e
tubing constantly to make it heat evenly on all sides, until it is
a dull red in color. It will then bend of its own weight if held
in one hand, but to allow it to do so is to make a flat place in
the bend. The heating should be continued until the red color is
quite bright, when the open end of the tube is put in the mouth
and a little pressure of air made in the tube by blowing. At the
same time, the tube is bent, steadily but gently. The compressed
air in the tube prevents it from collapsing during the process.

To make a bulb on the end of a tube, one end must be closed. This
is easily done by heating as before, and then pulling the tube
apart as shown in Fig. 4. The hot glass will draw, just like a
piece of taffy, each end tapering to a point. This point on one
length is successively heated and pressed toward and into the
tube, by means of a piece of charcoal, until the end is not only
closed, but as thick as the rest of the tube, as in Fig. 5. An
inch or more is now heated white hot, the tube being turned
continually to assure even heating and to prevent the hot end from
bending down by its own weight. When very hot, a sudden puff into
the open end of the tube will expand the hot glass into a bulb, as
in Fig. 6. These can be made of considerable size, and, if not too
thin, make very good flasks (Fig. 7) for physical experiments. The
base of the bulb should be flattened by setting it, still hot, on
a flat piece of charcoal, so that it will stand alone.

To weld two lengths of, glass tubing together, heat the end of a
tube and insert the point of a piece of charcoal in the opening,
and twirl it about until the end of the tube has a considerable
flare. Do the same to the end of the other tube, which is to be
joined to the first, and then, heating both to a dull red, let
them touch and press lightly together as in Fig. 8. As soon as
they are well in contact, heat the two joined flares together,
very hot, and, pulling slightly, the flares will flatten out and
the tube be perfectly joined. Tubes joined without previous
flaring have a constricted diameter at the joint.

To make a T-joint in two pieces of tubing, it is necessary to make
a hole in the side of one piece, as shown at A in Fig. 9. This is
accomplished by the aid of the principle of physics that gases
expand when heated. Both ends of the tube, which should be cold,
are corked tightly. The whole is then gradually warmed by being
held near the flame. When