These are vessels of different kinds used in distilling, that
is, when any volatile product has to be converted into vapour and
afterwards condensed, for the purpose of separating it from various
matters not otherwise separable. One of the oldest forms of still is
that even yet used in most chemical operations, called the “retort”
(fig. 1). It is blown out of glass in one piece, is easily made
of all sizes, not exceeding a few gallons; it is chiefly used for
distilling small quantities of fluids, and those which act on metals,
as the acids. For some purposes, chiefly those requiring a very
high temperature, earthenware retorts are used, and in other cases
retorts made of platinum; the retort is often “tubulated,” a name
given to those with an orifice in the upper part having a stopper
fitted to it, this opening is useful to introduce any substance
while the body of the retort is already partly filled with its
contents, or to add more of anything from time to time as it distils
over. An indispensable adjunct to the retort is a “receiver” for
condensing the liquid distilled; this is generally of a globular
form, with an opening to receive the spout of the retort, which is
also frequently “tubulated” that it may be attached by a bent tube
to a second or third receiver. The receiver is to be kept cool, and
this is generally done by a stream of cold water being poured on
it, or a cloth dipped in cold water being spread over it, &c. The
stills properly so called, such as are used in the manufacture of
large quantities of liquids, as, for example, in the distillation
of spirit, are generally made of copper tinned inside to prevent
the formation of verdigris, and consist of a body, a head, and a
condenser, the common form of which is seen at fig. 2. The condenser
consists of a long tube coiled up into a spiral and placed in a
large tub of water, having a supply tube to let in cold water at the
bottom, and one for the exit of the hot water at the top, for hot
water being lighter than cold, rises up to the top of the tub. A very
good form for a small portable condenser may be seen at fig. 3, in
which a constant current of cold water is made to pass through the
outer tube, and so keep the inner one cold.