logwood tree was first cultivated in Britain by Mr. P. Miller, in 1739*, who says, "there are some of these plants now in England which are upwards of six feet high, and as thriving as those in their native soil+; but this observation will not apply to the present time, for we have searched in vain for this plant through most of the principal garden stoves in the neighbourhood of London. The wood of this tree is of a solid texture, and of a dark red colour; it is imported into Europe principally as a dying drug, cut into junks or logs of about three feet in length; of these pieces, the largest and thickest are preferred, as being of the deepest colour. This wood has a sweetish subastringent taste, and no remarkable smell; it gives a purplish red tincture both to watery and spirituous infusions; but is chiefly used, and in great quantities, for dyeing purple, and especially black colours. All the colours, however, which can be prepared from it, are of a fading nature; and cannot by any art be made equally durable with those pre. pared from some other materials. Black, though not altogether a fixed colour, is the most durable of the whole. Dr. Lewis recommends it as an ingredient in making ink. "In dyeing cloth," says he, "vitriol and galls, in whatever proportions they are used, produce only browns of different shades: I have often been surprised that with these capital materials of the black dye, I never could obtain any true blackness in white cloth, and attri. buted the failure to some unheeded mismanagement in the process, till I found it to be a known fact among the dyers. Logwood is the material which adds blackness to the vitriol and gall brown; and this black dye, though not of the most durable kind, is the most common. On blue cloth a good black may be dyed by vitriol and galls alone; but even here an addition of logwood contributes not a little to improve the colour." Mr. Delaval, however, in his Essay on Colours, informs us, that with an infusion of galls and iron filings, he not only made an exceeding black and durable ink, but also dyed linen cloth of a very deep black. Hort. Kew. [Lewis, Woodville. Wildenow. + Dictionary abridged, sixth edition. SECTION VI Madder. Rubia tinctorum.-LINN. THIS is a native of the south of France, and flowers in July. The root is perennial, long, round, jointed, beset with small fibres; externally of a bright red, but towards the center yellowish. The branches stand in pairs at the articulations of the stalks, and upon their various subdivisions produce small terminal flowers of a yel. lowish colour. Madder is frequently mentioned by the Greek writers, who employed its roots with the same medicinal intentions for which they now are recommended by most of the modern writers on the Materia Medica. Our knowledge of the first cultivation of this plant in England is from Gerard *; and though an extensive cultivation of Madder in Britain seems to promise considerable advantage, both to the planter and to the nation, yet we find that the great quantity of madder roots used here by the dyers and calico-printers, has been for many years almost wholly the growth and export of Holland +. Madder appears to differ from other substances used for the purpose of dying, in having the peculiar property of tinging with a florid red colour not only the milk, urine, &c.§ but even the bones of those animals which have fed upon it; a circumstance which was first noticed by Antonius Mizaldus |, but not known in England till Mr. Belchier published an account of a pig and a cock, * Vide Hort. Kew. + Miller Dict. in which is also given a full account of the cultivation of this plant. But we are happy to observe, that by the laudable endeavours of the Society for the Encouragement of Arts, &c. considerable quantities of English madder have been produced, and found as good at least, if not better than any imported. See Transactions, p. 10. vol. i. Some other plants of the same natural order (stellata) have also the effect of tinging the bones, as the gallium mollugo and aparine. Vide Guettard Mem. de l'Ac, de Sc. a. 1746 & 1747. And the valantia eruciata. Böhmer Diss. de rad. rub. tinet. p. 42. Bönmer also found the serum of the blood reddened by the madder. Diss. rad. rub. tinct. &c. p. 13. And Levret observes, that it sometimes tinged the excretion by the skin. Sur les Accouchemens, p. 278. Memorab. ut. ac jacunda Cent. 7. Aph. 91. Lutet. 1566. whose bones became red by eating madder mixed with their food* ; since that time various experiments relating to this subject have been made, from which it appears that the colouring matter of madder affects the bones in a very short time; and that the most solid, or hardest, part of the bones first receives the red colour, which gradually extends, eb externo, through the whole osseous substance, while the animal continues to take the madder; and if this root be alternately intermitted and employed for a sufficient length of time, and at proper intervals, the bones are found to be coloured in a correspondent number of concentric circles. Ac. cording to Lewis, "the roots of madder have a bitterish somewhat austere taste, and a slight smell not of the agreeable kind. They impart to water a dark red tincture; to rectified spirit, and to distilled oils, a bright red; both the watery and spirituous tinctures taste strongly of the madder t." [Hort. Kewens. Millar. Lewis. SECTION v11. Copal +. Elæocarpus copalliferus.