ter Tube." That
illustrated by _c_ is made by the method explained under "A Spray
Arrester." No new manipulation is involved, and the construction should
be clear from a study of the drawings.

_Multiple and Branched Internal Seals._--A fuller consideration of these
will be found on page 39, but one general principle may well be borne in
mind; that, as far as is possible, a tube having both ends fastened
inside another tube or bulb should be curved or have a spiral or bulb at
some point in its length, otherwise any expansion or contraction will
put great strain on the joints.

_Sprays._--A spray which is easy to make, easy to adjust, and easy to
clean after use is shown by _e_, Fig. 9. The opening on the top of the
bulb is made by melting on a bead of glass, expanding, bursting, and
fusing the ragged edges. The two branches which form the spray producing
junction are made by the method used for an exhaustion branch and
described on page 18.

A spray which can be introduced through the neck of a bottle is shown by
_h_, Fig. 9. The various stages in making this are illustrated by _f_,
and _g_. If the inner tube is made by drawing out from a larger piece of
glass so that two supporting pieces are left on each side of the place
where it is intended to make the final bend, that bend can be made in a
flat-flame gas burner without causing the inner tube to come in contact
with the walls of the outer tube. Care must be taken when joining on the
side piece that the inner tube is not heated enough to fuse it. The
small hole in the side of the outer tube is produced by heating and
bursting.

_A Liebig's Condenser._--This consists of a straight glass tube passing
through an outer cooling jacket. In practice it is better to make the
jacket as a separate piece, and to effect a water-tight junction by
means of two short rubber tubes. It may, however, be made with two
internal seals of the class described under "A Spray Arrester." There is
much less risk of these seals cracking if the inner tube is made in the
form of a spiral or has a number of bulbs blown on it in order to give a
certain amount of elasticity.

_A Double-Surface Condenser._--Fig. 10 shows a condenser of this nature
which is supplied by Messrs. Baird and Tatlock. It may be built up in
stages as shown by _a_, _b_, and _c_, but the work involved requires
considerable skill, and the majority of laboratory workers will find it
cheaper to buy than to make.

[Illustr