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ARBUTIN-DATISCINESCULIN.

greenish-yellow colour, which gradually passes into dark brown. A solution of alum slowly develops a beautiful yellow colour in its solutions. Solutions of acetate of lead, acetate of copper, and stannous chloride, precipitate it in yellow flocculi. With ferric sulphate it produces an olive-green colour. When quercitrin is boiled with dilute sulphuric or hydrochloric acid, it is decomposed into glucose (Rigaud) and quercetin (Є2H16010; Hlasiwetz), a substance sparingly soluble in water, but readily soluble in alcohol: it may be obtained in minute lemon-yellow crystals. Quercetin is also soluble in solutions of potash and of soda, to which it communicates a golden-yellow colour: by boiling, these solutions yield phloroglucin (1493) and a quercetate of the form (KЄ,H,,). The decomposition of quercitrin by acids, however, according to Hlasiwetz and Pfaundler, yields not glucose, but a sweet unfermentable body (EH12,,H,) metameric with dulcite, yet not identical with it: so that it is not improbable that two analogous compounds exist, which have hitherto both been called quercitrin.

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(1495) ARBUTIN (Є12H160,=272; Strecker) is a crystallizable principle contained in the leaves of the Arctostaphylos uva ursi, which when treated with synaptase is decomposed into glucose, and a crystalline body originally termed arctuvin, but which Strecker finds to be identical with hydroquinone. Arbutin according to this chemist is not a homologue of salicin, though it differs from it in containing EH, less; the following equation representing the decomposition of arbutin under the influence of synaptase :

(1496) DATISCIN (21H22012; Stenhouse) is the name given to a crystalline colourless substance extracted from the Datisca cannabina, the leaves of which furnish a yellow colouring matter extensively used in India for dyeing silk. It is largely soluble in alcohol and in boiling water, sparingly so in cold water and in ether. It gives yellow lakes with oxides of lead and tin, and forms intensely yellow solutions with the alkalies. Dilute acids, when boiled with datiscin, cause it to split into glucose and datiscetin (1H1), a substance which crystallizes in colourless needles, soluble in ether and in alcohol, but nearly insoluble in water.

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(1497) ESCULIN, or Polychrome (1H2013; at 212°; Rochleder and Schwarz).-This substance is contained in the bark of the

horse-chestnut (Esculus hippocastanum). It contains H, more than datiscin, but does not present any of the properties of a hydrate of this body. It has 3 atoms more of oxygen than phloridzin. In order to obtain esculin, the aqueous infusion of the bark is treated with acetate of lead, and filtered, the excess of lead is removed by means of sulphuretted hydrogen, and the liquid is evaporated to the consistence of a syrup; in the course of a few days the esculin crystallizes: it may be washed with cold water, and recrystallized, first from weak alcohol (of sp. gr. o'940), and afterwards from boiling water. Esculin forms small colourless needles, which have a bitter taste and a slightly acid reaction. It is sparingly soluble in cold water and in ether, but is dissolved abundantly by boiling water, and less freely by hot alcohol. Solutions of esculin are particularly remarkable for their fluorescent power, in consequence of which they appear in certain positions to be of a deep blue, although colourless if viewed by transmitted light. Acids destroy this property, but the addition of an alkali to the liquid heightens the fluorescent character. Esculin fuses and loses water when heated to 320° (160° C.); at a higher temperature it is decomposed, emitting an odour of burnt sugar, whilst a small quantity of esculetin is sublimed in crystals. Esculin when boiled with dilute acids, or when digested with synaptase, undergoes decomposition into esculetin and glucose :

:

Esculetin is a substance which has a slightly acid reaction upon litmus; it is sparingly soluble in cold water, in cold alcohol, and in ether; but it is freely soluble in boiling alcohol, which deposits it in crystalline needles or plates resembling those of benzoic acid. Esculetin is soluble in solutions of the alkalies, forming a golden-yellow liquid; and a hot concentrated solution of it in ammonia, as it cools, deposits a yellow crystalline compound. The presence of a trace of a ferric salt gives to esculetin a dark green tinge, but the colour is destroyed on the addition of an acid. A solution of acetate of lead, when mixed with one of esculetin, produces a lemon-yellow precipitate (Є„H ̧PьÐ ̧). Fraxin [2(E32H3620), H2O; Rochleder] is a crystalline body similar to esculin, obtained from the bark of the ash, and from that of the horse-chestnut.

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Cyclamin (C2H4010; Martius), from the Cyclamen Europæum, is another crystalline body, which splits into glucose and a resinous compound on boiling it with dilute acids.

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(1498) SAPONIN (Є12H20, ?).—This substance is contained in a considerable number of plants, including the Saponaria officinalis, the Polygala senega, and the root of the common pink: it is also found in the pimpernel, in the fruit of the horse-chestnut, and in several varieties of Lychnis. Saponin is easily extracted, by means of boiling alcohol (of sp. gr. o'840), from the root of the Saponaria, or soap-wort; as the liquid cools the saponin is deposited as an amorphous sediment, which if coloured must be digested in ether, in order to remove the colouring matter.

When dry, saponin forms a colourless friable mass, which is destitute of odour, and of a sweetish, styptic, persistent taste. If applied to the mucous membrane of the nose it produces violent sneezing. Saponin is soluble in water in all proportions, yielding a somewhat opalescent liquid, which froths strongly on agitation, like a solution of soap, even though it may not contain more than a thousandth of its weight of saponin: the liquid when evaporated leaves the saponin in the form of a transparent, brittle varnish. Its solution, or an infusion of soap-wort, is sometimes employed instead of a solution of an alkaline soap, for cleansing the finer varieties of wool from grease. Saponin is also soluble in dilute alcohol, but insoluble in ether. Its solutions yield a white precipitate with basic acetate of lead.

