One of the superlative properties of all metals is crystallization, and on the exact condition of the crystals in any metal often hangs every degree of usefulness. An intimate glimpse into the complex nature of an ordinary steel is given in Fig. 1, in which the sharply separated crystals with boundary cement and internal granules are as plain as the stones in a building. The same applies to a sample of ordinary copper as seen in Fig. 2.
All metals have been found to crystallize on solidifying from the molten state; even after the severest strains and deformations, the crystal nature persists. Deformed crystals give birth to a new growth of crystals, if the temperature will allow the readjustment. Maximum ductility usually accompanies well-grown crystals; maximum strength accompanies the first incipient growths of a newly disseminated structure from some previous formation, probably through surface forces. Brittleness and weakness commonly are developed through the coalescence between large crystals of the material by some substances of friable nature; impurities and overheating thus form an aggravating combination.
An amorphous state is a plausible assumption to account for the cement between grains, the debris along slipped cleavage planes and colloidal metal solidified by pressure instead of fusion. The study of this condition is now assuming notice and promises brilliant results for science and industry.