Magnesium, the metallic base of magnesia; symbol, Mg.; chemical equivalent, 12; specific gravity, 1.74; hardness, that of calcareous spar. Davy proved its existence; but Bussy in 1830 first obtained it in sufficient quantity to test its properties, He decomposed the chloride of magnesium by transmitting through it when heated the vapors of potassium. Since the discovery of large deposits of the double chloride of potassium and magnesium, known as carnallite, in the the salt mines of Stassfurt, it has been proposed to use this mineral in the preparation of the metal; 1,000 parts of carnal-lite are fused with 100 parts of fluor spar and 100 parts of sodium. The metal resembles silver in appearance; it is malleable, ductile, and fuses at a dull red heat, and can be distilled like zinc. It does not change under water or in dry air, but in damp air it soon oxidizes. It consumes with a brilliant white flame when heated to redness, or when thrown into hydrochloric acid. It burns brilliantly in chlorine or in the vapors of bromine, iodine, sulphur, etc. It was proposed by Bunsen to employ this metal in the form of fine wire for illuminating purposes. He found that it might be lighted by the flame of an alcohol lamp, and in burning gave a perfectly steady and very intense light.
A wire 1/100 of an inch in diameter burns at the rate of about three feet in a minute, and gives a light equal to that of 74 stearine candles of five to the pound. The weight of such a wire three feet long is about two grains. Bunsen proposed to have the wire wound upon bobbins and furnished at a regular rate to the lamp. Should the metal be procurable at a considerably reduced cost, as may very likely follow an increased demand for it. it may then prove an excellent method of furnishing light for domestic purposes, and more particularly for lighthouses and uses requiring a great intensity of light. It is now used in magic lanterns and for photographing in places inaccessible to the light of day. For the latter application it is especially adapted by reason of the extraordinary power of the photo-chemical property of its light. The alloy of silicon with magnesium, when decomposed by hydrochloric acid, evolves a hydride of silicon, which is a spontaneously combustible gas. Metallic magnesium precipitates nearly all metals from their neutral solutions.