Metallography

Collier's New Encyclopedia (1921)

the study of the structure of metals and alloys, and their relation to the physical properties. Serious work along these lines was first begun in 1863 by Sorby. He made the first rock sections, and compared the structure of iron and steel with that of meteorites. The study was soon developed, until it has become the recognized method for testing the strength of materials, and the results of different alloys with iron, steel, and other metals. For the specific METALLURGY. treatment of the ores of copper, gold, iron, silver, tin, zinc, etc., see the articles on those metals. As now understood metallurgy is the art of extracting metals from their ores. The operations are partly mechanical and partly chemical. Those processes which depend principally on chemical reactions for their results have reference chiefly to the roasting and smelting of ores, and are described under the heads of the different metals. But there are certain preliminary operations of a mechanical kind which metallic ores undergo, such as crushing, jigging, washing, etc., which we shall describe here, as they are essentially the same for the ores of lead, copper, tin, zinc, and indeed most of the metals. Till comparatively recent times ore, or rather ore-gangue, as it came from the mine was in the first instance broken by hammers before being passed on to crushing rollers or stamps to be reduced to smaller pieces or grains. In the year 1858 Mr. E. W. Blake of New Haven, Conn., invented a stone or ore crusher which has become so extensively used that it has, except in special cases, superseded hand labor for breaking up large pieces of ore. After passing through this or some similar crusher, the vein stuff or impure ore is next taken either to the crushing rollers or to the stamping mill. In recent years there has been continued improvement in the methods of carrying on metallurgical processes. The conditions produced by the war called for a production of iron and steel on an immense scale, and many improvements were devised to produce this result. One of the most important was the synthetic cast made from steel turnings by melting in an electric furnace in contact with coke. By this process power consump-muth are so brittle that they may be tion was more than double and iron of a very high degree of purity is obtained. The use of electric furnaces continued to increase. Especially in the treatment of non-ferrous metals, some important improvements were made in the designs of blast furnaces in 1917. See MINERAL PRODUCTION, UNITED STATES. METALS. Though each metal is considered in a separate article, there are various points regarding the general physical and chemical characters of these bodies, and the method of classifying them, which require notice. A metal, from the chemical point of view, is an element which can replace hydrogen in an acid and thus form a salt. Hydrogen itself is, chemically, considered to be a metal. Those elements which are nonmetallic in this sense are called metalloids. The following are the most important of the physical properties of the metals: (1) All metals, unless when they are in a finely-pulverized form, exhibit more or less of the charactistic luster termed metallic. Two of the non-metallic elements, iodine and carbon, in some forms also present a metallic luster. (2) All metals are good conductors of heat and electricity, though in very unequal degrees. (3) With the exception of mercury, all the metals are solid at ordinary temperatures. With the exception of gold, copper, calcium, and strontium, the metals are, when light is only once reflected from them, more or less white. with a tendency to blue or gray. Most of them have been obtained in crystals, and probably all of them are capable of crystallizing under certain conditions. (4) Metals are remarkable for their opacity, except when they are chemically reduced to extremely thin films. (5) All the metals are fusible, though the temperatures at which they assume the fluid form are very different, and some of them, as mercury, arsenic, cadmium, zinc, etc., are also volatile. (6) Great weight, or a high specific gravity, is popularly but erroneously regarded as a characteristic of a metal; of a metal; while platinum, osmium, and iridium (the heaviest bodies known in nature) are more than 20 times as heavy as water, lithium, potassium, and sodium are actually lighter than that fluid. (7) Great differences are observable in the hardness, brittleness, and tenacity of metals. While potassium and sodium may be kneaded with the finger, and lead may be marked by the finger-nail, most of them possess a considerable degree of hardness. Antimony, arsenic, and biseasily pulverized in a mortar; while others, as iron, gold, silver, and copper, require great force for their disintegration. Taking iron and lead as representing the two extremes of tenacity, it is found that an iron wire will bear a weight 26 times as heavy as a leaden wire of the same diameter. Various classifications of the metals have been suggested by different chemists. The following is probably one of the most convenient: (I.) The LIGHT METALS, subdivided into- (1) The metals of the alkalies-viz., potassium, sodium, cesium, rubidium, lithium. (2) The metals of the alkaline earthsviz., barium, strontium, calcium, magnesium. (3) The metals of the true earthsviz., aluminium, glucinum, zirconium, yttrium, erbium, terbium, thorinum, cerium, lanthanum, didymium. (II.) The HEAVY METALS, subdivided into- (1) Metals whose oxides form powerful bases-viz., iron, manganese, chromium, nickel, cobalt, zinc, cadmium, lead, bismuth, copper, uranium, thallium. (2) Metals whose oxides form weak bases or acids-viz., arsenic, antimony, titanium, tantulum, tantulum, niobium, (or columbium), tungsten, molybdenum, tin, vanadium, osmium. (3) Metals whose oxides are reduced by heat-noble metals-viz., mercury, silver, gold, platinum, palladium, iridium, METAL-WORKING MACHINERY 203 ruthenium, rhodium, osmium. (Several of the rare metals are here omitted.) See MINERAL PRODUCTION, UNITED STATES.