Part IT. On Aqueous Solutions. 79 
of v. For any concentration a definite selection of types of 
particles exists in the solution and the sum total of the products 
of the type m,C,(const.) into the rate at which this particular 
type associates or dissociates as the temperature is varied is 
represented by the term 6. Therefore variation in the value of 
_ B implies variation of the stability of the molecular complexes. 
For a 2:23 normal solution of ferric chloride the constant B 
has a value which is 29°/, of the value of the susceptibility at 
50° C. (the mean temperature). The variation of the suscepti- 
bility with the temperature is well represented for this 
concentration by the hyperbolic relation * 
A 
= 5 ate B, 
_and it is remarkable that such a large positive quantity (the value 
of B is 751x10~, that of the susceptibility at 50°C. is 
26:15 x 10-*) which is independent of the temperature should 
enter into the expression for the variation of paramagnetic 
susceptibility with the temperature. 
For solutions of ferric chloride of concentration 3°62 normal 
and 1°76 normal, the values of B are nearly equal, but are much 
less than the value for a 2°23 normal solution. It appears there- 
fore that a solution of ferric chloride of this concentration has a 
unique constitution, and it is interesting to see if such a solution 
behaves abnormally with regard to other physical properties. 
(4) Measurements of the Viscosity of Ferric Chloride Solutions. 
The following experiments on the variation of viscosity of four 
solutions of ferric chloride with the temperature were carried out 
to investigate the complexity of strong solutions of this salt and 
to examine if any irregularity is shown by a 2:2 normal solution. 
Experiments have been made by C. Chéneveaut and R. F, 
D’Arcy{ on the viscosity of strong solutions of sulphuric acid in 
water, and they obtained evidence for the existence of complex 
groups of molecules over certain ranges of concentration. 
The apparatus used in the following experiments is a modifi- 
eation of that used by D’Arcy and is shown in fig. 4. The ferric 
chloride solution was drawn into the bulb b from the receiver f, 
and when it had acquired the temperature of the water bath 
inside the calorimeter C, it was driven out through the capillary 
tube c” back to the receiver R under a pressure head of water 
* It should be remarked that the solution referred to contains almost exactly 
the same quantity of iron per c.cm. as does the solution used by Townsend, and his 
results are shown graphically, fig. 3, curve 1. 
+ Comptes Rendus, t. chv., No. 2, 1912, p. 154. 
+ Phil. Mag. Vol. xxvitt., Ser. 5, 1889, p. 221. 
