22 MARINE PRODUCTS OF COMMERCE 



Table 7. Density and Salinity of Sea Water Used in Salt Making in California " 



Date of D tv S "fi ^^^* 



Source Collection „t^ , ^ . (asNaCl) 



1912 ^^- ^'^-"''y (%) 



San Francisco Bay at Mount Eden Oct. 5 3.53 1.025 3.44 



San Francisco Bay at Alvaredo Oct. 8 3.12 1.022 3.34 



San Diego Bay Oct. 17 4.10 1.029 4.00 



Sea water 1.027 3.72 



All but three of the sea salt works of California are situated on San Francisco 

 Bay because a large area of level marl lies in proximity to it. This permits the 

 making of solar salt in ponds without danger of dilution through the leaks in the 

 bottom of the ponds. The salt works in this vicinity cover 25,000 acres. The aver- 

 age annual yield of salt from an 1800-acre plant is 25,000 tons. 



Procedure at San Francisco Bay. At high tide bay water is admitted through 

 a gate into the main canal. Archimedean screws propelled by windmills, centrif- 

 ugal pumps operated by gasoline engines, or electrically driven water wheels 

 pump the water into settling ponds which are at least eighteen inches deep. Here 

 the suspended matter settles to the bottom and preliminary evaporation takes 

 place. In the first settling ponds silica, alumina, and iron sulfide precipitate out; 

 in the secondary or lime ponds calcium carbonate and more iron sulfide come 

 down. Walls built within the ponds make the brine circulate as it passes through 

 the reservoirs. In the settling ponds a lively growth of green and brown algae, 

 diatomaceae, and bacteria are found. Larvae of the marsh fly and other insects 

 are numerous in these ponds; and in the ponds containing nearly saturated brine 

 "brine- worms" (a small crustacean Artemia salina) are found in enormous num- 

 bers. 



The brine passes from the settling ponds to the so-called pickling ponds in 

 which most of the calcium sulfate separates in brown, green, or yellow crystalline 

 concrements. In addition to calcium sulfate iron sulfide is found in the sediment 

 of the pickling ponds; this sulfide is probably formed by the reduction of the 

 sulfates by the organic matter. The brine remains in the pickling ponds until it 

 reaches a specific gravity of 1.198 to 1.2085 (23.97° to 25.0° Be.). By this time 

 practically all the gypsum has been deposited. Even at 1.194 sp. gr. (23.45° Be.) 

 there is no danger of deposition of gypsum on the salt crystals in the crystalUza- 

 tion ponds. However, due to the irregularities in the density of the brine, which 

 varies at times even within the same pond, brine of lower density than 1.198 sp. gr. 

 (23.97° Be.) is never used in the crystallizing ponds. 



As the concentration of the brine approaches saturation the brine-worms and 

 algae die and the solution becomes pinkish in color due to the growth of certain 

 red and pink bacteria. This change of color indicates that the brine is ready to 

 be transferred to the crystalhzation ponds. 



From the liming ponds the brine, or pickle as it is sometimes called, passes to 

 the crystallization ponds where the salt begins to crystallize at a density of 1.2104 

 sp. gr. (25.16° Be). When the ponds are filled to a depth of 10 or more inches, 

 large salt crystals are usually obtained. However, the temperature of the brine and 



* Phalen, W. C, "Technology of Salt Making in the United States," U. S. Bureau of 

 Mines Bull, 146 (1917). 



