thyl radical in a position para to the benzylidene camphor, R4 is an --SO3 H radical and R3 is a hydrogen atom, namely, 2-methyl-5-(3-methylidenecamphor)benzenesulfonic acid; or those in which R2 is a chlorine atom in a position para to the benzylidene camphor, R4 is an --SO3 H radical and R3 is a hydrogen atom, namely, 2-chloro-5-(3-methylidenecamphor)benzenesulfonic acid; and those in which R2 i