A (Fig. 31).
Begin by reducing the size of the end of tube A till B will just slip
in quite easily. With B about one-quarter inch in diameter, a
clearance of about one-twentieth of an inch, or less, in all (i.e.
one-fortieth of an inch on each side) will be proper.

Heat B by itself at the proposed zone of junction, and blow out a very
narrow ring; then compress this slightly so that it forms an almost
closed ring of glass. The figure refers to the close of this
operation (Fig. 31, B). It does not matter much whether the ring
remains a mere flattened bulb, or whether it is a solid ring, but it
must be one or the other. Some judgment must be exercised in
preparing the ring. In general, the beginner will collect too much
glass in the ring, and consequently the joint, when made, will either
be thick and liable to crack easily, or it will be blown out into an
erratic shape in endeavours to reduce this thickness. Accordingly,
the operator will, if necessary, thin the tube B by drawing slightly,
if he considers it desirable, before the little enlargement is blown
out. In general, two heats must be used for this operation.

Fig. 32.

Get the approximating parts of both A and B up to a temperature just
below that at which they will adhere, and having closed the other end
of A, place B carefully within it up to the ring, and if it can be
arranged, have a mica wad in A, with a central hole through which the
end of B can project. This will very much facilitate the operation,
especially if B is long, but may be dispensed with by the exercise of
care and skill.

The operation is now simple. Fuse the junction and press the tubes
lightly together, being careful not to collect more glass than can be
helped; finally, blow out the joint and reduce the thickness by mild
drawing (Fig. 33). In order to make a really good joint, two points
must be particularly attended to--the rim must be thin and its plane
perfectly perpendicular to the axis of tube B; the end of tube A must
be cut off quite clean and perpendicular to its axis before B is
inserted. So important are these conditions--especially the latter
that the writer has even occasionally used the grindstone to get the
end of A into a proper condition, an admission which will probably
earn the contempt of the expert glass-worker.

Fig. 33.

Now for the second method, which is often practised in Germany, where
soda glass is chiefly used. With this glass the chie