At all times engineers have needed to know something of the properties of materials, but of late for a reason that is new. The materials of the nineteenth century were lew and traditional: brick and stone, timber, wrought and cast iron, copper and its alloys with zinc and tin, all these had been used for generations, their properties were familiar, and machines had changed the tempo rather than the methods of their fabrication. Mild steel came to replace wrought iron in structural work. Steel castings were found, for certain purposes, preferable to castings in iron. Reinforced concrete showed how the merits of two materials could be combined. But the engineer, though quick to accept and use these novelties, still maintained his traditional attitude. Only in recent years, by the work of the chemist and the physicist, has his successor been given glimpses of a future in which his problems of fabrication will be solved (the italics are Dr. Houwink's) by the deliberate synthesis of materials with definite clastic and plastic properties. Already his list of constructional materials is lengthened by the addition of plastic resins, cellulose and protein products, artificial rubbers: what is more significant, the macroscopic studies of the nineteenth century (only towards its close was the microscope employed for the elucidation of finer structure) have been largely superseded by methods incomparably more refined, in which the individual crystal as unit is replaced by the complex molecule, the crystalline micro‐structure by the crystal lattice as revealed by X‐rays. We are passing, in materials, from an age of acceptance to an age of control, and henceforth engineering will demand a knowledge of materials both wider and deeper than what sufficed before the War.
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