Magnetic Permeahilily of various Alloys of Iron. 



79 



The above results are plotted in the curves shown in fig. 4. The last 

 specimen contains high carbon, and hence its conductivity is of a lower order 

 than it would otherwise be. One other specimen of nickel steel containing high 

 carbon is not included in the foregoing table, as it belongs to a different batch. 

 It is marked 1267 B, and contains 4-75 per cent, of nickel, and 0'8 per cent, of 

 carbon. Its conductivity in the unannealed state was 3-8, and in tlie annealed 

 state 5"1, copper being taken as 100. 



6 



Pe,T-CATita,ga of Ni/okel/. 

 Fig 4. 



It will be noticed annealing has a marked effect in increasing the conduc- 

 tivity of those steels : in fact the particular thermal treatment that certain alloys 

 of nickel steel are submitted to after manufacture is of considerable importance 

 in modifying their physical proj^erties. This will be strikingly seen when the 

 magnetic permeability of these specimens is given. Three specimens of 1287 K 

 and three of 1287 L (19'64 and 24*5 % nickel) were made, one being unannealed 

 or left as rolled ; the next annealed by slow cooling for 100 hours in the annealing 

 oven ; and the third, heated to whiteness, and then suddenly quenched in water. 

 The electric conductivity of each was determined, the water-quenched specimens 

 in each case were found to have a conductivity midway between the rolled and 

 annealed specimens given above in Group 3.* 



*The specimens 1287 K and L remained bright, with but slight oxidation, in an atmospl sre whict 

 had oxidised most of the other alloys, and some of them very considerably. 



