ALDEHYDE, ACETIC, often called ORDINARY ALDEHYDE, or simply ALDEIIYDE. A colorless liquid having a peculiar pungent and suffocating odor. It is very volatile and inflam mable; it boils, at 20.8° C.. and has at 0° C. a specific gravity 0.801. It occurs in crude alcohol and wood spirit, and is readily made from ordinary alcohol by oxidation with chromic acid. If a mixture of three parts of alcohol and tour parts concentrated sulphuric acid is run into a vessel kept in a warm water-bath and contain ing three parts of coarsely powdered potassium bi chromate and twelve parts water, a reaction takes place, during which a considerable amount of aldehyde is formed. The latter is isolated in a somewhat impure state by distillation, and may be purified by the use of ammonia. Alde hyde combines with ammonia to form a solid crystalline substance called aldehyde-ammonia, and having the formula ; alco hol and aeetal, which are generally contained as impurities in crude aldehyde, form no solid compound with ammonia. Therefore, to separate aldehyde from these substances, crystalline al dehyde-ammonia is produced by the direct action of ammonia, washed with ether, and broken up by distillation with dilute sulphuric acid. The aldehyde thus obtained is further dehydrated by distillation with dry calcium chloride. Aldehyde is used ill the manufacture of certain valuable dyes. If added to an ammoniacal solution of sil ver nitrate, it produces a precipitate of metallic silver, which may form a mirror if evenly de posited on a glass surface. By the action of re
ducing agents, aldehyde is converted into alco hol; oxidizing agents convert it into acetic acid. If a drop of strong sulphuric acid is added to aldehyde, the latter is transformed into paralde hyde, a colorless, transparent liquid having the molecular formula it has a strong char acteristic odor and a somewhat burning taste; if cooled below 0° C., it solidifies, form ing crystals whieh melt at C. Paralde hyde is moderately soluble in water, its solubil ity decreasing with an increase of temperature. If taken internally in doses of from one to four cubic centimeters, paraldehyde produces sleep without a Ifeeting the heart; it is, therefore, used as a substitute for chloral, though it has the dis agreeable mrecl of imparting a persistent and offensive odor to the breath. Paraldehyde may be readily reconverted into aldehyde by distilling with dilute sulphuric acid. By the action of acids on aldehyde at a low temperature, another compound having the same percentage compo sition as aldehyde is obtained; this compound is called metaldchyde: it is colorless, crystalline, insoluble in water, and is readily converted into aldehyde by heating with dilute acids. Aldehyde was first isolated and studied by Liebig in 1835.