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Acetic Acid

alcohol, temperature, water, wood, acetate and liquid

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ACETIC ACID (Formula, C, 2 weight, 6o. Synonyms, purified pyrolig neous acid, methane carboxylic acid. Methyl formic acid, formed by the acetous fermentation of alcohol. Acetic acid is a monotonic monobasic acid, and its salts are termed acetates.

Alcohol, when quite pure, is not affected by exposure to the air, but as soon as it is diluted and a portion of yeast added to it, the yeast soon acts as a ferment, and causes the spirit to unite with the oxygen of the atmosphere and become sour from the formation of acetic acid. A tray of finely-divided, spongy platinum is placed on a triangle over a porcelain dish containing a little alcohol, gently warmed, and the whole covered with a bell glass, standing on a wedge and opened at the top to allow a gentle current of atmosphere to pass through the apparatus. The oxidation of the alcohol proceeds very rapidly and acetic acid condenses in abundance on the inside of the jar. In this method of production, however, aldehyde is developed as an intermediate product. The addition of ferments greatly assists the oxidation of the alcohol. In France and Germany, wine is used • in England, malt vinegar is obtained in this manner, it being nothing more than acetic acid diluted and a little coloring matter added. Concentrated acetic acid may be obtained by neutralizing common vinegar with carbonate of soda, and crystallizing the acetate of soda thus formed. This acetate is then deprived of its water of crystallization, and fused at a gentle heat. After it is cooled, 82 parts of this salt are to be distilled with 98 of strong sulphuric acid, which removes the soda and liberates acetic acid. The acetic acid, being very volatile, distills over, and may be condensed.

Another method of preparation is by the destructive distillation of wood. Wood is heated in closed iron cylinders connected with condensers. In these receivers a watery liquid condenses, consisting of water, alcohol, acetic acid, acetone and other products. This liquid is re-distilled to remove some of the alcohol, and chalk is added to the residue. With this addition,

the volatile acetic acid is conversed into non-volatile calcium acetate, which, on distillation to dryness, remains behind, the water and other volatile matters escaping. The impure calcium acetate is then gently heated to decompose the tar which it contains, and re-distilled with hydrochloric acid, when crude acetic acid passes over and calcium sulphate remains behind. The density of the acetic acid thus obtained is about i.o6, and it can be purified by re-distillation and the addition of a small quantity of sodium carbonate or potassium dichromate. The wood usually employed in the preparation of acetic acid is known as coppice wood.

Glacial Acetic Acid is a term applied to the pure acid of sp. gr. 1.0635 at 64 deg. Fahr., because at ordinary temperature it becomes a crystalline solid. Pure acetic acid solidifies at or below so deg. Fahr. in colorless prismatic or tabular crystals, soluble in water, alcohol and ether. If heated above this temperature the crystals will melt, and it becomes a limpid liquid, with a sour pungent taste and odor. It blisters the skin, and acts as an acid poison. It boils at 118 deg. Fahr., and its vapor is inflammable.

Commercial Acetic Acid is generally described as being "glacial," or solid, at a certain temperature. The higher this temperature the stronger is the acid ; therefore it is often diluted with water, and very often adulterated with sulphuric acid, added for the purpose of counter acting the effect of dilution by causing it to still retain its property of solidifying at a moderate temperature, and by this means deceive the purchaser of its true strength. The strength of commercial acetic acid can be approximately judged by its solidifying point. Place two or three drachms in a thin glass test tube, and lower it into powdered hypo to cool. A thermometer placed in the liquid will give the temperature, which should be read off directly the acid is seen to solidify, and compared with the following table.

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