METALS. The elements which compose all natural objects are divided by chemists into two classes, metals and non-metals. Formerly the classification was based on physical prop erties, and the metals were then defined as those elements which were opaque, had a metal lic lustre and were good conductors of heat and electricity; now the division is made on chemical properties, upon the foundational prin ciple that the hydroxides of metals are bases, while the hydroxides of non-metals are acids. However, no sharp line can be drawn between the metals and non-metals, since a few of the elements will classify as either. Some metals have a high specific gravity, but lithium, sodium potassium, etc., float on water, and in general the metals of highest specific gravity are least active chemically. Of the 83 recognized ele ments, 64 are regarded as metals.
The following classification of the elements usually placed in the group metals is that aris ing from the application of the periodic law (q.v.).
Class I. Two sub-classes: (1) Lithium, so dium, potassium, rubidium and caesium; (2) copper, silver and gold.
Class II. Two sub-classes: (1) Calcium, strontium, barium and radium; (2) glucinum (or beryllium), magnesium, zinc, cadmium and mercury.
Class III. Three sub-classes : (1) Aluminum, gallium, indium and thallium; (2) cerium, lanthanum, neodymium, praseodymium, samar ium, europium and gadolinium; (3) terbium, dysprosium, holmium, yttrium, erbium, thulium, ytterbium scandium, lutecium and celtium.
I Class V. Two sub-classes: (1) Titanium, zirconium and thorium; (2) germanium, tin and lead.
Class V. Two sub-classes: (1) Vanadium, niobium (or columbium) and tantalum; (2) arsenic, antimony and bismuth.
Class VI. Chromium, molybdenum, tungsten and uranium.
Class VII. Manganese.
Class VIII. Three sub-classes: (1) Iron, nickel and cobalt ; (2) rhodium, ruthenium and palladium; (3) osmium, iridium and platinum.
A mass of any metal is considered to be composed of atoms arranged in molecules, and any change in the arrangement of the molecule means a change in physical characteristics. Thus
crystalline structure may be obliterated by roll ing or hammering a metal and by the same means the specific gravity may be increased, since the molecules are forced nearer together.
All metals with the exception of bismuth are lighter when molten than when cold. Bismuth, like water, reaches its greatest density just before solidifying. The relative specific gravi ties of some common metals in the solid and in the liquid state are shown by the following table, compiled by Sir Roberts-Austen.
The fracture of a metal is not a distinguish ing property but an evidential feature which gives much information about the manner in which it cooled, the presence of impurities, etc., and is of great practical value. Thus foundry iron is in many instances still graded and sold by its fracture, and in smelting copper and re fining lead the decisive points in the are determined by the fracture of test samples. Slow cooling, as with chemical solutions, tends toward the formation of large crystals, giving a coarse fracture, while a sudden cooling may prevent the formation of crystals and thus give a fracture of fine texture. Crystalline structure, which determines fracture, may be affected by repeated shocks or vibrations. In this way the wrought-iron chains on railroad cars to Prevent accident in case of a coupler breaking may by the jolting of ordinary service become so crys talline as to break when needed. Very low temperatures, as shown by the experiments of Dewar, also affect in a marked manner the crystalline structure of some metals. Any metal is fusible: though arsenic sublimes at 356° F., it may be fused under the pressure of its own vapor. When heated, metals show a red and finally a clear white color. The tem peratures corresponding to these colors are approximately: incipient red, 975° F.; dark red, 1290'; incipient cherry red, 1470'; clear cherry red, 1830'; white, 2370'; dazzling white, 2730 .