This is an officinal of the British Pharmacopoeia, made by mixing solutions of sulphate of iron, and of arseniate and acetate of soda. A white precipitate falls, which soon becomes green on exposure to the air. It is amorphous, inodorous, insipid, and insoluble in water, but is readily dissolved by muriatic acid; and, when first formed, consists of three eqs. of protoxide of iron and one of arsenic acid. On exposure, however, the protoxide absorbs oxygen, and the preparation, therefore, contains a portion, though indefinite, of the sesquioxide. It has been introduced into use, under the idea that it might exercise upon the system the combined virtues of arsenic and iron. It is in fact useful in cutaneous affections, such as yield to arsenic; but the proportion of iron contained in it is too small to be of account; and this salt must be regarded simply as arsenical. In this respect, I know no superiority which it possesses over Fowler's solution. The dose is from the eighth to the tenth of a grain, which may be given in the form of pill three times daily.