WELD.

409

colouring matter contained in this plant has been studied by MM. Chevreul,*Moldenhauer,f and Schiitzenberger and Paraf.j; The mode of extradting thecolouring matter from this plant employed by the two last-named authors, isbased upon the fadt that luteolin is readily soluble in water, heated underpressure to 250° (equal to a pressure of about 40 atmospheres or 4i'32 kilos,to the square centimetre), and crystallises, on cooling, in the shape of yellowneedles, which are perfedtly pure, and free from a peculiar, easily fusible,resinous matter, which accompanies the luteolin in large quantity. The rawweld is first cut up in small fragments, and exhausted in a displacementapparatus with boiling alcohol. The solution thus obtained is first concen-trated by evaporation, and next precipitated by water, which throws downan abundant dirty green yellowish flocculent substance. This matter is putalong with water into a glass cylinder, which is placed inside a cast-steel ora stout sheet copper cylinder, closed with a screw cap, and heated to 250° forabout twenty minutes. On cooling, the slides of the glass cylinder are, forthe space occupied by the water, found lined with brilliant golden needle-shaped crystals, while at the bottom of the glass the resin is accumulatedfused to a cake. The mother-liquor, in the midst of which this crystallisationtook place, is perfectly clear and transparent. The crystals are purified byanother operation of the same kind as just described, and the resin is separatelysubmitted for two or three times to the same treatment, whereby it is entirelyfreed from colouring matter.

The process employed by M. Moldenhauer is the following:—The dried plantis exhausted with alcohol, and the tindture obtained is evaporated, whereby aportion of the luteolin is deposited ; this substance is washed with water,and next boiled with concentrated acetic acid. Being filtered while hot thisacid solution deposits the luteolin on cooling ; the deposit is first washedwith water, next dried in vacuo over sulphuric acid, then treated with ether,and re-dissolved in alcohol; to this solution from 24 to 28 parts of water areadded, and the fluid boiled, whereby the luteolin separates in the purecrystalline state. Luteolin thus obtained is a yellow needle-shaped crystallinesubstance ; its taste is bitter and astringent; it is free from smell, fuses atabout 320°, and sublimes, undergoing a partial decomposition ; it is sparinglysoluble in cold, and not freely so in hot, water, but readily in alcohol andether. Luteolin dissolves in caustic and carbonated alkaline lyes, yieldingdeep yellow solutions. In concentrated sulphuric acid it dissolves, yieldingan orange-red liquid, from which water re-precipitates the luteolin unal-tered. Luteolin is also soluble in boiling acetic and hydrochloric acids,but not in these fluids when cold; treated when dry with anhydrous phos-phoric acid luteolin is converted into a red body, soluble in ammonia, with aviolet colour; nitric acid converts luteolin into oxalic acid. The aqueoussolutions of this dye are coloured green by perchloride of iron, and are pre-cipitated by nearly all metallic saline solutions. The formula of luteolin,dried at 150°, is C I2 H80 5 , and the formula of the pigment, dried over sul-phuric acid in vacuo, is Ci 2 H80 5 H 2 C>5; luteolin is not a glucoside. Weld orwold only yields colours upon previously mordanted fabrics. The shades

* ‘‘Journal de Chimie Medicale,” vi., 157.

t " Journal fur Praktische Chemie,” lxx., 428. “ Ann. der Chem. und Pharmacie,” cxii., 107 .

* *' Bulletin de la Societe Chimique de Paris,” first series, 1861, p. 18.