Characters. - Minutely crystalline friable fragments, having a metallic lustre on the fractured surfaces, or a greyish black powder permanent in the air having a faint odour and taste of phosphorus.

Solubility and Reactions. - Insoluble in water or alcohol, but com-pletely soluble in hydrochloric or sulphuric acids with evolution of phospho-retted hydrogen.

Dose. - Not more than 1/20 grain at first.

Uses. - Its action is similar to that of phosphorus, and it is used in place of it. Each grain contains nearly 1/4 grain of phosphorus.