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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    I mixed an ounce and a half of salt of tartar with three ounces of black lead, a substance of any the most unchangeable by chemical operations. This mixture I exposed for several hours, in a covered crucible, to a fire somewhat stronger than what is necessary to keep salt of tartar in fusion. When allowed to cool, I found it still in the form of a loose powder ; and, taking out one half, I diluted it with water, and, by filtration, obtained a ley, which, when poured into a solution of white marble, in aqiia-fortis, precipitated the marble under the form of a weak quick-lime : for, the turbid mixture gave a green colour to the juice of violets, and threw up a crust like that of lime-water ; and the precipitated powder, collected and mixed with salt-ammoniac, immediately yielded the scent of the volatile alkali. Lest it should be here suspected, that the alkaline qualities of this mixture, and of the precipitated marble, were not owing to a lime into which the marble was converted, but to the alkali itself which was added, it is proper to observe, that I mixed so small a proportion of the ley with the solution of marble, as made me sure, from certain experiments, that the whole of the alkali was spent in performing the precipitation, and was con- sequently converted into a neutral salt by attracting the acid. The properties, therefore, of the mixture, can only be referred to a lime, as is indeed sufficiently evident from the crust which is peculiar to lime-water. I was therefore assured by this experiment, that an alkali does really lose a part of its air, and acquire a degree of causticity, by the proper apphcation of heat; but, finding, by several trials, that the degree of causticity which it had thus acquired was but weak, and that the quick-lime produced in this experiment was exhausted and rendered mild by a small quantity of water, I exposed the crucible, togethe rwith that half of the alkali which