wooden shovels and placed in conical vessels with a hole in their lower part to drain off all the moisture; it is then dried by stoves and is fit for use; when no more salt falls down, the impure liquor, called “bittern,” is drawn off and used to procure Epsom salts from, by mixing it with sulphuric acid. The bittern contains chloride of magnesium, and the sulphuric acid changes it into sulphate of magnesia, which, when purified, forms the Epsom salts sold by druggists. About half a million tons of salt are made in England every year. Salt, besides its general use as a condiment, and in preserving food for storing ships, &c., is also used for several manufacturing purposes. By adding sulphuric acid and heating it, the acid called “hydrochloric” is given off, which is largely used for many purposes; but the chief use made of salt by the manufacturing chemist is to prepare soda for cleansing and soap making. STONE. Illustration: STONE QUARRY. Stone for building is chiefly of four kinds:--lime-stone, sand-stone, granite, and marble. Slate is never used for building, but is very suitable for roofing. The most common stone is limestone, and that brought from Portland Island is especially good for building-stone; it is called Portland stone, and it is of this stone that St. Paul’s Cathedral is built, and most of the other public buildings of London: it is rather soft when first dug from the quarry, but hardens with age. Sandstone is a very coarse kind of stone, and is only used where not much exposed to the weather; it consists of grains of sand adhering so firmly together as to form a stone of considerable hardness. Granite is a very hard stone, and very durable; so hard that it cannot well be carved, and is therefore only used where durability and plain solidity are required; London Bridge and the Euston Square Terminus of the Birmingham Railway are built of granite. Marble is a very fine heavy kind of limestone, sometimes quite white, and generally partly transparent; the white kind is very expensive, and is used for statuary, that is to say, for carving into figures, vases, &c.; it is very durable, but is too expensive for general use. Chimney-pieces, slabs for washing-stands, and other articles of that description, are also made of it. Limestone, marble, and also chalk (a soft kind of limestone), all become changed into lime if made red hot, hence the name, limestone, is often applied to all three.