poured into water, the solution takes a splendid cherry-red. On rapid filtration it is found that the filtrate is rapidly decolourised, with the separation of white flakes. If the red alcoholic solution is dropped into an acid, there is obtained a lemon-yellow amorphous precipitate, which quickly changes on exposure to the air, and turns white. The white body produced does not yield a red solution with aqueous potassa, and is insoluble in this reagent. It is anthraquinon.

Care must be taken not to heat the melted potassa too strongly, as otherwise a violent development of hydrogen gas sets in, and the anthraquinon undergoes further decomposition.

This ultimate product has not yet been further examined. The yellow compound which dissolves in alkalis with a red colour can also be obtained by another method, by which its preparation is free from all difficulty, and the nature of the substance is rendered intelligible. If a mixture of anthraquinon and zinc-powder is covered with aqueous potassa, the liquid becomes red even in the cold. The action is completed by heating for a few minutes to 100°, when the anthraquinon is quantitatively transformed. Where the air has access, either anthraquinon or an intermediate compound is separated. The mixture is filtered and precipitated with an acid, air being excluded. The yellow precipitate is placed upon a filter in a current of carbonic acid. The filter is supported by a Plantamour's funnel, in which the precipitate is dried. It dissolves with difficulty in sulphide of carbon. It is soluble in alcohol and ether with a yellow colour and a splendid green fluorescence, but the greater portion is converted into anthraquinon unless the air is excluded. From hot carbolic acid it is obtained in small yellow needles. Concentrated sulphuric acid dissolves it with a violet colour, which changes almost instantly into the ordinary yellow of a solution of anthraquinon in sulphuric acid. Hitherto the quinon-like nature

of anthraquinon had only been inferred from its composition and its direct formation out of anthracen on oxidation, from its behaviour with phosphorus perchloride, and from the fact that on the introduction of two hydroxyls it yields alizarin, which must be unconditionally regarded as a quinon. The proof that an anthrahydroquinon exists-to which anthraquinon bears the same relation as that of quinon to hydroquinon-had previously not been furnished. The above-described compound supplies this deficiency, it being simply anthrahydroquinon or anthraquinonhydron, or probably a mixture of both.

It is possible that the yellow colour of the reductionproduct and the red colour of its alcoholic solution may be derived from anthraquinonhydron, and that the anthrahydroquinon itself is colourless.

If the dry product of the reduction is covered with strong potash lye, the surface becomes for a short time a splendid dark-green, probably due to anthraquinon-hydron.

In an alkaline solution anthraquinon-hydron absorbs oxygen, reduces Barreswill's liquid, though the anthraquinon which is separated out at the same time makes the reaction indistinct. The production of this substance on fusion with potassa is easily explained by the reducing action of the hydrogen evolved in the melted mass. It may also be detected, although with greater difficulty as in smaller quantity, on boiling anthraquinon with alcohol, sodiumamalgam, and a little potassa.

Bibromanthraquinon, C1H¿Br2(02).

6

It has been already observed above that bibromanthraquinon can be obtained by two methods. It is formed firstly by the direct action of bromine upon anthraquinon

at 160°. The calculated quantities of the ingredients are introduced into a tube, mixed as well as possible-upon which the success of the reaction essentially depends-the tube is sealed and heated in the air-bath until all or nearly all bromine vapours have disappeared, which requires a considerable time. On opening the tube large quantities of hydrobromic acid escape, and the appearance of the contents is found to have become modified. The resulting mass is recrystallised from benzol. This method of preparation is not readily successful, as hard masses are almost always formed, in which a portion of the anthraquinon escapes the action of the bromine.

Bibromanthraquinon may be more conveniently obtained from tetrabromanthracen. One part of the latter is heated with two parts chromate of potash and five to six parts of colourless nitric acid of specific gravity 14 in a spacious flask. The reaction is very violent at first; bromine escapes in large quantity, and the liquid sometimes froths strongly.

