For reducing the size of wrought-iron work, the process shown in the following engraving may be employed. a a is the section of a wrought-iron square box or tube, which is supposed to be made red hot and placed suddenly in the water, B, from its end, C, to the point D; the result is that the metal in the water, from C to D, contracts or shrinks in diameter, and compresses the hot metal immediately above the water-line, as the small cone at D denotes. If then the box or tube is slowly immersed in the water, its form, when cold, will be as in the right-hand figure, that part from C to D maintaining its original size, and the remainder being smaller.

It must then be reheated and suddenly immersed from the end, E, nearly to D, until it is cold, and then slowly lowered in the water, as before, which will contract the part from D to C, making the entire length parallel but smaller, both in diameter and bore, than before it was thus operated upon.