AbstractThe sorption isotherms are reported for the β‐soluble anhydrite form of calcium sulfate (Drierite) exposed to moist air at one atmosphere total pressure and 90, 100, 125, 150, 175, and 200°F. A concentration‐temperature coordinate has been identified which when plotted against the amount sorbed caused all isotherms to collapse into a single sorption therm. The latter has been fit by a three‐term expression based on a combination of sorption theories. A graphical comparison is made between a curve calculated from the analytical expression and actual experimental datum points.Curve fitting was done by machine and involved minimizing the square of the deviations. Maximum deviations up to 4% are experienced in the high range. In the low range these tend to increase but so do the experimental