Potassium Arsenides

Potassium combines with arsenic with incandescence, and the arsenide K₃As may be obtained by heating the elements in the correct proportions in a glass tube. The pure arsenide is prepared by heating to redness in a closed iron vessel a mixture of the elements containing an excess of potassium, the uncombined metal being subsequently removed from the cooled product by means of liquid ammonia; the arsenide remains in the form of black crystals after removing ammonia by heating in nitrogen. Another method of preparation consists in treating arsenic with an excess of potassammonium, NH₃K, when a brick-red compound, K₃As.NH₃, results; this, when heated at 300° C. in vacuo, yields the black arsenide. The latter, like other alkali arsenides, reacts with water to yield solid arsenic mono-hydride and some arsine. If the potassammonium is heated with excess of arsenic, the product is an orange-coloured solid, K₂As₄.NH₃, which when heated in vacuo a little below 300° C. yields a cinnabar-red arsenide K₂As₄.