ntine by distilling pine-resin;
Zosimus of Panopolis, a voluminous writer of the 5th century A.D.,
speaks of the distillation of a "divine water" or "panacea" (probably
from the complex mixture of calcium polysulphides, thiosulphate, &c.,
and free 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 plants and plant juices,
alcohol by the distillation of wine, and also distilled water. The
alchemists gave great 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. Prior to about the 18th century three forms of distillation
were practised: (1) _destillatio per ascensum_, in which the retort was
heated from the bottom, and the vapours escaped from the top; (2)
_destillatio per latus_, 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 pipe passing through the bottom. According
to K. B. 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 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. Frankland introduced the "reflux condenser,"
i.e. a condenser so placed that the condensed vapours return to the
distilling flask, a device permitting the continued boiling of a
substance with little loss; W. Dittmar and R. Anschutz, independently
of one another, introduced "distillation under reduced pressure"; and
"fractional distillation" was greatly aided by the columns of Wurtz
(1855), E. Linnemann (1871), and of J. A. Le Bel and A. Henninger
(1874). In chemical technology enormous strides have been made, as is
apparent from the coal-gas, coal-tar, mineral oil, spirits and mineral
acids industries.

The subject is here treated under the following subdivisions: (1)
ordinary distillation, (2) distillation under reduced pressure, (3)
fractional distillation, (4) distillation with steam, (5) theory of
distillation, (6) dry disti