120 
MESSRS. W. R. BOUSFIELD AND C. ELSPETH BOUSFIELD 
pointed out (‘ Thermochemische Untersuchungen,' I., 52, 1882) that there was a 
close relation between the volume changes and the specific heat changes which took 
place on the dilution of a solution, but he did not arrive at any definite quantitative 
relationship, nor was he immediately concerned with the bearing of his results on the 
elucidation of the theory of solutions. One object of the present investigation was 
to obtain the necessary data to bring out with sufficient accuracy the true relationship 
between volume changes and specific heat changes. The examples chosen possess 
the advantage that certain other physical data are already available which are of 
material assistance. Freezing-point and vapour-pressure determinations, and also 
densities, conductivities, and viscosities over the range of temperature and concen¬ 
tration to be studied all have a bearing on the elucidation of the results. In the 
case of sodium chloride solutions at 20° C. adequate data exist over a sufficient 
portion of the range to enable accurate deductions to be drawn. There are still but 
few substances for which a complete systematic investigation of the various physical 
properties exists of sufficient accuracy and over a sufficient range of temperature and 
concentration. The multiplication of such systematic data is essential for secure 
generalization. In the meantime, the two examples studied in this communication 
lead to useful results. 
In the search for the true theoretical relation between specific heat changes and 
density changes four empirical linear relations presented themselves. One set of 
these relations pointed to the specific heat lowering of the solution as a linear 
function of the contraction ; the other to the mean specific heat lowering of the 
water as a linear function of the contraction. Both are so close to the truth that 
it was difficult to decide between them, but upon the whole the latter is to be 
preferred, and it gives a rational interpretation to the phenomena. Upon this view 
the fundamental laws which result can be expressed as follows :— 
(1) The specific heat of the solute may he taken as practically constant at all 
dilutions. 
(2) The solution of the solute lowers the mean specific heat of all the water 
(both free and combined) by an amount which is proportional to the mean 
specific contraction of the water. This latter relation may be expressed by 
ds^/div^ = L, where is the mean specific heat of the water and w u is the 
mean specific volume of the water. 
In a former paper (Bousfield, ‘Boy. Soc. Proc.,’ A, vol. 88, 149, 1913) it was 
found that the heat evolution attributable to the reduction of internal energy 
brought about by the contraction which took place upon the combination of certain 
pairs of elements bore a constant ratio to the contraction, the ratio being independent 
of the nature of the combining substances. This principle appears to be connected 
with the present result, although the actual value of the ratio depends on the heat 
required for certain changes of state which take place with rise of temperature. 
