30 MARINE PRODUCTS OF COMMERCE 



("flashes") into (a) steam that escapes from the upper part of the drum and 

 (b) concentrated hot brine, filled with "seed" crystals, that escapes from the 

 lower part of the drum into a mechanically raked grainer of large area. On the 

 brine surface of the grainer the seed crystals rapidly form small, thin-walled 

 hoppers, consisting of only a minimum proportion of apex cubes. Flash grainer 

 salt is light and fluffy and in mass has a "soft" appearance due to the volume of 

 thin-walled hoppers contained in it. When dried and screened the flash-grainer 

 product, viewed under a magnifying glass, appears to consist largely of thin, 

 splintered flakes which, of course, are the broken walls of the thin hoppers. 



The composite-salt grainer system operates by discharging dust salt from 

 refinery screens, or fine grained salt from a vacuum pan, into a steam-heated, 

 mechanically raked grainer in which concentrated brine is being evaporated at 

 moderate heat. This supercharging bunches the hopper crystals of the usual 

 medium-temperature grainer and the fine particles of added salt into more bulky 

 crystallii:ie units, resembling relatively coarse standard grainer salt. More rapid 

 evaporation produces a finer-grained aggregate. Composite salt has a ready market, 

 and the method used converts the dust salt into a better marketable product, 

 without the need of dissolving and re-evaporating it. The steam-grainer system is 

 one of the most flexible and adaptable of all salt-making systems because it can 

 make use of live steam to boil the brine and produce fine grained salt, or, at lower 

 temperatures, to produce any of the flaky or hopper crystal formations. It requires 

 less skilled labor than the vacuum system and can be operated at reduced capacity 

 by shutting down one or more grainers when desired, whereas vacuum pans should 

 operate only at full capacity. Mechanically raked grainers, equipped with surface 

 splashers or agitators, permit the sinking of hopper crystals at any given stage 

 of their growth. The finished product can be either quickly or slowly raked out so 

 as to closely control its physical characteristics. 



The direct-fired pan system is similar to the steam grainer. However, this sys- 

 tem has practically been discarded throughout the United States due to the danger 

 of the plates buckling by overheating when scale deposits on the hot surface 

 and the consequent high cost of upkeep. In addition this system usually heats the 

 brine unevenly, resulting in a badly mixed product. 



Solar salts, evaporated from brine obtained from wells, and sea water are mostly 

 coarse and heavy crystals, having the distinct characteristic shape of the original 

 hopper. When cracked, crude solar salt breaks into somewhat cubical particles; 

 finer grinding breaks it into jagged and sharp-edged grains. The smooth cubical 

 crystal form of vacuum pan salt and the flaky characteristics of steam evaporated 

 grainer salt are not present in the finely screened grades of solar salt. 



Refining by Rewashing. Only the very best solar salts can be converted into 

 high grade refined salts without recrystallization. Careful control of the ponds 

 during the evaporation season is required to produce a salt of suJBBciently high 

 quality. Consequently, only a few salines on the California coast make pure enough 

 solar salt to be refined by washing. 



The washing process is usually carried out in a revolving screen, two-thirds 

 submerged in an alkaline sodium chloride solution. After washing, the salt is 

 screened to separate the coarse from the fine grains, the latter being sold as fish salt. 

 The coarse salt, which is purer, is used for the preparation of higher-grade salt [i.e.. 



