MANUFACTURE OF SALT FROM SEA-WATER 53 



sediment on the bottom of the storage reservoir, and 

 the preliminary evaporation has taken place, the 

 dilute brine passes into a series of concentrating 

 ponds in which carbonate of lime and then gypsum 

 crystallize out. The brine is held in the last of the 

 concentrating ponds, called the pickling pond, until 

 all of the gypsum has crystallized. The "pickle" is 

 then nearly saturated with salt, and is run into the 

 crystallizing ponds. As long as the brine in the 

 crystallizing ponds continues to deposit pure salt, 

 it is permitted to crystallize. When impurities begin 

 to come down with the sodium chloride, the pickle 

 or mother liquor is drawn off and utilized for its 

 magnesium chloride content. About an inch of salt 

 is deposited for each six inches of net annual evapo- 

 ration; therefore in the San Diego Bay region the 

 annual deposit of salt is about eight inches. This 

 may seem like a shallow layer of salt, but an acre 

 of this depth yields 880 tons of salt. The pond area 

 of the California plants varies from 500 to 2000 

 acres. Crystallizing ponds constitute approximately 

 one tenth of the total area. 



Many of the San Francisco Bay plants are very 

 picturesque, as they have installed a considerable 

 number of small windmills to pump the brine from 

 one pond to another. The huge piles of salt as they 

 glisten in the sun look like mountains of snow mir- 

 rored in the ponds. 



In the smaller salines, the salt is harvested with 

 picks and shovels and is hauled to the piles in wheel- 

 barrows. The larger and more up-to-date plants use 



