ON THE SPECIFIC HEAT OF AQUEOUS SOLUTIONS. 
121 
It follows that the calculation of the specific heat of a series of solutions at a given 
temperature from the densities requires the experimental determination of only two 
constants. (See Section 23, Table XVIII.) Given these constants, the specific heat 
of a solution of any concentration at the given temperature can be calculated with 
great accuracy from the densities and the known specific heat of water. 
The change which takes place in the constitution of the free water of a solution 
through the agency of a solute is a matter of the greatest interest for the theory of 
solutions. The study of viscosities had already led to the hypothesis that certain 
changes in the constitution of the free water might be taken as proportional to the 
concentration of the solute. The examples studied in this communication lead to 
the conclusion that 
(1) The specific heat and specific volume of the combined water may be treated as 
approximately constant; 
(2) The lowering of the specific heat and specific volume of the free water on the 
introduction of a solute are each proportional to the percentage concentration 
of the solute. 
An important object of the present investigation was to compare the temperature- 
variations of the specific heats of solutions with those of pure water. For this 
purpose the range of temperature of about 0° C. to 40° C. has been taken divided 
into three intervals, the mean specific heat for each interval being found. As was 
to be expected, in dilute solutions the specific heat curve approximates to that of 
water, which has a minimum value in the neighbourhood of 25° C. In concentrated 
solutions the minimum disappears, and in the most concentrated solutions the 
variation of the specific heat with temperature appears to follow a nearly straight- 
line law. This behaviour is to be attributed to the simplification of the water by 
the considerable destruction of ice and steam molecules and is entirely analogous to 
the corresponding phenomenon noted in a former communication with respect to 
densities (Bousfield and Lowry, ‘ Phil. Trans.,’ A, vol. 204, 283, 1905). 
Incidentally a relation emerges between heat of solution and contraction which 
may be expressed as 
I \ — t (Jk.) 
\doJ H \duje 
The method and apparatus, which were originally designed for their present use, 
have been described in a former communication (W. R. and W. Eric Bousfield, 
‘Phil. Trans.,’ A, vol. 211, 199, 1911) relating to the variation of the specific heat 
of water with temperature and the value of the calorie. The perusal of the former 
communication will greatly facilitate the task of following the experimental portion 
of the present paper. 
2. Apparatus and Method .—The two chief points of the method described in the 
r 2 
