LABOUR. [Wants.] LAC, a resinous eubstnee, which in the East Indies flows from certain trees in the state of a milky fluid, on account of the puncture made by a small insect, the Coccus few, in their branches, in order to deposit its ova. The trees are principally the Ficus Indica, Ficus reliqioaa, and RI/amnia jujube.
There are three kinds of lac known in commerce, and they are dis tinguished by the names of stick-lac, seed-lac, and shell-loc. Stick-lac is the substance in its natural state; it is of a reddish colour, and aocflate small twigs; when broken of and boiled in water, it loses its red colour, and is then termed seed-lac; and when melted and reduced to the 'state of thin plates, it is called shell-lac, which has a yellowish. brown colour. Mr. Hatchott appears to have been the first chemist who minutely examined these substances, but Dr. John, who has more recently examined sticklaa, gives as its composition— Notwithstanding the seeming accuracy of the details of the above mentioned analysis, it would appear that further experiments are still required to determine the nature of lac ; for Unverdorben has, since this analysis was published, stated the results of his examination ; let, laccin; 2nd, red colouring matter ; 3rd, resin soluble in alcohol, but not in ether ; 4th, resinous looking matter, slightly soluble in cold alcohol ; 5th, cryetailisablo resin; 6th, uncrystallisable resin, soluble in alcohol and ether, but not in naphtha ; 7th, wax ; 8th fat of coccus, not saponifiable, and some oleic and margaric acids.
Shell-lac is largely employed in the manufacture of sealing-wax ; it answers this purpose better than any other resinous matter, because it melts without charring, and consequently without giving much smoke, and also because it is hard and less brittle thanapther resins. Shell lac is also used in varnishes ; and is so good an insulator of electricity that a needle made of it is said to remain somo daye excited.
Laccin.—The properties of the substance to which this name has been given, and which remained after the lac had been repeatedly digested in alcohol and water, are, that it ie hard and brittle, of a yellow colour, and slightly transparent.. It is insoluble in water, but softens in it when hot ; and it also swells and 'softens, but without dissolving, in elcoho either cold or hot ; nor do ether, or oils take it up. It is dissolved by concentrated sulphuric) acid. Concentrated nitric acid, when heated, dissolves it slowly. Solution of potash dissolves it readily.
Lactic acid separates from solution in water, by spontanoods evapo ration, In crystalline grains. It attracts moisture from the air, does not precipitate either the salts of limo or baryta, but throws down those of mercury and load ; the persalta of iron are precipitated white by It. With the alkalies and with limo it forme salts which arc soluble in alcohol and in water, and are deliquescent.
The colouring matter of stick-Inc is mid to be similar to that of cochineal. It Is used for the same purpoem, and yields a scarlet but little inferior to it.
Lac Dye and Lac Lake, two preparations of ,lao which arc manu factured in the East Indies, and used to a very considerable extent in scarlet dyeing : they appear to bo prepared by dissolving stick-lac iu an alkali, as potash or soda, and then adding a solution of alum ; by this there is precipitated a mixture of the alumina of the alum and the resinous and colouring matter of the stick-lac. The Inc dye is much the more valuable of the two.
The principal uses to which lac in Its various forms is applied are for the snaking of scaling-wax, for varnishes. for japanning, and for scarlet dyeing. The trade in lac has of late years become of some importance.