ndensed
vapour; (3) the column is encircled by a jacket through which a liquid
circulates at the same temperature as the boiling-point of the most
volatile component. To the first type belongs the simple straight
tube, and the Wurtz tube (see fig. 3), which is simply a series of
bulbs blown on a tube. These forms are not of much value. Several
forms of the second type are in use. In the Linnemann column the
condensed vapours temporarily collect on platinum gauzes (a) placed at
the constrictions of a bulbed tube. In the Le Bel-Henninger form a
series of bulbs are connected consecutively by means of syphon tubes
(b) and having platinum gauzes (a) at the constrictions, so that when
a certain amount of liquid collects in any one bulb it syphons over
into the next lower bulb. The Glynsky form is simpler, having only one
syphon tube; at the constrictions it is usual to have a glass bead.
The "rod-and-disk" form of Sidney Young is a series of disks mounted
on a central spindle and surrounded by a slightly wider tube. The
"pear-shaped" form of the same author consists of a series of
pear-shaped bulbs, the narrow end of one adjoining the wider end of
the next lower one. In this class may also be placed the Hempel tube,
which is simply a straight tube filled with glass beads. Of the third
type is the Warren column consisting of a spiral kept at a constant
temperature by a liquid bath. Improved forms were devised by F. D.
Brown. Kreusler's form is easily made and manipulated. A tube closed
at the bottom is traversed by an open narrower tube, and the
arrangement is fitted in the neck of the distilling flask. Water is
led in by the inner tube, and leaves by a side tube fused on the wider
tube. Many comparisons of the effectiveness of dephlegmating columns
have been made (see Sidney Young, _Fractional Distillation_, 1903).
The pear-shaped form is the most effective, second in order is the Le
Bel-Henninger, which, in turn, is better than the Glynsky. The main
objection to the Hempel is the retention of liquid in the beads, and
the consequent inapplicability to the distillation of small
quantities.

4. _Distillation with Steam._--In this process a current of steam,
which is generated in a separate boiler and superheated, if necessary,
by circulation through a heated copper worm, is led into the
distilling vessel, and the mixed vapours condensed as in the ordinary