SALT. Chloride of sodium. Chemically, salt is a compound of one atom of chlorine and one of sodium, and occurs naturally in every part of the globe as a rock, interstratified with marls, sandstones, gypsum, etc. ; also as an element of springs and salt lakes; Salt Lake, in Utah, being the most remarkable of this latter, its water heing a saturated solution of salt. The propor tion of the constituents of salt are chlorine, 60.4 per cent. and sodium 39.6 per cent. Its impuri ties, as found in rock salt, are gypsum, oxide of iron and clay, chlorides of calcium, potassium and magnesium, and sulphates of soda and magnesia. The ocean contains notable quanti ties of salt, and is one principal source of the supply of salt by evaporation. A peculiarity of salt is its power of transmitting heat, clear rock salt transmitting ninety-two parts out of one hundred, while plate glass transmits but twenty f our parts. Salt is the only mineral substance universally regarded as an article of food by man, and the higher orders of the animal king dom. As a preservative also it is indispensable, and as a manure it is of growing importance, especially in inter-continental climates. In the
United States, the principal sources of supply are from the salt springs ot New York State, and those of Michigan, though more or less salt is manufactured in various States. In 1797, the first salt was made at Onondaga, New York. At least that was the first date of the lease; 25,474 bushels were manufactured in that year. In 1849, the amount was 5,083,369 bushels; in 1855, it was 6.082,885 bushels. Since then the quantity has fluctuated above and below these figures. Since 1860 the salines of Michigan have supplied the West with a large and increasing quantity of salt. The three principal salines of Michigan are the Salina, the Michigan salt group and the coal measures—of these the Michigan salt group supplies the largest number of productive wells. These salines lie at an average of about 800 feet, the brine being often at or near the saturation point, and practically inexhaustible.