330° C., and is more sparingly soluble in glacial acetic acid than in alcohol; almost insoluble in benzol, chloroform, and ether; soluble in sulphuric acid, with a deep-red colour ; easily soluble in cold baryta- and lime-water, as also in alcoholic acetate of lead. Free isoanthraflavic acid is precipitated from the aqueous solution of the barytic salt by carbonic acid, which is reformed, however, on boiling. The solutions in alkalis and alkaline earths are of a deep-red colour. It sublimes in shining yellow needles, and does not dye with mordants.

This salt is readily soluble in water, and crystallises with difficulty in dark-red shining needles. On exposure to the air it is readily decomposed. If dried at 150°, it loses its water of crystallisation.

Tetrabromisoanthraflavic Acid, CH,Bг.04.

This compound is obtained by dissolving isoanthraflavic acid in alcohol, and adding drop by drop a large excess of bromine. In a few minutes the solution congeals to a crystalline paste of yellow needles, sparingly soluble in alcohol, but more freely in glacial acetic acid.

Diacetylisoanthraflavic Acid, C1H。(C2H2O)2O1·

2

This acid is formed by the reaction of anhydrous acetic acid upon isoanthraflavic acid at 160°-180°, and is sparingly soluble in alcohol, but more easily in glacial acetic acid. From the former solvent it is obtained in pale-yellow microscopic crystals. They frit together at 175°, and melt completely at 195°. If heated with alcoholic potassa, the acetyl-group is separated.

Diethylisoanthraflavic Acid, C1H。(C2H5)2O4•

To obtain this compound, isoanthraflavic acid is heated to 120° with soda-lye, iodide of ethyl, and a little alcohol. In a few hours the reaction is completed, and a body is formed, insoluble in potassa-lye, and which is obtained in long, shining, pale-yellow needles on recrystallisation from alcohol. It is quite insoluble in water, sparingly soluble in alcohol and ether, more freely in glacial acetic acid and benzol. It dissolves in concentrated sulphuric acid with a reddish-violet colour. The solution shows two indistinctlydeveloped absorption-bands in the green and the yellow. If the solution is more concentrated, an absorption-band appears also in the blue. The melting-point of this compound is at 1930-194°.

Anthraxanthic Acid, C14H8O4.

This acid was discovered by Ulrich and Perger in the 'new red' of the alizarin manufactory of Przibram and Co., and can be obtained by the sulphation of chemically pure anthracen only under certain circumstances. According to statements hitherto published, this acid takes up no water of crystallisation; it is insoluble in cold glacial acetic acid, and sparingly soluble even at the boiling-point; sparingly soluble in cold alcohol, but more readily with the aid of heat. From hot alcohol it crystallises in small gold-coloured needles, which are deposited as the solution cools. It is insoluble in benzol, and more readily soluble in ether than in alcohol. In concentrated sulphuric acid it dissolves with a red colour. It is almost insoluble in cold baryta-water, but dissolves in the same liquid when hot, and crystallises on cooling in redbrown needles. The ammoniacal solution of the acid is completely decomposed and precipitated by baryta-water, an excess of which renders it insoluble. In hot lime-water it is

sparingly soluble, more easily when cold. It is very slightly soluble in cold alcoholic sugar of lead. The solution in alkalis is of a fine orange colour, and after a short time, if the solutions are not too dilute and if the alkali is in excess, the salt crystallises out in splendid felted needles, varying in colour from orange to the redness of chromic acid. If the solution is sufficiently concentrated, it becomes gelatinous. The pure soda salt is easily recrystallised. It is soluble in alcohol, from which it crystallises on the addition of ether. If heated in a tube with access of air, a portion is decomposed, whilst the rest sublimes in splendid iridescent yellow leaflets. If melted with alkali, it undergoes no change, and does not dye with mordants.

