MANUFACTURE OF SALT FROM SEA-WATER 57 



rated brine falls rapidly when it is introduced into 

 a vacuum-pan, and because it is kept rapidly boiling, 

 vacuum-pans produce very fine cubical grained salt. 



By-Products of the Sea-Salt Industry 



Although salt has been produced by the solar 

 evaporation of sea-water since prehistoric times, no 

 use had been made of the bittern or mother liquor 

 from the crystallization of salt until about 1850. 

 In that year an unusually clever chemist named 

 Balard worked out a process of separating potas- 

 sium chloride, magnesium chloride, sodium sulphate, 

 and bromine from the bittern. Despite the fact that 

 the science of chemistry has made great advances 

 since that time, Balard's process is still in use at 

 Giraud, France. Many chemists have studied the 

 problem, but no one seems able to get more from the 

 mother liquor than Balard. The procedure followed 

 by him is rather complicated; on this account his 

 process has not been adopted elsewhere. 



In California, bath-salts, magnesium chloride, 

 magnesium oxychloride cement, and artificial stone 

 are produced from the bittern. Magnesium oxychlo- 

 ride cement is a valuable product used in the prepa- 

 ration of composition floorings, artificial stone, 

 cement for joining metal to glass, and for other ad- 

 hesive purposes. It is prepared by mixing finely 

 powdered, dry, calcined magnesite and dry mag- 

 nesium chloride; or, if it is to be used immediately 

 after preparation, it may be made by mixing cal- 

 cined magnesia with an aqueous solution of mag- 

 nesium chloride. 



