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The Specification describes dyes of the general formula wherein R1 is an alkyl group of 1 to 3 carbon atoms, R2\t is an alkyl group of 1 to 5 carbon atoms which is unsubstituted or substituted by -CO2- or -SO3- ions to form an internal salt with the nitrogen atom, R3 is hydrogen, halogen, alkyl or alkoxy, Ph is a phenyl group which may be substituted by alkyl, aryl or alkoxy groups or by halogen atoms, A completes a heterocyclic nucleus and X, which is present only when R2 is unsubstituted alkyl, is an anion. They may be prepared by condensing a 2-phenyl-indole with 2-formylmethylene-1; 3; 3-trimethylindoline in the presence of acetic anhydride and an acid HX, or by condensing a 1-methyl-2-phenyl-3-formyl-indole with a 2-methyl cyclammonium salt in the presence of acetic anhydride. Examples of dyes are given wherein A completes a benzthiazole, benzoxazole, benzselenazole, 1,3,4-thiadiazole or 3,3-dimethylindolenine nucleus. Specification 825,965 is referred to.