Licence: Public Domain Mark
Credit: Qualitative chemical analysis / by C. Remigius Fresenius. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![26, 27.] § 26. 3. Acetic Acid, -KO,CJIfi, = ILO,A [C,H,0,]. Highly concentrated acetic acid is not required in qualitative ana- lytical processes; the acidum aceticum of the British Pharmacopoeia, which contains 33 per cent, of glacial acetic acid, and has a sp. gi'. of 1*044, fully answers the purpose. Tests.—Pure acetic acid should leave no residue when evaporated, and, after saturation with carbonate of soda, emit no empyreumatic odour. Sulphuretted hydrogen, nitrate of silver solution, and solution of nitrate of baryta should give no precipitate or cloud with the dilute acid, neither should it be discoloured by sulphide of ammonium after neutraHzation with ammonia. Solution of indigo must not lose its colour when heated with the acid. Empyreumatic matter is best detected by neutralizing the acid with carbonate of soda, and adding solution of permanganate of potash. If the solution loses its colour and afterwards deposits a brown precipitate, empyreumatic matter is present. If the acid is not pure, add some acetate of soda and- re-distil from a glass retort, but not quite to dryness ; if it contains sulphurous acid (in which case sulphuretted hydrogen will produce a white turbidity in it), digest it first with binoxide of lead or finely-pulverized binoxide of man- ganese, and then distil with acetate of soda. Uses.—Acetic acid possesses a greater solvent power for some sub- stances than for others, and is used therefore to distinguish between themthus it serves, for instance, to distinguish oxalate of lime from phosphate of lime. Acetic acid is also used occasionally to acidify liquids where the employment of mineral acids is undesirable. § 27. 4. Tartaric Acid, 2HO,03HPi^ = 2II0,T [C.HAl- C'ommercial tartaric acid is sufficiently pure for analytical purposes. It should form a clear solution with water; and this should give no coloration, precipitate, or turbidity with sulphuretted hydrogen, oxalate of ammonia or chloride of barium. It is kept best in powder, as its solution suffers decomposition after a time. Before use, it is dissolved in a little water, warming gently. Uses.—The addition of tartaric acid to solutions of ferric oxide, alumina, and various other oxides of metals, prevents the usual pre- cipitation of these metals by an alkali; this non-precipitation is due to the formation of double tartrates, which are not decomposed by alkalies. Tartaric acid may therefore be employed to effect the separation of these metals from others the precipitation of which it does not prevent, Tartaric^ acid forms a sparingly soluble salt with potassa, but not with soda; it is therefore one of our best reagents to distinguish between the two alkalies. Bitartrate of soda answers this latter purpose still better than the free acid. This reagent is prepared by dissolving one of two equal portions of tartaric acid in water, neutralizing the solution with carbonate of soda, then adding the other portion of the acid, and evaporating the solution to the crystallization point. For use, 1 part of the salt is dissolved in 10 parts of water.](https://iiif.wellcomecollection.org/image/b21966953_0065.jp2/full/800%2C/0/default.jpg)
