Life depends on it, industry can't do without it, and five books have had a lick in the last few years. The staple is salt, here seen as formed in surface deposits and underground beds; as a catalyst in the French Revolution, India's fight for independence, Napoleon's rout from Russia, at length as the lack of the Confederacy; also as made--first by the ancient Chinese, and, little differently, by the infant American salt industry. Reaching the present, a well-illustrated section explains underground mining, ""hydraulic mining,"" solar evaporation, then follows salt through processing till it's 99.99% pure. Last are ""everyday uses""--in general (66% to the chemical industry, only 5% for flavoring) and for special purposes (preventing goiter, making rain, etc.). Froman's The Science of Salt is far more technical, Vander Boom and Brooks are younger (and variously deficient); only Olive Burt's The First Book of Salt (unavailable for re-examination), comes 'close--both are well-conceived, well-executed and comprehensive. Some of the historical material here is unique, and it all makes agreeable reading.