Derivatives of dyestuffs, having enhanced solubility in water as compared with the dyestuffs, are manufactured by acting on a dyestuff containing at least one hydroxy group, particularly a dyestuff which is sparingly soluble or insoluble in water, in the presence of a tertiary base with an acylating agent which contains, in addition to the acylating group, at least one substituent which forms a salt or is converted into a quaternary ammonium group by reaction with the tertiary base or which can be subsequently converted to a quaternary ammonium group by simple addition of an alkyl salt, such as sulphonic, carboxylic or tertiary alkylamino groups, or groups which combine with tertiary bases to form quaternary ammonium compounds. Suitable acylating agents are: halides of organic acids containing more than one salt-forming group, such as halides of polycarboxylic or polysulphonic acids, or sulpho-carboxylic acids in which either or both of the acids groups is in the form of halide or in which the sulphonic group is esterified and the carboxylic group is in the form of halide, also 4-dialkylamino-1-benzoyl halides or 4-halogenalkyl-1-benzoyl halides. Instead of using isolated acid halides there may be employed directly the products of reaction of a phosphorus halide, e.g. trichloride or pentachloride, on the acid; or a solution of the dyestuff and the acid in the tertiary base may be treated with phosphorus pentachloride or trichloride. Dyestuffs suitable as starting materials are: azo-dyestuffs in which at least one component contains a hydroxy group or an enolizable keto group, e.g. mono-, dis-, or polyazo-dyestuffs obtainable from diazotized aromatic amines of the benzene or naphthalene series, which may contain substituents, e.g. hydroxy groups, and coupling components, e.g. arylamines, phenols, or compounds having methylene groups capable of coupling, advantageously azo-dyestuffs in which at least one component lends affinity to vegetable fibres, e.g. diphenyl, stilbene, thiazole, diarylazoxy and carbazole derivatives, amines united to urea, thiourea, diazine, triazine, benzoyl and cinnamoyl residues, and certain aminonaphthols; also azo-dyestuffs containing metals, e.g. chromium, copper, iron, nickel or cobalt, in complex union; dyes of the anthraquinone series containing a hydroxy group; and hydroxy derivatives of dyes of the azine, oxazine, thiazine, arylmethane and rhodamine series. The products may be converted by saponification to the parent dyestuffs. They may be used in the dyeing of various materials, e.g. vegetable and animal fibres such as wool, silk and leather, artificial fibres such as regenerated cellulose or cellulose derivatives, and artificial masses. If dyes are used which can form metallic complexes, the products may be treated in substance with a compound yielding a metal, whereby a metalliferous compound is obtained on saponification. In examples, the following compounds are heated together in the presence of pyridine: (1) the azo-dyestuff a -naphthylamine --> b -naphthol and 4-chloromethyl-1-benzoyl chloride; (2) the azo-dyestuff a -naphthylamine --> 2 : 3-hydroxynaphthoic anilide and 4-chloromethyl-1-benzoyl chloride; (3) the azo-dyestuff benzidine \sQ b -naphthol and 4-chloromethyl-1-benzoyl chloride; (4) the azo-dyestuff