The ionization of 16 thiocarbonyl indicators of overlapping range has been used to establish an acidity function HT for 10-90% sulfuric acid. Agreement with an earlier HT scale of Tissier and Tissier using different thiocarbonyl indicators is good. Protonation constants p K TH+ derived by the classic Hammett-Deyrup approach are in good agreement with those derived by the Bunnett-Olsen relations, but in less satisfactory agreement with those derived by ...