Though of other composition, the earliest known aniline colourmauveine-may be conveniently described here. Its sulphate: C27H24N4,H2SO4, is formed when dilute solutions of a mixture of aniline and toluidine sulphates and potassic dichromate are mixed. The solution is purple red. Addition of alkalies liberates the free base, C27H24N4, as a nearly black crystalline powder, soluble in alcohol with violet colour. All its salts are crystalline and have a cantharidine green lustre. Its formation may be represented by the equation: CH,N+3C,H,N + 50 C27H24N4 + 5H2O. 9 = 1182. Paratolyl-diphenyl methane: C20H18 (C6H5)2CH.C6H4.CH3, = results by heating tolyl-diphenyl carbinol with benzene and phosphoric anhydride. It forms colourless crystals, melting at 71° and boiling above 360°. On oxidation it yields an acid : C20H1603 = (C6H5)2: C(OH).CH.CO.OH, difficult to crystallise, melting at 187°, and giving a barium salt crystallising in silky interlaced needles: (C20H1603)2 Ba,70H2, difficulty soluble in water. Phthaleins. 1183. Phthalic anhydride and phenols, on gently heating with a dehydrating agent, such as sulphuric acid, combine to form the socalled phthaleins, probably according to the equation : ·CO·0 + 2(C¿H)(6−x)(OH), = OH, CHACO. .CO.CH( −x)(OH) + C6H4.CO.CH(5-3)(OH), They are all soluble in alkalies with formation of brilliant-coloured solutions. By acting on the bodies in alkaline solution with nascent hydrogen from zinc dust, colourless additions products, phthalines, are obtained, and may be precipitated by acidifying the solutions. On heating the phthaleïns to a high temperature with sulphuric acid a phenol group in combination with the phthalic acid radical is generally split off in the form of a sulphonic acid, and an anthraquinone derivative is simultaneously produced, thus: giving a mixture of the two hydroxy-anthraquinones (§ 1167, 2). Resorcin phthaleïn gives alizarine and hydroquinone phthaleïn chinizarine. Of the numerous compounds already prepared in this group only the following can be mentioned here: 1184. Phenol phthalein, C20H1401 = C6H1(CO.C6H4.OH)2, isomeric with the phenyl salts of the phenylene dicarbonic acids (§ 1106), is formed by heating five parts of phthalic anhydride with ten parts of phenol and four parts of sulphuric acid at 120°-130°. The red mass, when extracted with water, leaves a resin, which is converted into a clear yellow powder by boiling with benzene. This dissolves in solution of potassic hydrate with fine red colour, without doubt forming CH(CO.C6H4.OK)2, from which addition of hydrochloric acid precipitates phenol phthaleïn as a flocculent mass. The alkaline solution is soon decolourised by contact with powdered zinc, and then yields, on addition of hydrochloric acid, colourless phenol phthaline, C20H1604, whose alkaline solution on exposure to air soon reoxidises and regains its fine colour. 1185. Resorcin phthalein, or fluoresceïn, can be obtained even without the aid of sulphuric acid by fusing two molecules of resorcin with one molecule of phthalic anhydride at 195° until water is no longer evolved. The melt is then boiled with water and the residue, after drying, dissolved in three times its weight of hot acetic acid, the diacetate being formed, which, on addition of alcohol, separates in plates; it is recrystallised from acetone and saponified by boiling with alcoholic potassic hydrate. Addition of acetic acid precipitates the phthalein, which can finally be recrystallised from alcohol. Fluoresceïn exists in two states: as tetrahydrate, C20H1406 = .CO.C6H3(OH)2 C6H4.CO.CH(OH)2 .CO.C,H,(OH).0 and as anhydride dihydrate, C20H1205 = C6H4' 4.CO.CH(OH). 3 The first is invariably precipitated in yellow flocks, also the latter, from alkaline solutions by supersaturating with acids, and is converted into the anhydride dihydrate by crystallisation from boiling alcohol, by heating alone at 130°, or by heating with sulphuric acid, acetic anhydride, &c. This latter form is obtained first in the synthesis of fluoresceïn; it forms a crystalline brick red powder, nearly insoluble in water, ether, and benzene, difficultly soluble in alcohol and acetone. On dilution of the alcoholic solution it separates in clear yellow stellate needles. It yields alizarine on heating with acids. It dissolves in solutions of alkalies and ammonia with a beautiful red colour. The ammoniacal solution is characterised by its extraordinarily strong green fluorescence. The diacetate, CH4 CO.CH3(O.CHO). .CO.CH3(O.C2H3OO, crystallises in colour less plates, melts at 200°, and is not soluble in aqueous alkalies. Alkaline solutions of fluorescein are decolourised by zinc dust; addition of acids then precipitates resorcin phthaline or fluorescine; oxidising agents reconvert it into fluoresceïn. 8 Tetrabrom-fluorescein, or eosine, C20H,Br,O,, is readily obtained by the action of bromine on fluoresceïn. It forms a brownish red powder, which crystallises from acetic acid in yellow prisms. The potassic and baric compounds, C20HBrOK, and C20H6Br40,Ba, form red crystals of golden green lustre, dissolving in water and alcohol with a beautiful deep red colour, and on sufficient dilution imparting a greenish yellow fluorescence to the liquid. 