LAC. A species of resin secreted from the puncture made by an insect called the Coma flew, in the branches of various plants which grow in the East Indies.
Lac is a very important article in manufactures, because not only is the resin useful for making varnishes, sealing wax, 8r,c., but the colouring matter combined with it forms a magnificent red dye, which is extensively used as a substitute for cochineal. In conse quence of the puncture of the insect, the twig of the plant becomes encrusted with a red resinous substance, sometimes as much as a quarter of an inch thick. These encrusted twigs are called " stick lac." R contains about 7 per cent. of resin, and one-twentieth part of that quantity of colouring matter. This valuable colouring mat ter is removed by pulverizing the stick-lac, and triturating it with water. What remains is called " seed-lac." In India this is put into oblong bags of cotton stuff, and a man at each end of the bag holds it over a charcoal fire. The liquefied resin drops through, and is received upon smooth stems of the banyan tree ; m this way it is formed in thin plates, and is called " shell-lac." Shell-lac consists of two or more resins, one of which is soluble in all proportions in anhydrous alcohol, .ether, and volatile and fat oils.
The alcoholic solution is of a reddish colour, and forms an excellent spirit varnish in photography. (See " Varnish.") Shell-lac may also be easily dissolved in dilute hydrochloric and acetic acids, and also in a solution of borax, with the aid of heat. Before dissolving it in alcohol, it should be very finely pulverized and exposed to the air for some months. Shell-lac may be bleached with Chlorine, and then makes colourless varnishes. The bleaching is effected by first dissolving it in caustic potass, and then passing chlorine gas through the solution, after which it is pulled and washed in hot water, and twisted into sticks.
_ Shell-lac is much used in making sealing wax ; q. v.
Lac dye is made by evaporating to dryness the liquid in which the pounded crude lac is digested, and making the residue into cakes. This is soluble in dilute sulphuric or hydrochloric acid, and the mordant is protochloride of tin, and bi-tartrate of potass. It gives a fme scarlet colour.