er blowing out part of the joint, to allow that part a few
seconds to set before going on with the rest, keeping the whole joint
warm meanwhile in or near the smoky flame. This helps to prevent the
twisting of the joint, or other distortion incident to the handling of a
piece of work of awkward shape.

In making a joint on a very long or heavy piece by this method, it is
often advantageous to attach a piece of rubber tubing to the open end,
hold the other end of this tubing in the mouth during the process, and
blow through it, rather than attempt to bring the end of the glass up to
the mouth. This enables one to keep closer watch on the joint, and avoid
drawing it out or distorting it in handling. On the other hand, the
rubber tube is an inconvenience on account of its weight and the
consequent pull on the end of the apparatus, and makes rotation
difficult.

EXERCISE NO. 3

THE "TEE" TUBE

The operations involved are two: the blowing of a short side tube on a
piece of tubing, and sealing another piece of tubing on this, by what is
essentially the second method as just described.

[Illustration: FIG. 7.--The "tee" tube.]

The two pieces of tubing to be used each have one end cut square and the
other sealed in the usual manner. The longer of the two is now heated at
the point at which the joint is to be made, until it begins to color the
flame. A small flame is used, and the tube rotated until the flame
begins to be colored, when the rotation is stopped, and only one spot
heated until a spot the diameter of the tube to be sealed on has become
red hot and begun to shrink. This is now gently blown out into a small
bulb, as in _a_, Fig. 7, and it will be noted that this bulb will have
walls tapering from the thick walls of the tube to a very thin wall at
the top. The sides of this bulb, below the dotted line, are to form the
small side tube to which the main side tube is to be sealed. The top of
the bulb is now softened by directing a small flame directly upon it,
and as soon as it shrinks to the level indicated by the dotted line, it
is removed from the flame and quickly blown out to form a thin bulb, as
indicated in _b_, Fig. 7. This will usually be so very thin that a
stroke of the file or glass-knife will break it off at the dotted line,
leaving the side tube, to which the short piece of tubing is now sealed
according to the second method (Exercise No 2). In doing this, care is
taken to direct the flame partly o