= Solution
\b[The main distinction is between metallic <iron>, <iron(II)> preparations, <iron(III)> preparations, and mixed <iron oxides>.] The old prefixes “proto-” and “per-” ordinarily distinguish the lower and higher <oxidation states> here. “Peroxide of <iron>” means the historical <iron(III) oxide> preparation, not a modern <peroxide> containing an oxygen–oxygen bond.
The principal medicinal preparations can be grouped by the chemical form supplied:
* \b[<Iron(II) sulfate>]: \i[Ferri sulphas], its granulated form, and its dried form supply <iron(II)>. The ordinary and granulated <salts> are represented as $\mathrm{FeSO_4\cdot7H_2O}$; the 1867 dried preparation is represented as $\mathrm{FeSO_4\cdot H_2O}$. Drying principally changes the <water of crystallization>, rather than converting <iron(II)> into <iron(III)>.
* \b[<Iron(II) carbonate>]: \i[Ferri carbonas saccharata], the carbonate pill, and the compound <iron> mixture contain freshly formed <iron(II) carbonate>, $\mathrm{FeCO_3}$. Exposure to air introduces higher <iron oxides>; <sucrose> helps preserve the lower <oxidation state>. Thus the saccharated material is a protected preparation rather than a pure, permanently stable <salt>.
* \b[<Iron(II) iodide>]: \i[Ferri iodidum], its syrup, and its pill supply mainly $\mathrm{FeI_2}$. The historical solid includes <water of crystallization> and some <iron oxide>; the syrup again employs <sucrose> to retard deterioration.
* \b[<Iron(II) phosphate>]: \i[Ferri phosphas] and the corresponding syrup supply the lower <iron phosphate>, conventionally $\mathrm{Fe_3(PO_4)_2}$. The official precipitated material is partly oxidized, so describing the actual powder as chemically pure <iron(II) phosphate> would be too strong.
* \b[<Iron(III) chloride>]: the solution and tincture of “perchloride of <iron>” contain the higher <chloride>, $\mathrm{FeCl_3}$, in an acidic liquid. This historical “perchloride” is unrelated to a <perchlorate>.
* \b[<Iron(III) nitrate>]: solution of “pernitrate of <iron>” contains the higher <nitrate>, $\mathrm{Fe(NO_3)_3}$, again in an acidic liquid. The solution of “persulphate” used to manufacture several other preparations supplies <iron(III) sulfate>, $\mathrm{Fe_2(SO_4)_3}$; it is useful to distinguish this manufacturing reagent from the widely administered <iron(II) sulfate>.
* \b[<Iron(III)> with organic acids]: citrate of <iron> and <ammonium>, and tartarated <iron>, contain the higher <iron> in citrate or tartrate combinations. Citrate of <iron> and <quinine> is prepared from a higher <iron> compound, but should not be assumed to contain exclusively <iron(III)>: the 1867 monograph reports blue reactions with both <potassium ferrocyanide> and <potassium ferricyanide>, consistent with an <iron(II)> component as well. The tartarated preparation also contains <potassium>; citrate of <iron> and <quinine> is made with <Ammonia>. They should be described as soluble pharmaceutical combinations, without pretending that every historical batch had a single simple molecular formula. The acetate tincture similarly contains the higher <iron> combined with <acetic acid>.
* \b[<Iron oxides>]: \i[Ferri peroxidum hydratum] (dried hydrated “peroxide”) and \i[Ferri peroxidum humidum] (the moist material) contain <iron(III)> as <iron(III) oxide> or hydrated <iron(III) oxide>. The magnetic oxide is a mixed <iron(II)>–<iron(III)> oxide preparation; $\mathrm{Fe_3O_4}$ expresses the ideal mixed oxide, rather than a claim that the historical hydrated powder was pure crystalline <magnetite>.
* \b[Metallic <iron>]: \i[Ferrum redactum], used also in lozenges, contains finely divided <iron> in <oxidation state> zero together with magnetic oxide. The official preparation is therefore not all elemental <iron>. <Iron> wine made by contacting wire with wine obtains a dissolved tartrate-containing <iron> preparation from reaction with the wine's acids; the wire placed in the vessel should not be confused with the chemical form in the liquid ultimately dispensed.
These identifications follow the historical monographs, rather than the names of present commercial supplements.<British Pharmacopoeia by the General Medical Council (1867)>[“Ferri carbonas saccharata” through “Ferrum tartaratum”, pp. 130–141; the iron solutions, pp. 186–189; “Vinum ferri”, p. 367]{ref} A green <iron(II) sulfate> solution gives the characteristic blue reaction with <potassium ferricyanide>, whereas the higher <iron> solutions give blue with <potassium ferrocyanide>. Those diagnostic reactions explain why the official tests distinguish the two <oxidation states>; the historical colour test alone does not establish every detail of a complex preparation's composition.
Back to article page
