MAGNESIUM (Mg). This metal was first obtained by Sir Humphry Davy, but its oxide or magnesia, and carbonate, or magnesia alts,, have been known since the commencement of the last century. Its com pounds are frequently met with in the inorganic kingdom, but are not so abundant as those of lime.
Magnesium may be obtained from its chloride by heating with potassium or sodium, or by subjecting the same salt to a voltaic current obtained by means of a few cells of a Bunsen's battery.
Deville and Caron give the following details for the reduction of the metal. Six parts of chloride of magnesium are well mixed with one part of a fused and powdered mixture of chloride of potassium and sodium, one part of pure fluoride of calcium, and one of sodium in small pieces. The mixture is transferred to a red-hot earthen crucible, fitted with a lid. After some time the reaction takes place, and when the hissing noise has ceased, the lid of the crucible is removed, and the mixture stirred with an iron rod until the whole appears uniformly mixed, and the upper portion of the liquid mass is clear. The crucible is then removed from the fire, and when the saline mass is nearly solidifying, it is to be stirred with an iron rod so as to collect the suspended particles of metal. When cold, the mass is broken up, and the globules of crude magnesium picked out.
The metal thus obtained may be purified by placing it in a carbon tray, and heating it to whiteness in a carbon tube, a current of hydro gen being at the same time passed over it ; it is subsequently re melted with chloride of magnesium, chloride of sodium, and fluoride of calcium.
If, in the above process, the current of hydrogen is rapid, the vapour of the magnesium is to a certain extent carried out of the tube, and on being ignited, burns with an exceedingly beautiful flame.
Magnesium is a metal of silvery white colour, and semi-crystalline or fibrous fracture. It fuses and votalilises at about the same tempe rature as zinc, to which metal it in many other points bears a very close analogy. It is malleable and ductile, may be easily polished,
readily filed, and yields well to the chisel. Its specific gravity is 1'75. It does not tarnish in dry air, and in a damp atmosphere oxidises but slowly. This metal takes fire at about the temperature at which glass Melts, and burns with a steady and most brilliant flame. Could a chewer roceas be discovered for the manufacture of magnesium, thin wires of it spun into a wick might no doubt be advantageously used in many instances as a source of light. Magnesium crystallises In octo hedra. It acts but very slightly upon cold water, and is not rapidly oxidised by hot water. It Ignites when brought into contact with hydrochloric acid; sulphuric acid dissolves it slowly with evolution of hydrogen.
The equivalent of magnesium is 12.
Megamiam and caries form only the following oxide :— Magnesia,eaftieed magnesia, or oxide of magnesium (Mg0). Prepared by heating the carbonate to full red heat. Its density depends upon that of the carbonate employed ; if a light variety has been used, then light calcined magnesia results, but If a heavy carbonate, then beery calcined magnesia is obtained.
Magnesia is a white powder, very voluminous, inocloroun, and taste less. In the oxyhydrugen blowpipe flame it fuses to a hard opaque enamel. Moistened with water it acts upon test paper like an alkali. Magnesia is a powerful base, forming salts with the acids that are usually very stable.
Hydrate of magnesia (31g0, HO) is precipitated in a semi-gelatinous state when an alkali is added to an aqueous solution of a salt of mag nesia. It also occurs native. [MAONESIA, in NAT. lItss. Dir.] Iodide of magnesium (Mg I). Magnesia dissolves in aqueous hydri odic acid. forming a difficultly crystallisabla salt. On exposure to heat, it gives off bydriodie acid, end magnesia is left, Bromide of magnesium (31g13r) may be prepared in the nano manner as the iodide, than which it l3 far more stable. This salt is also found in sea water, and in many salt springs.