d escape
freely from _E_ when this is done. Gradually bring the line of contact
of _B_ and _E_ and the surrounding parts of the tube before a pointed
flame, after previously warming them by holding near a larger flame, and
rotate them before the flame so that the glass may soften and adhere.
Then heat the joint spot by spot as usual. In blowing this joint, take
care that the glass on each side of the actual joint is slightly
expanded. It should present the form shown by the dotted lines in III.
(these are purposely exaggerated, however). Finally, heat the whole
joint between the lines _JI_ till it softens, and simultaneously blow
and draw it into its final shape as seen at III.

The side tube _F_ should not be too near the end _E_. If, however, it is
necessary to have them close together, the joint _F_ must be very
carefully annealed when it is made; it must also be very cautiously
warmed up before the construction of the joint at _H_ is begun, and must
be kept warm by letting the flame play over it from time to time during
the process of making the latter joint.

A good joint may be recognised by its freedom from lumps of glass, its
regularity of curve, and by a sensibly circular line at _H_, where the
two tubes are united.

When the joint after annealing has become quite cold, the pin-hole at
_C_ on the inner tube may be closed, after removing the paper support,
by warming the outer tube, and then directing a fine pointed flame
through _D_ on to _C_. And the end _D_ of the outer tube may be closed
in the ordinary manner, or a narrow tube may be sealed to it. As the end
of glass at _D_ will be too short to be held by the fingers when hot,
another piece of tube of similar diameter must be attached to it to
serve as a handle (see p. 35, Fig. 9).

=Blowing a Bulb or Globe of Glass.=--For this purpose it is very
important that the glass tube employed shall be of uniform substance.
The size and thickness of the tube to be employed depends partly on the
dimensions of the bulb desired, and partly on the size of neck that is
required for the bulb. It is easier to blow large bulbs on large-sized
tubes than on those of smaller size. When it is necessary to make a
large globe on a small tube, it can be done, however, if great care be
taken to avoid overheating that part of the small tube which is nearest
to the mass of viscous glass from which the bulb is to be formed. For
the purpose of blowing a very large bulb on a small