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, several preparations have been introduced into use, all of analogous composition, and probably identical medical properties, but differing somewhat in the proportion of their ingredients. They consist of the two oxides of iron, the protoxide and sesquioxide, in different proportions, with or without water. The oxides are combined chemically, the sesquioxide acting the part of acid, and the protoxide that of base; and it is in consequence of this combination that they undergo no change on exposure. If they were mixtures of the two oxides, the protoxide would gradually absorb oxygen until converted into the sesquioxide. Three of them merit particular notice; 1. the scales of iron. 2. the hydrated oxide of the late Edinburgh Pharmacopoeia, and 3. the magnetic oxide of the late Dublin and present British Pharmacopoeias.
This is the true old Martial Ethiops. It consists of the scales which fall from heated iron when hammered on the anvil. These are first powdered coarsely, then purified by the magnet, and finally brought to the state of an impalpable powder by levigation and elutriation. They are of variable composition; the sesquioxide seeming to unite with different equivalent quantities of the protoxide, forming different definite compounds, which are then mixed in uncertain proportions.
This, though directed in the late Edinburgh Pharmacopoeia, has been discarded in the British. It is prepared by precipitating, by means of ammonia, mixed solutions of the sulphates of the protoxide and sesquioxide of iron. The two bases are thrown down, combined with water. According to Wohler, who originally proposed this preparation, it consists of two equivalents of protoxide, one of sesquioxide, and two of water.
The magnetic oxide is prepared by decomposing, by means of soda, a solution of persulphate and protosulphate of iron, the former having been obtained by boiling a little nitric acid with sulphate of protoxide of iron so as to sesquioxidize the protoxide. A ((impound is precipitated, consisting of sesquioxide and protoxide of iron; and the formula was so calculated as to give an equivalent of each of these oxides in the resulting compound, which corresponds in composition with the native magnetic black oxide.
In all these forms, the black oxide is a blackish or gray -ish-black powder, inodorous and tasteless, with decided magnetic prop-perties, and insoluble in water. The stronger acids dissolve it without effervescence, showing that it contains no metallic iron. It is unchangeable in the air.
The black oxide has all the effects of the chalybeates upon the system, and is very mild in its operation. It is more readily dissolved in the stomach than the sesquioxide, but not so readily as the reduced iron above described. It may be used whenever it is desirable to bring the system generally under the influence of iron. The dose is from five to twenty grains.