1885.] on the Beat of Dissolution of Salts. 409 



In the solution of anhydrous carbonate and sulphate of sodium in 

 water, evolution of heat occurs, and the amount of heat evolved in- 

 creases with the temperature, but is not so great as would be inferred 

 from the application of Person's formula. On the other hand, 

 sulphate of potassium, the solution of which is attended by absorp- 

 tion of heat, gives a gradually diminishing absorption as the tempera- 

 ture is raised, but the observed absorption is greater at the higher 

 temperature than the calculated amount. That is to say, in all these 

 cases, whether the act of solution is attended by rise or fall of tem- 

 perature, there is a consumption of energy corresponding to an 

 absorption of heat, which is not accounted for by the difference 

 between the specific heats of the materials, and of the solution which 

 results from their union. 



From the connexion already established between fusibility and 

 solubility,* and from a, priori considerations, it seemed probable that 

 the thermal change attending the solution of a solid must vary 

 according as by raising the temperature the cohesion of the solid is 

 diminished, or by lowering the temperature the cohesion is increased. 

 For if a salt dissolves in water with absorption of heat, this absorp- 

 tion will be less at higher temperatures when the cohesion of the 

 solid has been reduced, and therefore the energy required for its 

 liquefaction by the solvent also lessened. On the other hand, if a salt 

 dissolves with evolution of heat, the heat evolved must be greater at 

 higher temperatures for the same reason. 



Some very fusible salts were therefore taken in order to ascertain 

 whether the difference between the observed and calculated heats of 

 solution was notably greater or less than the difference observed in 

 the case of the sodium carbonate and sulphate and potassium sul- 

 phates. 



* Carnelley, " Phil. Mag.," March, 1882 Tilden ; and Shenstone, " Phil. Trans.," 

 1884, I j Tilden, " J. Chem. Soc," July, 1884. 



