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 bosom of the earth.” In another of his works Hoffmann distinguishes the magnesian salt from one of lime, showing particularly that the latter was but slightly soluble and had scarcely any taste. Crabs’ eyes and egg shells he notes combine with sulphuric acid and form salts with no taste. The sulphate of this earth (Epsom salt) he found had a strong bitter taste.
The true character of magnesia and its salts was not clearly understood until Joseph Black unravelled the complications of the alkaline salts by his historic investigation, which became one of the most noted epochs of chemistry by its incidental revelation of the combination of the caustic alkalies with what Black termed “fixed air,” subsequently named carbonic acid gas by Lavoisier in 1784. When Black was studying medicine at Edinburgh a lively controversy was in progress in medical circles on the mode of action of the lithontriptic medicines which had lately been introduced. Drs. Whytt and Aston, both university professors, were the leaders in this dispute. Whytt held that lime water made from oyster shells was more effective for dissolving calculi in the bladder than lime water prepared from ordinary calcareous stone. Alston insisted that the latter was preferable. Black was interested, and his experiments convinced him of the scientific importance of his discoveries. He postponed taking his degree for some time in order to be sure of his facts. His graduation thesis, which was dated June 11, 1754, was entitled “De humore acide cibis orto et magnesia alba.” His full treatise, “Experiments upon magnesia alba, quicklime, and some other alkaline substances,” was published in 1756. It had been previously believed that the process of calcining certain alkaline salts whereby caustic alkalies were produced was explained by the combination with the salt of an acrid principle derived from the fire. Now it was shown that something was lost in the process; that the calcined alkali weighed less than the salt experimented with. The something expelled Black proved was an air, and an air different from that of the atmosphere, which was generally supposed to be the one air of the universe. He identified it with the “gas sylvestre” of Van Helmont, and named it “fixed air.” Magnesia alba first appeared in the London Pharmacopœia of 1787 under that name.