Solution and tincture of per-chloride of iron are commonly compounded with quinine sulphate for retail purposes, but not so frequently prescribed. The sulphate is readily soluble in either liquid. Quinine sulphate is much more soluble in tinct. ferri perchlor. than in liq. ferri perchlor., owing to the alcohol contained in the former. The amount of acid in both preparations is insufficient (in the doses generally given) to account for the solubility, and interaction between the quinine sulphate and ferric chloride appears to take place, as in the first of the following:

No. I. mixture is muddy in appearance as soon as compounded, and this is generally attributed to the precipitation of 'ferric oxychloride.' There are many compounds which go by that name; some are soluble (e.g., Fe2Cl6ioFe2O3), others (all hydrated) insoluble. In such a mixture as No. I. the formation of Fe2Cl610Fe2O3 from 11Fe2Cl6 is induced by the greediness of the quinine for a solvent, and the reaction gives it 60HCI; but once the equilibrium of the ferric chloride is disturbed, the hydration process goes on to the precipitation-point, and is not restored until some free acid is added. Twenty-four minims of dilute hydrochloric acid suffices to keep the mixture perfectly bright. No. II. mixture was muddy when dispensed with tap-water (containing earthy carbonates), and clear with distilled water. The muddiness was due to ferric hydroxide. A similar precipitate to No. I. might be expected in No. II., but it will be observed that the amount of tincture is larger, and the glycerin retards precipitation.

Mixtures of this class should either be prescribed with quinine hydrochloride or, if the sulphate is desired, each grain of it should have a single minim of dilute hydrochloric acid (or dilute nitric acid) ordered along with it, and the quinine salt should be got into solution before the ferric-chloride preparation is added. It is well to note that ferric chloride in solution is unstable, especially in presence of alcohols, and numerous changes are possible in mixtures containing it and organic substances, such as the precipitation of ferric hydroxide and reduction of part of the chloride to ferrous chloride. Light plays a part in the precipitation, and to prevent this we know nothing better than the use of a minim of acid, nitric, dil. for each grain of quinine sulphate in the mixture. The nitric acid is better than hydrochloric acid, as it helps to keep the iron ferric.