Salt, the general name for sodium chloride (NaCl). It occurs either as bay salt from the artificial or recent evaporation of seawater or as rock-salt, in beds resulting from such natural evaporation in past geological times. In seawater it varies in proportion from under 3 per cent. in polar seas to over 3.5 per cent. at the equator. This sea-salt is still the chief source of the salt of commerce in many dry countries such as France; Spain, Portugal, and Austria. Being generally impure, It is known in France as sel gris ("grey salt"). In its gradual concentration the seawater deposits many of the double potassium and magnesium sulphates and chlorides which occur associated with rock salt in the mines at Stassfurt in Saxony. Rock-salt occurs in beds of almost every geological formation, from the Salina group of the Silurian in Canada, the Permian of Middlesborough, Yorkshire, and the Hala (Salt) range in Sindh, and the Trias of Cheshire and Salzburg, to the Cretaceous of Wieliczka, in Galicia, and even more modern deposits. It is often associated with bitumen, and almost invariably with gypsum, and much salt is pumped to the surface as brine. This has led to extensive subsidences in Cheshire and elsewhere, and the formation of lakes or "meres." The salt occurs pure white, ochreous, blue, violet, green, or other colours, and crystallised in cubes or in ho11ow cubes of remarkable construction. [CRYSTAL.] It is 2 in the scale of hardness. We export over a million tons annually, mostly from LIverpool, India and the United States between them taking more than half that amount. As mineral or supplementary salt is not requisite to a dietary of milk and raw or roast meat, but is so to cereal or vegetable food, many primitive nomadic peoples have done without it, whilst its use has come in with agriculture. Salt thus also early became, and remains, an important article of commerce, many old trade routes being created by this traffic, such as that between Syria and the Persian Gulf by way of Palmyra, a place celebrated for its salt. Cakes of salt have been used as money in Abyssinia, in Thibet, and elsewhere, and Government monopolies or heavy taxes on the trade have been very genera1. Its value to health has invested it with a quasi-sacred character, so that Homer calls it "divine," and among many nations, ancient and modern, it is a sign of hospitality and of the bond of honour thereby created.