Page:Proceedings of the Royal Society of London Vol 1.djvu/169

Rh liqueﬁed by ﬁre, and formed into cakes. And, 4. Shell lac, being the original comb, liqueﬁed in water, strained through a cotton cloth, and spread upon ajunk of a plantain—tree so as to form thin transparent laminae : this kind contains the least of the tinging substance, as may well be expected from the mode in which it is prepared.

Among the chemists who have hitherto analysed this substance, none deserve notice except M. Geoﬂ’roy; but our author’s present labours render his investigations of little or no avail.

The ﬁrst section of this paper treats of the effects of different menstrua on the varieties of lac, from which it appears that it is so- luble in alkalies, and in some of the acids. And the second section contains an account of the analytical experiments made on stick, seed, and shell lac. From the ample series of facts herein contained, of which it is in vain to attempt a compendious abstract, we collect in general that the varieties of lac consist of four ingredients, namely, extractive colouring matter, resin, gluten, and a peculiar kind of wax; and that the resin is the predominant ingredient, insomuch that, strictly speaking, We ought to consider lac as consisting prin- cipally of resin mixed with certain proportions of a particular kind of wax, gluten, and colouring extract. The mean results of the ex- periments give the proportions as follows:—100 parts of stick lac are found to contain resin 68, colouring extract 10, wax 6, gluten 5%, and extraneous matter 6% ;—-seed lac. resin 88%, colouring extract 2%, wax 4%, gluten 2 ;—and shell lac, resin 90‘90, colouring extract %, wax 4, and gluten 2'80. Each of these ingredients, we must ob- serve, has been separately and carefully analysed.

The third and last section contains a number of general obser- vations, chieﬂy relating to the uses of this substance. From the whole of the experiments here related, it appears that although lac be indisputably the production of insects. yet it possesses few of the characters of animal substances; and that the greater part of its ag- gregate properties, as well as those of its component ingredients, are such as more immediately appertain to vegetable bodies. Its uses are various, and some of them important. The Indians manufacture it into rings, beads, and other female ornaments. When formed into sealing-wax, it is employed as a japan, and is likewise manufactured into different coloured varnishes. The colouring part is formed into lakes for painters; and as a dyeing material it is in very general use. The resinous part is employed to make grindstones, by melting and mixing it with about three parts of sand, or with a like proportion of powder of corundum for those stones which are used by lapidaries. We owe to Mr. Wilkins the information, that a peculiar and ex- cellent kind of ink is prepared by the Hindoos of shell lac, dissolved in water by the mere addition of a little borax, and by adding to the solution a certain quantity of ivory— or lamp-black. This process has the further advantage of teaching us to prepare an aqueous solution of lac, which probably will be found of very extensive utility, espe- cially in the preparation of varnishes and pigments, which, when perfectly dry, will not be easily affected by damp or water.