438 



Crystallized manganese sulphate does not show distinct deviations 

 from Curie's law till hydrogen temperatures are reached and there- 

 fore belongs to class a of § 1 ; the anhj'^drous salt on the other hand 

 shows deviations over the whole range (class b). For both substan- 

 ces the agreement between observed and calculated values appears 

 satisfactory, although the differences seem somewhat larger than the 

 experimental errors. In the same manner we found: 



for crystallized ferrous sulphate: — = 10 



for crystallized manganese chloride: -^ = 13. 



k 



For a substance like platinum the deviations from Curie's law 



are enormous and the value of — must be correspondingly large. 



k 



The measurements with platinum made at Leiden (Comm. N". 1326) 



give — ^ about equal to 1500, those by Honda (above normal tem- 



k 



perature) give a still higher value. 



§ 6. The above shows that substances which deviate strongly 

 from Curie's law give large values of — . This result is in itself 



evident, considering that substances with a high value of — must 



k 



also have a large zero-point energy (è ln\), so that U \ ov — j will 



V xy 



be far from proportional to T at low temperatures. 



According to (3) x\ is inversely proportional to the moment of 

 inertia of the molecule. It may therefore be expected that substances 

 with large moment of inertia (i.e. small rj will show small 

 deviations from Curie's law and vice-versa. This is in general well 

 confirmed by the results. A substance like gadolinium-sulphate 

 Gdj (SOJ3 . 8 H^O (comp. Comm. N". 122^) with very heavy molecules, 

 each moreover loaded with 8 molecules of water of crystallization, 

 shows hardly any deviation from Curie's law even in liquid 

 hydrogen. Anhydrous manganese sulphate deviates strongly even at 

 the ordinary temperature; with the crystallized salt, each molecule 

 of which carries 4 water molecules and must therefore have a 

 large moment of inei'tia, distinct deviations from the law only 

 appear at hydrogen temperatures. Platinum which deviates very 

 strongly would have molecules with very small moment of inertia. 



