90 Chemistry. [Lecture 27. 



of any matter as it is capable of holding in solu- 

 tion, it is said to be saturated. Saturation is 

 sometimes single, sometimes double: camphor 

 in spirit of wine is an instance of the first; volatile 

 salts and the sulphuric acid are an instance of the 

 second, for both may be saturated ; the salts by 

 having a proportion of the acid lose their pun- 

 gency, and the acid its sourness. If more than 

 this portion is added of either, the overplus re- 

 tains its separate qualities. 



Chemists have a power of separating, by the 

 application of heat, such bodies as differ in vo- 

 latility, and are not too strongly united ; but in 

 some instances of solution we find it very difficult. 

 If we endeavour to separate them by heat, we 

 find them capable of enduring a great deal more 

 than any of the bodies, when separate, could 

 have done ; and if we apply a still greater heat, 

 the vapour rises without any separation of parts, 

 the volatile carrying the fixed along with them. 

 A mixture of the sulphuric acid and water is an 

 instance : the water in its separate state would 

 be converted into vapour at 212, the acid at 600; 

 but mixed, the water will not evaporate at 212; 

 the heat must be greatly increased, and then the 

 vapour of the water rises mixed with the acid. 

 The alkaline salt known by the name of ammonia 

 is very volatile, but when mixed with sulphuric 

 acid, its volatility will be depressed by the acid, 

 so that it has not the least smell ; and if heat is 

 applied, the alkali cannot be raised without a 



