t ragged, it is
essential that the angle between the inner and outer tubes at the joint
be very nearly a right angle. For this reason the two tubes should not
be of too near the same size, or if this cannot be avoided, a small bulb
should be blown on the end where the joint is to be made. If this bulb
be made with the same wall-thickness as the rest of the tube, and
somewhat pear-shaped, it may be drawn out to the same size as the rest
of the tube, if necessary, after the joint has been made.

This method is used wherever possible in preference to the second method
(Exercise No. 9), as it is easier to get a good joint with it. It may
also be used where it is desired to seal the tube through the side of a
tube, or for a tube sealed through the wall of a bulb, as in a Geissler
potash bulb or similar apparatus. Where there is not space to join the
inner tube to the blowing tube by a rubber tube, this joint may be made
with a small piece of gummed paper, which can readily be broken when
desired.

EXERCISE NO. 9

SEALING A TUBE THROUGH ANOTHER TUBE

_Second Method--Making a Suction Pump_

Select a piece of tubing 3/8 to 1/2 inch in diameter, with walls about
1/16 inch or a little less in thickness, heat a place about 4 inches
from one end and draw it out so that when cut off at the proper point it
will look like _a_, Fig. 12; the open end of the drawn out part being
small enough to slip inside another piece of the original tube. A small
thick-walled bulb is now blown as indicated by the dotted lines, and
annealed. A piece of the original tubing is now prepared, 7 or 8 inches
long, with one end cut square off and the other closed. A piece of
1/4-in tubing about 2 inches long, and drawn out at one end to a tail
several inches long is also prepared, to form the inlet tube for the
air. Another piece of the 3/8-inch tube is prepared, about 4 inches
long, and provided with a tail drawn out as indicated in _b_, so that
when cut off at about 2-1/2 or 3 inches from the main tube its inner
diameter may be slightly less than that of the narrowest point of the
tube _a_. A small thick-walled bulb is blown at the point indicated by
the dotted lines, and annealed. Care must be taken in drawing the
capillary and blowing the bulb in both _a_ and _b_ that the capillary
tubes are in the axis of the main tube, and in the same straight line
with it.

[Illustration: FIG. 12.--Suction pump.]

The open end of the 8-inch piece of tube and