Repeat this whole operation a third time and blow just enough to leave the joint the same size as the remainder of the tube or a little larger. [Illustration: FIG. 75 MAKING A LARGE HOLE ] This heating and blowing has worked the joint back and forth until the glass is fairly uniform. It makes a strong joint. Cut off the closed end and smooth the edge. Repeat with a piece of No. 4 tube. [Illustration: FIG. 76 MAKING A TEE ] Experiment 54. To join tubes of different sizes. Take a piece of No. 4 tubing about 3 inches long and close one end. [Illustration: FIG. 77 THREE-ARMED SIPHON ] Take a piece of No. 6 tubing, attach a handle to one end, heat the No. 6 tube in the blowpipe flame about 1 inch from this end and draw it down to smaller size. Break the small part at a point where it is about the size of the No. 4 tube. If the hole is too large, heat the edge until it is a little too small and flare it out with the flaring tool. If the hole is too small, heat the edge and flare it out. Now heat the ends of both tubes (Fig. 74), and join them as described in the last experiment. Repeat the operation of heating and blowing at least three times. Join a No. 4 and a No. 2 tube in the same way. Experiment 55. To make a large hole. Take a piece of No. 4 tube about 6 inches long, close one end, smooth the other, and allow it to cool. [Illustration: FIG. 78 A REPEATING AIR GUN ] Now to make a large hole in the side of this tube, proceed as follows: Heat in the blowpipe flame the point at which you wish to make the hole, and blow a slight bulge (1, Fig. 75). Then heat the top of this bulge until it is red hot over an area about equal to the size of the hole you wish to make, and blow hard to make a thin bubble (2, Fig. 75). Break away the thin glass of the bubble, smooth the edges, and the hole is made. The edge of this hole will project beyond the side of the tube (3, Fig. 75). If you wish to make the edge even with the side of the tube, heat it in the blowpipe flame until it shrinks back level with the tube. [Illustration: FIG. 79 FOUR-WAY JUNCTION ] Experiment 56. To make a tee. Take a piece of No. 4 tube about 6 inches long, close one end, smooth the other, and allow it to cool. Take another piece 3 inches long, close one end, and allow it to cool. Now make a hole in the side of the first tube at a point 3 inches from the closed end. Do this as described in the last experiment but leave the hole projecting beyond the side of the tube (1, Fig. 76). [Illustration: FIG. 80 MAKING A Y ]