This mineral is found in nearly every country of the globe: but, in a native state, has not hitherto been discovered except in combination with some acid.[[3]] The process of purifying lime, or depriving it of the acid with which it is combined, is by burning. This is done in a large kind of furnace, called a kiln, where the limestone and fuel are heaped in alternate layers. After it has gone through this process it is called quick-lime, and has the above-mentioned appearance and qualities.
[3]. With carbonic acid ([26]) it forms common limestone, marble, chalk, and some other substances; with sulphuric acid ([24]) it constitutes alabaster, or gypsum; and with fluoric acid ([27]) it becomes that beautiful production, the Derbyshire spar.—All these, having lime for their bases, are denominated CALCAREOUS SUBSTANCES.
The uses of lime are numerous and important. The principal of these is in the formation of mortar, or cement for buildings. For this purpose it is first slaked, by having water poured upon it: a violent heat is thereby excited, and the lime falls into powder: it is then formed into paste by working it with water and sand. This, when dry, becomes extremely solid, hard, and durable. Various examples might be mentioned of buildings nearly two thousand years old, where the lime is, at this day, as hard as the stones which it cements together. Lime is also used for agricultural purposes: when spread upon land it is supposed to hasten the dissolution and putrefaction of all kinds of animal and vegetable substances, and to impart to it a power of retaining the moisture which is necessary for the vigorous growth of corn or grass. It is employed in the refining of sugar, in the manufacture of soap, in the melting of iron, and by tanners, in a state of solution, for dissolving the gelatinous parts of skins, and removing the hair from them. The manufacturers of glue mix it with that article, for the purpose of adding to its strength, and preventing its becoming flexible by the absorption of moisture. This mineral, if well dried, pounded, and mingled with gunpowder, in the proportion of one pound to two, is of great utility in the rending of stones and rocks: the mixture, it is said, will cause an explosion equal in force to three pounds’ weight of gunpowder. Lime, if swallowed or inhaled, is a virulent poison. Hence persons employed in lime-works are subject to very distressing complaints; and hence, if bread be adulterated with lime, it is extremely injurious. Notwithstanding this pernicious quality, lime is of considerable use in medicine. It is chiefly given in a state of solution, and in the proportion of half a pound of quick-lime to twelve pints of boiling distilled water. This preparation is called lime water.
The superb basin of Lampi, one of the principal reservoirs which furnishes the canal of Languedoc with water, was, some years ago, found to leak at the junction of the stones. The engineer who had the direction of the works caused lime to be slacked in the water. This, passing through the apertures betwixt the stones, formed a crust, or very white covering, over its whole surface, of so hard and durable a nature, that it now constitutes one solid and undivided substance, which the water cannot penetrate.
CARBONAT OF LIME.
140. COMMON LIME is a variety of carbonat of lime, or of lime in combination with carbonic acid ([26]), which is harder and heavier than chalk, usually of a greyish colour, and is always found in a massive state.
Vast mountains of limestone occur in several countries of the globe; but no where is lime more abundant than in some parts of England and Wales. It forms, in particular, nearly the whole mountainous districts of Derbyshire and Shropshire, and encloses, in its substance, numerous veins of lead ore, calamine, and other important mineral productions.
Its uses have been already described ([139]).
141. CHALK is a white or yellowish kind of limestone, too well known to need any description.
It is found abundantly in many of the southern counties of England, and is usually procured from large open places, called chalk-pits, by digging. In some parts of Kent, however, the workmen save themselves, in this respect, much trouble. They undermine the sides of hills to a certain depth, then dig a trench at the top as far distant from the edge as the mining extends at the bottom. This trench they fill with water, which soaks through during the night, and the whole mass is thereby loosened, and falls down before morning.