104. Of all the metallic salts which affect the colour of cochineal, the most important is the oxide of tin. About the year 1630, it was discovered by the acciden tal falling of a solution of the nitrate of tin into a de coction of cochineal, that the colour of the latter in stantly passed from purple to a vivid scarlet. Different salts of tin produce different effects ; but we must re serve the particular consideration of their properties un til we come to examine the nature of mordants.
105. When alum is added to a decoction of cochineal, it combines with its colouring matter, and forms the beautiful lake called carmine. A certain proportion of antour, a bark brought from the Levant, of a colour paler than cinnamon, and in general, chouan, the seed of a plant likewise brought from the Levant, are added. Berthollet supposes that these two substances furnish, with alum, a yellow precipitate, which serves to bright en the colour of the cochineal lake. Carmine was for merly prepared from kermes, from which it takes its name, and the nature of which we shall now consider.
106. Kermes. (coccus ilicis), is an insect found in se: veral parts of Asia, and the south of Europe. It ap pears to have been employed at a very early period as a dye, and was known to the ancients by the name of coccus bafitrims, coccus infectorius, Branum tinctorium. The term kermes is supposed to be of Arabic origin, and signifies a little worm. The Italians afterwards formed from it the words cherniisi, cremesino, and chermesind and the French those of carmesen, carmine, and cia: moisi. The English words carmine, and crimson, are of the same origin. At a later period, kermes was also called coccum scarlatinum, though the time at which it first received this appellation cannot now be accurately ascertained. The term gran= was applied to it on ac count of its resemblance to a grain or berry ; and hence colours dyed from this insect were frequently called grain, or engrain colours.
107. When the living insect is bruised, it yields a red colour, the smell of which is not unpleasant. Its taste is bitter, harsh, and pungent. In the dried state, it imparts this smell and taste to water and alcohol, giv ing to both a deep red colour, which is retained by the extracts made by these infusions.
108. Kermes is one of the most ancient dyes with which we are acquainted, but it has fallen greatly into disuse since the introduction of cochineal. Most of the writers on dyeing admit, that the colour which kermes imparts to wool, is inferior in beauty to the scarlet made with cochineal. Dr Bancroft, however, maintains, that by employing along with it a solution of tin or nitro muriatic acid, he procured a scarlet in every respect as beautiful and estimable as any which can be dyed with that insect. This statement deserves attention, as the colour communicated by the kermes is more durable, and spots of grease may he discharged from it without injury. Hellot mentions that the red draperies of the figures represented in the ancient Brussels, and other Flemish tapestries, were all dyed from kermes, and that this colour, after having stood more than 200 years, seems to possess the same brilliancy as at first. Beck man affirms the same thing with respect to some pieces of tapestry supposed to have been dyed with kermes about the twelfth century. Dr Bancroft states, that the decoction of kermes exhibits, in almost every case, the same appearances with the different chemical agents as cochineal : and lie has accordingly concluded, that the colour of both is " exactly similar." 109. The coccus ftolonicus is a small round insect, si milar to the kermes, and employed for nearly the same purposes. It is found adhering to the roots of a species of polygonum (scleranthus fterennis). Before the intro
duction of cochineal caused the use of it to be abandoned in Europe, it was chiefly collected in the Ukraine and other provinces of Poland, under the name Czerwiec. The juice of the coccus polonicus is still employed, as a dye by the Turks and Armenians, particularly for wool, silk, and horse hair. The women also use it to colour their nails.
110. Several other insects might be noticed which af ford a red colour, and some of them have been employ ed for that ptirpose in Europe ; but the advantages of fered by cochineal have entirely superseded their use, and caused them to fall into neglect.
111. Lac is a colouring matter, of animal origin, ha ving a colour more or less red. It is produced in the East Indies by the coccus lacca, a small winged insect, and is generally deposited on the small branches of the croton laccfferum. "The fly is nourished by the tree, and there deposits its eggs, which nature has provided with the means of defending from external injury, by a collection of this lac, evidently serving the twofold pur pose of a nidus and covering to the ovum and insect in its first stage, and food for the maggot in its more ad vanced state. The lac is formed into complete cells, finished with as much regularity and art as a honey comb, but differently arranged. The flies are invited to deposit their eggs on the branches of the tree, by besmearing them with some of the fresh lac, steeped in water, which attracts the fly, and gives a better and a larger crop. The egg, which is about the size of an ant's, is of a pure red, perfectly transparent, except in the centre, which exhibits evident marks of the embryo forming." 112. The cells are filled with a glutinous liquid, which is sweetish to the taste, and of a fine red colour, soluble in water. This liquid is secreted by the insect, and is destined as a food to the embryo, from the time of its animation till able to quit its cell in (Idlest of food. The natives of Assam use it as a dye, and cotton dipped in it makes afterwards g very good red ink. The eggs, and dark coloured glutinous liquid with which they arc sur rounded, communicate a very beautiful red colour to water while they are fresh; but after they have been dried and kept for some time, the colour they afford is less bright. " It would therefore be well worth while," says Dr Roxburgh, " for those who are situated near places where the lac is plentiful, to try to extract and preserve the colouring principles by such means as would prevent them being injured by keeping. I doubt not," continues he, " but in time a method may be dis covered to render this colouring matter as valuable as cochineal." 113. As an article of commerce, lac is known in Eu lope under the appellations of atic•-lar, Reed-lac. and oh cl-hr The fit is t tr Lie in its native state, as it is I •und Ai het a, to the to i ;s on wick it was twirl pose ed. The set d-lac is sal I to be the stic k-lat broke into small pit Les, aid t ins app •aring in a granula ted turm. Tbis, Lowe% cr, is a mistake; seed-lac bring the yellowish tt Id re asint us pun der, which remains after t Ie oud colour of stick-lac has been extracted, as far as It can convel iu tly be done, by water. Shell-lac is pro duct d Irum act d-lac, by putting the lattt r into long cy lihdti, ul Ihigs ul cotton cloth ; nicking it, by holding the user a t harcull lire ; and w len the lac melts, strain ing it through the cloth, by twisting the hags. The lac tl us stained, is allowed to fill upon the smooth junk of a plantai.. trot, and is there spread into thin plates. In this form it is brought to Europe, and is chiefly employ ed in the composition of varnishes and sealing-wax.