s a methyl radical in the position para to the benzylidene camphor, R4 is a hydrogen atom and R3 is an --SO3 H radical, namely, 3-(4-methyl) benzylidenecamphor-10-sulfonic acid. ##STR4## in which R5 and R7 are each a hydrogen atom, a hydroxyl radical, a linear or branched alkyl radical having about 1 to 8 carbon atoms, at least one of the radicals R5 and R7 being a hydroxyl, alkyl or alkoxy radica