The metallic oxides are, without exception, solid bodies, insoluble in water, and usually present a white or colored earthy appearance. Hence the old name of metallk car for these oxides.
Those oxides which are termed basic possess the property of directly uniting with the so-called oxy-acids (such as sulphuric, nitric, carbonic, and silicic acid), and of forming a new chemical compound of the second order, termed a salt (q.v.).
The compounds of the metals with chlorine, iodine, bromine, and fluorine, such, for instance, as chloride of sodium, or common salt (C1Na), are termed haloid salts (q.v.). The same metal may often combine both with chlorine and with oxygen in more than one proportion. For example, we have subchloride of mercury (ligIC1); suboxide of mercury (1420); chloride of rnercury (HgC1); oxide of mercury (Hg0). For the com pounds of the metals with sulphur, see SULPHYDES OF THE METALS.
Metals enter into combination with one another when they are fused together, and such combinations are termed a//erys (q.v.), unless when mercury is one of the combin ing metals, in which case the resulting compound is termed au amalgam. lt is doubtful whether all alloys are true chemical compounds. Definite compounds of the metals with each other do, however, certainly exist, aud are sometimes found native, as, for example, the crystallized silver and mercury compound represented by the formula In consequence of their strong affinities for the metalloids, the metals are seldom found in a free or uncombined state, even in the inorganic kingdom, and never in ani mals or plants. The more common metals, in consequence of their strono. affinity for oxygen and sulphur, are very rarely met with in the uncombined state; liut some of those which are less abundant, such as gold, silver, and platinum, are found uucombined, in which case the terms native and virgin are applied to them; and other metals. as mer
cury and copper, occur both in a free and in a combined state. Many native alloys are found, but the ordinary sources of the metals are oxides, sulphides, chlorides, and car bonates, sulphates, and other salts. These are termed the ores of the metals. The methods of obtaining the metals from their various ores fall under the head of METALLURGY.
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, cmsium, rubidium, lithium.
2. The metals of the alkaline earths—viz., barium, strontium, calcium, magnesium.
3. The metals of the true earths—viz., aluminium, glucinum, zirconium, yttrium, erbium, terbium, thorinum, cerium, lanthanum, didymium.
H.—The heavy metals, subdivided into 1. Metals whose oxides form powerful bases—viz., iron, manganese, clu.omium, nickel, cobalt, zinc, cadmium, lead, bismuth, copper, uranium, thallium.
2. Metals whose oxides form weak bases or acids--viz., arsenic, antimony, titanium, :tantalum, 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, ruthemum, rhodium, osmium. (Several of the rare metals are here omitted.) Another classification is that by which the metals are arranged in six groups, each group being named after a metal which possesses the common characters in ft well marked degree: viz., (1) the sodium group; (2) the calcium; (3) the iron; (4) the copper; (5) the platinum; and (6) the antimony groups.