LIME, or calcareous earth, predomi nates in most stones which are soft enough to be scratched with a knife. These are chalk, lime-stone, marble, spars, gypsum, or plaster-stone, and va rious others. As the lime is most fre quently combined with carbonic acid, it is usual for mineralogists to drop a small quantity of nitric acid upon the stones they are desirous of classing; and if they froth by the escape of the acid, they con clude that lime enters into the composi tion. To obtain pure calcareous earth, powdered chalk must be repeatedly boil ed in water, which will deprive it of the saline impurities it frequently contains. It must then be dissolved in distilled vine gar, and precipitated by the addition of concrete volatile alkali. The precipi tate, when well washed and dried, will consist of lime united to carbonic acid ; the latter of which may be driven off by heat, if necessary.
If chalk, marble, limestone, spar, or any other specimens of this earth, con taininfr earlInnie. 9,41 hp to env, tinned ignition, they give out carbonic acid and water, to the amount of nearly half their weight. The remainder, con sisting chiefly of lime, has a strong ten dency to combination, and attracts water very powerfully. The addition of water to lime produces a very considerable heat, attended with noise, and agitation of the parts, which break asunder ; a con siderable vapour arises, which carries up with it part of the lime; and a phosphoric light is seen, if the experiment be made in the dark. Lime thus saturated with water is said to be slaked. Water dis solves about one five-hundredth part of its weight of lime, and is then called lime-water. This solution has an acrid taste, and turns syrup of violets to a green colour. If lime-water be exposed to the open air, the lime attracts carbonic acid, and is by this means converted into chalk ; which, not being soluble in water, forms a crust on the surface, formerly called cream of lime, which, when of a certain thickness, breaks, and falls to the bottom : and in this way the whole of the lime will in time be separated. If the fire have been too violent in the burning of lime, the stones become hard, sono rous, and incapable of absorbing water with the requisite degree of avidity. This
effect seems to arise from part of the cal careous earth having entered into fission with the clay, flint, or other contaminat ing, earths, with which it forms a glass that covers and defends the rest.
The paste of lime and water, called mortar, has a degree of adhesion and duc tility, though much less than clay. When dry, it is more or less friable, like chalk. A mixture of sand, or broken earthen vessels, greatly increases its firmness, which it seems to effect by rendering it more difficult for the parts to be remov ed with respect to each other. When mortar is left to dry by the gradual eva poration of its superfluous water, it is very long before it obtains its utmost de gree of firmness. But if dry quick-lime be mixed with mortar, it gradually ab sorbs the superfluous water, and the mass becomes solid in a very short time. See MORTAR.
Lime has an affinity for tannin, whence it is probable that a portion of it is retain ed in tanned leather, perhaps not to the improvement of its quality. It has an edulcorative power with respect to ani mal oils, by combining with the putrid gelatine in them; but its action on them in forming a soap is too strong to admit of its being used for this purpose with ad vantage, unless in small quantities. Fea thers, however, may be very convenient ly cleaned, by steeping three or four days in strong lime-water, and afterward washing and drying them.
Though infusible in the strongest heats of our furnaces, it is nevertheless a very powerful flux with regard to mixtures of the other earths. These are all fusible by a proper addition of lime. Compounds are still more fusible ; for any three of the five well-known earths may be fused into perfect glass, if they be mixed to gether in equal portions, provided the cal careous be one of them.
The earthy part of animals is chiefly, if not altogether, calcareous : in most cases it is united with phosphoric acid, but fre quently with the carbonic.
Lim c.stone. The native indurated car. bonate of lime. It is usually more or less bluish from iron, and of a granulated frac ture ; and it is connected with lime by ig nition in lime-kilns, for the purpose of making mortar. See LIME ; also MOR TAR.