Selenic acid is a colourless liquid, which may be heated to 536°, without sensible decomposition; above that it changes, and is, rapidly resolved into oxygen and selenious acid at 554°. Heated to 329°, its specific gravity is 2.524; at 512°.6 it is 2.6; at 509° it is 2.625; but by that time selenious acid has been formed in it. A portion of concentrated acid, from which the selenious acid had [p473] been removed, consisted of 84.21 selenic acid, and 15.75 water; but it is certain that the selenic acid begins to decompose before it has resigned the last portions of water.
Selenic acid has a powerful attraction for water, and evolves much heat when mixed with it. It is not decomposed by sulphuretted hydrogen; so that the latter body may be used to decompose the seleniates of lead and copper. When boiled with muriatic acid it produces selenious acid and chlorine, and the mixture, like aqua regia, will dissolve gold or platina. Selenic acid dissolves zinc and iron, evolving hydrogen; it dissolves copper, evolving selenious acid; and it dissolves gold, but not platina. Sulphurous acid has no action on selenic acid, but instantly decomposes the selenious acid. A solution containing selenic acid is easily decomposed, by first boiling it with muriatic acid, and then adding sulphurous acid.
Selenic acid is but little inferior to sulphuric acid in its affinity for bases; seleniate of baryta is not completely decomposed by sulphuric acid. Its combinations being isomorphous with those of sulphuric acid, and possessing the same crystalline forms, and the same general chemical properties, present but very slight, though very interesting differences from the sulphates. These will be resumed by M. Mitscherlich in a future memoir, with the express object of illustrating the theory of Isomorphism.—Ann. de Chimie, xxxvi. 100.
14. Preparation of Hyposulphuric Acid.
15. Singular Habitude of Phosphoric Acid with Albumen.
16. Economical Preparation of Deutoxide of Barium.
The decomposition and effect are precisely the same as those lately pointed out by Mr. Phillips as occurring with potassium when the nitrate of potash is decomposed by heat.—See p. 483 of the last volume of this Journal.