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LEFT METALS 202 METALS 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 in- stance 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Conn., invented a stone or ore crusher which has become so extensively used that it has, except in special cases, superseded hand labor for breaking up large pieces of ore.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 con- tinued 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 vnth coke. By this process power consump- 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 im- provements were made in the designs of blast furnaces in 1917. See MINERAL Production, United States. ^ METALS. Though each metal is con- sidered 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 non- metallic in this sense are called metal- loids. 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 ele- ments, 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 de- grees. (3) With the exception of mer- cury, 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 re- flected 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 tem- peratures 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; while plati- num, 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 dif- ferences 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 bis- muth are so brittle that they may be easily pulverized in a mortar; while others, as iron, gold, silver, and copper, require great force for their disintegra- tion. Taking iron and lead as represent- ing the two extremes of tenacity, it is found that an iron vdre 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 diflPerent chem- ists. The following is probably one of the most convenient: (I.) The Light Metals, subdivided into — (1) The metals of the alkalies — viz., potassium, sodium, caesium, rubidium, lithium, (2) The metals of the alkaline earths — ' viz., barium, strontium, calcium, magne- sium. (3) The metals of the true earths — » viz., aluminium, glucinum, zirconium, yttrium, erbium, terbium, thorinum, cerium, lanthanum, didymium. (II.) The Heavy Metals, subdivided into — (1) Metals whose oxides form power- ful bases — viz., iron, manganese, chro- mium, nickel, cobalt, zinc, cadmium, lead, bismuth, copper, uranium, thallium, (2) Metals whose oxides form^ weak bases or acids — viz., arsenic, antimony, titanium, tantulum, niobium, (or colum- bium), tungsten, molybdenum, tin, vana- dium, osmium, (3) Metals whose oxides are reduced by heat — ^noble metals — viz., mercury, silver, gold, platinum, palladium, iridium,