Fig. 1.
Apparatus. [Fig. 1]. A needle; a cork, Ck (No. 2); lighted candle (No. 3). The bottom of the candle should be warmed and stuck to a pasteboard base.
5. Directions. (A) Stick the point of the needle into Ck, [Fig. 1], then hold the needle in the flame until it is red-hot. (The upper part of the flame is the hottest.)
(B) Allow the needle to cool in the air.
(C) Test the brittleness of the steel by bending it. Test its hardness with a file ([Exp. 1]).
6. Annealing. This process of softening steel by first heating it and then allowing it to cool slowly, is called annealing. All pieces of iron and steel are, of course, hard; but you have learned that some pieces are much harder than others.
EXPERIMENT 3. To find whether a piece of annealed steel can be hardened.
Apparatus. The needle just annealed and bent; cork, etc., of [Exp. 2]; a glass of cold water.