ation: Fig. 10]

_A Spherical Condenser._--Such a condenser as that shown by _f_, Fig 10,
involves a method which may find application in a number of cases. The
outer bulb is blown from a thick piece of tubing which has been inserted
in a smaller piece (see _d_, Fig. 6); then the inner bulb by similar
method. It is now necessary to introduce the smaller bulb into the
larger, and for this purpose the larger bulb must be cut into halves. A
small but deep cut is made with the file or glass-blowers' knife in the
middle of the larger bulb, and at right angles to the axis of the tube
on which it is blown. A minute bead of intensely heated glass is now
brought in contact with the cut in order to start a crack. This crack
may now be led round the bulb as described on page 30. If the work is
carried out with care, it is possible to obtain the bulb in two halves
as shown by _d_, and these two halves will correspond so exactly that
when the cut edges are placed in contact they will be almost air-tight.
The two tubes from the smaller bulb should be cut to such a length that
they will just rest inside the larger, and the ends should be expanded.
Place the inner bulb in position and fit the two halves of the outer
bulb together, taking great care not to chip the edges. If the length of
the tubes on the inner bulb has been adjusted properly, the inner bulb
will be supported in position by their contact with the tubes on the
outer bulb. Now rotate the cracked portion of the outer bulb in front
of a blowpipe flame and press the halves together very gently as the
glass softens. Expand slightly by blowing if necessary. If a small
pin-hole develops at the joint it is sometimes possible to close this
with a bead of hot glass; but if the bulb has been cut properly there
should be no pin-holes formed. The condenser is finished by joining on
the side tubes and sealing the inner tube through by the methods already
given. In order to blow bulbs large enough to make a useful condenser,
it will be convenient to employ the multiple-jet blowpipe described on
page 4.

_A Soxhlet-Tube or Extraction Apparatus._--This involves the
construction of a re-entrant join where the syphon flows into the lower
tube. It is of considerable value as an exercise and the complete
apparatus is easy to make.

A large tube is sealed at the bottom and the top is lipped, as in making
a test-tube. A smaller tube is then joined on by a method similar to
that given on pag