YELLOW DYES-QUERCITRON-FUSTIC-SAFFRON.

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of the colouring matters of organic origin, nitrogen is an essential constituent, though in a still greater number it is absent. The colouring matters in most frequent use exhibit the properties of very feeble acids. The concentrated alkalies, especially in the presence of free oxygen, however, for the most part decompose them rapidly; but they are more soluble in dilute alkaline liquids than in pure water, and they form definite insoluble compounds with the earths, and with some metallic oxides, such as those of lead and of tin. Such compounds with the metallic oxides usually possess great tinctorial or colouring power, and are termed lakes. The formation of these insoluble compounds is a circumstance of fundamental importance to the dyer and calico-printer, since upon it depends the general method of mordanting (1533), used in the arts of dyeing and calico-printing.

(1501) YELLOW DYES.-The most important yellow dye-stuffs are quercitron, fustic, saffron, turmeric, annatto, and weld. The colouring matters of the Persian berries, of purree, and of rhubarb, are less frequently employed.

1. Quercitron is the bark of the Quercus tinctoria. It yields a yellow crystallizable principle, quercitrin (1494), of feebly acid properties, soluble in alcohol, sparingly so in water, freely so in alkalies.

2. The Morus tinctoria, or Old fustic, is particularly employed for dyeing woollens yellow; it is also used to impart to them green and olive hues when mixed with indigo and salts of iron. Fustic furnishes a yellow colouring matter, which may be obtained in crystals by evaporating its aqueous infusion. To this body the name of morin (H.; at 212°, Hlasiwetz) has been given. Besides this, fustic contains a tannic glucoside, termed moritannic acid (1332; 18H1610 Wagner); or maclurin (E13H1006, H2; Hlasiwetz). It has a bitter taste, is soluble in ether, and gives a green precipitate with salts of iron. Acids and alkalies deepen the tint of the aqueous solution without producing any precipitate. When mixed with alum it produces no precipitate, but on the addition of potassic carbonate to this solution, a yellow lake is formed.

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3. The Rhus cotinus, or Young fustic, contains a different. yellow dye, which is very soluble in water; potash renders it purple, passing into a reddish yellow; while the acetates of lead and of copper produce an orange-coloured lake with a decoction of this wood. Wool mordanted with alum acquires a bright yellow dye in a bath of this colouring principle.

4. The Crocus sativus yields Saffron, a colouring matter con

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YELLOW DYES-TURMERIC-ANNATTO-RHUBARB-WELD.

tained in the anthers of the flower; it is very soluble in water and in alcohol. Crocin (EH?), the pure colour, is a glucoside, and is decomposed by boiling with dilute acids.

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5. Curcumin, or the colouring matter of Turmeric (Curcuma longa), is of a resinous nature; it is nearly insoluble in water, but is dissolved freely by alcohol and by ether. Alkaline solutions take it up abundantly, and change the colour to brown. This change of colour is often employed in the laboratory to indicate the presence of free alkali, since paper tinged yellow with tincture of turmeric becomes brown when immersed in a solution containing uncombined alkali. Curcumin is soluble without change of tint in the acetic, phosphoric, hydrochloric, and sulphuric acids. It is employed for dyeing wool and silk, as well as for colouring the curry powder of India.

6. Annatto. This colouring matter is in the form of a paste, prepared from the seeds of the Bixa orellana, and is used for dyeing nankeen. It appears to contain an orange-red colouring substance called bixin, and a less important yellow one termed orellin. Bixin (Є16H322; Kerndt) is a resinous matter sparingly soluble in water, but freely so in alcohol and in ether. The alkalies dissolve it, producing a deep red colour, and on neutralizing the solution with an acid it falls as an orange precipitate. The fixed oils also dissolve this colouring principle, which closely resembles that of the turmeric.

