is affected as measured and shown by a galvanometer. The ultraviolet part can, to some extent, be made visible by photography, but the easier process is, as before mentioned, by the use of a Soret's ocular.

The red colouring-matters of the grape and various reds used to colour wines are dealt with specially in the article on Wine. As with other colours, so with red tints generally; if they are once identified, imitation mixtures can be made and estimated colorimetrically; or, if the absorption factor is known, they may be estimated by a spectroscope with a double slit and a suitable shutter connected with the ocular.

§ 60. ORANGE AND YELLOW.-The most common oranges and yellows are the annatto colours: curcuma, picric acid, fustic, chrysophanic acid, gamboge, and aniline oranges and yellows.

The Annatto Colours.-The colouring-matters of the annatto are two substances, one a yellow, orellin; another a cinnabar red substance, bixin. The latter is described in the article on "Annatto." The annatto colouring-matters are not soluble in water, but are easily dissolved by alcohol. The alcoholic solution is orange red, and non-fluorescent. On the addition

of nitric acid it becomes turbid. On dilution with water, there is a strong fluorescence, and it becomes yellow-green. It then absorbs, like ferric chloride, the whole left side of the spectrum E, and half to D.

Turmeric is the root of Curcuma longa. The colouring-matter is curcumin, CH10O3, insoluble in cold water, and sparingly soluble in boiling water. It is very soluble in alcohol, and forms brilliant yellow crystals. Turmeric moistened with boric acid and dried assumes an orange colour, changed by alkalies into a blue; this is due to the formation of a compound soluble in alcohol, forming a red solution, and crystallising in lustrous green crystals, to which the name of rosocyanin has been given. No. 32 shows the spectroscopic appearances of curcumin.

Pieric Acid (CH(NO)O), also called carbazotic acid and trinitrophenol, is formed commercially by acting on phenol, by dissolving it in sulphuric acid, and then treating the solution with nitric acid. It crystallises from hot water in yellow plates, having a very bitter taste. The salts are explosive. It is taken up from acid watery solutions by petroleum-ether, ether, or benzine, and hence can be readily obtained pure enough for examination.

Picric acid is not precipitated by acetate of lead. The chief chemical test is the production of isopurpurate of potash, which is the result of adding cyanide of potassium, and gently warming.

The reaction is represented as follows:

C6H3(NO2)3O+3CNK+2H2O=C3H4N¿O¿K+CO3K2+NH3.

Isopurpurate of potash is of a blood-red colour.

Fustic is the general name for yellow colours found in the wood of the Morus tinctoria.

8

The wood contains two distinct colouring-matters; the one, moritannic acid, C13H1606+ H2O, soluble in hot water, and forming yellow crystals; the other, morine, C12HO, is but sparingly soluble in water; crystallised from alcohol the substance forms yellow needles. Both give yellow precipitates with acetate of lead. The spectroscopic appearances of fustic are shown in No. 34 (a.) in concentrated, (b.) in dilute solution.

Chrysophanic Acid, C15H1004, appears to be dioxymethylanthraquinone. It is contained in the rhubarb and wall lichen (Parmelia parietina). In commerce it is in the form of six-sided tabular crystals, of a pale to an orange-yellow colour. It is very readily extracted from rhubarb which has been previously macerated in water, pressed, and dried, by digesting the rhubarb in benzine. The crystals are soluble in ether, oil of turpentine, coal-naphtha, benzine, and other hydrocarbons.

The spectrum of chrysophanic acid is very similar to that of natural alizarine. Solutions of chrysophanic acid give, with alkalies, a rich purple colour. An ammoniacal solution of chrysophanic acid yields, with alum, a beautiful rose-coloured precipitate. An alcoholic solution of subacetate of lead gives, in the alcoholic solution, a red-white precipitate. Chrysophanic acid, on being oxidised with nitric acid, yields methylanthraquinone, C1H1009.