1186. Hydroquinone phthalein, isomeric with the preceding, is obtained by heating phthalic anhydride, hydroquinone, and sulphuric acid. It crystallises from water in colourless nacreous plates: C20H1406 (tetrahydrate), which at 170° is converted into the dihydrate anhydride, C20H1205, a colourless mass melting at 233°. It dissolves in concentrated sulphuric acid with brick red colouration, in alkalies with a violet colour. Chlor-acetyl converts it into a crystalline diacetate, C20H10(C2H30)205. When strongly heated with sulphuric acid it yields chinizarine. 1187. Pyrogallol phthalein, or galeïn, is obtained directly by heating phthalic anhydride with double its weight of pyrogallol. It dissolves difficultly with red colour in hot water, more readily in alcohol. It can be recrystallised from hot dilute alcohol, and then forms a brownish red mass with blue reflex of the formula: C20H1408 = C6H4:[CO.C6H2(OH)3]2 converted at 180° into the anhydride tetrahydrate : C20H1207 = .CO.C6H2(OH)2.0 Gallin, or pyrogallol phthaline, C20H1807, obtained from it by reduction, forms large colourless crystals. Mellitic and pyromellitic acids yield similar compounds with hydroxy derivatives of benzene. CONJUGATED COMPOUNDS WITH FOUR BENZENE NUCLEI. 1188. Triphenyl benzene, C24H18 = C6H3(C6H5)3(?), is formed by heating phenyl-methyl ketone with phosphoric anhydride or hydrochloric acid gas. It crystallises from absolute alcohol and benzene in short prisms, and melts at 169°-170°. Tetraphenyl methane, C25H20= C(C6H5)4, is formed by the action of aluminic chloride on a mixture of carbonic tetrachloride and benzene, also in the dry distillation of baric benzoate. It forms colourless needles, melting at 170°. Diphenyl-phenylene methane, C25H20= (C6H5.C6H4)2:CH2, is obtained by the action of cold sulphuric acid on a solution of diphenyl and methylal in glacial acetic acid (comp. § 1145). It is purified by precipitation with water and solution in benzene, and on evaporation of that solvent forms small colourless monoclinic crystals, melting at 162°. Chromic and sulphuric acids readily oxidise it to diphenylphenylene ketone, С25H18Ō = (C6H5.C6H4)2: CO, which forms granular crystalline aggregates, and readily combines two atoms of nascent hydrogen, forming diphenyl benzhydrol, or diphenyl-phenylene carbinol, (C6H5.C6H4)2:CH.OH. This secondary alcohol crystallises in white needles, readily soluble in alcohol and melting at 151°. CH(CHS) , is obtained by heating benzo-pinacone, hydriodic acid, and phosphorus. It crystallises in prisms, melts at 206°, and can be sublimed. Tetraphenyl ethylene, C26 H20, is obtained by dechlorinising diphenyl carbon dichloride (§ 1147) by silver: C(C6H5)2 and, together with other hydrocarbons (diphenyl methane, &c.), by heating benzo-phenone and zinc dust. It crystallises from benzene in spear-shaped needles, and is difficultly soluble in alcohol and ether. Mauveïne probably also belongs to this group. COMPOUNDS CONTAINING CONDENSED BENZENE NUCLEI. 1189. In these compounds the carbon atoms in the nucleus are arranged in such a manner that the compound is built up of two or more closed hexacarbon chains, a pair of carbon atoms being common to two chains. Assuming the tetravalent nature of carbon, and the correctness of the formula assigned to benzene, no other probability exists than that the carbon atoms common to two rings are neighbouring and are in divalent union, as shown in the following formula: These atoms belonging to the two nuclei can evidently not combine with any further elementary atoms (as long as the alternate mono- and divalent union remains), whilst all the others have each one bond available for union with other elementary atoms. If this latter is hydrogen, the hydrocarbons, C10H,,C14H10, &c., result. In such hydrocarbons the hydrogen atoms are replaced by other elements or groups according to essentially the same rules as those that regulate substitution in benzene. If the substituting groups are organic radicals, the new compounds formed stand in the same relations to the original molecules that the aromatic compounds containing more than six carbon atoms, previously mentioned, do to benzene. From their known chemical behaviour naphthalene and phenanthrene must be included in this group. NAPHTHALENE AND ITS DERIVATIVES. Naphthalene, C10H8. 1190. The most important arguments for assigning the more simple nucleus given above to naphthalene are its oxidisability to phthalic acid and the conversion of several of its substitution products into substituted phthalic acids. From the first it follows that naphthalene must contain at least one orthophenylene nucleus, which remains unchanged in phthalic acid, with which the group C4H, must be united by means of two of its carbon atoms. If in the latter group two atoms of |