The first use of carbonate of magnesia medicinally was in the form
of a secret medicine which must have acquired much popularity in the
beginning of the eighteenth century. It was prepared, says Bergmann,
by a regular canon at Rome, sold under the title of the powder of the
Count of Palma, and credited with almost universal virtues. The method
of preparation was rigidly concealed, but it evidently attracted the
attention of chemists and physicians, for it appears that in 1707
Valentini published a process by which a similar product could be
obtained from the mother liquor of “nitre” (soda) by calcination. In
1709 Slevogt obtained a powder exactly resembling it by precipitating
magnesia from a solution of the sulphate by potash. Lancisi reported
on it in 1717, and in 1722 Hoffmann went near to explaining the
distinction between the several earthy salts, which in his time were
all regarded as calcareous.
Hoffmann’s process to obtain the powder was to add a solution of
carbonate of potash to the mother liquor from which rough nitre had
been obtained (solution of chloride of magnesium), and collect the
precipitate. This being yielded by two clear solutions gave to the
carbonate of magnesia precipitated the name of Miraculum Chemicum.
Magnesia was the name of a district in Thessaly, and of two cities in
Asia Minor. The Greek “magnesia lithos,” magnesian stone, has been
frequently applied to the lodestone, but this can hardly have been
correct, as the magnesian stone was described as white and shining
like silver. Liddell and Scott think talc was more 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 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.
[Illustration: JOSEPH BLACK LECTURING (AFTER JOHN RAY)
(From a print in the British Museum.)
]
The oxide of magnesia was believed to be an elementary substance until
Sir Humphry Davy separated the metal from the earth by his electrolytic
method in the presence of mercury. By this means he obtained an
amalgam, and by oxidising this he reproduced magnesia and left the
mercury free, thus proving that the earth was an oxide of a metal.
In 1830 Bussy isolated the magnesium by heating in a glass tube some
potassium covered with fragments of chloride of magnesium, and washing
away the chloride of potassium formed. Magnesium in small globules
was left in the tube. The metal is now prepared on an industrial
scale either by electrolysis, or by fusing fluor-spar with sodium. At
present the uses of magnesium and of its derivatives are infinitesimal
in comparison with the vast quantities available in deposits, as in
dolomite, and in the sea.