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When boiled with dilute acids saponin yields a peculiar acid, the saponic or esculic, and at the same time a substance resembling gum (EH) is separated (Rochleder and Schwarz). Saponic acid may also be obtained by digesting saponin in weak alkaline solutions. The composition of saponic acid is doubtful, but it presents well-marked characters. It is nearly insoluble in water and in ether, but is readily dissolved by alcohol, which deposits it in granular crystals. Its salts with potassium, sodium, and ammonium, are soluble in hot water, and the liquid on cooling sets into a jelly. A solution of these salts in dilute alcohol, of sp. gr. o'960, deposits them in pearly crystals. Saponic acid forms compounds with calcium, barium, copper, and lead, which are insoluble in water, but soluble in dilute alcohol.

(1499) A variety of other neutral crystallizable and often poisonous principles have been obtained from plants, many of which are used medicinally; but few of them have been minutely examined. It is probable that many of these bodies will prove to be identical with substances already known, and many others will most likely be found to belong to the class of glucosides.

The following are some of these bodies:

1. Antiarin (H205, 2 H.; Mulder), the poisonous prin

OTHER CRYSTALLINE PRINCIPLES.

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ciple of the Upas antiar, which when introduced into a wound causes vomiting, convulsions, and death. It crystallizes in pearly scales, soluble in alcohol, sparingly so in ether; 27 parts of boiling ether dissolve I part of antiarin.

2. Daphnin, from the bark of Daphne mezereum, forms colourless radiated needles, soluble in hot water, alcohol, and ether.

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3. Elaterin (H285; Zwenger) is the active principle of Momordica elaterium. It is a white silky crystalline powder, insoluble in water and dilute acids, but soluble in alcohol, ether, and the oils: when heated, it melts and sublimes.

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4. Gentianin (EH100; Baumert), the bitter principle of Gentiana lutea, crystallizes in yellow needles freely soluble in alcohol and in ether, sparingly soluble in cold water, more abundantly soluble in boiling water. It possesses the properties of a

weak acid.

5. Hesperidin is a white, tasteless, crystallizable body extracted from the white spongy part of the rind of oranges and lemons.

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6. Picrotoxin (Є.H; Oppermann) is an intensely bitter substance to which Cocculus Indicus owes its activity: the name is derived from πικρός, bitter, τοξικὸν, poison. It forms small colourless stellate needles soluble in 25 parts of boiling alcohol.

7. Santonin (E,1,H1803; Heldt).-This substance possesses feebly acid propertios; it is obtained from the seeds of Artemisia santonica, and several others of the wormwood tribe. It is soluble in water and in alcohol. In order to obtain it, the seeds should be digested in alcohol with lime; a combination of lime and santonin is dissolved, from which the alcohol is expelled by distillation, and on adding acetic acid the santonin crystallizes. 8. Colocynthin (H2?) is a crystallizable bitter substance insoluble in ether, which is contained in the Cucumis colocynthis, and which by boiling with acids is separated into glucose and a resin.

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(1500) THE substances which are about to be treated of in the present chapter under the head of colouring matters, are grouped together on account of the similarity in the modes of applying them in the arts, and not from any well-marked chemical rela

tions which exist between them. The relations of several of these bodies to other groups are, however, remarkable, and present many points of considerable interest.

The colouring matters are found in all the organs of plants. In the madder, turmeric, and alkanet they are obtained from the roots; in logwood, Brazil-wood, and fustic they are found in the wood; in quercitron in the bark; in safflower they are furnished by the petals, and in saffron by the anthers of the flowers; whilst in the Persian berry and in annatto they are obtained from the seed. Many colouring matters in the form in which they exist in the growing plant give little or no indication of their tinctorial power. This is the case with indigo, and with the blue colouring matters of the lichens; but by the action of fermentation and of atmospheric oxygen, or by the effect of ammonia, or by the action of other chemical agents, they may be made to furnish dye-stuffs of great brilliancy and beauty.

Most of the organic colouring matters fade or change their hue under the combined influence of oxygen and solar light; they undergo a species of slow combustion, and are in many cases rendered colourless. Many of them are also deprived of colour by reducing agents, such as sulphuretted hydrogen, the sulphides of the alkaline metals, and the ferrous and stannous salts; but in these cases of deoxidation, the colouring matter, when it is again exposed to the air, recovers its original hue. The roots of the plant appear to exert a reducing effect upon many colouring matters, whilst in the flower the opposite effect takes place; this is beautifully shown in an experiment by Persoz:-If the roots of a transparent plant, such as balsam (impatiens), be immersed in a coloured solution, such as one of logwood, the coloured liquid is absorbed by the radicles, it is deprived of a portion of oxygen, and loses its colour; in this form it continues to circulate through the plant until it reaches the petals of the flowers, where it again absorbs oxygen and resumes its original hue.

All organic colouring matters are destroyed by chlorine, which acts in some cases by displacing hydrogen, in others by decomposing water and setting oxygen at liberty, and thus producing new compounds destitute of colour. Sulphurous acid also in many instances combines with the colouring body, and produces new compounds not possessed of tinctorial power.

Almost all the colouring matters require a preparation more or less elaborate before they are fit for use; many of the processes employed in brightening and fixing their tints are of a complex nature, and still retain their original empirical character. In several