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The cork may now be removed from the open end of the large tube, this end heated in a large flame, caught together with a scrap of glass tubing and drawn off into a cone so that the base of the cone is about opposite the end of the inner tube. The lump of glass is drawn off the point of this cone and it is reblown to form a rounded end, as previously described.

When this stage is reached, the glass should be very hot and fluid, and the mass of hot glass thick enough to remain at its working temperature for about five seconds after removal from the flame. The glass is now reblown as indicated in f, to form a bulb having walls of practically the same thickness as the original tube.

If the shape of the bulb or its size are not satisfactory, it may be shrunk again and reblown. Such shrinking should begin in a large yellow flame, with just enough air to give it direction. The amount of air may be gradually increased as the bulb shrinks and the walls become thick enough to bear it without collapsing.

Care must be taken not to leave knots or lumps of glass in the finished joint, and the latter should be well reblown, and if necessary left as a small bulb or enlargement, rather than have it have too thick walls. Spirals of glass tubing are probably best made free-hand before the blow-pipe, unless one has a great many of them to make, and extreme accuracy is desired.