Make a pollywog as in Experiment 12, but bend its tail twice as shown in 1, Fig. 27; the nozzle is at one side and points sidewise. [Illustration: FIG. 29 THE SPIDER TRICK ] Put it in the bottle full of water, then press down and release the stopper. Does it sink and rise, and does it also whirl around most beautifully as it rises? Make another pollywog (2, Fig. 27), but bend its nozzle in the opposite direction. Does it whirl in a direction opposite to that of the first pollywog? Put them in the bottle together and treat your friends to a pollywog dance. The pollywog whirls because the water rushes out of the nozzle in one direction and forces the nozzle in the opposite direction. Experiment 15. To make glass spider-web. Heat the end of a piece of No. 2 tube in the blowpipe flame until it is melted and very hot. Now touch the end of another piece of glass to the melted glass, remove from the flame, and quickly pull the two pieces apart as far as you can (Fig. 28). Do you find that you have pulled part of the melted glass out into a very fine glass spider-web? Repeat, but ask a friend to touch the second piece of glass to the first and run away as fast as he can. Do you get a much finer spider-web? Is the glass spider-web fairly strong and very flexible? Experiment 16. The ancient spider trick. [Illustration: FIG. 30 ATTACHING A HANDLE ] Attach an imitation spider—or the dead body of a real spider—to the end of the glass spider-web and surprise your friends, as shown in Fig. 29. The glass spider-web is much less visible than a thread for this purpose. Experiment 17. To make working handles. You can save glass in many cases by attaching a short piece of glass to the piece you intend to work with, as follows: Heat an end of each piece in the lamp flame until red hot, press them together, remove from the flame, and hold until solid. The short piece then serves as a working handle (Fig. 30) for the large piece. Experiment 18. To close a large tube. You closed small tubes in Experiment 5 by simply heating the end in the blowpipe flame. This method does not serve for large tubes, however, because it leaves a very large lump of glass which may crack on cooling or reheating. [Illustration: FIG. 31 CLOSING A LARGE TUBE ] [Illustration: FIG. 32 MAKING A SUBMARINE ] Practice the following method of closing a large tube; first with a piece of No. 4 tube, and then with a piece of No. 6: Attach a working handle to the end to be closed, heat the tube ½ inch from the end in the blowpipe flame, turn constantly, and when soft pull apart until the tube has the shape 1, Fig. 31. Heat, turn, and pull the end away to leave the tube as in 2. Heat the end and blow out until it has the shape 3. The end is now closed and the glass has about the same thickness as the remainder of the tube. Experiment 19. To make a submarine.