Characters. - Colourless, translucent, monoclinic prisms, permanent in the air, odourless, having a cooling, saline, and feebly alkaline taste, and a slightly alkaline reaction.

Solubility. - Soluble in 12 parts of water at 15° C. (59° F.) and in 1.1 parts boiling water; insoluble in alcohol.

Reactions. - Its aqueous solution with excess of test-solution of nitrate of silver gives a white precipitate and a neutral filtrate.

Action. - Its actions in medicinal doses appear to be nearly the same as those of the phosphate, but probably it would have a greater influence on the nervous system.

Uses. - To prepare the pyrophosphate of iron.