Salts. 131 



merely to throw the acid into the water : by this, 

 however, some of the linen was always cor- 

 roded ; for the sulphuric acid sinks to the bottom, 

 and there remains a long time before it is dis- 

 tributed. When mixed thoroughly by agitation, 

 the salt will never separate again ; for the solu- 

 tion of salts is as perfect as any in chemistry. 



Salts are separated by evaporation in two 

 ways: 1st, By a brisk heat till all the water is 

 dissipated. This is called evaporation to diyness, 

 and the salt appears a shapeless,] pretty firm 

 mass, but the particles are very small. If this 

 operation is often repeated, it is observed that 

 some of the salt is always lost. 2d, By a gentle 

 heat, and partial evaporation. The salts then 

 shoot into regular masses with polished surfaces, 

 more or less transparent, called crystals, from 

 their resemblance to that stone. Salts deposited 

 in this manner have a tendency to a particular 

 form, though the different manner of conducting 

 this process produces some variety in the figure 

 of the crystals. The crystals are larger and 

 more regular if the liquor is not evaporated too 

 much, and if it is cooled slowly in a vault or 

 cellar. There is a degree of transparency in the 

 concretion ; and if the process is repeated ever so 

 often, the salt will have the same form. Each 

 particular species of salt has a distinct form 

 of crystals peculiar to itself. Nitrat of potass 

 (common nitre) appears in the form of oblong 

 pillars with six sides : muriat of soda (common 