Gamboge. This is a colouring-matter derived from the Garcinia morella, var. pedicellata. It is a gum resin, to which the formula of C30H350 has been ascribed. It is very insoluble in water, but soluble in alcohol.

In order to detect it in sweetmeats, to which it has occasionally been added, the yellow colouring-matter is dissolved in alcohol, and precipitated by water, a reaction at once showing that it is of a resinous nature. The precipitate, if gamboge, will give a red colour with an alkali. It is without doubt a poisonous colour, but the question of quantity must be considered. Sixty grains have caused death, and five grains is a medicinal dose; and since some persons, especially children, are peculiarly susceptible to the action of medicines, even quantities so small as a third of a grain in a couple of ounces of sweets, should be considered as having possibly an injurious action.

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Aniline Oranges and Yellows.-Eosine, C20HOBг Na, the alkali salt of tetra-bromo-fluoresceine, is a reddish-brown powder soluble in water, the solution being of a reddish-orange with green fluorescence; it gives a yellow-red colour, or, if in strong solution, a red precipitate with hydrochloric acid. All the derivatives of fluoresceine have a similar spectrum, of which eosine may be taken as the type. Moderately diluted, there is an intense dark band in the green; this, farther diluted, divides into two well marked bands, the respective centres of which (in an alcoholic solution) are 2525 and 2491; the same bands, slightly altered in position, are seen in ethyl-eosine, rose bengal, and phloxin. Eosine as a dye may often be recognised by the spectrum of the fabric strongly lit by the reflected rays of the sun, or by the lime or electric light. The fibre may also be digested in slightly acidified alcohol; the alcoholic extract is then taken up by amyl alcohol, a drop of ammonia added, and the spectroscopic appearances noted. The absorption factors of eosine from a solution of 0.01 mgrm. per cc. have been ascertained by Krüss for the following wave lengths :

16

2

Croceine Orange (Ponceau 4), CH,,N,O,SNa, is the sodium salt of benzene-azo-3-naphthol-3-sulphonic acid. This dye is soluble in water with an orange colour. Hydrochloric acid gives a brownish-yellow precipitate. It gives a spectrum in which a single broad band occupies half of the green and some of the blue; the band in dilute solution extends from about 2526 to 2438.

17

Orange T (Mandarin G R), C1H13N2O4SNa, is the sodium salt of sulpho-o-toluene-azo-3-naphthol, it is soluble in water, and precipitated by hydrochloric acid in brown flocks. It gives a similar spectrum to the above.

2

Orange I (Tropæoline 000), C16H1N,O,SNa, is the sodium salt of p-sulpho-benzene-azo-a-naphthol, while Orange II is the similar compound of 3-naphthol; the former gives a brownishyellow colour to hydrochloric acid, and precipitates in brown flocks. It gives a spectrum similar to croceine orange; 0.2 mgrm.

in 1 cc., viewed in a stratum of 4 mm., gives a band extending from 2530 to 2.399.

9

Resorcin Yellow (Tropæoline O), C12H,N,O,SNa, is the sodium salt of p-sulpho-benzene-azo-resorcinol; it is soluble in water, and not changed by hydrochloric acid; dissolved in the proportion of 0.2 mgrm. in a cc. of water, and viewed in a stratum of 4 mm., it gives a single band from 2475 to 2361 (Hartley).

Diphenylamine Orange (Orange IV-Tropæoline 00-Fast yellow), CH4NO,SNa, is the sodium salt of p-sulpho-benzeneazo-diphenylamine. The salt dissolves in water readily; it gives a violet precipitate with hydrochloric acid. It gives no bands, but cuts off the violet and blue rays.

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Chrysoidine, CH1N4Cl, is the hydrochloride of diamido-azobenzene. In commerce it is more often mixed with other colours; thus, mixed with magenta, it is known as cardinal;" with safranine, it is known as "scarlet for cotton ;" it is soluble in water, and strikes with hydrochloric acid an orange-brown colour. It gives a band in the visible spectrum, when in the concentration of 0.8 mgrm. per cc., and viewed through 2 mm., extending from 2494 to 2439; in a stratum of 3 mm. there is a band in the ultra violet from λ247 to λ232 (Hartley).

