On the possibility of a thermal effect accompanying sudden changes in the magneton-numbers in CuCl<SUB>2</SUB> and NiSO<SUB>4</SUB>7 H<SUB>2</SUB>O

1. The temperature variation of the paramagnetic susceptibility of most of the solids follows the generalised Curie law &#968; = C/ T &#x2213; &#952;' as found first by Kamerlingh Onnes and Weiss. This gives a linear relation between 1/&#968; and T. The value of C is a measure of the atomic magnetic moment, and if this moment is expressed in terms of the Weiss magneton-number p, then p = 14.07 &#8730;CM where CM is the value of C when &#968; refers to a gram-molecule. The experimental results for a paramagnetic substance are usually expressed in terms of p and &#952;. Weiss (1), Foex (2), Cabrera and others have found that in some substances there are discontinuities in the slope of the 1/&#968;, T curve. Thus Weiss (3) finds that magnetite above its Curie point shows several sudden changes in the 1/&#968;, T curve, which he has interpreted as corresponding to the magneton-numbers p = 4, 5, 6, 8,10. Similarly, for cupric chloride (anhydride) Weiss (4) gives p= 9.2 and 10, for the temperature ranges - 140&#176; to 20&#176; and 20&#176; to 500&#176; respectively. Nickel sulphate (5) has also been found to possess a transition point at about - 113&#176;, where the p value on cooling changes from 14.6 to 18.2