36. To harden steel, heat as before, then suddenly plunge the red-hot piece into cold water. This will make the steel very hard and brittle.
Small pieces may be held by pinching them between two pieces of wood. Needles and wires may be stuck in a cork, which will serve as a handle. (See text-book.)
Fig. 11.
37. Alcohol Lamp. Fig. 11. An alcohol lamp is very useful in many experiments, and it is better than a candle for annealing or hardening steel needles when making small magnets ([App. 21]). You can make a good lamp by using a small bottle with a wide opening. A vaseline bottle or even an ink bottle will do. Make a hole about ¼ in. in diameter through the cork with a small round file, or burn it through with a hot nail. Make a cylinder of tin about 1½ in. long and just large enough to push through the hole. The tin may be simply rolled up. If you have glass tubing, use a short length of that instead of the tin. For the wick, roll up some flannel cloth. This should not fit the inside of the tin tube too tightly. The alcohol should be put into the lamp when you want to use it, and that left should be put back into the supply-bottle when you have finished, as alcohol evaporates very rapidly. The flame of this lamp is light-blue in color, and very hot.
Caution. Do not have your supply-bottle of alcohol near the lamp when you light the latter, or near any other flame. The vapor of alcohol is explosive.
38. Spool Holder for Wire. Fig. 12. When winding magnets it is necessary to have the spool of wire so arranged that it will take care of itself and not interfere with the winding. If you have a brace and bit, bore a hole in a base ⅞ in. thick for a ¼ in. dowel. The dowel should fit the hole tight. The spools of wire purchased can then be placed upon the dowel, where they will unwind evenly. The base may be nailed or clamped to a table.