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.
Phosphate of iron is prepared, according to the directions of our officinal code, by mixing solutions of sulphate of iron and phosphate of soda. A double decomposition takes place, resulting in the formation of sulphate of soda, which remains in solution, and phosphate of iron, which is precipitated. This is then washed and dried. If the salt of iron employed be a pure sulphate of the protoxide, the resulting phosphate will contain the iron in the same condition, and will be white when thrown down; but this almost never happens; and if it do, oxygen will be quickly absorbed, and the salt assume its characteristic colour.
Composilion. As employed, this salt always consists of a mixture of the phosphates of the protoxide and sesquioxide of iron, which are in variable proportion. As the phosphoric acid is tribasic, the composition of the protosalt, which greatly predominates, is two equivalents of protoxide of iron, one of water, and one of the acid; that of the sesquisalt, probably one equivalent of sesquioxide, and one of acid.
Phosphate of iron is a bluish-white powder, nearly tasteless, insoluble in water, but soluble in the acids.
Its operation is that of the insoluble chalybeates generally; that is, it produces the usual effects of the chalybeates on the system, without much affecting the mucous surface of the stomach. It was brought prominently before the notice of the profession by Mr. Carmichael, of Dublin, in his work on cancer, published in 1809, as a remedy in that disease, in which he employed it both internally, and as an application to the ulcerated surface. In a treatise on diabetes, published in 1825, Dr. Venables speaks highly of its usefulness in that disease; and Dr. Prout confirms his favourable estimate, stating that he regards it as an excellent remedy. (Stom. and Ben. Dis., Lond. 1848, p. 50.) The late Dr. Thos. T. Hewson, of Philadelphia, was in the habit of using it for the general purposes of the ferruginous preparations; and, at his recommendation, it was introduced into the Pharmacopoeia of the United States. It is no doubt a good chalybeate, capable of doing what can be accomplished by iron in the improvement of the blood, and of the general health, and is thus far useful in cancer and diabetes; but it has no special power over these formidable diseases, and is altogether inadequate to their cure. It is probably in no degree superior to the pill of carbonate of iron, if equal to that excellent preparation. The dose is from five to ten grains, which may be given in the form of powder, pill, or electuary. Locally, it may be applied to cancerous ulcers, either by being dusted over them, or in the form of a lotion suspended in water, or mixed with water or glycerin to the consistence of a thin paste, and spread over the surface.
Other combinations of phosphoric acid and oxidized iron have been recommended; but there is probably no one which surpasses the officinal phosphate, either in mildness or efficiency.