-LINN. THE elæocarpus genus comprises five species, of which all are trees, chiefly indigenous to India or Australasia: the copal-tree, copalliferous, constitutes one of these, and which is also found in Africa and America. The resinous substance, called gum copal, and which is supposed to be a secretion from this tree, is imported from Guinea, where it is found in the sand on the shore. It is of a yellow colour, faintly glistening, imperfectly transparent, and apt to break with a con. choidal fracture. It is tasteless, and, when cold, inodorous. It is used dissolved in rectified spirits of wine, or other volatile solvents, both as a varnish, and as an astringent medicine. In North Ame rica, the natives obtain a very considerable quantity of this resin Phil. Trans. vol. xxxix. p. 287. & p. 299. See also vol. xli. Afterwards experiments were prosecuted by Bazanus, Geoffroy, Du Hamel, Fougeroux, Bergius, and others. + Mat. Med. p. 546, For gum lac and cochineal, see the next book, from the rhus copallinum, but it is of an inferior quality to that brought from Guinea and Spanish America. The specific gravity of copal varies from 1.045 to 1.139. Mr. Hatchett found it soluble in alkalies and nitric acid, with the usual phænomena. Copal varnish used by the English japanners is made as follows. Four parts by weight of copal in powder are put into a glass matrass and melted. The liquid is kept boiling till the fumes condensed upon the point of a tube, thrust into the matrass, drop to the bottom of the liquid without occasioning any hissing noise, as water does. This is a proof that all the water is dissipated, and the copal has been long enough melted. One part of boiling hot linseed oil (previously boiled in a retort without any litharge) is now poured into it, and well mixed. The matrass, if then taken off the fire, and the liquid, while still hot, is mixed with about its own weight of oil of turpentine. The varnish thus made is transparent, but it has a tint of yellow, which the japanners endeavour to conceal by giving the white ground on which they apply it a shade of blue. It is with this varnish that the dial plates of clocks are covered, after having been painted white. A correspondent in the 17th volume of the Transactions for the Encouragement of Arts, &c. informs us, that copal may be dissolved in spirit of turpentine by the following process: having prepared a glass vessel, of sufficient capacity to contain at least four times the quantity intended to be dissolved, and which should be high in proportion to its breadth, reduce two ounces of copal to small pieces, and put them into the vessel. Mix a pint of spirit of turpentine with one-eighth of spirit of sal ammoniac; shake them well together; pour them on the powder, cork the glass, and tie it over with a string or wire, making a small hole through the cork. Set the glass in a sand heat, so regulated as to make the contents boil as quickly as possible; but so gently, that the bubbles may be counted as they ascend from the bottom. The same heat must be kept up exactly, till the solution is complete. It requires the most accurate attention to succeed in this operation; for, if the heat abate, or the spirits boil quicker than is directed, the solution will be impeded, and it will afterwards be in vain to proceed with the same materials; but, if properly managed, the spirit of sal ammoniac will be seen gradually to descend from the mixture, and at tack the copal, which swells and dissolves, except a very small quantity. It is of much consequence that the vessel should not be opened till some time after the liquid has become perfectly cool; as it frequently happens that the whole of the contents are blown with violence against the ceiling. The spirit of turpentine should be of the best quality. Mr. Sheldrake has lately favoured the public with another and easier method of dissolving copal. This method is as follows: Provide a strong vessel made of tin or other metal; it should be shaped like a wine bottle, and capable of holding two quarts; it will be convenient to have a handle strongly rivetted to the neck; the neck should be long, and have a cork fitted to the mouth, but a notch or small hole made in the cork; that, when the spirit is expanded by heat, a small portion may force its way through the hole, and thus prevent the vessel from bursting. Dissolve half an ounce of camphor in a quart of spirit of turpentine, and put it into the vessel; take a piece of copal the size of a large walnut, reduce it to a coarse powder or very small pieces; put them into the tin bottle, fasten the cork down with a wire, and set it, as quick as possible, upon a fire so brisk as to make the spirit boil almost im. mediately; then keep it boiling very gently for about an hour, when so much of the copal will be dissolved as will make a very good varnish; or, if the operation has been properly begun, but enough of copal has not been dissolved, it may be again put on the fire, and by boiling it slowly for a longer time, it may be at last brought to the consistence desired. [Phil. Trans. Trans. Arts. Commerce, &c. Pantol, SECTION VIII. Gum Arabic. Mimosa Nilotica*.-MUTIS. THE nilotica, or true Egyptian acacia, from which this vegetable article is chiefly obtained, rises to fourteen or sixteen feet in height. The fruit is a long pod, resembling that of the lupin, and contains many flattish brown seeds. It is a native of Arabia and Egypt, and flowers in July. Although the mimosa nilotica grows * Acacia vera,-WILDEN. |