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7. The root of the common Rhubarb yields a yellow colouring matter, termed rhein or chrysophanic acid (from Xpúσɛʊç, golden, paivo, to appear; €10H3; Rochleder and Heldt), which is also found in one of the lichens (Parmelia parietina). It is sparingly soluble in water, but freely soluble in the alkalies, producing a reddish-brown coloured liquid, from which on the addition of acetic acid it may be precipitated in flocculi; this change from yellow to red is effected by a minute trace of alkali, so that paper stained with rhubarb may be used as a test for the presence of a free alkali. Rhein is accompanied by a portion of resin, which may be precipitated by the addition of ether to the alcoholic solution. Chrysophanic acid is soluble in ether and in hot alcohol, from which it may be obtained in crystals of a golden yellow metallic lustre.

8. The Weld, or Reseda luteola, also furnishes a yellow colouring matter, which is highly prized for its solidity and durability. Luteolin (20H1403; Moldenhauer), as this substance is termed, may be extracted from the dried plant by means of boiling water; it is freely soluble in alcohol, less so in ether, and but very

YELLOW DYES-PERSIAN BERRIES-PUrree.

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sparingly soluble in water. It may be sublimed unaltered, and condenses in yellow needles. The alkalies, both caustic and carbonated, dissolve it abundantly, and form deep yellow solutions. Cold sulphuric acid also dissolves it, and deposits it unaltered on dilution. Its solutions yield yellow lakes with alum, stannous chloride, and acetate of lead.

9. Persian Berries.-The fruit of various species of Rhamnus, when gathered before it is fully ripe, contains a considerable amount of a yellow colouring matter, termed chryso-rhamnin (Є23H2211?). This substance may be extracted by means of ether, which deposits it in brilliant stellate groups of golden yellow crystals; an alcoholic solution of this compound yields with an alcoholic solution of acetate of lead a yellow lake (2 Pb,Є2H22O11?). Chryso-rhamnin is nearly insoluble in cold water, but if boiled with water it is partially dissolved, and is converted into a compound termed xantho-rhamnin (Є23H2414?), which is also one of the constituents of the ripe berries (Kane). Gellatly found that xantho-rhamnin is a glucoside, and splits, when treated with a dilute acid, into a resin and glucose.

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10. Purree, or Indian Yellow.—This substance has been particularly examined by Stenhouse and by Erdmann. It is a colouring matter highly esteemed by artists, and is supposed to be of animal origin; it is sold in masses of three or four ounces in weight, which have exteriorly a dark-brown colour, but when broken are of a bright orange yellow. Its odour is peculiar, and resembles that of castoreum. This substance consists chiefly of the magnesian salt of a peculiar acid, termed purreic or euxanthic acid. Purree is scarcely soluble in water or in alcohol, but it is entirely soluble in boiling dilute hydrochloric, or in acetic acid; as it cools pale yellow needles of euxanthic acid (HE2H1711; Laurent) are deposited in stellate groups. It is somewhat soluble in boiling water, and is readily dissolved by boiling alcohol and by ether. Cold water dissolves but very little of it; alkaline solutions dissolve it, and form a yellow liquid. A solution of potassic euxanthate when mixed with the solutions of the salts of the earths gives brilliant yellow sparingly soluble precipitates; with acetate of lead it forms a yellow insoluble lake.

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When euxanthic acid is heated in a small tube to a temperature a little above 212°, it melts, and a yellow sublimate of purrenone or euxanthone (EH) is formed, whilst water and carbonic acid are evolved: it is also obtained by transmitting chlorine through a hot solution of euxanthic acid in absolute alcohol; and the same compound is produced when euxanthic acid is dissolved in oil of

vitriol, the solution gradually depositing crystals of euxanthone. The sulphuric solution contains a new colligated acid, termed sulphohamathionic acid, the composition of which is doubtful.

The yellow dyes are not often used alone. They are generally employed in combination with other colours, to modify shades, or to produce compound colours, as when mixed with blues to produce green.

(1502) THE RED DYES are of greater importance; of these, madder, logwood, Brazil-wood, camwood, sandal-wood, safflower, cochineal, lac dye, and the aniline dyes, are those in most extensive use.

