By using the criteria of melting point and sol fraction, a study has been made of the stoichiometric efficiencies of hardeners for gelatin, as distinct from their rates of reaction. The factors which affect these measurements were investigated. Both melting point and sol fraction distinguish gelatins in respect of molecular weight and origin. Sol fraction measurements give evidence of molecular weight distribution. Various hardeners have a wide range of molecular efficiencies, and these do not correlate with rates of reaction as judged from solution viscosity rise methods. Sol fraction measurements can separate hardeners which would have been considered similar from melting point behavior.