AbstractIn an effort to throw more light on the evaporation and condensation of alkali‐salts metal in high‐temperature furnaces, measurements have been made of the rate of evaporation of captive potassium sulphate droplets at temperatures up to 1500°. Observations on the evaporation rate in nitrogen and in oxidising atmospheres are consistent with the view that, in those conditions, the rate is controlled by the well‐known laws relating to the diffusion process. In the presence of hydrogen or carbon monoxide, the rate of loss of weight is very much increased because the potassium sulphate is then reduced on the surface of the droplet and the reduction products are much more volatile. the rate of weight‐loss then depends on a balance of the transport of the reducing gases to the surface and the diffusion of the reduction products from the