As soon as the development of bromine-vapours ceases, the action is complete. It is then diluted with water; the mass, which has become pale yellow, is collected upon a filter, washed, and recrystallised from benzol. The oxidation succeeds also well with glacial acetic acid and chromic acid.

Bibromanthraquinon crystallises in light yellow needles and sublimes undecomposed in the same form.

It is very sparingly soluble in alcohol, but more readily in benzol and chloroform. It undergoes double decomposition much less easily than the chlorised and bromised quinons of benzol and naphthalin. Potassic hydrate only acts upon it at temperatures above 200°. Alizarin is then formed according to the subjoined equation, and combines with two molecules of potassa to alizarate of potassa:

C11H ̧Br2(O2)"'+2KHO=C12H(HO)2(O2)”+2KBr,

6

Bibromanthraquinon.

14 6

Alizarin.

This reaction corresponds exactly to the production of chloranilic acid from chloranil :

C¿C1(02)”+2KHO=C(HO)2Cl2(O2) +2KC1,

Monobromanthraquinon, C1H,Br(O2).

This compound is obtained from tribromanthracen exactly as is bibromanthraquinon from tetrabromanthracen.

It crystallises in light yellow needles, melts at 187°, and sublimes undecomposed in needles. It is sparingly soluble in alcohol, tolerably freely in hot, but scarcely in cold benzol. If concentrated along with hydrate of potassa, it is converted, not into the corresponding oxygen compound, but into bioxyanthraquinon-i.e. alizarin, as will be analytically proved below. Monobromanthraquinon behaves in this respect like trichloroquinon, which is converted by alkali into chloranilic acid.

Hydrate of potassa has therefore in both cases a further oxidising action.

C ̧HCl(O2)”+KHO+H2O=C(HO) 2Cl2(O2)” + KCl+H2,

Trichlorquinon.

2

Chloranil acid.

C,H,Br(O,)+KHO+H,O=CH (HO),(O,) +KBr+H,,

Bichloranthraquinon, C1HCl,(0,).

This compound is obtained in a similar manner to bibromanthraquinon. Tetrachloranthracen is oxidised either by means of glacial acetic acid and chromic acid, or by nitric acid, as described above under bibromanthraquinon.

In its external properties it completely resembles the corresponding bromine compound; it crystallises in yellow needles, and dissolves not very readily in benzol, but more

freely than the corresponding bromine compound. It is sparingly soluble in alcohol and ether.

On fusion with hydrate of potassa it yields alizarin.

Mononitroanthraquinon, CH,(NO2)O2•

In order to nitrate anthraquinon, it is dissolved with the aid of heat in at least 6 parts, but preferably in 10-12, or even larger proportions of nitric acid of from 1.48 to 1.5 sp. gr., and the solution kept at a brisk boil from 30 to 45 minutes in case of small quantities, or a correspondingly longer time if the quantity is large.

Afterwards the liquid is poured into an excess of cold water, and the pale yellow flakes precipitated are washed with water. The preparation is therefore very simple, but the product is naturally not quite free from quinon. If pure anthraquinon is used, higher oxidation-products are formed, only in very small quantities.

Mononitroanthraquinon, when dried, is a pale yellow, and, like most of the anthraquinon compounds, a very electric powder. At high temperatures it sublimes readily in minute needles, pale yellow, or almost white, which, at 230°, melt to a yellow liquid. It is insoluble in water, scarcely soluble in ether, very sparingly in alcohol, more readily in acetic ether, benzol, chloroform, oil of turpentine, also in glacial acetic acid, from which it crystallises in fine needles, which readily dissolve with a brownish-yellow colour in concentrated sulphuric acid and in aniline, with the latter of which, like the dinitro-compound, it forms a resinoid combination, which dissolves with a rich magenta colour in acetic acid, acetic ether, and other ethereal solvents. It is readily soluble in nitrobenzol, whence it can be obtained in narrow, neat monoclinic columns. If dissolved in concentrated sulphonitric acid, it is readily and completely converted into a dinitroanthraquinon, which is in part at once deposited from the acid solution.