ON THE SPECIFIC HEAT OF AQUEOUS SOLUTIONS. 
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24. Changes in the Free Water of a Solution. —To discover the true law governing 
the changes in the free water of a solution is an essential problem for the foundation 
of a rational theory of aqueous solutions. One is constantly brought face to face with 
this problem in considering the physical properties of an aqueous solution. In 
considering the densities of sodium hydroxide in a former paper (Bousfield and 
Lowry, ‘Phil. Trans.,’ A, vol. 204, pp. 280-283, 1905) it appeared that the 
simplification in certain phenomena of concentrated solutions must be attributed to a 
simplification of the solvent by the action of the solute. In a later paper (Bousfield, 
‘ Phil. Trans.,’ A, vol. 206, pp. 129-142, 1906) the matter had to be considered in 
relation to the viscosity of aqueous solutions of sodium and potassium chlorides. It 
was there stated ( loc. cit., p. 136) that 
“ There is good reason for believing that the introduction of a solute into water 
somewhat lowers the radion of water, since the process of abstraction of water 
molecules by the solute breaks up some of the molecular complexes of the uncombined 
water, and therefore lowers the average molecular size of the uncombined water. 
The investigation of the amount of this lowering is a complex matter, and we 
shall neglect it, as it does not seriously affect the general character of our results, 
though it involves a slight loss of accuracy. ’ 
Later investigation showed that improved results' in the calculation of the 
viscosities of aqueous solutions could be obtained by treating the change in the radion 
of the free water as being proportional to the concentration of the solute. 
Generally it may be said with regard to the physical properties of aqueous solutions 
that no relation can be formulated which is accurate over the whole range from 
great dilution to saturation which does not take into account the progressive change 
in the constitution of the free water. Certain properties of very dilute solutions can 
he accurately formulated over a range in which the concentration is so small that the 
constitution of the water may be considered as constant and practically unchanged. 
Certain properties can be accurately formulated over a range in which the 
concentration of the solute is so great that the constitution of the water is again 
practically unchanged, being mainly dihydrol. But to fill the gap between dilute 
and concentrated solutions the consideration of the changes taking place in the free 
water over the whole range seems to be essential. 
A study of the ionisation law of LiCl in relation to the law of mass action over the 
whole range of concentration in a former paper (Bousfield, ‘ Trans. Chem. Soc.,’ 
vol. 105, pp. 1823-1828, 1914) well illustrates the point at which the constitution of 
the free water becomes a necessary element in the completion solution. It was shown 
that the application of the law of mass action to the ionisation of a solution involved 
the application to the dissociation constant of a factor dependent upon the progressive 
change which takes place in the free water as dilution proceeds. 
The foregoing treatment of the matter in the consideration of the specific heats and 
specific volumes of aqueous solutions appears to throw further light on the problem. 
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