This page is available here: http://www.saltinstitute.org/3.html
Excerpt:
Humans need salt to live. Prehistoric man obtained salt from the meat of hunted animals. When man developed agriculture, salt was added to supplement the vegetable and cereal diet and the quest for salt became a primary motivation in history. In the mid-1800s, salt's value as an important raw material for the chemical industry was established when the Solvay process in Belgium converted salt to synthetic soda ash. Salt is, today, the largest mineral feedstock consumed by the world chemical industry. A summary of a 1997 book, The Economics of Salt, is available online.
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