= Solution
\b[Prepare <quinine sulfate> by acidic extraction of <cinchona bark>, alkaline precipitation of the <quinine> base, conversion into the <sulfate>, and purification by <crystallization>.] “<Quinia>” is the historical name for <quinine>.
The 1867 process starts with one pound of yellow <cinchona bark> in coarse powder, three fluid ounces of <hydrochloric acid>, four pints of solution of <sodium hydroxide>, and sufficient <distilled water> and diluted <sulfuric acid>. The <hydrochloric acid> is diluted with ten pints of <distilled water>. The bark is first moistened with diluted <sulfuric acid>, macerated for twenty-four hours with occasional stirring, and then exhausted in a <percolator> with the diluted <hydrochloric acid>. The historical endpoint is disappearance of the bitter character of the emerging liquid. This describes the period's test, not an instruction to taste an unidentified medicinal material.<British Pharmacopoeia by the General Medical Council (1867)>[“Quiniæ sulphas”, pp. 268–269, ingredients and extraction]{ref}
The soluble <alkaloid> salts enter the percolate. Adding solution of <sodium hydroxide> liberates the much less water-soluble <quinine> base. After settling, the liquid is decanted and the precipitate collected on a filter and washed with cold <distilled water> until the washings cease to be coloured. The precipitate is then treated warm with <distilled water> and diluted <sulfuric acid>, added gradually to obtain a neutral liquid with nearly all the precipitate dissolved. The hot solution is filtered through paper, the filter washed with <distilled water>, and the filtrate concentrated until a surface film appears. It is then set aside for <crystallization>; the crystals are dried on filter paper without applied heat. This is a separation of a naturally occurring <alkaloid>, not a synthesis of the <quinine> skeleton.
Writing $B$ for the <quinine> base, the central changes are:
$$
\mathrm{BH^+ + OH^- \longrightarrow B\downarrow + H_2O},\qquad
\mathrm{2B+H_2SO_4\longrightarrow (BH)_2SO_4}.
$$
The successive changes in <solubility> explain the apparatus: a <percolator> washes soluble salts out of the powder; a filter retains the liberated base; a heated porcelain vessel dissolves the crude base as its <sulfate>; cooling then recovers the less soluble crystals. Other <cinchona alkaloids> can accompany the product, which is why appearance and bitterness are insufficient evidence of purity.
The 1867 “Characters and Tests” combine identity and purity checks. They must be read as a group:
* \b[Appearance and <solubility>]: filiform, silky, white crystals, sparingly soluble in <water>, with the characteristic bluish appearance of the solution. A little dilute acid increases <solubility>. The visible blue phenomenon is associated with <quinine fluorescence>.
* \b[<Sulfate> identity]: <barium chloride> gives a white precipitate insoluble in <nitric acid>. The precipitate is <barium sulfate>.
* \b[<Quinine> identity]: treating the solution first with chlorine water and then with <Ammonia> gives an emerald-green colour, the <thalleioquin test>. A positive colour reaction establishes a characteristic chemical response, rather than proving that no other <alkaloid> is present.
* \b[Strong-acid colour test]: dissolution in pure <sulfuric acid> gives only a faint yellowish tint, with no further colour change on gentle warming. Marked colouring suggests foreign organic matter, such as <sucrose> or other readily altered material.
* \b[Acid dissolution and liberation of the base]: ten grains with ten minims of diluted <sulfuric acid> and half a fluid ounce of <water> form a complete solution; <Ammonia> then gives a white precipitate. Material insoluble under the acid conditions would fail the dissolution requirement.
* \b[Ether separation]: the precipitated base must pass into <diethyl ether> on shaking the whole with half a fluid ounce of <diethyl ether>, without crystalline matter remaining at the boundary between the two liquid layers. Less ether-soluble <cinchona alkaloids>, particularly <cinchonine>, can leave material at this boundary. This is a period screening test, not a modern quantitative determination of every related impurity.
* \b[<Water of crystallization>]: twenty-five grains lose 3.6 grains on drying at $212\,{}^\circ\mathrm{F}$, equivalent to $100\,{}^\circ\mathrm{C}$. This checks excessive moisture or a materially different degree of hydration.
The historical quantity and endpoint requirements belong to the 1867 monograph.<British Pharmacopoeia by the General Medical Council (1867)>[“Quiniæ sulphas”, pp. 268–269, “Characters and Tests”]{ref} Its formula represents the then-described heptahydrate; the current <International Pharmacopoeia by the World Health Organization>[“Quinine sulfate”] instead specifies a dihydrate and modern tests for related <cinchona alkaloids>. The modern specification explains that distinction; the exam's historical tests remain those listed above.<International Pharmacopoeia by the World Health Organization>[12th edition, 2024, “Quinine sulfate (Quinini sulfas)”, formula, loss on drying and related cinchona alkaloids]{ref}
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