56 THE WEALTH OF THE SEA 



sea-salt is refined by solution and recrystallization, 

 either in grainers or in vacuum evaporators, or pans 

 as they are usually called. 



Soft-grained, flaky salt may be prepared by re- 

 crystallizing solar sea-salt in steam-heated grainers. 

 The crude solar salt is dissolved in fresh water until 

 no more will be dissolved. This brine is limed and 

 allowed to settle ; it is then preheated and evaporated 

 in the grainers. A grainer consists essentially of a 

 long, narrow, shallow vat built of wood or metal 

 containing a number of pipes which carry the steam 

 required to evaporate the water. Automatic scraping 

 conveyers carry the salt to one end and then out of 

 the grainer. Curiously, this soft-grained, flaky salt 

 does not taste as salty as crushed solar salt or the 

 cubical vacuum-pan salt crystals. Dairymen prefer 

 this grade, as it mixes well into butter. When the 

 butter is eaten, the teeth do not grate on hard 

 crystals. 



Vacuum-pan salt is preferred for shaker-salt for 

 dining-table use. This may be produced by recrys- 

 tallizing solar salt in single or multiple-effect 

 vacuum pans. In the multiple-effect system, each 

 vacuum-pan (except the last one) acts not only as an 

 evaporator but also as a boiler producing steam for 

 boiling the brine in the next succeeding pan, and as 

 the condenser for the pan immediately preceding. In 

 such an apparatus one pound of steam may evapo- 

 rate several pounds of water. This arrangement is 

 made possible by having a slight vacuum on the first 

 pan and gradually increasing the vacuum on each 

 succeeding pan. Since the temperature of the satu- 



