A good bend has the same diameter in the bend as in the remainder of the tube (1, Fig. 41). It is rather difficult to make because the tube tends to cave in on the inside of the bend (2) or flatten on the outside (3), or both. [Illustration: FIG. 42 A DRINKING TUBE ] Make the bend as follows: Heat a piece of No. 2 tube about 2 inches from one end in the lamp flame, turn it constantly and move it back and forth endwise to heat a length of about 2½ inches. When soft, take the tube out of the flame, and bend the ends =upward= until the angle is 90°. If the bend is flat on the inside or outside, close one end of the tube in the blowpipe flame, smooth the other end and allow them to cool, then heat the flat side of the bend in the blowpipe flame and blow it out slightly. This makes the diameter of the tube at the bend equal to that of the remainder of the tube. Cut off the closed end, smooth the edge, and your bend is complete. Make bends with No. 4 tube. [Illustration: FIG. 43 A SIPHON ] Experiment 30. To make a drinking tube. Many times when there is sickness in the house, it is convenient to have a glass drinking tube (Fig. 42), through which the patient can drink without raising his head. Make such a tube from a piece of No. 4 tubing. The short arm is equal in length to the depth of the tumbler; the long arm, or mouthpiece, is about 1 inch longer than this. Experiment 31. To make a siphon. Cut off a piece of No 4 tubing 8 inches long, make two right-angled bends about 1 inch apart at the center, smooth both ends, and your siphon is complete (Fig. 43). [Illustration: FIG. 44 A SIPHON ] Experiment 32. Magic. Put one arm of the siphon in a tumbler of water and suck air out of the other end. Does the water start running and does it continue to run in a most magical way (Fig. 44) until the water is below the end of the siphon in the tumbler? [Illustration: FIG. 45 FROM THE HIGH LEVEL TO THE LOW ] Fill the tumbler with water again, start the water running, put the outer arm of the siphon in an empty tumbler, and stand both tumblers on the table (Fig. 45). Does the water run up one arm of the siphon and down the other into the empty tumbler? Does it stop running when the levels are the same? Stand the first tumbler on a book. Does the water run again and stop when the levels are again the same (Fig. 46)? Place the lower tumbler on the book and the upper tumbler on the table. Does the water now run in the opposite direction until the levels are again the same? Raise one tumbler a foot or so above the table. Does the water run up over the edge and drop into the second? Now before the upper tumbler is empty, lower it in such a way that an arm of the siphon is in each tumbler, and raise the second tumbler. Does the water now run in the opposite direction? [Illustration: FIG. 46 THE WATER STOPS WHEN LEVELS ARE THE SAME ]