Experiments upon magnesia alba, quick-lime, and other alcaline substances / by Joseph Black.

  • Black Joseph, 1728-1799.
Date:
1893
Catalogue details

Licence: Public Domain Mark

Credit: Experiments upon magnesia alba, quick-lime, and other alcaline substances / by Joseph Black. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    now described. Thus, if a small quantity of any cal- careous matter be reduced to a fine powder, and thrown into spirit of vitriol, it is attracted by this acid with a brisk effervescence; but little or no dissolution ensues. It absorbs the acid, and remains united with it, in the form of a white powder, at the bottom of the vessel, while the liquor has hardly any taste, and shows only a very hght cloud upon the addition of an alkali.* The same white powder is also formed when spirit of vitriol is added to a calcareous earth dissolved in any other acid; the vitriolic expelling the other acid, and joining itself to the earth by a stronger attraction; and, upon this account, the magnesia of sea-water seems to be different from either of those described by Hoffman. He says expressly, that the solutions of each of his powders, or, what is equivalent, that the hquors from which they are obtained, formed a coagulum, and deposited a white powder, when he added the vitriohc acid ;t which experi- ment I have often tried with the marine bittern, but without success. The coagulum thus formed in the mother of nitre, may be owing to a quantity of quick- ime contained in it; for quick-hme is used in extracting the salt-petre from its matrix.—But it is more difficult to account for the difference between Hoffman's bittern and ours, unless we will be satisfied to refer it to this, that he got his from the waters of salt-springs, which may possibly be different from those of the sea. Magnesia is not less remarkably distinguished from the * Mr Margraaf has lately demonstrated, by a set of curious and accurate experiments, that this powder is of the nature, and possesses the properties, of the gypseous or selenitic substances.— That such substances can be resolved into vitriolic acid and cal- careous earth, and can be again composed by joining these two ingredients together. Mem. de I'Acad. de Berlin, ann. 1750, p. 144.