AL′DEHYD

(-hīd). [ al -(cohol)- dehyd (rogenatus).] C 2 H 4 O. Syn. Hydrated oxide of acetyle ; Hydrate of othyle *; Hydroxide of O .* Literally, dehydrogenated alcohol. In chemistry , a peculiar ethereal liquid, first obtained in a pure form by Liebig, from alcohol. It is produced under various circumstances, particularly during the destructive distillation of certain organic matters, and in several proce es of oxidation. The following are the most convenient methods of preparing it:— Prep. 1. (Liebig.) Sulphuric acid, 3 parts; is diluted with water, 2 parts; and as soon as the mixture has cooled, alcohol of 80%, 2 parts, is added; and, subsequently, peroxide of manganese (in fine powder), 3 parts. The whole, after agitation, is then distilled at a very gentle heat, from a spacious retort into a receiver surrounded with ice, the connection between the two being perfectly air-tight. The proce is continued until frothing commences, or the distillate becomes acid which generally occurs when about one third (3 parts) has pa ed over. The distillate is next agitated in a retort, with about its own weight of fused chloride of calcium, in powder; after which about one half only is drawn over at a very gentle heat (85° to 90° Fahr.), by means of a water bath. This rectification is repeated in a precisely similar way. The last distillate is ANHYDROUS ALDEHYD only slightly contaminated with foreign matters. 2. (Liebig.) Aldehyd-ammonia, 2 parts, is di olved in an equal weight of distilled water; and, after being placed in a retort, sulphuric acid, 2 or 3 parts, previously diluted with rather more than its own weight of distilled water, and allowed to cool, is added. The whole is now distilled, by means of a water bath, into a receiver surrounded with ice, or (preferably) a freezing-mixture, the temperature of the bath at first being very low, and the operation being stopped as soon, or rather before the water begins to boil. The distillate is then placed in a retort connected with a well-cooled receiver, as before; and after all the joints are made perfectly tight, powdered fused chloride of calcium, in weight equal to that of the liquid in the retort, is added through the distillation to commence, after which it is carried on, by means of a water bath, at a temperature ranging from 80° to 82° Fahr. This rectification being very carefully repeated, the last distillate is PURE ANHYDROUS ALDEHYD . Prop., . Limpid, colourle , ethereal, neutral, inflammable; mixes in all proportions with alcohol, ether, and water; odour peculiar, penetrating, and, when strong, exceedingly suffocating, the vapour, in quantity, producing spasmodic contraction of the thorax; boils at 72° Fahr. (70°—Ure, 5th ed.); sp. gr. ·790 at 60°, and ·800 at 32° Fahr.; sp. gr. of vapour, 1·532; by exposure to air it is gradually converted into acetic acid, and speedily so under the influence of platinum-black; heated with caustic potash, a brown substance resembling resin ( ALDEHYD-RESIN ) is formed; gently heated with protoxide of silver, or its solutions, metallic silver is deposited on the inner surface of the ve el, in a uniform and brilliant film, whilst ALDEHYDATE OF SILVER remains in solution; heated with hydrocyanic acid it yields ALANINE . By age, even in close ve els, it pa es into one or more isomeric compounds ( ELALDEHYDE ; METALDEHYDE ), with change of properties. Aldehyde for experiments should, therefore, be always recently prepared; and it must be kept in a well-stopped bottle, in a very cold place, and preferably in ice. Obs. Aldehyd is important for its a umed position in the acetyl-series, and the part which it plays in the proce of acetification, . The word is now also commonly employed, by chemists, as a generic term for any organic substance which, by a imilating two atoms of hydrogen, yields, or would yield, a compound having the composition or properties of an alcohol; or which, by taking up one atom of oxygen, yields an acid. Many of the e ential oils (as those of almonds, cinnamon, and cumin) are composed principally of bodies which may thus be called aldehyds. One of the most valuable properties of these substances, is their strong tendency to combine with the bisulphites of ammonium, pota ium, and sodium; and by which they may be separated from complex mixtures.