334 B. 0. Peirce— Properties of Seasoned Magnets. 



Art. XLII. — On the Properties of Seasoned Magnets made 

 of Self Hardening Steel ; by B. O. Peirce. 



In searching for a material of which to make a set of stand- 

 ard measuring magnets which should be as permanent as 

 possible and have small temperature and induction coeffi- 

 cients, I have tested a large number of magnets made of 

 some of the brands of self-hardening tool steel now in com- 

 mon use for lathe tools. It is obvious that self-hardening steel 

 has certain disadvantages as compared with ordinary fine tool 

 steel : it is not generally obtainable in the form of slender, 

 polished, accurately cylindrical rods, it is extremely difficult to 

 work while cold, and most magnets made of it are some- 

 what weaker than similar magnets made of the best drill rod. 



My experiments seem to show that comparatively short sea- 

 soned magnets made of self-hardening steel have decidedly 

 smaller induction coefficients than magnets of the same dimen- 

 sions made of tool steel. The diiference in the case of the 

 temperature coefficients is much less, though the advan- 

 tage appears to be on the side of the self -hardening steel. 

 It is comparatively easy to get a long uniform rod of self- 

 hardening steel and extremely difficult to make a very long 

 slender rod of tool steel uniformly glass-hard and at the same 

 time straight. The temperature and induction coefficients of 

 long magnets of the two kinds of steel seem not to be very 

 different. 



Most of the experiments here recorded were made on pieces 

 cut from cold rods of self-hardening steel by the help of a 

 Yery thin elastic emery wheel, which did not unduly heat the 

 material. Large rods of glass-hard tool steel cut under water 



by the same wheel showed no disturbance of temper at the 

 ends of the pieces. The susceptibilities of many of these 

 specimens of self-hardening steel were then determined in an 