a -naphthylamine --> 2 : 3-hydroxynaphthoic anilide and m-sulphobenzoic acid dichloride; (5) the azo-dyestuff a -naphthylamine --> b -naphthol and m-sulphobenzoic acid dichloride; (6) the azo-dyestuff benzidine \sQ b -naphthol and m-sulphobenzoic acid dichloride; (7) the azo-dyestuff a -naphthylamine --> b -naphthol and benzoic acid-m-sulphochloride; (8) the same dyestuff and benzoic acid-3 : 5-disulphochloride; (9) the azo-dyestuff benzidine \sQ b -naphthol and benzoic acid-3 : 5-disulphochloride; (10) the azo-dyestuff 4-chloro-o-toluidine --> 2 : 3-hydroxynaphthoic acid 2-methyl-4-methoxyanilide and benzoic acid-3 : 5-disulphochloride; (11) the azo-dyestuff 1-aminonaphthalene-4-sulphonic acid --> 2 : 3-hydroxynaphthoic anilide and benzoic acid-m-sulphochloride; (12) the azo-dyestuff a -naphthylamine --> b -naphthol and 5-sulphosalicylic acid dichloride or 3 : 5-disulphosalicylic acid trichloride; (13) the azo-dyestuff acetyl-p-phenylenediamine --> 2-benzoylamino-5-naphthol-7-sulphonic acid anilide and benzoic acid-m-sulphochloride; (14) the complex copper compound obtained by the action of cupric acetate on the azo-dyestuff 2-amino-4-chlorophenol --> b -naphthol and benzoic acid 3 : 5-disulphochloride. Further products are listed in tables, the following additional dyestuffs being specified: azo-dyestuffs: aniline --> a -naphthol or 2 : 4-dihydroxyquinoline, a -naphthylamine --> barbituric acid or the anilide of benzoyl-, acetyl- or phenyl-2 : 5 : 7-acid, p-anisidine --> p-cresol, dianisidine \sQ b -naphthol, 2 : 5-dichloraniline --> 2 : 3-hydroxynaphthoic anilide or o-anisidide, 2-amino-4-chloranisole --> 2 : 3-hydroxynaphthoic-o-anisidide, 4-nitro-2-toluidine --> 2 : 3-hydroxynaphthoic anilide, 4-(41-methyl)-phenoxyacetylamino- or 4-benzoylamino-2 : 5-diethoxyaniline --> 2 : 3-hydroxynaphthoic anilide, 41-chloro-2-aminodiphenyl ether-4-carboxylic acid diethylamide --> 2 : 3-hydroxynaphthoic-o-anisidide, 1-methoxy - 2 - aminobenzene - 4 - diethylsulphonamide --> 2 : 3-hydroxynaphthoic acid 2 : 4-dimethoxy - 5 - chloranisidide, 4 - chloro - 2 - toluidine --> 2 - hydroxycarbazole - 3 - carboxylic acid p-chloranilide, 4-aminoazobenzene --> b -naphthol, 3 : 31-diaminobenzanilide \sQ b -naphthol or p-cresol, 4 : 41-diaminodiphenylurea \sQ b -naphthol, 2 : 3-hydroxynaphthoic anilide or 1 - hydroxy - 4 - benzoylnaphthalene, 4 - chlorobenzeneazo - 41 - amino - 31 - methylnaphthalene --> b -naphthol, 4-chlorobenzeneazo-41-amino-31-methoxynaphthalene --> 2 : 3-hydroxynaphthoic anilide, 2-methyl-4 : 41-diamino-5-methoxyazobenzene \sQ a - or b -naphthol, p-cresol, 2 : 3-hydroxynaphthoic anilide or the anilide of benzoyl-2 : 5 : 7-acid, 4-amino-41-acetylamino-21-p-toluenesulphon-azobenzene --> b -naphthol, 4 : 41-diaminodiphenylamine \sQ b -naphthol, 4 : 41-diaminodiphenylmethane or 4 : 41-diaminodiphenyl ether \sQ 2 : 3-hydroxynaphthoic anilide, 4-aminoacetanilide --> the anilide of acetyl- or phenyl-2 : 5 : 7-acid, o-anisidine --> 1-hydroxy-4-benzoylnaphthalene; other dyes: 1 : 5 - dibenzoylamino - 4 : 8 - dihydroxyanthraquinone and 1-hydroxy-4-p-tolylaminoanthraquinone. Specification 482,184 is referred to. Samples have been furnished under Sect. 2(5) of products obtained by the interaction, in the presence of pyridine, of: (I) the azo dyestuff 1 - aminonaphthalene - 4 - sulphonic acid --> 2 : 3 - hydroxynaphthoic anilide and benzoic acid - 3 - sulphochloride; (II) the azo dyestuff a - naphthylamine --> 2 : 3 - hydroxynaphthoic anilide and naphthalene - 1 : 3 : 6 - trisulphonic acid; (III) 21 : 41 - dinitrophenyl - 1 - amino - 8 - naphthol and benzoic acid-3-sulphochloride; (IV) 1 : 5 - dibenzoylamino - 4 : 8 - dihydroxyanthraquinone and p - chloromethylbenzoyl chloride; (V) 1 : 5 - diamino - 4 : 8 - dihydroxyanthraquinone and benzoic acid-3-sulphochloride; (VI) Bz-2-Bz1-21-dihydroxydibenzanthrone and benzoic acid-3 : 5-disulphochloride; (VII) the azo dyestuff 4-(41-methyl)-phenoxyacetylamino-2 : 5-dimethoxy-1-aminobenzene --> 2 : 3 - hydroxynaphthoic anilide and furane-a : a 1-sulphocarboxylic acid chloride. The Specification as open to inspection under Sect. 91 comprises in general the treatment of dyestuffs containing at least one hydroxyl group with acylating agents which contain, in addition to the acylating group, at least one substituent which, if desired after suitable transformation, determines or enhances the solubility of the dyestuff, in the presence or absence of an acid-binding agent. It describes in the tables further products obtained from the following additional reactants: azo dyestuffs: aniline --> 1 - hydroxy - 4 - methoxynaphthalene, aminoazotoluene --> 1-hydroxynaphthalene - 4 - benzylsulphone, 4 - chloraminophenol --> resorcinol \sM dehydrothiotoluidine, o - aminoazotoluene --> p - cresol, 1 - hydroxy - 3 - chloro - 4 - methylbenzene or b - naphthol, 4 - amino - 41 - ethoxydiphenylamine --> b - naphthol, b - naphthylamine --> b - naphthol, m - chloraniline --> 2 : 3 - hydroxynaphthoic anilide, 4-(41-methyl)-phenoxyacetylamino - 2 : 5 - dimethoxyaniline --> the methylanilide of phenyl - 2 : 5 : 7 - acid, 4 - benzoylamino - 2 : 5 - diethoxyaniline --> 1 - hydroxy - 3 : 4 - dimethylbenzene, 4 : 41 - diamino - 5 - methoxy - 2 - methylazobenzene --> 1 - hydroxy-3 - chloro - 4 - methylbenzene, 1 - amino - 4 : 5 - phenylazimidobenzene --> 1 - hydroxy - 3 : 4 - dimethylbenzene or b - naphthol, 1 - amino - 4 : 5 - (41 - chloro) - phenylazimidobenzene or 2 - phenyl - 5 - aminobenzimidazole --> 1 - hydroxy - 3 : 4 - dimethylbenzene, 1 - (41 - chloro) - phenyl - 2 - phenyl - 5 - aminobenzimidazole --> 1 - hydroxy - 3 : 4 - dimethylbenzene or b - naphthol, 4 - amino - 3 - methoxyazobenzene --> p - cresol, 1 - amino - 2 - methoxynaphthalene - 4 - (41 - chloro) - azobenzene --> 1 - hydroxy - 3 - methyl - 4 - chlorobenzene, 2-aminonaphthalene - 1 - sulphonic acid --> b - naphthol, xylidine --> m - aminobenzoyl - 2 : 5 : 7 - acid --> b - naphthol, 1 - aminonaphthalene - 4 - (21 - methoxy) - azobenzene --> b - naphthol, 1 - amino - 4 - nitrobenzene - 2 - methylsulphone --> 1 - amino-5-naphthol; other dyes: dihydroxy-N-dihydro-1 : 2 : 21 : 11 - anthraquinoneazine, 1 : 2 - dihydroxyanthraquinone, Eriochromazurol (Colour Index No. 720), Modern Violet; acylating agents: 1 - benzoylaminobenzene - 3 - carboxylic acid - 31 : 51 - disulphochloride, sulphochloracetic acid chloride, benzene-1 : 3 : 5 - tricarboxylic acid chloride, benzenehexacarboxylic acid chloride, naphthoic acid-disulphochloride, benzoic acid-2 : 4-disulphochloride. It also contains examples of the use of the products in dyeing and pr