tube, it is best to
unite a wide tube to that which is to serve as the neck, as it will save
some time in collecting the necessary mass of glass from which to form
the globe.

[Illustration: FIG. 20.]

_To blow a Bulb at the End of a Tube._--Select a good piece of tube, say
1.5 cm. in diameter, and about 30 cm. long; draw out one end to a light
tail (_a_, Fig. 20) about 3 inches in length. Then heat up a _short_
length of the tube at _b_, with a small brush flame, by rotating the
glass in the flame, and gently press it together when soft to thicken
it; blow into it if necessary to preserve the regularity of its figure.
Repeat this process on the portion of tube nearest to that which has
been first thickened, and so on, till as much glass has been heated and
thickened as you judge will serve to make a bulb of the size desired.
You should have a mass of glass somewhat resembling that shown at _B_
(Fig. 20), but probably consisting of the results of more successive
operations than are suggested in that diagram. Apply the flame as before
to the narrower parts _cc_ of _B_, gently compress and blow until all
the small bulbs first made are brought together into a mass still
somewhat resembling the enlarged end of _B_, but more nearly
cylindrical, with the glass as regularly distributed as possible, and of
such length from _d_ to the contracted part that the whole of it may
easily be heated simultaneously with the large brush flame of your
blow-pipe. Take great care in the foregoing operations not to allow the
sides of the mass of glass to fall in and run together, and, on the
other hand, do not reduce the thickness of the glass needlessly by
blowing it more than is necessary to give the glass as regular a form as
possible. When you are satisfied with the mass of glass you have
collected, melt off the tail _a_, and remove the pointed end of glass
that remains, as directed on page 33. Turn on as large a brush flame as
is necessary to envelop the whole mass of glass that you have collected,
and heat it with constant rotation, so that it may gradually run
together to the form seen at _C_ (Fig. 20), taking care that it does not
get overheated near _d_, or the tube which is to form the neck will
soften and give way.

The position in which the mass of heated glass is to be held will depend
upon circumstances; if the mass of glass be not too great, it is best to
keep it in a nearly horizontal position. If the mass of glass be very