(1503) 1. MADDER is the root of the Rubia tinctorum, a plant which is grown largely in the Levant, in the south of France, and in Alsace. It is consumed in enormous quantities for dyeing reds and purples; Turkey red cloth owes its brilliant hue to the colouring matter of this root. The composition of the madder root has been the subject of many chemical investigations, the most recent though still incomplete being those of Rochleder and Schunck.

According to the microscopic observations of Decaisne, the madder root, whilst growing, does not contain any red colouring matter; but its cells are filled with a yellow substance which increases in quantity with the age of the root; and this body by exposure to the air absorbs oxygen, after which the red colour is developed; an observation which agrees with the experiments of Higgin and of Schunck.

According to the last-named chemist, the madder root of commerce, in addition to ligneous fibre, contains several distinct substances; viz., a bitter principle, rubian,—which by its decomposition yields two colouring matters, alizarin and rubiacin,—two resins, pectic acid, and a brown substance which is probably a product of oxidation of some of the foregoing bodies. It also contains calcic oxalate and phosphate, besides other saline matters.

Some of these bodies are injurious to the brilliancy of the dye. Alizarin, according to Schunck, is the only true dyeing principle of the madder root. It has already been stated that alizarin does not exist ready formed in the growing root, but that it is produced by the decomposition of rubian; and it is well known to the dyer that the full colouring power of the root is not developed until after the dye-stuff has undergone partial fermentation.

In order to extract the whole of the colouring material, Schunck dissolves out the soluble matter from the root with water, and decomposes this solution by boiling it with dilute acid, when the whole of the colour-giving portion, including the alizarin, is pre

RED DYES-MADDER-ALIZARIN-RUBIAN.

671

cipitated. If this precipitate be boiled with water, the alizarin is dissolved, and the rubiacin and the resins are left. Another plan of obtaining alizarin consists in reducing the root to a coarse powder, treating it with hot sulphuric acid, and well washing it till the last traces of acid are removed; the earthy matters are thus rendered soluble, and everything which water will take up is removed; but nearly the whole of the alizarin remains untouched, since it is insoluble in water containing free acid; the undissolved mass when dried is largely used in the print-works under the name of garancin. By boiling this garancin in a large quantity of water, the colouring matter is dissolved, and on adding sulphuric acid it is precipitated mixed with several impurities. If this precipitate be well washed, dried, and submitted to sublimation, beautiful orange-coloured needles of alizarin are obtained; these, if washed with cold alcohol and dried, are perfectly pure.

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(1504) Alizarin (¤ ̧Н ̧Ð ̧, 2 H ̧Ð; Strecker).—This, which has received its designation from alizari, the name by which madder is known in the Levant, is a red crystalline matter destitute of odour and of taste; it is neutral to test-papers, and is almost insoluble in cold water. It is but sparingly soluble in hot water; hot alcohol dissolves it more freely, and if this solution be evaporated, alizarin is deposited in plates resembling those of mosaic gold. It is also soluble in ether; acids brighten its tint, but do not dissolve it. Potash dissolves it freely, and strikes a beautiful purple; but it is precipitated unaltered on adding an acid; with lime, baryta, and ferric oxide, it forms insoluble purple lakes. With alumina it forms a beautiful red lake. Alizarin is not decomposed even by boiling sulphuric acid, which dissolves it, and on dilution deposits it unchanged. Boiling dilute nitric acid. converts alizarin into phthalic (alizaric) acid, and probably into oxalic acid (Strecker and Wolff), whilst nitrous vapours are evolved :

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The crystals of alizarin deposited from its spirituous or aqueous solution lose about 18 per cent. of water at 212°. By a heat of about 419° (215° C.) alizarin is sublimed, but part of it undergoes decomposition. The sublimate forms beautiful transparent orange-coloured needles, which are anhydrous and of high lustre.

(1505) Rubian (E28H34015? Schunck); the Ruberythric Acid of Rochleder?—This is a bitter uncrystallizable principle, which under the influence of acids, of alkalies, and of a peculiar azotised ferment termed erythrozym (from ¿pv9pòç, red, Evμn, ferment),