See also:form; it has for its
See also:object the separation or
See also:purification of substances by taking
See also:advantage of differences in volatility . The apparatus consists of three parts:—the " 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
See also:distillation be nearly of
See also:constant 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 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 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:Zosimus of Panopolis, a voluminous writer of the 5th century A.D., speaks of the distillation of a " divine
See also:water " or " panacea " (probably from the complex mixture of calcium polysulphides, thiosulphate, &c., and
See also:sulphur, which is obtained by boiling sulphur with 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 alembic (q.v.); they discovered many ethereal 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: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 top; (2) destillatio per
See also:lotus, in which the vapours escaped from the 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 .
See also:Hoffmann the earliest mention of destillatio per descensum occurs in the writings of Aetius, a 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 Liebig; A . 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 solution into ions (see ELECTROLYSIS; SOLUTION) .
DISTRACTION (from Lat. distrakere, to pull asunder)...
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