l--this is the distillation with live steam of laboratory
practice. The details of the plant--the material and fittings of the
still, the manner of heating, the form of the condensing plant,
receivers, &c.--have to be determined for each substance to be
distilled in order to work with the maximum economy.

For the distillation of liquids the retort is usually a cylindrical
pot placed vertically; cast iron is generally employed, in which case
the bottom is frequently incurved and thicker than the sides in order
to take up the additional wear and tear. Sometimes linings of
enamelled iron or other material are employed, which when worn can be
replaced at a far lower cost than that of a new still. Glass stills
heated by a sand bath are sometimes employed in the final distillation
of sulphuric acid; platinum, and an alloy of platinum and iridium with
a lining of gold rolled on (a discovery due to Heraeus), are used for
the same purpose. Cast iron stills are provided with a hemispherical
head or dome, generally attached to the body of the still by bolts,
and of sufficient size to allow for any frothing. It is invariably
provided with an opening to carry off the vapours produced. In its
more complete form a still has in addition the following
fittings:--The dome is provided with openings to admit (1) the axis of
the stirring gear (in some stills the stirring gear rotates on a
horizontal axis which traverses the side and not the head of the
still), (2) the inlet and outlet tubes of a closed steam coil, (3) a
tube reaching to nearly the bottom of the still to carry live steam,
(4) a tube to carry a thermometer, (5) one or more manholes for
charging purposes, (6) sight-holes through which the operation can be
watched, and (7) a safety valve. The body of the still is provided
with one or more openings at different heights to serve for the
discharge of the residue in the still, and sometimes with a glass
gauge to record the quantity of matter in the still. For dry
distillations the retorts are generally horizontal cylinders, the
bottom or lower surface being sometimes flattened. Iron and fireclay
are the materials commonly employed; wrought iron is used in the
manufacture of wood-spirit, fireclay for coal-gas (see GAS:
_Manufacture_), phosphorus, zinc, &c. The vertical type, however, is
employed in the manufacture of acetone and of iodine.

Several modes of he