he
larger tube and cut off the drawn-out end at the part where its diameter
is equal to that of the smaller tube, then seal the smaller tube to the
contracted end of the larger according to the directions given for
joining tubes of equal size. When a good joint has been made, the tube
presents the appearance of _A_, Fig. 15, the union being at about _bb_.
Next heat the whole tube between the dotted lines _aa_, and blow it into
the shape of _B_ in which the dotted line _dd_ should correspond to the
actual line of junction of the two tubes.

In making all joints it is important to leave no thick masses of glass
about them. If the glass be fairly thin and uniformly distributed, it is
less likely to break during or after annealing under any circumstances,
and especially if it has to bear alternations of temperature.

_Joining a Tube to the Side of another Tube_ (Fig. 16).--One of the
tubes must be pierced as at _A_ in Fig. 16 (for the method, see p. 37),
and its two ends closed with small pieces of cork. The edges of the
opening, and one end of the other tube, must then be heated till they
melt, and united by pressing them together. The joint may then be
finished as before.

[Illustration: FIG. 16.]

A properly blown joint will not present the appearance of _B_ (Fig. 16),
but rather that of _C_. This is secured by directing the pointed flame
upon the glass at _aa_ (_B_) spot by spot, and blowing out each spot
when it is sufficiently softened. If the tubes are large, the whole
joint should subsequently be heated and blown, but in the case of small
tubes this is of less importance. Finally it is to be wrapped whilst hot
in cotton wool for the annealing process.

If a second tube has to be joined near to the first one, say at _b_, it
is well to proceed with it before the joint first made cools down, and
the joint first made, especially if soda glass be used, must be held in
the flame from time to time during the process of making the second
joint to keep it hot; if this be not done the first joint is very likely
to break. A joint previously made may, however, be re-heated, if well
made and well annealed.

A three-way tube, like that in Fig. 17, is made by bending _A_ (Fig. 16)
to an angle, and joining _B_ to an opening blown on the convex side of
the angle; or, _A_ of Fig. 16 may be bent as desired after attaching _B_
in the ordinary way.

[Illustration: FIG. 17.]

Tubes may also be joined to openings made in the sid