920 



those of a normal paramagnetic substance. Should this hypothesis be 

 correct, it would be of importance to take notice of the atomic 

 concentration, in studying paramagnetic substances. To determine 

 the number of magnetons in a paramagnetic i.\ >i\\, we should therefore 

 have to take (complex) compounds, which lulfd this condition of 

 being sufiiciently "diluted". This condition is fulfilled by many 

 of the materials which have been used for the calculations about 

 magnetons ^). 



If we arrange the substances according to the value of their 

 atomic concentration, we see that in genei-al the deviations from 

 Curie's law at low temperatures seem to appear sooner in substances 

 with a liigh concentration. Oosterhuis's calculations (Comm. Suppl. 

 !N". 31) give particulars of the amount of the deviation in different 

 substances. It will therefore be desirable, if we want to determine 

 the number of magnetons in an alom at low temperature, to go 

 down to very small concentrations. This is no difficulty for the 

 measurement, for, although the specific susceptibility at small 

 concentration is small, it increases considerably according to Curie's 

 law for a given concentration with the transition to low temperatures. 

 We should come upon chemical ground if we were to discuss what 

 compounds would be suitable for this purpose. Double salts and 

 complex compounds seem to be particularly suitable, provided we 

 are able to apply the correction for diamaguetism. 



It is very likely that with high atomic concentiations A may rise 

 to very high values. Something of this sort might be the case with 

 platinum (see § 12) and willi the ferromagnetic substances the inves- 

 tigation of which first led Weiss and FoËx to ihe introduction of a 

 negative magnetic field. 



For crystals, a "linear concentration" may have to be introduced. 

 The value of A for different directions would have to be brought 

 into connection with this. 



In the further study of the deviation from Curie's law, use will 

 have to be made of the results of Werner's investigation of the 

 constitution of complex compounds on the one hand, and 

 on the other hand of the data which experiments upon the diffraction 

 of Röntgen rays, such as Bragg in particular has made, may yield. 

 What these can teach concerning the arrangement of the atoms and 

 the structure of the atomic lattice, is of great importance from the 

 above point of view. {To he continued). 



^) In ferric alum is realised a case of solution of a paramagnetic in a practically 

 neutral substance, of the same kind as that wliicli Weiss considered by extra- 

 polation in his discussion of the ferro- magnetic alloys when he was searching for 

 the law of distance for the molecular field'. 



