THEORY OF SOLUTION AND CRYSTALLISATION. 2^3 



regularly, though the density of the liquid is always greater than 

 the mean density of the water and solid salt. 



6. The adhesion of water or other liquid to substances which may 

 be dissolved in it, is shown in a variety of ways. Many salts are 

 deliquescent. That is, when exposed to an atmosphere containing 

 water in a state of vapour, they unite with that vapour and cause it 

 to liquefy. Vapour of alcohol is in like manner absorbed in large 

 quantity by many resins and other substances which are soluble in 

 alcohol. And we cannot doubt that this liquefaction of the vapour 

 is attended by evolution of heat, although in the case of deliquescent 

 substances, the liquefaction of the solid may partly or wholly use 

 it up. A very interesting experiment bearing upon this part of the 

 question is recorded by Mr. Gossage, who found that steam at 

 100°, passed into a saturated solution of nitrate of soda, was capable 

 of raising the temperature to 121^,5. The condensation of the 

 steam by the salt thus caused an accumulation of heat, which was 

 not dissipated by any compensating process of liquefaction or 

 vaporisation. 



The adhesion of solvents to dissolved sohds is further illustrated 

 by the fact, long ago established by Regnault, that the vapour 

 evolved from aqueous solutions, and from crystals containing 

 water of crystallisation, has a smaller tension than the vapour 

 emitted from water at the same temperature. It is also very well 

 known that the boiling point of a liquid is raised by the addition 

 of substances soluble in that liquid. 



Boiling Points of Saturated Solutions. 



Name of Salt. 



Acetate of Potassium 

 Acetate of Sodium 

 Nitrate of Potassium 

 Chloride of Sodium 

 Etc 



