This section is from the book "A Treatise On Therapeutics, And Pharmacology Or Materia Medica Vol1", by George B. Wood. Also available from Amazon: Part 1 and Part 2.
Under this name, a preparation of iron has been introduced into the present edition of U. S. Pharmacopoeia, consisting of sesquiphosphate of sesquioxide of iron, which is insoluble in water, and citrate of ammonia, by means of which it is rendered soluble. It is denominated pyrophosphate in the Pharmacopoeia, because the acid contained in it is the form of phosphoric acid, disposed to unite with two eqs. of base, and called pyrophosphoric, because produced by the action of heat on the tri-basic acid. (See U. S. Dispensatory.) The salt is in scales of a greenish colour, and an acidulous somewhat saline taste, and is wholly soluble in water. It is a mild chalybeate, not disagreeable to the taste, and probably capable of being used for the same systemic effects as the other ferruginous preparations, while it has the advantage over several of them that, from its solubility, it may be administered in any desirable form, whether in pills, watery solution, or syrup. The dose is from two to five grains.