revolutionary France to Gandhi’s 1930 salt march to Dandi Salt Production People have been gathering crystalline salt since prehistoric times, both from the seacoasts and from inland salt deposits The rock-salt deposits, some of which are hundreds of millions of years old, are masses of sodium chloride that crystallized when ancient seas were isolated by rising land masses and evaporated, and their beds then covered over by later geological processes Until the 19th century, salt was produced mainly for the preservation and flavoring of foods Nowadays large amounts are used in industrial manufacturing of all kinds, as well as in the de-icing of winter roads, and salt production itself has been industrialized Most rock salt is now mined by solution, or pumping water into the deposits to dissolve the salt, then evaporating the brine down in vacuum chambers to form solid crystals While some sea salt is still produced by gradual solar evaporation from open-air salt pans in sufficiently warm, dry regions, much is now produced by more rapid vacuum evaporation Removing Bitter Minerals Salt comes from seawater, and seawater contains significant quantities of several bitter minerals, the chloride and sulfate salts of magnesium and calcium Producers have a couple of ways of dealing with these minerals They can remove them from rock salt by dissolving the salt, then adding sodium hydroxide and carbon dioxide to the brine to precipitate magnesium and calcium They can remove them from seawater by the same means, or else by slow and gradual concentration in open-air pans, during which the calcium salts become insoluble, crystallize, and settle before the ... the chloride and sulfate salts of magnesium and calcium Producers have a couple of ways of dealing with these minerals They can remove them from rock salt by dissolving the salt, then adding sodium... sodium hydroxide and carbon dioxide to the brine to precipitate magnesium and calcium They can remove them from seawater by the same means, or else by slow and gradual concentration in open-air... pans in sufficiently warm, dry regions, much is now produced by more rapid vacuum evaporation Removing Bitter Minerals Salt comes from seawater, and seawater contains significant quantities of several bitter minerals, the