inlet pressure was 3 atm.abs. and the outlet pressure 2 atm.abs. The following temperature measurements were available: inlet, 600°C; 20% of coil length, 740°C; 80% of coil length, 812°C; outlet, 838°C. The following heat flux profile was generated from independent simulations of the heat transfer in the fire box: first tube, 22 kcal/ m2 s; second tube, 20; third, 18; fourth, 17; fifth, 15; sixth, 13; seventh, 11; eight, 8; ninth and tenth tube, 6. With this heat flux profile, the conversion, temperature, and total pressure profiles of Figure 13 were obtained. The Application of Hildebrand's theory of the solubility of microsolutes in ordinary solvents, and of the Flory-Huggins theory to the solubility of steroids in polymers, has permitted the derivation of a predictive correlation between polymer permeability and steroid crystalline melting temperature, other correlating parameters being the entropy of fusion of the steroid and the (computed) solubility parameters of steroid and polymer. The correlation permits prediction of the permeability of any steroid in any polymer with reasonable accuracy.