METALLURGY, the extraction of metals from their ores and so refining and fashioning them as to fit them for use in the metal indus tries, is the most ancient of arts. The annals of history show that the degree of civilization attained by a race was directly proportional to the extent to which they made use of metallur gical processes. In fact, a prominent metal lurgist of the 19th century when delivering an introductory address to students of metallurgy was accustomed to charge them that "in propor tion to the success with which the metallurgic art is practised in this country, will the inter ests of the whole population directly or indi rectly in no inconsiderable degree be pro moted.° As an industry, it requires a wide knowledge of the sciences, embracing chemistry, physics and mineralogy, as well as the professions of mechanical and electrical engineering. As some of the oldest historical works make reference to metallurgical processes, the actual practice of the art must go much farther back into pre historic ages. It had its inception at the time when men, ever advancing, replaced their stone implements by others of greater usefulness made from metals. Their methods of extract ing and refining were in many respects com parable with those used to-day except in the introduction of mechanical improvements. The early development of chemistry was very closely allied with metallurgy. Many of the older treatises on theories of chemistry are attempts to explain metallurgical reactions. Prominent among these was the separation of lead from the precious metals, gold and silver, by its combination with oxygen, a process prac tised and much speculated upon by the ancients. Gold was probably the first metal known as it occurs naturally in the metallic state, is bright, heavy and easily worked. Iron, copper, silver, tin and lead were other metals known to pre historic men. Quicksilver is mentioned in the times of the Greeks and Romans. In the 15th and 16th centuries we hear of antimony, bis muth and zinc, with arsenic added at the close of the 17th century. Nickel, cobalt, manganese and platinum came in the 18th century, the re mainder belonging to the 19th and 20th.
There are four great periods,in the annals of metallurgy. The first extended from pre historic times• to the 1st century A.D., when Pliny, the Elder, in his work, 'Naturalis His toria,' collected all existing knowledge con cerning metals to his The second period ending with the 15th century had as its chroni cler Agricola, in `De Re Metallica.' Next came a I period of important stagnation with rela tively few mportant advances until the 19th century ushered in the fourth, our present period, one filled with development.
Properties of Metals.—All metals are dis tinguished by numerous characteristic proper, ties which fit them for their various industrial applications. A brief outline of these follows; Density.—All common metals except aluminum are relatively heavy, specific gravities ranging from 6 to 225/z. The density of metals varies, within moderate limits, due to methods of cast ing, rates of cooling and subsequent mechanical treatments. All metals except, bismuth are lighter when liquid than when solid; i.e., they
contract on 'solidification. Color and Lustre.— The metals vary considerably in,color and ire and many industrial uses depend upon these differences, particularly .in reference to the use of metals for ornamentation. Opacity. —This is a property of all metals under normal conditions. Crystailization.—All metals crys tallize in definite geometrical forms on free solidification. Structure.— This is revealed in fractures examined by the eye and in polished and etched sections examined under the all powerful eye of the microscope. Unmistakable evidence of the thermal and mechanical treat ment which the metal has undergone is fur nished the expert by such examination. Such a study often serves to distinguish one metal from another, making unnecessary the resort to chemical analysis. Hardness.— There are sev eral methods of determining this property: scratch hardness, or resistance to abrasion; in dentation hardness, or the resistance offered to penetration by a body of greater hardness, as in the familiar Brinell method where a hard ened steel ball is used for this purpose; re bound hardness, measured by the height to which a hard body will rebound when allowed to fall upon the metal being tested as typified by the Shore sclerescope method; cutting hard ness, or the resistance offered to cutting by a hard tool. This is usually measured by deter mining the number of revolutions of a standard drill to produce a given penetration. Strength. — This property is measured by resistance to rupture; by slow direct pull, bend, compression or twist; by sudden blow; by repeated bending or blows or a combination of both. Brittleness and Toughness.— These two, opposing proper ties, are indicated by the way in which the metal behaves when subjected to strength tests. The same metal may appear as brittle or tough, depending on the conditions of test. Plasticity. —This property accounting for malleability and ductility, is the ability of the metal to flow under pressure in the hot and in the cold state. It is all important in the working of metals in the industries. If metals did not possess this property, the operations of hammering, rolling, drawing, spinning, etc., through which all metal articles must pass, during fabrication, would be impossible. Weldability.—This is the ca pacity of pieces of metal to unite into one con tinuous metal when heated and brought into intimate contact. Fusibility.—All metals ex cept mercury are solid at ordinary tempera tures, yet they can be melted — brought into a state of fusion—by application of sufficient heat. Volatility.—All metals may be vapor ized at high temperatures. Diffusion.— This is the property of molecules of one metal to mi grate into another when brought into intimate contact, either in the liquid or solid states. Occlusion.—The rapidity and ease with winch metals dissolve gases is augmented by high temperatures. Expansion and contraction with changes in temperature; thermal and electrical conductivity; magnetic permeability, or ability to conduct lines of magnetic force, are all prop erties which find great application in the in dustrial use of metals.