The multiplicative field norm $N(m+n\sqrt{-7})=m^2+7n^2$ is an integer. Units have field norm one and are exactly $\pm 1$. A nontrivial factorization of 2 would force both factors to have field norm two, which the displayed quadratic form cannot represent. Thus 2 is an irreducible element. It is not a prime element, since it divides $(1+\sqrt{-7})(1-\sqrt{-7})=8$ but neither factor. This is an example in a nonmaximal quadratic order, rather than the full ring of integers of $\mathbb{Q}(\sqrt{-7})$; the precise ring matters for factorization.

Mistura Ferri Composita is a compound iron-containing mixture. Its several ingredients and suspended or dissolved components make it different from one pure iron salt.^[ref]

Ferri Arsenias is an iron-arsenate medicinal material. Its inclusion in historical practice identifies a toxic arsenic-containing preparation, not evidence of modern therapeutic suitability.^[ref]

Ferri Carbonas Saccharata is an iron-carbonate preparation combined with sugar. The sugar-containing article is distinct from a pure dry carbonate and from a finished carbonate pill.^[ref]

Ferri Iodidum is the historical iron-iodide medicinal article. The salt differs from free iodine and from its syrup or pill formulations.^[ref]

Ferri Oxidum Magneticum is a historical magnetic iron-oxide preparation. The named material was described through mixed higher and lower iron oxides, rather than as metallic iron.^[ref]

Ferri Peroxidum is a historical higher iron-oxide preparation. Its state of hydration and processing must be distinguished from the fresh wet material called Ferri Peroxidum Hydratum.^[ref]

In the 1864 British standard, the fresh wet hydrated ferric-oxide preparation, preserved without drying. Later naming must not be assumed to denote the same material. ^[ref]

Ferri Phosphas is a historical iron-phosphate medicinal material. Period descriptions can include more than one oxidation state; the name alone does not establish one pure modern crystal composition.^[ref]

Ferri Sulphas is the historical medicinal ferrous-sulfate article. Hydration and oxidation state matter when relating a mass of the preparation to its iron content.^[ref]

Ferri et Ammoniae Citras is an iron-and-ammonium citrate preparation. Its historical formulation should not be mistaken for a universally fixed single-molecule composition.^[ref]

Ferrum Redactum is a finely divided reduced-iron medicinal material. The physical form and possible oxide content distinguish the preparation from an arbitrary bulk piece of iron.^[ref]

Ferrum Tartaratum is a tartarated-iron medicinal material. Complexation and associated salts affect its solution behavior, so it should not be equated with metallic iron.^[ref]

Liquor Ferri Perchloridi is a ferric-chloride solution. It is a solution designation distinct from the tincture of the related salt.^[ref]

Liquor Ferri Pernitratis is a solution of ferric nitrate. The solvent and chemical form distinguish the finished liquid from a generic mass of iron.^[ref]

Liquor Ferri Persulphatis is a solution of ferric sulfate. The historical per- terminology distinguishes the higher oxidation-state preparation from ferrous sulfate.^[ref]

Pilula Ferri Carbonatis is a pill preparation based on an iron-carbonate material. The compound ingredient, its oxidation state and the finished pill require distinct descriptions.^[ref]

Pilula Ferri Iodidi is a pill preparation containing iron iodide. A solid unit preparation differs from the syrup bearing the related ingredient name.^[ref]

Syrupus Ferri Iodidi is a syrup of iron iodide. The sugar-containing vehicle and the iron salt are different components of the formulation.^[ref]

Syrupus Ferri Phosphatis is a syrup containing an iron-phosphate preparation. Its dissolved and acidified preparation is distinct from an equal mass of dry phosphate material.^[ref]