45. Directions. (A) With H M magnetize the nail; this is made of soft steel.
(B) Test the lifting and pointing powers of W N ([Exp. 19]).
(C) Strike W N several times with a hammer to jar it.
(D) Again test its lifting and pointing powers.
46. Discussion. Soft steel has a greater retentivity than soft iron. It contains less carbon than cast or tool steel, and is called mild steel or machinery steel. You do not want soft steel for permanent magnets.
EXPERIMENT 21. To test the retentivity of hard steel.
Apparatus. A hard steel sewing-needle (No. 1); other articles used in [Exp. 20].
47. Directions. (A) Magnetize the needle with H M.
(B) Test its lifting and pointing powers ([Exp. 19]).