1. (a) C. Rochester, Acidity Functions, Academic Press, New York, 1970; (b) M. Liler, Reaction Mechanisms in Sulphuric Acid, Academic Press, London, 1971.
2. M.M. Davis, Acid–Base Behavior in Aprotic Organic Solvents, National Bureau of Standards Monograph 105, Washington, DC, 1968.
3. A. Hantzsch, Z. Elektrochem., 29 (1923) 221.
4. The name “hydron” has been recommended for the positive ion of H in natural isotopic composition, to be distinguished from the isotopically pure species “proton”, “deuteron”, and “triton”. See J.F. Bunnett and R.A.Y. Johnes, Pure Appl. Chem., 60 (1988) 1115.
5. (a) A. Hantzsch, Z. Phys. Chem., 61 (1907) 257. See also: (b) A. Hantzsch and K.S. Caldwell, Z. Phys. Chem., 58 (1907) 575; (c) H. Goldschmidt and O. Ubby, Z. Phys. Chem., 60 (1907) 728.