Abstract Statistical examination of a section of Cady's experimental results relating the partial pressure of hydrofluoric acid over solutions of potassium fluoride in hydrofluoric acid to composition and temperature yields the equation: where P is the partial pressure of hydrofluoric acid (mm. Hg), T is the absolute temperature and C is the concentration of hydrofluoric acid in the solution, expressed as a weight percentage. Although this equation is subject to bias the error in values of P calculated from it may be presumed to be less than 5% in the region of 38–44% concentration and at temperatures of 70–150°C. A Table is given of the calculated values of the partial pressure of hydrofluoric acid within this region at 0.5% intervals of concentration and 5.0°intervals of temperature.