Magnesium Sulphide, MgS

Crude MgS has been prepared by the action of hydrogen sulphide on magnesium nitride or heated magnesium, or heated magnesium filings and sulphur. Reichel heated magnesium in sulphur vapour. The crude product obtained by heating magnesium in a current of hydrogen and then in hydrogen and sulphur vapour can be purified by heating it in a highly evacuated quartz tube to 600°-700° C. for two hours (the excess of metal is thus volatilised), or by dissolving out the excess of magnesium in ethyl iodide, which is mixed with ether and contains a crystal of iodine. The purified sulphide is then washed with ether and dried in a vacuum desiccator placed in a water-bath. Pure magnesium sulphide has also been prepared by igniting the oxide or anhydrous sulphate in nitrogen containing carbon disulphide vapour.

Pure magnesium sulphide is a reddish-white amorphous powder. It is converted into cubical crystals by heating in an electric furnace, and the same crystals are obtained by substituting a mixture of magnesium chloride and stannous sulphide for the magnesium sulphide.

Mg₄S₅ is said to have been obtained by heating magnesia to redness in carbon disulphide vapour.

The heat of formation of MgS is 79.600 Cal.

Magnesium sulphide is reduced by calcium carbide in an electric furnace - magnesium volatilises and calcium sulphide remains.

Pure magnesium sulphide becomes phosphorescent by the addition of small amounts of manganese, bismuth, or antimony. The crystalline form is scarcely attacked by water at ordinary temperatures, and steam is needed for the reaction

MgS+H₂O = MgO+H₂S.

The amorphous form reacts readily with water or moist air -

2MgS+2H₂O = Mg(SH)₂+Mg(OH)₂.