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DISTILLATION (from the Lat. distillar...
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See also:DISTILLATION (from the See also:Lat. distillare, more correctly destillare, to drop or trickle down) , an operation consisting in the See also:conversion of a substance or mixture of substances into vapours which are afterwards condensed to the liquid See also:form; it has for its See also:object the separation or See also:purification of substances by taking See also:advantage of See also:differences in volatility. The apparatus consists of three parts:—the " See also:retort " or " still," in which the substance is heated; the " See also:condenser," in which the vapours are condensed; and the "See also:receiver," in which the condensed vapours are collected. Generally the components of a mixture will be vaporized in the See also:order of their boiling-points; consequently if the condensates or " fractions " corresponding to definite ranges of temperature be separately collected, it is obvious that a more or less partial separation of the components will be effected. If the substance operated upon be practically pure to start with, or the product of distillation be nearly of See also:constant See also:composition, the operation is termed "purification by distillation" or" rectification"; the latter See also:term is particularly used in the spirit See also:industry. If a complex mixture be operated upon, and a separation effected by See also:collecting the distillates in several portions, the operation is termed " fractional distillation." Since many substances decompose either at, or below, their boiling-points under See also:ordinary atmospheric pressure, it is necessary to See also:lower the boiling-point by reducing the pressure if it be desired to distil them. This variation is termed " distillation under reduced pressure or in a vacuum." The See also:vaporization of a substance below its normal boiling-point can also be effected by blowing in See also:steam or some other vapour; this operation is termed "distillation with steam." "Dry distillation" is the term used when solid substances which do not liquefy on See also:heating are operated upon; "sublimation" is the term used when a solid distils without the intervention of a liquid phase. Distillation appears to have been practised at very remote times. The Alexandrians prepared oil of See also:turpentine by distilling See also:pine-See also:resin; See also:Zosimus of Panopolis, a voluminous writer of the 5th See also:century A.D., speaks of the distillation of a " divine See also:water " or " See also:panacea " (probably from the complex mixture of See also:calcium polysulphides, thiosulphate, &c., and See also:free See also:sulphur, which is obtained by boiling sulphur with See also:lime and water) and advises " the efficient luting of the apparatus, for otherwise the valuable properties would be lost." The Arabians greatly improved the earlier apparatus, naming one form the See also:alembic (q.v.); they discovered many ethereal See also:oils by distilling See also:plants and plant juices, See also:alcohol by the distillation of See also:wine, and also distilled water. The alchemists gave See also:great See also:attention to the method, as is shown by the many discoveries made. Nitric, hydrochloric and sulphuric acids, all more or less impure, were better studied; and many ethereal oils were discovered. See also:Prior to about the 18th century three forms of distillation were practised: (I) destillatio per ascensum, in which the retort was heated from the bottom, and the vapours escaped from the See also:top; (2) destillatio per See also:lotus, in which the vapours escaped from the See also:side; (3) destillatio per descensum, in which the retort was heated at the top, and the vapours led off by a See also:pipe passing through the bottom. According to K. B. See also:Hoffmann the earliest mention of destillatio per descensum occurs in the writings of See also:Aetius, a See also:Greek physician who flourished at about the end of the 5th century. - In See also:modern times the laboratory practice of distillation was greatly facilitated by the introduction of the condenser named after Justus von See also:Liebig; A. See also:Kolbe and E. See also:Frankland introduced the " reflux condenser," i.e. a condenser so placed that the condensed vapours return to the distilling See also:flask, a See also:device permitting the continued boiling of a substance with little loss; W. first type; N2O4-22NO2, of the second (see CHEMICAL See also:ACTION). Electrolytic or ionic See also:dissociation is the separation of a substance in See also:solution into ions (see See also:ELECTROLYSIS; SOLUTION). Additional information and CommentsThere are no comments yet for this article.
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