4-[[6'-(diethylamino)-3'-hydroxy-3-oxospiro[isobenzofuran-1(3H),9'-[9H]xanthen]-2'-yl]azo]-3-hydroxynaphthalene-1-sulphonic acid, sodium salt

4-[[6-(Diethylamino)-3-hydroxy-3'-oxospiro[9H-xanthene-9,1'(3'H)-isobenzofuran]-2-yl]azo]-3-hydroxy-1-naphthalenesulfonic acid/sodium,(1:x) salt