114. For the put poses of dyeing, stick-lac of the (kept st colour should be chosen. The colour which it affords is less brilliant than the scarlet obtained from cochineal ; but it has the advantage of possessing greater durability. Berthollet says, that it may be employed to nr od purpose by 'nixing a certain quantity in the cochi ncal, tt lien, if it be not in too large proportion, the scarlet tall be remitted more permanent, without losing any thing of its beauty.
115. Water dissolves lac, and the decoction is of a deep crimson colour. The solubility is increased by al kaline substances. Pure potash and soda completely dissolve the different kinds of lac. Pure ammonia, and carbonate of ammonia, also act on its colouring matter. To separate the part soluble in water, and calculate its proportion to the wax or resin, Hellot used to extract it by means of water and mucilage of comfrey, to precipi tate the colouring matter with alum, and to collect and dry this precipitate, the weight of which was only one fifth of the lac. This precipitate is a compound of the colouring matter and alumine : Ilellot used it for dye ing.
116. Dr Bancroft seems to be of opinion, that lac employed with the nitro-muriate of tin and tartar, might be made to dye scarlets, equal in vivacity and beauty to any which have been produced from cochineal, and by the same means, taking care only to employ them in a proportion somewhat larger. He ascertained, in the course of his experiments on this substance, that water, at the ordinary temperature of the atmosphere between the tropics, dissolved and extracted almost as much of the colour of powdered stick-lac, as when assisted by a boiling heat. Ile discovered also, that water of this tem perature extracted the colouring matter free from other substances, which were dissolved by it at the boiling point. I laving carefully evaporated a few quarts of this cold infusion of powdered stick-lac, made during some warm days in the early part of September, he obtained an extract, which, when dried and rubbed in a mortar, broke readily into fine powder, and was afterwards found to dissolve almost as readily as refined sugar ; and ha ving tried this powder to dye small pieces of broad cloth, with the usual mordants, he says he had no difficulty in producing therewith scarlet colours equal to the best which could be any where found, and with little more than half as much in weight of the powder as would have been required of cochineal to produce similar colours. In consequence of these results, and considering the low price of stick-lac in the East Indies, he was convinced that this colouring matter might be successfully introdu ced as a substitute for cochineal. He accordingly corn
municatt d his opinion on the subject to the Chairman of the Court of Directors of the East India Company, and offered to disclose the result of his experiments, for a moderate but suitable remuneration. The Committee of Directors, bt fore coining to a final determination, pru dently proposed the dyeing of a piece of long-ell (thc woollen cloth of which the Company's exports are chiefly composed,) in order that the practicability of the method might be ascertained on a sufficiently large scale ; the samples which Dr Bancroft had produced being taken from small bits of cloth. The first experiment succeed ed so well, that the colour produced was approved of by very competent judges ; but in some subsequent trials, the results fell short of expectation, the colour being deficient in brightness. When the decoction of the be began to acquire a little of the consistency of a soft ex tract, a sudden and remarkable diminution of the beauti ful colour of the liquor was observed. The change was ascribed to the absorption of oxygen ; Dr Bancroft having noticed a similar effect produced on logwood in the same circumstances. To obviate this inconvenience, he has proposed to obtain the extract by evaporation with the heat of the sun only ; but it is extremely doubtful whether the absorbtion of oxygen from the atmosphere would not take place in an equal degree, during so pro tracted a mode of extracting the colour. He has also proposed to collect the colouring matter of lac by preci pitating it from its aqueous solution by the oxide of tin, and after letting off the superincumbent to separate the precipitate from all the remaining moisture, by sus pending it in close linen bags, and afterwards drying it in the sun, or even in the shade. One pound of muriate of tin, in which the acid of the ordinary strength (1. 170) was saturated with the metal, appeared capable of pre cipitating as much of the colouring matter of lac, as, in its effects, would be equal to one pound of cochineal. He accordingly attempted to dye a piece of cloth with this precipitate, hut owing to deficiency of colouring matter, and other causes which he mentions to account for the failure, the experiment was not successful. He still seems to think, however, that in this, or some other form, lac might be used with considerable advantage as a dye, and even as a substitute for cochineal.