350 
DR. A. DUPRE OUST TIIE SPECIFIC HEAT AND OTHER 
Apart from all speculation as to the cause of these phenomena, for which the existing 
data seem insufficient, a more extended study of the relations pointed out cannot fail to 
throw much light on the vexed question of the constitution of solutions and mixtures. 
It is also evident that proposition 1 will enable us to calculate the specific heat of 
one constituent of a mixture if we know the specific heat of the other, the specific heat 
of the mixture, and the units of heat evolved or absorbed at the two different points of 
temperature between which these specific heats have been determined. 
This calculation will serve not only as a check on the accuracy of the various experi- 
mental data involved, but may in certain cases enable us to calculate the specific heat 
of an element in a condition in which this could not be directly determined. If, for 
example, we can estimate the heat evolved or absorbed at two different temperatures 
during the combination of two elements, of which one is, say, in the nascent state, the 
specific heat of the element in that condition could be calculated. 
Lastly, these considerations show how important it is to give, in all cases in which 
the heat of combination &c. is estimated, not only the quantities of substance employed, 
but also the exact temperature at which the experiment was performed. Without this 
the results are well nigh valueless. 
Let z be the weight of a mixture, x and y the weights of its two constituents, U and 
U' the units of heat evolved at the temperatures t and t', of which t is the lower, 
and S, S' and S" the specific heat of the mixture and of its two constituents x and y 
respectively ; then, if S and S' are known, we have 
s „_ S z(t'-t) -U + U'-S >x{t'-t) 
If heat is absorbed in the formation of the mixtures, U and U' may be taken as repre- 
senting the units of heat absorbed at t and t', and the above equation becomes correct 
if the signs for U and U' are reversed. 
The specific heats of the four solids above considered, calculated with the help of this 
formula, are as follows : — 
Potassium chloride from the weaker solution T47 
„ „ „ ,, stronger „ -135 
„ „ as estimated by Kopp directly . . . . T73 
Sodium chloride calculated *229 
„ ,, as estimated by Kopp . -214 
Potassium nitrate from the weaker solution ...... *227 
„ „ „ „ stronger „ T92 
,, „ as estimated by Kopp *2388 
Potassium hydrate calculated -274 
Potassium hydrate lias not yet been directly estimated. 
