The paper describes a gravimetric method of determining the volatility (evaporation rate) of pesticides. The measuring apparatus may be set at any temperature between ∼15 and 80°C; the dry air flowing through the apparatus is regulated by valves between ‐0.2 1/h and 300 1/h. Figures available for vapour pressure reveal a mathematical relation between vapour pressure and evaporation rate. This can be used as a simple method of determining the vapour pressure of any substance at 20°C by determining the evaporation rate when the air current is flowing at 50 l/h. The effects of the temperature and the air flow rate on the evaporation rate are also analysed.

Hitherto it has been possible to determine vapour pressures only at a temperature of 20°C when using the method previously described for measuring the evaporation rate. The scope of application of the method has now been extended to temperatures of 30, 40, 50 and 60°C; because of the known temperature dependence of the vapour pressure, the vapour pressures at all the intermediate temperatures can then be calculated from these values.