= Solution
\b[The 1864 iron list includes metallic, ferrous, ferric and compound preparations; its wet <Ferri Peroxidum Hydratum> was used historically as an <antidote> to <arsenic poisoning>.] It must be distinguished from dried <Ferri Peroxidum> and from later editions' reassignment of similar Latin names.
The officinal articles and preparations are:
* metallic forms: <iron wire>, \i[Ferrum], and <Ferrum Redactum>;
* simple salts and oxides: <Ferri Arsenias>, <Ferri Carbonas Saccharata>, <Ferri Iodidum>, <Ferri Oxidum Magneticum>, <Ferri Peroxidum>, <Ferri Peroxidum Hydratum>, <Ferri Phosphas>, <Ferri Sulphas>, <Ferri Sulphas Exsiccata> and <Ferri Sulphas Granulata>;
* complex salts: <Ferri et Ammoniae Citras>, <Ferri et Quiniae Citras> and <Ferrum Tartaratum>;
* solutions: <Liquor Ferri Perchloridi>, <Liquor Ferri Pernitratis> and the preparative <Liquor Ferri Persulphatis>;
* compounded forms: <Mistura Ferri Composita>, <Pilula Ferri Carbonatis>, <Pilula Ferri Iodidi>, <Syrupus Ferri Iodidi>, <Syrupus Ferri Phosphatis>, <Tinctura Ferri Perchloridi> and <Vinum Ferri>.
<The Essentials of Materia Medica and Therapeutics by Alfred Baring Garrod (1865)>[Iron and successive British iron monographs; Solution of Persulphate of Iron, Appendix A; British compounds distinguished from American additions and older London preparations]{ref} <The Prescriber's Analysis of the British Pharmacopoeia by John Birkbeck Nevins (1864)>[pp. 43–45, iron additions, omissions and names; pp. 55, 63, 67 and 72, compound forms]{ref}
\b[Prepare the hydrated peroxide by inducing <precipitation> from the ferric solution with <sodium hydroxide>, collecting and washing the wet precipitate, and preserving it without drying in a covered vessel.] The starting solution is <Liquor Ferri Persulphatis>, whose “persulphate” here means ferric sulfate, not a modern peroxydisulfate salt. Add the appropriately diluted ferric solution to the alkaline liquor with stirring, allow the <precipitate> to settle, collect it on a calico <filter>, and wash with <distilled water> until the washings no longer give a <precipitate> with <barium chloride>. This tests removal of soluble <sulfate>. The resulting fresh, hydrated material is kept wet; drying gives the separate dried preparation. <The Essentials of Materia Medica and Therapeutics by Alfred Baring Garrod (1865)>[Ferri Peroxidum Hydratum; Ferri Peroxidum; Solution of Persulphate of Iron]{ref}
In modern chemical notation the precipitation can be idealised as
$$
\mathrm{Fe^{3+}+3OH^-\longrightarrow Fe(OH)_3(s)}.
$$
The fresh solid is a hydrated ferric oxide material with variable water content; the equation is not a claim that every pharmaceutical batch is one pure, crystalline <iron hydroxide>. Its historical use depended on binding dissolved <arsenic> into less available material in the digestive tract, especially the freshly precipitated, wet state. It was not a universal antidote to every metal or every stage of absorbed <arsenic poisoning>. Contemporary discussion explicitly identified the new hydrated peroxide as an arsenic antidote. <The British Pharmacopoeia in Chemical News (1864)>[6 February 1864, p. 65, iron preparations and freshly precipitated antidote]{ref} <A Manual of Practical Therapeutics by Edward John Waring (1865)>[§1231, preparation, washings tested with barium chloride, preservation without drying and recent preparation]{ref}
Modern treatment of significant <arsenic poisoning> concerns systemic toxicity and may involve specialist-directed <chelation therapy>; a nineteenth-century ferric paste is not the modern treatment standard. <Clinician Brief: Arsenic by ATSDR>[Patient management, acute exposure and specialist consultation for chelation]{ref}
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