Naphthalide indicator dyes

An indicator dye having the formula ##STR14## wherein R' and R" each are selected from hydrogen, carboxy, hydroxy, o-hydroxyphenyl, --NH--SO.sub.2 --R wherein R is alkyl containing 1 to 20 carbon atoms, aryl selected from phenyl and naphthyl, alkyl-substituted phenyl containing up to 18 carbon atoms or phenyl-substituted alkyl containing up to 18 carbon atoms, --SO.sub.2 --NH--R.sup.o wherein R.sup.o has the same meaning as R, and the group ##STR15## wherein R.sup.1 is --OH, R.sup.2 is hydrogen, alkyl having 1 to 20 carbon atoms, aryl selected from phenyl and naphthyl, alkyl-substituted phenyl having up to 20 carbon atoms or perhalomethyl, R.sup.1 and R.sup.2 when taken together represent .dbd.O, R.sup.3 is perhalomethyl, and n is an integer O or l, at least one of R' and R" being hydrogen and one of R'" and R"" being said group ##STR16## and the other being hydrogen.