Part IT. On Aqueous Solutions. ae 
(3) Application of the Equation (13) to Aqueous Solutions 
of Iron Salts. 
It is only in the cases of strongly magnetic solutions, such as 
those of salts of the ferromagnetic elements, that a satisfactory test 
of the applicability of the formula (13) can be obtained. For 
other salt solutions the value of the susceptibility is little different 
from that of water, and in measuring such small differences as 
those produced by change of temperature the errors are liable to 
be large. On the other hand, in the case of strong solutions of 
the salts of ferromagnetic elements, the paramagnetic suscepti- 
bility is so great compared with the variation of the diamagnetic 
susceptibility with the temperature that it is permissible, at least 
for the strong solutions, to neglect the latter. The dependence of 
diamagnetism on the temperature is expressed by the term CS in 
the equation (13), and this term will accordingly be neglected. 
The diamagnetic susceptibility, in so far as it does not vary with 
the temperature, is included in the constant B. The expression 
connecting the susceptibility and the temperature may now be 
written 
x= +B Dahan eee (15), 
where B=(3 top. Op. %»)+(Fo-5 ty BMy - Hp): 
The relation (15) is hyperbolic. If the groups do not break 
up with change of temperature, all the factors v, in the first term 
of the expression for B are zero, and as in this case the second 
term of B represents the diamagnetic susceptibility (p const.) the 
above relation (15) reduces to the unmodified Curie-Langevin 
form. If the groups do break up with the change of temperature 
then the first term in the expression for B will not be zero, and 
the value of B may be positive or negative according as 
il 
ype Ge ivy = Ff = Mow Olly « by ° 
That the curves connecting susceptibility with temperature are 
approximately hyperbolae, for solutions of iron salts, can be seen 
from fig. 3. This diagram is reproduced through the kindness of 
Prof. J. S. Townsend*. As the numerical data corresponding to 
the curves were not published, it is impossible to test equation 
(15) by these observations, but from the trend of the curves it 
appears that an equation of this form would be suitable for the 
representation of Prof. Townsend’s results. 
* Phil. Trans. Roy. Soc., Vol. 187, A. p. 547, 1896. 
