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Sodium selenides

The monoselenide, Na2Se, is formed by the action of selenium on a solution of excess of sodium in liquid ammonia, and separates out. It can also be produced by the interaction of selenium and sodium hyposulphite, Na2S2O4. It melts above 875° C., and on exposure to air its solution in water acquires a reddish colour, and deposits selenium. In solution it is extensively hydrolyzed, and under these conditions may be regarded as a mixture of sodium hydrogen selenide, NaSeH, and sodium hydroxide. Four hydrates are known, with 4½, 9, 10, and 16 molecules of water respectively. For the heat of formation of the anhydrous compound Fabre gives 59.7 Cal., and for the heat of solution at 14° C., 18.6 Cal. He has also investigated the heat of solution of the hydrates.

When excess of selenium reacts with a solution of sodium in liquid ammonia, sodium tetraselenide, Na2Se4, separates. By fusion of sodium with selenium, Mathewson has isolated between 500° and 250° C. the diselenide Na2Se2, triselenide Na2Se3, tetraselenide Na2Se4, and hexaselenide Na2Se6. They are dark-grey substances, unstable in air, and readily soluble in water to red solutions.

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