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An organic substance may also contain nitrogen, sulfur, phosphorus, halogens and, in some cases, metals or other elements. “Organic” does not mean “made of only carbon, hydrogen and oxygen”. Detection generally requires converting a covalently bound element into a species that an appropriate inorganic test can recognize.

A historically available general method is the sodium fusion test. Fusion converts suitable nitrogen-containing material into cyanide, sulfur into sulfide, and chlorine-, bromine- or iodine-containing material into the corresponding soluble halides. The cooled reaction material is worked up to an aqueous extract, with separate portions reserved for separate tests. The transformations are analytical conversion principles, not claims that every nitrogen or sulfur compound must give quantitative recovery under any fusion conditions. Blanks and a known positive material are essential when a negative result is to be interpreted.^[ref]

For nitrogen, a suitable cyanide-containing extract is treated with a fresh iron(II) reagent and then brought through the appropriate oxidation and acidification sequence to obtain Prussian blue. Formation of ferrocyanide is represented byThe eventual ferric ferrocyanide material provides the blue observation. It is not sufficient simply to add any iron salt and assume that a positive blue must appear. Another classical principle converts nitrogen in suitable organic materials into Ammonia by heating with alkaline reagents, then recognizes the ammonia in a receiver. That test has substrate-dependent limitations and is not a universal replacement for complete nitrogen analysis. A later specialized nitrogen-digestion protocol must not be silently attributed to 1865.

For sulfur, a sulfide-containing alkaline extract can give black lead sulfide with a suitably introduced lead reagent:The strongly acidic form of the reagent conditions changes the available sulfide, so conditions must be controlled. Oxidizing the material to sulfate and identifying a persistent barium sulfate precipitate supplies another principle, using sulfur-free reagents and excluding pre-existing sulfate contamination. If nitrogen and sulfur occur together, thiocyanate formation can alter a fusion test; failure of the expected cyanide reaction is not conclusive evidence that nitrogen is absent.

For chlorine, bromine and iodine, remove interfering cyanide and sulfide by an appropriate controlled treatment of a separate extract portion, then use silver nitrate under suitable nitric-acid conditions. The precipitates are ordinarily white silver chloride, cream silver bromide and yellow silver iodide. Their differing behaviour with aqueous Ammonia provides corroboration: chloride dissolves relatively readily, bromide requires stronger conditions, and iodide is resistant. Do not use hydrochloric acid to prepare the portion in which original chloride is being sought. Fluorine requires a different recognition method: soluble silver fluoride means this precipitation scheme does not provide an equivalent fluoride test.

For phosphorus, oxidize a suitable portion to phosphate, then apply a phosphate test such as yellow ammonium phosphomolybdate formation under the proper acidic conditions. Arsenic species and other interferences must be excluded when relevant. Mineral ash can reveal metal constituents through their specific precipitation or flame reactions, but oxidation during ashing can change their original chemical form. Absence of a visible ash does not prove absence of every metallic or otherwise volatile element.

A positive result identifies an element or an operationally generated ion; it does not establish which functional group contained it in the original molecule. Conversely, an incomplete conversion can give a false negative. This is why the three-element premise used in the preceding combustion calculation should be checked rather than accepted merely because a substance is described as organic.

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.^[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: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:

The historical quantity and endpoint requirements belong to the 1867 monograph.^[ref] Its formula represents the then-described heptahydrate; the current “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.^[ref]