to the tube. The rubber bulb may
also be used to advantage on some of the coarser capillary tubing.

When a bulb is to be joined to a piece of capillary tubing, the joint is
preferably made before blowing the bulb, and will then be taken up a
little way on the bulb during the process. Care must of course be taken
not to constrict the capillary; the pear-shaped bulb blown on the end
(_a_, Fig. 14) may well extend back a little further than usual into the
tube so as to prevent this. If a bulb is required in the middle of a
capillary tube, the latter is usually best cut and a piece of ordinary
tubing of suitable size sealed in to provide material for the bulb.

GLASS ROD

Joints, tees, etc., in glass rod are made on the same principle as in
tubing, except that of course they cannot be blown, and regularity must
be obtained by accumulating a small mass of uniformly heated glass, and
then drawing it to a suitable rod, on the same principle as Exercise No.
1.

Great care must be taken in heating and cooling this, as in the case of
the capillary tubing, and for the same reasons.

By joining pieces side by side, pressing with carbon plates or a plate
and a rod, and other suitable manipulations, stirrers, spatulas, and
other objects may easily be made from rod, and its manipulation is
relatively easy on account of the fact that one does not have to worry
about the bore of the tube. But the same general rule about not having
thick and thin spots in contact, and making all changes in diameter on a
taper if possible instead of abruptly, applies here. Thick pieces will
cool and contract at different rates from thin ones, and cracks are
likely to develop where they join. Work which has been formed with any
tool must always be heated to the softening point afterward before
allowing it to cool in order to remove the stresses caused by the
contact of the tool with the hot glass.

When it is necessary to join a piece of rod to the side of a piece of
tubing, the end of the rod is made very hot while the wall of the tube
at the spot desired is heated to just below the softening temperature.
The rod can then be pressed into firm union with the tube and drawn a
little to remove the excess of glass without deforming the tube.

MENDING STOPCOCKS

=Mending the Plug.=--The plug of the stopcock occasionally falls out and
is broken. If the break is in the main part of the plug, nothing can be
done except to search for a spare plug of