134- Chemistry. [Lecture 29. 



the whole mass of the salt may be sometimes se- 

 parated. 



Salts have generally been treated by chemists 

 under the form of crystals, and under this state 

 are the most remarkable ; but this is not the 

 most simple state of salt. Crystals abound 

 with water : sulphat of soda contains one-third 

 water; hence the phenomenon of their watery 

 fusion, efflorescence, and decrepitation. Crystals 

 put in vessels over a fire soon assume the form 

 of a watery fluid; for the water they contain 

 is sufficient, when heated, to dissolve them : if 

 the heat is increased, the water will boil with 

 violence, till it evaporates; a salt will then be 

 formed that has lost much of its former weight. 

 This dissolution is called the watery fusion. It 

 generally happens at the same degree of heat at 

 which water boils, and must be distinguished 

 from the true fusion of salts, which takes place 

 after the water is evaporated. 



Efflorescence takes place when the crystals, 

 being exposed to the dry air, lose their transpa- 

 rency, and crystalline form, and fall into white 

 powder, as happens to sulphat of soda, &c. The 

 reason of this is, much of the water evaporating, 

 the rest is not sufficient to preserve them in the 

 crystallized form. But this does not happen 

 with those crystals that do not contain so much 

 water : these will require a brisk heat to render 

 them fluid ; the quantity of water contained in 

 them is small; and when separated, by being 



