Phosphor-tin

Phosphor-tin, made by adding phosphorus to molten tin, is largely employed in the preparation of phosphor-bronze. It is characterised by extreme brittleness and brilliant fracture; and microscopic examination of its surface shows it to be traversed by numerous intercepting straight lines, between which is a softer matrix. By treatment of the alloy with dilute nitric acid the matrix is removed, and a phosphide of tin in the form of white, shining plates remains, which is found to have the composition Sn₃P₂. When this compound is heated in hydrogen some of the phosphorus is removed, and when it is acted upon by concentrated hydrochloric acid spontaneously inflammable phosphine is liberated. If the phosphide Sn₃P₂ is heated alone it loses some phosphorus, yielding a lower phosphide of the composition Sn₉P, which may also be obtained by the union of phosphorus with spongy tin. When, however, finely divided tin is heated in phosphorus vapour, the compound SnP is obtained as a white, brittle mass.

Stannic Phosphate or Pyrophosphate is a solid of rather indefinite composition formed by the combination of phosphoric and β-stannic acids. The formation of this substance serves to separate phosphoric acid from a nitric acid solution, and is sometimes employed for this purpose in qualitative analysis. Tin-foil is added to the nitric acid solution of a mixture containing phosphate, and all the phosphoric acid enters into combination with the β-stannic acid as it is formed, so that the solution is freed from phosphate.

There is metallographic evidence of the existence of the following arsenides of tin:

Sn₃As₂, Sn₄As₃, SnAs.