1. On quenching cylindrical samples in cold water and aqueous salt and alkali solutions film boiling is absent and nucleate boiling occurs. During nucleate boiling the surface of the sample is cooled uniformly. 2. When the temperature of the cooling liquid is raised to 50°C or higher intensive film boiling begins; it is characterized by irregular cooling of the surface. 3. For a certain time the surface temperature of the body remains approximately constant during nucleate boiling and differs little from the boiling temperature of the cooling liquid, i.e., a selfregulating thermal process is established. 4. The reduction of the effective heat transfer coefficient with increasing size of the body during nucleate boiling and the selfregulating process approaches a hyperbolic relationship and Biot's general criterion remains almost constant. 5. With increasing concentrations of NaCl and NaOH in the quenching solutions the effective heat transfer coefficient first increases, reaches a maximum at concentrations of 10–12%, and then begins to decrease.