magnesite

[English magnes ( ia ); suff. -ite ( Min.).] Min.: A mineral belonging to the group of rhom. bohedral carbonates, consisting e entially of car bonate of magnesia, having the formula MgOCO2, but in the crystallized forms having more or le of the magnesia replaced by protoxide of iron, forming ferriferous varieties like breunnerite (q. v.). The crystallized varieties present a perfectly rhombohedral cleavage; luster vitreous; color white to various shades of brown. The ma ive and purer kinds are white, mostly compact; luster dull; fracture resembling unglazed porcelain. The Brit . Mus . Cat , reserves this name for the pure mineral only, and groups the ferriferous carbonates of magnesia under ankerite, breunnerite, and mesitite (q. v.). Used in the manufacture of Epsom salts. Magnesite formerly included meerschaum (q.v.). Brongniart, in 1802, and subsequent French mineralogists, still used this name for the silicate. măg-ne-si-um (s as sh), s. [Latinized from Magnesia, a city in Asia Minor.] Chem.: A diatomic metallic element; symbol, Mg; atomic weight, 244; specific gravity 1743. Fuses sin, aş; expect, Xenophon, exist. ph = f. and volatilizes at a red heat. Magnesic sulphate (Epsom salts) was known in the middle of the seventeenth century, but the metal was first isolated by Davy. The compounds of magnesium are widely distributed in nature, occurring as magnesite, MgO CO; ophite or serpentine, MgO 3 Si2O; talc, MgO4S1506; dolomite, kainite, epsomite, . It may be obtained by the electrolysis of fused magnesium chloride, or by reducing magnesium chloride with metallic sodium. Itis a brilliant metal, almost as white as silver, and preserves its luster in dry air. It is more brittle than silver at ordinary temperature; but at a higher temperature it becomes malleable, and may be pre ed into the form of wire or ribbon. Magnesium ribbon may be ignited at the flame of a candle, and burns with a dazzling bluish-white light, rich in chemically active rays, a property which has led to its use in photography, When burned in an atmosphere of carbonic acid gas, it decomposes the gas, forming magnesic oxide, and throwing down the carbon in powder. Magnesium di olves in dilute acids, with violent evolution of hydrogen, but it does not decompose water even at 100%. magnesium-chloride, s. Min.: A mineral said to have occurred in the sa 2598 and then sending an electric current through the wire. The harder the steel the more difficult it is to magnetize, but the more completely does it retain its magnetism. Permanent magnets are either straight or are bent into the form of a horseshoe. magnet ish magnetic-equator, s . A line pa ing round the globe near the equator, at every point of which the dip of the needle is nothing. The general inclination of the magnetic to the terrestrial equator is about 12°. and are thus able to act simultaneously on the same magnetic substance. A magnet consisting of only one bar of steel is called a simple magnet; but since region affected by it. In one sense it may be said to be infinite; but the law of inverse squares diminishes the intensity so rapidly that practically the by fastening together several thin steel bars prev i point is the intensity of the field at that point, and magnets are very powerful. Far more powerful than any permanent magnets are electro-magnets, which may be either straight or bent into the form of a norseshoe, and consist of a bar or core of soft iron, round which is coiled insulated copper wire. Through this wire an electric current is sent, and so long as the current pa es the iron is a powerful magnet. The strength of an electro-magnet depends on the strength of the current and on the number of coils of wire round the core, and upon various other circumstances. Electro-magnets have been made capable of supporting more than a ton. When used for supporting weights, ., a smooth piece of iron, termed an armature, is placed in contact with IMG:content-0821.png:[blocks in formation] Chem.: Mg(C2H5)2. A colorle mobile liquid, obtained by heating ethyl iodide with magnesium filings to 130°. It po e es an alliaceous odor, takes fire when exposed to the air, and is violently decomposed by water, with the formation of magnesium hydroxide.