'50 



THEORY OF SOLUTION AND CRYSTALLISATION. 



account for all the common phenomena observed. And although 

 certain cases have at the outset been excluded, the reply to the 

 simple form of question propounded will in part satisfy their 

 requirements also. 



1. All substances are not soluble, and liquids are not capable 

 of acting as indiscriminate solvents. Thus water dissolves a large 

 number of acids and metallic salts, but relatively few carbon com- 

 pounds except such as partake of the character of acid or alcohol. 

 Alcohol dissolves a few salts, besides many resins and nearly all 

 organic bases, whilst it will not dissolve freely the common 

 metallic salts which are readily soluble in water. Benzine again, 

 a liquid hydrocarbon, takes up large quantities of nearly all solid 

 hydrocarbons, though very few, if any, substances of saline character. 



2. The solubility of a given substance in a liquid almost always 

 increases as the temperature rises. The following table exhibits 

 a few cases by way of example. 



This statement, however, is not universally true. Some of the 

 exceptions, for instance, sulphate of sodium, admit of explanation 

 without difficulty, and it is probable that the explanation of such 



