PIECES OF TUBING, END TO END--FIRST METHOD

This exercise is most easily learned on tubing with an exterior diameter
of 1/4 inch, or a little less, having moderately heavy walls. A piece of
such tubing is heated before the blow-pipe at a point ten or twelve
inches from the end, and there drawn out to a capillary as previously
described (page 9). The capillary is sealed off about two inches from
the main tube, and the latter is cut near the middle. Care should be
taken to get square ends where the cut is made (page 7). The flame is
now so regulated that it is a little broader than the diameter of the
tube, the sealed half of the tube taken in the left hand and the other
half in the right. The open end of the sealed part and one of the ends
of the other part are now held in opposite sides of the flame, inclined
at a slight angle to one another as indicated in Fig. 5, and rotated and
heated until the surfaces of both ends are just softened. The two ends
are then carefully and quickly brought together (_a_, Fig. 6), removed
from the flame and pulled apart a little, to reduce the lump formed at
the joint as much as possible, as indicated in _b_. The joint is then
tested by blowing into the open end of the tube to see if it is tight.
If so, the flame is reduced to half or less than half of its former
size, and the joint heated in it, holding the tube and continually
rotating it as directed in the last chapter (page 13).

[Illustration: FIG. 5.--Softening ends of two pieces of tubing.]

[Illustration: FIG. 6.--Joining two pieces of tubing end to end--first
method.]

As the tube softens and tends to shrink, the two ends are pressed
together a little and the walls allowed to thicken slightly, as in _c_.
It is then quickly removed from the flame and gently blown as indicated
in _d_, continuing the rotation of the tube during the blowing, and at
the same time pressing the ends of the tube together a little so as to
make a _short_ thick-walled bulb. The joint is then returned to the
flame and reheated, rotating as before, shrinking to about the shape of
_e_. When this stage is reached, the glass should be very hot and fluid,
and the mass of hot glass thick enough to remain at its working
temperature for about five seconds after removal from the flame. The
glass is now reblown as indicated in _f_, to form a bulb having walls of
practically the same thickness as the original tube. As soon as the bulb
is blown, the tube is removed