184 On Steam and Brines 



whence we obtain 



which expresses in such cases the principle of thermal mixture, 

 namely, the amount of heat lost by the hotter mass is equal to 

 that gained by the colder mass. 

 From this we obtain 



and s is the virtual specific heat of the water W under the 

 influence of the salt, considered as an imponderable, to dis- 

 tinguish it from the specific heat of the solution in which the 

 mass of the dissolved salt is taken into account. 



The value of s so obtained for the virtual specific heat of 

 the water l is affected by any thermal reactions which take 

 place when two portions of the liquid are mixed at the same 

 temperature. When no such thermal reaction takes place, 

 then the values of s obtained from the boiling-points of 

 solutions of different degrees of dilution are identical. If the 

 values so obtained for s show a regular variation, then some 

 such thermal reaction may be presumed and it will require at 

 least one independent experiment for its determination. 



In the following table three cases are chosen to illustrate 

 the calculation of the virtual specific heat of the water W of 

 the solution of highest boiling-point by combination seriatim 

 with the other values of W and the corresponding values 

 of t, which is used to denote the elevation of the boiling 

 temperature. 



Potassium chloride has been taken as representative of 

 salts under the influence of which the virtual specific heat of 

 water is depressed below unity, and sodium nitrate has been 

 chosen as representative of those which raise it above unity. 

 The third case illustrates the influence of mechanical pressure 

 under which the virtual specific heat of water is also raised 

 above unity. 



In all the three cases the values of the virtual specific heat 

 are very concordant in each series. The slight rise exhibited 



