Previous workers have shown that the corrosion rate of metals in acid media is frequently much greater under heat-transfer conditions than it is under simple immersion conditions. In the work described here it has been found that the rate of corrosion of a metallic heating surface is critically dependent upon the temperature of the heating surface in relation to the boiling point of the liquid heated. Experiments have been made with copper and stainless steel heat-transfer surfaces over the temperature range 75°-140° in acetic and sulphuric acids. It was found that there was a pronounced increase in the corrosion rate when. the temperature of the heat-transfer surface was held atapproximately the boiling point of the liquid being heated. At this temperature the corrosion rate was some five times that of the corrosion rates at higher and lower temperatures.