same as spring water, but liable to impregnation, owing to the land springs filtering through the walls, and conveying impurities into it. This is sometimes prevented by lining them with cast-iron cylinders, or by bricks laid in water-cement. Dr. Percival affirms, that bricks harden the softest water, and give it an aluminous impregnation. The old wells must, therefore, furnish much purer water than the more recent, as the soluble particles are gradually washed away. It contains a greater

proportion of earthy salts, and of air, and has a greater specific gravity than other

spring waters. Owing to the fact, that it contains a larger quantity of bicarbonate and sulphate of lime, than river water, it decomposes and curdles soap, and is then denominated hard water, to distinguish it from those waters which mix with soap, and are therefore called soft waters. The reason that hard water does not form a pure opaline solution with soap, is, because the lime of the calcareous salts, chiefly the sulphate, forms an insoluble compound with the margaric and oleic acids of the

soap. Here a double decomposition ensues, the sulphuric acid unites with the alkali of the soap, setting free the fatty acids, which unite with the lime to form an insoluble earthy soap. Hard water is a less perfect solvent of organic matter than soft water; hence in the preparation of infusions and decoctions, and for many economical purposes, as making tea and coffee, and brewing, it is much inferior to soft water, and for the same reasons it is improper as a drink in dyspeptic affections, causing irritation, and a sensation of weight in the stomach. The abundance of this earthy salt in the water of Paris, and London, of many parts of Switzerland and this country, cause uncomfortable feelings in strangers who visit these places.