Magnetic and Electric Saturation Values. 353 



- Io at constant field-strength, and as it is proportional to' 

 the temperature , it may be put equal to RT. Hence 



RT=B/TI 2 , (4 a) 



and therefore 



: » = \/| ^ 



Thus tiie calculation of the limiting intensity of magneti- 

 zation (I,)) only involves a knowledge of the well-known 

 gas constant and the reciprocal of Curie's constant. 



The truth of equation (5) mav be tested by comparing 

 the calculated values of the limiting magnetization with the 

 experimentally determined maximum values of magnetization 

 where they are known with approximate accuracy. 



As examples the ferromagnetic metals Iron, Nickel, and 

 Cobalt will be selected. 



Iron. 



The constant R must be taken for one cubic centimetre. 



Putting the gas constant equal to 83'15 x 10 6 ergs per 

 degree centigrade for a gram molecule, and taking the 

 atomic weight of iron to be 55 85 and the density to be 7*86, 

 then 



R = -£— ? x 7-86 x IO 6 = 11-7 x IO 6 , 



assuming there is one atom in the molecule of iron in the 

 solid state. 



R' = 3'56 when A = 0'281 (Curie, (Enures, p. 327) ; 

 therefore /ll*7 



T »=\/:«6 xl03 = 1817 - 



This number for the calculated limiting magnetization 

 compares favourably with the following experimental 

 saturation values : 



Io. 



1706 Weiss, J. de Phys. ix. p. 373. 1910. 



.1730 Ewing, Phil. Trans, clxxx. p. 221. 1889. 



1798 Taylor Jones, Phil. Mag. xli. p. 161. 1896. 



1798 Williams, Phys. Rev. vi. p. 404. 1915. 