Methyl Orange (Orange III-Helianthine), C11H14NSONа, is the sodium salt of p-sulpho-benzene-azo-dimethylaniline; it is a common laboratory reagent as an indicator for alkalies and acids. It is readily soluble in water to an orange solution, and strikes a magenta red with hydrochloric acid and other acids. Methyl orange in a concentration equal to 0.3 mgrm. per cc., and viewed through a stratum of 3 mm., gives a band extending from 2509 to 2361; it, therefore, shuts off all the violet and blue rays, as well as some of the green. It also, under the same conditions, gives a spectrum in the ultra violet, extending from 7.270 to 256. In a more dilute solution (0.06 mgrm. per cc.) it gives a band from 2458 to 2407 (Hartley).

Metanil Yellow, C18H14N,O,SNa, is the sodium salt of m-sulphobenzene-azo-diphenylamine; it is soluble in water, and gives a crimson colour with hydrochloric acid. It gives no band in the visible spectrum, but shuts off all the violet and blue rays.

Phosphine (Chrysaniline), C9H16N4O3, is the nitrate of diamido-phenyl-acridine and its homologues. This colour is soluble in water, and does not change colour with hydrochloric acid. It gives a shadowy band from 2486 to 508 in the visible spectrum.

§ 61. The GREENS-are chlorophyll and the aniline greens. Chlorophyll, the green colouring-matter of plants. It would appear that it is now possible to separate chlorophyll in a crystalline state. The merit of this discovery belongs to A. Gautier, who crystallised chlorophyll in 1877,* and two years afterwards Hoppe-Seyler, without knowing of Gautier's paper, described the same substance under the name of chlorophyllone. Gautier's method is as follows:-The leaves are pounded in a mortar, and sodic carbonate added in quantity nearly sufficient to neutralise the acid juices, and the product strongly pressed. The marc is then exhausted at 55°, and again strongly pressed; to the exhausted substance alcohol is added, and the whole digested at 83°; chlorophyll, wax, pigments, fat, and other matters dissolve. The liquid is filtered and digested with coarse animal charcoal, which has been previously washed. At the end of four or five days it has lost its green colour, and becomes yellowish- or brownish-green. The charcoal retains the chlorophyll, and is now washed with alcohol at 65°; the latter removes a yellow crystallisable substance generally accompanying chlorophyll, and intimately allied to it in composition.

From the animal black thus freed from the yellow substance, chlorophyll may be extracted by anhydrous ether, or very light petroleum ether. A slow evaporation in the dark will yield it in crystals. Thus obtained, chlorophyll forms flat, often radiating crystals, which may be more than a centimetre in length, soft in consistence, and of an intense green colour when recent, but slowly changing to yellowish-green, or greenish-brown. If the crystallisation is too rapid, these long crystals are not obtained, but green masses composed of microscopical crystals, belonging to the rhombohedral system.

Diffused light changes chlorophyll to yellowish-green, and ultimately decolourises it. The crystals dissolve in ether, chloroform, petroleum, carbon disulphide, and benzine. Digested with hydrochloric acid, chlorophyll splits up into two new substances, one giving a beautiful blue solution, the other remaining insoluble, but dissolving with a brown colour in hot ether and alcohol, from which it appears inclined to crystallise. Fremy, who was the first to notice this splitting-up of chlorophyll, called the first substance phyllocyanine, and the last phylloxanthine.

The ultimate analyses of chlorophyll by Hoppe-Seyler and Gautier agree fairly well, especially as Hoppe-Seyler's chlorophyll being derived from monocotyledonous and Gautier's from dico

* Bulletin de la société chem. T. xxviii., 1877, p. 147. Comptes rendus, lxxxix., p. 861.

+ Bericht der deutschen chem. Gesellschaft, 1879.