(From the Arabic lakah). Lac, or gum lac; ancosa; is a concrete brittle substance, of dark red colour, brought from the East Indies, incrusted on pieces of sticks, internally divided into cells. It is the gummy resinous substance from two species of ficus, viz. they. Indica and religiosa Lin. Sp. Pl. 1514, effused in consequence of the puncture of a species of coccus. The nest in which the insect also is sometimes found adhering to the branches is called stick lac. In the cells small red bodies are often observed, which appear to be the young insects.,if the stick lac is broken into small pieces, and infused in warm water until it ceases to give any tincture to the liquor, the remainder appears of a transparent, yellowish brown colour, and is called seed lac: and on raising the heat so as to melt the seed lac, it rises to the surface, and is formed into what is called shell lac. When melted, and cast in cakes, it is styled lac in tablets.
The seed and shell lacs being robbed of the colouring animal matter, seem to be of an intermediate nature between that of wax and resin, and to partake of the nature of both. They crumble on chewing, and do not soften or unite again; laid on a hot iron, they inflame, and soon burn. If distilled like wax, they yield an acid spirit, and a butyraceous oil. Alkaline lixivia, and volatile alkaline spirit, dissolve them into a purplish liquor. With the help of heat, they dissolve in rectified spirit of wine. Alum promotes their solution in boiling water. Lac is not used in medicine; but the colouring matters serves as a paint, and the remainder is an ingredient in sealing wax. See Neumann's Chemical Works. Lewis's Materia Medica.
From lac an acid is procured, styled the laccic acid. Dr. Anderson, in 1786, received from the interior parts of Hindostan nests of insects, resembling cowry shells, which he found to be the coverings of the females of an undescribed species of coccus. Some of this matter, which resembled bees' wax, was sent to England; and, in 1794,Dr. Pearson, in the Philosophical Transactions, published an analysis of it.
About one quarter of this white lac contains a reddish acid, which tasted saltish, and not sour, though it changes paper, stained with turnsole, to a red colour. When heated, the smell is that of newly baked bread. The properties of this acid are very distinct; but as it has not been employed in medicine, they need not detain us.