414 



PRINCIPLES OF CHEMISTRY 



tion and for economising fuel, which are mainly based on an artificial 

 draught to carry off the steam as it is formed, and on subjecting the 

 saline solution to a preliminary heating by the waste heat of the steam 

 and furnace gases. Furthermore, the first portions of the salt which 



FIG. 64. Graduator for the evaporation of the water of saline springs. 



crystallise out in the salt pans always contain gypsum, owing to the 

 water of saline springs always containing this substance. It is only 

 the portions of the salt which separate later that are distinguished by 

 their great purity. The salt is ladled out as it is deposited, and left to 

 drain on inclined tables and then dried, and in this manner the so- 

 called bay salt is obtained. Since it has become possible to discover 

 the saline deposits themselves, the extraction of table salt from the 

 water of saline springs by evaporation, which was before in general use, 

 has begun to be rejected, and is only able to hold its ground in cases 

 where fuel is cheap. 



In order to understand the full importance of the extraction of 

 salt, it will be enough to mention that on the average 20 Ibs. of table 



