Tin Arsenides

A study of the system Sn-As has been made over the complete range from pure tin to almost pure arsenic. The elements alloy in all proportions and form two definite compounds, Sn₃As₂ and SnAs, as shown by two distinct maxima on the fusion curves and by photomicrographs. Crystals of the former have been isolated. The melting point of tin is not lowered by the addition of arsenic. Gehlen observed a vigorous action when powdered arsenic was stirred into the molten metal, heat and light being evolved. He also obtained alloys by heating white arsenic with tin. Arsenides other than the above have been described: for example, Sn₂As₃, obtained by heating a mixture of the two elements under fused boric acid; Sn₃As₄, by subjecting the mixture of elements to high pressure; Sn₄As₃ and Sn₆As. The existence of none of these as chemical compounds has been confirmed, however.

The alloys of tin and arsenic are very hard and readily crystallise. When the arsenic is not present in excess they are white, sonorous and brittle, and attacked by hydrochloric acid with liberation of arsine. When heated strongly, arsenic volatilises. The electrical conductivity of thin rods, of composition Sn₂As₃, SnAs and Sn₃As₂, has been measured between -81° and 400° C. In each case it passes through a maximum, at 25°, 0° and -25° C. respectively.