212 Mr. J. R. Ashworth. Methods of making Magnets 



The irreversible loss of original magnetic intensity which results 

 from a series of heatings and coolings is tabulated under the heading 

 B in column VII, ft being calculated from the formula 



where 1/ and Ij are the final and initial intensities. 



The limits of temperature t and t' in these experiments were 10° to 

 20° C. and about 100° C., giving a range of 80° or 90°. 



The centigrade scale of temperatures and the C.Gr.S. system of 

 units are to be understood throughout. 



In every case a record has been kept of the scale readings at the 

 temperatures i and t' during the progress of the operations of heating 

 and cooling, and the brief example here cited may be taken as 

 typical. 



Three per cent. Tungsten Steel. 



Temperature. 



Scale readin 



gs at 







t. 







t'. 



Zero 0-0 



6-5 



184 -8 











99-6 









142 6 





7-5 



161-3 











99-6 









140 -2 





7-5 



160*2 











99-6 









137 -9 





7*5 



158-8 











99-6 









137 -9 





7 '5 



158-6 









Zero -0-1 



The table which is annexed gives a synopsis of the results 

 obtained. 



Each number in the first column represents a separate piece of 

 iron or steel, but where comparative tests of the same material were 

 desired, as, for example, in the cast irons, when either annealed or 

 hardened, the precaution was taken to employ two pieces of origin- 

 ally a single rod. Tims ISTos. 15 and 16 are two parts of the same 

 rod cut through the middle, and similarly with Nos. 17 and 18 and 

 others. 



In the first place, several varieties of steels were tested. No. 1 is 

 a steel from Sheffield, supplied specially for making magnets ; "Nbs. 

 2 and 3 are Hadfield's well-known non-magnetic steel; the next 

 four are tungsten steels, of which Nos. 6 and 7 are known as Mushet's 

 self -hardening steel, having the property of hardening even when 

 cooled slowly. These were both cut from the same rod ; No. 6 was 



