Cresol red (0.1% in ca. 20% ethanol); o-Cresolsulphonephthalein; o-Cresol Red; o-Cresolsulfonphthalein; 4,4'-(1,1-dioxido-3H-2,1-benzoxathiole-3,3-diyl)bis(2-methylphenol); 2-[(Z)-(4-hydroxy-3-methylphenyl)(3-methyl-4-oxocyclohexa-2,5-dien-1-ylidene)methyl]benzenesulfonic acid