Recalescence

—A sudden check in the proce of cooling a bar of iron or steel from a white heat, when the metal glows more brightly for a short while upon reaching a certain temperature, and then continues cooling. On bringing a piece of iron to a white heat and letting it cool in a dark room, it will cool regularly, the colors fading to a dull red as the temperature falls. When a certain point is reached, about 1000° F., not only is the rate of cooling retarded, but the iron bursts out into a glow as if reheated, before fading again. This recalescence is occasioned by molecular changes in the metal, as iron is magnetic below the point of recalescence, non magnetic above that point.