This body was obtained from hydrochrysamid by Liebermann and Giessel. A sulphuric solution of hydrochrysamid is mixed with water till it has a pasty consistence. It is kept cool with snow, and a current of nitrous acid is passed through it till the paste liquefies, turns a cherry-red, and till nitrous vapours escape unabsorbed. The mass is then introduced into well-cooled alcohol with constant stirring, and the brown-red precipitate of a diazo-compound is quickly removed by filtration. It is next heated with alcohol to 60° till nitrogen and aldehyd begin to escape, and after the reaction is completed it is boiled for some time. A considerable quantity of a nitrogenous substance insoluble in alcohol is then filtered off, and the alcoholic filtrate is precipitated with water, agitated with ether, evaporated to dryness, and recrystallised from alcohol or acetic acid. Chrysazin is obtained from glacial acetic acid in red-brown, shining needles, but from alcohol in golden-yellow leaflets. Both forms, however, are identical, and are respectively capable of conversion. It melts at 191° C., dissolves in alkalis with an orange colour, but only in mere traces in the alkaline carbo

N

nates and in ammonia. Salts of lime and baryta produce red precipitates. It does not dye with mordants. If heated with zinc-powder it yields anthracen. From chrysazin are derived chrysammic acid, tetranitrochrysazin, and the tetramido (or diamidoimido) chrysazin of hydrochrysamid.

It is obtained on heating chrysazin with anhydrous acetic acid at 170°. It crystallises from alcohol in yellowish leaflets resembling benzoic acid; it is capable of sublimation, and melts at 226°-230°.

Tetranitrochrysazin, or Chrysammic Acid, CH,(NO2)404.

This compound was first obtained by Braconnot on treating aloes with nitric acid, and is also formed, according to W. De la Rue and H. Müller, from chrysophanic acid by the action of the same reagent. More recently it has been prepared by Liebermann and Giessel by the nitration of chrysazin, and submitted to a closer examination. By its preparation from chrysazin it has been proved to be a derivative of anthracen. De la Rue and Müller, who advocated the duplication of the formerly assumed formula C,H, N2O, regarded chrysammic acid as tetranitrochrysophanic acid. But the researches of Liebermann and Fischer, which proved that chrysophanic acid is a derivative of methylanthracen, and the most recent investigations on chrysazin, have demonstrated this view as untenable.

2 69

Chrysammic acid, as Graebe and Liebermann formerly declared, must be regarded as a tetranitrobioxyanthraquinon, C1,H2(NO2),(OH)2O2. The two hydrogen atoms of the hydroxyls can be replaced by metals, yielding the salts which have been examined in detail by Schunck, Mulder, Stenhouse, and Müller, and which have the general formula,

C1H2(NO2), (OM),O,. This formula also renders intelligible the composition of the body known as chrysammid, and obtained by the action of ammonia upon chrysammic acid. The analyses of Schunck and Mulder agree well with the formula proposed by the latter, C14H,NO1(C=6_0=8), and cannot therefore be harmonised with the correct atomic weight of oxygen on the assumption of only 7 atoms of carbon in chrysammic acid. Gerhardt, therefore, regarded the above compound as a mixture of C,N,H,O,+C,N2H ̧ ̧.

11

4 5

According to present views the compound in question is considered not as chrysammid, but as the ammon-salt of amidotetranitrochrysazin, CH,(NO2),(H2N)(OH)O„. The ammon-compound is formed in accordance with the following equation:

C12H2(NO2), OH+2NH, C11H2(NO2), NH2+H2O

OH

=

14

4

OH.NH3.

This equation agrees also with the amount of water obtained on passing ammonia over chrysammic acid. The behaviour of the compound is also rendered intelligible by this view. Whilst on treatment with strong acids chrysammic acid is re-formed, there is obtained by means of dilute hydrochloric or sulphuric acid an intermediate link containing more nitrogen than chrysammic acid and having the character of an acid. This is evidently free chrysammidic acid, C11H2(NO2), (NH2) (OH) O2, which Schunck obtained not perfectly free and described as amidochrysammic acid. As this chemist observed, the salts of this acid are formed also from the ammonia-salt on mixing it with the soluble salts of the respective metals.

For the preparation of chrysammic acid there are various methods. According to Stenhouse and Müller, the most abundant yield is obtained as follows: 6 vols. of nitric acid of spec. grav. 1.36 are placed in a retort provided with a good condenser. The acid is heated almost to a boil and