the glass while blowing, the
bulb will be flattened; by slightly drawing apart the two ends of the
tube, it will be elongated.

A pear-shaped bulb may be obtained by gently re-heating an elongated
bulb, say from _a_ to _a_, and drawing it out. It is easiest to perform
this operation on a bulb which is rather thick in the glass.

If the tubes _bb_ are to be small, and a globe of considerable size is
wanted, contract a tube as shown in Fig. 22, taking care that the narrow
portions of the tube are about the same axis as the wider portions, for
if this be not the case, the mouths of the bulb will not be
symmetrically placed; seal at _C_, cut off the wider tube at _B_, and
make the bulb, as previously described, from the glass between _AA_.
If, as probably will be the case, the contracted portions of the tube be
not very regular, they may be cut off, one at a time, near the bulb, and
replaced by pieces of tube of the size desired.

[Illustration: FIG. 22.]

When a bulb has to be blown upon a very fine tube, for example upon
thermometer tubing, the mouth should not be employed, for the moisture
introduced by the breath is extremely difficult to remove afterwards. A
small india-rubber bottle or reservoir, such as those which are used in
spray-producers, Galton's whistles, etc., securely attached to the open
end of the tube, should be used. With the help of these bottles bulbs
can be blown at the closed ends of fine tubes with ease, though some
care is necessary to produce them of good shape, as it is difficult to
rotate the hot glass properly when working in this way.

=Making and Grinding Stoppers.=--Apparatus which is to contain chemicals
that are likely to be affected by the free admission of air, needs to
have stoppers fitted to it. Making a good stopper is a much less tedious
process than is commonly supposed.

Suppose that the tube I. of Fig. 23 is to be stoppered at _A_, it must
be slightly enlarged by softening the end and opening it with a pointed
cone of charcoal; or a conical mouth for the stopper may be made by
slightly contracting the tube near one end, as at _B_, cutting off the
cylindrical end of the tube at the dotted line _C_, and then very
slightly expanding the end at _C_ with a charcoal cone after its edges
have been softened by heat. In either case the conical mouth should be
as long and regular as possible.

[Illustration: FIG. 23.]

For the stopper take a piece of rather thick tube, of such si