Characters. - A white or greyish-white powder, permanent in the air, odourless and nearly tasteless.

Solubility. - It is only slightly soluble in water, more readily so in presence of hypophosphorous acid, freely soluble in hydrochloric acid, or in solution of citrate of sodium, forming with the latter a green solution.

Reactions. - When strongly heated in a dry test-tube, the salt evolves a spontaneously inflammable gas (phosphoretted hydrogen), and on ignition leaves behind ferric pyrophosphate. The salt is readily oxidised by nitric acid or other oxidising agents. It should be completely soluble in acetic acid (absence of ferric phosphate). This solution, when mixed with test-solution of oxalate of ammonium, should not afford a white precipitate soluble in hydrochloric acid (absence of calcium).

Dose. - 5 to 10 grains in pill, more generally given in syrup. Uses. - In nervous debility with anaemia, and also in phthisis.