. The tube is next
taken in both hands and held horizontally above the flame so that the
scratch is exactly over it. The tubing is now rotated rapidly about its
axis, and lowered so that the flame is just tangent to its lower side.
After about ten seconds of heating, it is removed from the flame and the
hot portion quickly breathed upon, when it will generally crack apart
very nicely. Care must be taken to hold the tube at right angles to the
flame during the heating, and to rotate it so that only a narrow strip
of the circumference is heated, and the scratch should be in the center
of this heated strip. By this means tubing as large as two inches in
diameter is readily broken.

Griffin's glass cutter, which contains a hardened steel wheel, like that
on any ordinary window-glass cutter, and a device by which this can be
made to make a true cut clear around the tube, is a very handy article,
especially for large tubing, and may be obtained from any dealers in
chemical apparatus.

=Bending Glass.=--Inasmuch as this is one of the commonest operations in
the laboratory, it is assumed that the reader knows how to perform it.
However, it should be noted that in order to obtain the best results a
broad (fish-tail burner) flame should generally be used, and the tube
rotated on its axis during the heating, and allowed to bend mostly by
its own weight. If large tubing is to be bent, one end must be stoppered
and great care used. Whenever the tube shows signs of collapsing or
becoming deformed, it must be gently blown out into shape, heating the
desired spot locally if necessary. A blast-lamp is likely to be more
useful here than the fish-tail burner.

=Drawing Out a Tube.=--Most students learn this the first day of their
laboratory work in chemistry, but few take pains to do it well. The tube
should be heated in the flame of a Bunsen burner, or blast lamp
(preferably the latter) until it is very soft. During this time it must
be continuously rotated about its axis, and so held that the edges of
the heated zone are sharply defined; _i.e._, it should not be allowed to
move back and forth along its own axis. When so hot that it cannot
longer be held in shape, the tube is removed from the flame, and the
ends slowly and regularly drawn apart, _continuing the rotation of the
tube about its axis_. By regulating the rate of drawing and the length
of tube heated, the desired length and diameter of capillary may be
obtained. The tube sh