Every process involves time, labor, and expense, and is employed in whole or in part only because it accomplishes a definite and necessary purpose. Its use must be justified as a necessary step toward a definite result, else there would be no reason for employing it. A process may not be perfect, although it may bring excellent results, and improvements in processes are being made constantly, despite the remarkable degree of skill at present existing in the production and shaping of metals for a great variety of uses.

From a superficial knowledge of the properties of metals, many remarkable processes of shaping them hot or cold have been gradu-2 ally evolved or improved upon by patient and persistent experiments, and methods for shaping metals are now in vogue which were deemed impossible a decade ago. Success along these lines comes only from testing the properties of a material beyond the known range, studying the causes of failure, and bringing to one's aid improved apparatus for holding, pressing, cutting, heating, etc., as necessity may require.

The details of many processes vary because of difference in the skill of workmen, or difference in equipment or quality of materials with which they work.