fancy being that it attracts the flesh as the lodestone attracts iron.
Hoffmann's observations on magnesia and its salts, which were published in the first quarter of the eighteenth century, were very intelligent, and undoubtedly it was he who first distinguished magnesia from chalk. He says "A number of springs, among which I may mention Eger, Elster, Schwalbach, and Wilding, contain a neutral salt which has not yet received a name, and which is almost unknown. I have also found it in the waters of Hornhausen which owe to this salt their aperient and diuretic properties. Authors commonly call it nitre; but it has nothing in common with nitre. It is not inflammable, its crystallising form is entirely different, and it does not yield aqua fortis. It is a neutral salt similar to the arcanum duplicatum (sulphate of potash), bitter in taste, and producing on the tongue a sensation of cold." He further states that the salt in question appears to proceed from the combination of sulphuric acid with a calcareous earth of alkaline nature. The combination "is effected in the
