From quick-lime, as already described.

Characters And Tests

The hydrate of lime, though it can absorb 31 per cent. of its weight of water, remains perfectly dry, and is itself very sparingly soluble in water (1 in 900), and less soluble in hot than in cold water; at 32° F. twice as much lime is dissolved as at 212° F. At ordinary temperatures water dissolves only about 1/2 gr. to the ounce, but its solvent power is increased by syrup or by glycerin to the extent of nearly 8 gr. to the ounce. Lime does not melt at the highest temperature, and hence its use for the electric and oxyhydrogen lights; sp. gr. 2.078.

The chief test for lime is the white precipitate formed with oxalate of ammonium, insoluble in acetic acid, but soluble in hydrochloric or nitric acid. Lime readily absorbs carbonic acid, the presence of which is detected by effervescence with acids. (This power of absorbing CO2 has been utilized by Liebig to purify close rooms, for lime placed in them will, by such absorption, create a partial vacuum, to supply which air passes in through crevices. The same absorptive power partly causes the dampness of a new house, for the lime of mortar absorbs the carbonic acid of the air and the breath, leaving the moisture to condense on the walls.)

The Liquor Calcis of the Pharmacopoeia is a solution in water containing about 1/2 gr. to the ounce (that being its point of saturation). It is prepared by digesting slaked lime in eighty times its weight of cold water for some hours, and is a colorless liquid when recently made, but on exposure to air, or if breathed into, an insoluble carbonate readily forms and precipitates. If warmed, the liquor calcis becomes turbid from deposition of some of the lime. It forms an ingredient in the black and the yellow "mercurial wash."