_Prop._ Pure hydrated acetic acid is a thin, colourless liquid above 62 Fahr.; at 50° to 55° it crystallises in large, brilliant, colourless, transparent needles and plates, and even at 60° if a crystal of the acid be dropped in; at 40° it is a solid crystalline mass. Sp. gr.——liquid, 1·063 (Mollerat) to 1·0635 (Mohr);[3]——crystallised, 1·135 at 55° Fahr. (Ure). Odour, intensely pungent when concentrated, but grateful, fragrant, and refreshing, when diffused; taste, intensely sour and acrid, becoming agreeable and refreshing, on sufficient dilution with water; volatile; inflammable, burning with a white flame; vapour of boiling acid highly combustible; dissolves camphor, resins, gum resins, volatile oils, gelatin, gliadin, coagulated albumen, and fibrin (as muscle or the crassamentum of the blood); it coagulates casein, but not liquid albumen (as the serum of the blood and white of egg): miscible with alcohol, ether, and water in all proportions; boils at 248° Fahr.;[4] and is decomposed at a red heat. Its salts are called ACETATES (which _see_). [Footnote 3: 1·064——H. M. Witt (Ure’s ‘_Dict., of Arts, M. & M._,’ 5th ed.); 1·063 to 1·065——Muspratt (‘_Chemistry, Theor. & Prac._,’ p. 2); 1·06296——Pereira (4th ed.); 1·0629——Brande; 1·062——Ure; 1·057——Berzelius (‘_Jahr. ber._,’ xvi, 192):——variations evidently arising from difference of purity in the acid examined, or from difference of temperature. The sp. gr. 1·080, with other numbers given by Prof. Lehmann (‘_Chemistry_,’ Day’s Transl.), is probably a misprint.] [Footnote 4: This is the boiling-point given by the best authorities, and confirmed by Gerhardt (‘_Chimie Organique_,’ i, 718). Ure made it 230°(an error corrected in 5th ed.), Lehmann says 243·140, and others give it at 235°, 240°, &c. An acid of about 80% (sp. gr. 1·073 to 1·0743), its maximum density, boils at 219° to 220° Fahr.] _Char., Tests, &c._——1. Free acetic acid reddens litmus paper, like the other acids; and may be readily recognised by its odour and volatility:——2. Sesquichloride of iron being added, and the acid then nearly saturated with ammonia, the fluid acquires a deep dark-red colour. _Estim._ See ACETIMETRY. Organic mixtures that cannot be thus tested, or from which the acid cannot be obtained by simple distillation, may be neutralised, if acid, with carbonate of lime, boiled for a few minutes, cooled, filtered, the lime precipitated with dilute sulphuric acid, and the whole submitted to distillation, when the acid contents of the distillate may be estimated as above.