of glass for the little side tube which
is desired. In this way it is also easier to blow out a side tube with a
sufficiently small diameter. If the diameter of this tube should be much
greater than that of the small tube, the latter may be enlarged with a
carbon or a flanging tool.

EXERCISE NO. 4

TO JOIN TWO TUBES OF DIFFERENT DIAMETERS

In this case the first method (Exercise No. 1) is to be used whenever
possible, as it gives a much smoother joint than the second method. The
directions given will describe the adaptation of this method to the
problem: if the second method must be used on account of awkward shape,
etc., of the work, the modifications required will be obvious to any one
who has learned to make the joint by the first method.

After sealing or corking one end of the larger tube, the other end is
drawn out to form a tail as described on page 9, taking care to have the
tube uniformly heated, and to draw the tail rapidly enough so that the
cone is short, as indicated in _a_, Fig. 8. The tube is now rotated, a
small flame directed against the cone at right angles to an element of
it, and it is allowed to shrink a little, as indicated in _b_, Fig. 8,
so that its walls will thicken. When the tail is cut off, at the dotted
line, the diameter of the opening and the thickness of the walls at that
point should correspond with the dimensions of the tube to be sealed on.
As the glass is hot, the scratch for cutting it must be made with a file
(moisten the edge!), and it often will not break square across. Before
proceeding to seal on the small tube, any large projections on the cut
end are best removed, by warming the cut surface a little, directing the
small flame upon each projection in turn and touching it with a warm
scrap of glass. It will adhere to this and may then be removed by
rotating this scrap a little so as to wind up the projection on it, and
then drawing it off, while the flame is still playing on the spot. This
must be done rapidly and care taken not to soften the main part of the
cone.

[Illustration: FIG. 8.--Joining two tubes of different diameters.]

The large tube is now taken in the left hand, the small one in the
right, the ends heated and joined in the usual manner, taking care not
to get any larger lump at the joint than necessary. A small flame is now
directed on the cone at right angles to its elements as before, and the
tube rotated so as to heat the whole circumference. The fla