(C) Hammer the needle and test again as in (B).
EXPERIMENT 22. To test the effect of heat upon a magnet.
Apparatus. A magnetized sewing-needle; the candle, cork, etc., of [Exp. 2]. (See [Fig. 1].)
48. Directions. (A) Test the needle for magnetism.
(B) Stick the needle into the cork ([Fig. 1]), and heat it until it is red-hot.
(C) Test the needle again for magnetism.
(D) See if you can again magnetize the needle.
49. Discussion. Heating a body is supposed to thoroughly stir up its molecules. Jarring or twisting a magnet tends to weaken it. (See [Exp. 19].)
The molecules of steel do not move about or change their relative positions as readily as those of soft iron. When the molecules of hard steel are once arranged, by magnetizing them, for example, they strongly resist any outside influences which tend to mix them up again.
A magnet does not attract a piece of red-hot iron. The particles of the hot iron are supposed to vibrate too rapidly to be brought into line; that is, the iron cannot become polarized by induction. (See [Exp. 24].)