To join Tubes of Unequal Sizes End to End ([Fig. 15]).—Draw out the larger tube and cut off the drawn-out end at the part where its diameter is equal to that of the smaller tube, then seal the smaller tube to the contracted end of the larger according to the directions given for joining tubes of equal size. When a good joint has been made, the tube presents the appearance of A, [Fig. 15], the union being at about bb. Next heat the whole tube between the dotted lines aa, and blow it into the shape of B in which the dotted line dd should correspond to the actual line of junction of the two tubes.
In making all joints it is important to leave no thick masses of glass about them. If the glass be fairly thin and uniformly distributed, it is less likely to break during or after annealing under any circumstances, and especially if it has to bear alternations of temperature.
Joining a Tube to the Side of another Tube ([Fig. 16]).—One of the tubes must be pierced as at A in [Fig. 16] (for the method, see [p. 37]), and its two ends closed with small pieces of cork. The edges of the opening, and one end of the other tube, must then be heated till they melt, and united by pressing them together. The joint may then be finished as before.
Fig. 16.
A properly blown joint will not present the appearance of B ([Fig. 16]), but rather that of C. This is secured by directing the pointed flame upon the glass at aa (B) spot by spot, and blowing out each spot when it is sufficiently softened. If the tubes are large, the whole joint should subsequently be heated and blown, but in the case of small tubes this is of less importance. Finally it is to be wrapped whilst hot in cotton wool for the annealing process.
If a second tube has to be joined near to the first one, say at b, it is well to proceed with it before the joint first made cools down, and the joint first made, especially if soda glass be used, must be held in the flame from time to time during the process of making the second joint to keep it hot; if this be not done the first joint is very likely to break. A joint previously made may, however, be re-heated, if well made and well annealed.
A three-way tube, like that in [Fig. 17], is made by bending A (Fig. 16) to an angle, and joining B to an opening blown on the convex side of the angle; or, A of [Fig. 16] may be bent as desired after attaching B in the ordinary way.
