The uses of lime are very numerous. Its most important application is in the manufacture of mortar and other cements used in building. It is also very exten sively used in this country as a manure to fertilize land. But it is a curious fact that the use of lime as a manure is en tirely a European practice, its employ ment in this way having been never so much as dreamed of by the natives of Asia or Africa.
Native preparations of Cale Spar, in colorless crystals, is scratched by the nail. Spec. gray. 2.7.
2. Stalactitic, or concretionary carbon ate of lime, composed of fibrous bands, undulated and parallel. These are found in caves and vaults, being formed by the dropping of water highly charged with limestone and carbonic acid. That which remains on the roof is called stal actite, that which forms on the ground is called stalagmite, or oriental alabaster : its rings are spread out of a reddish yel low color, with distinct zones, and sus ceptible of a fine polish. This alabaster is made into furniture ornaments.
3. Calcareous tufa are incrustations of carbonate of lime upon vegetable remains made by the deposition of calcareous petrifying rivulets. It is porous, cellu lar, soft, impure, and of a dirty gray color ; it is rough and irregular. The incrustations are occasionally so large, that buildings are made of them. The travertino with which the monuments of Rome are made, are deposits from the Anio. They harden in the air.
4. Compact limestone has an even grain ; does not polish or afford large blocks—to this class belongs the Mag nesian limestone, or zechstem, in which the lithographic limestone is included according to Brogniart.
5. Oolite or roe stone, found in small grains of various size.
6. Chalk. Neither of these two varie ties exist to any extent on this continent.
7. Manly limestone, very common on clay slate lands, and in basin-shaped lakes, and fresh water formations. This crumbles in the air : it must not be con founded with common marl.
8. Siliceous limestone, compact, scrat ches steel ; leaves insoluble silica when acted on by hydrochloric acid.
9. Calp, fine grained, compact, hard, blue-black in color ; leaves silica and alumina when acted on by acid ; found in extensive beds.
10. Bituminous limestone, found near the coal formations ; of a blue color, burns white.
Of all common limestones the purity may be most readily determined by the quantity of carbonic acid which is evolved during their solution in dilute nitric or muriatic acid. Perfect carbonate of lime loses in this way 40 per cent. ; and if any particular limestone loses only 23 per cent., we may infer that it contains only one half its weight of calcareous carbonate. This method is equally applicable to marls, which are mixtures in various pro portions of carbonate of lime, clay, and sand, and may all be recognized by their effervescing with acids.
The chief use of calcareous stones is for procuring quicklime by calcination in proper furnaces ; and they are all adapted to this purpose provided they are not mixed with too large a proportion of sand and ferruginous clay, whereby they ac quire a vitrescent texture in a high heat, and will not burn into lime. Limestone
used to be calcined in a very rude kiln, formed by inclosing a circular space of 10 or 15 feet diameter, by rude stone walls 4 or 5 feet high, and filling the cyl indrical cavity with alternate layers of turf or coal and limestone broken into moderate pieces. A bed of brushwood was usually placed at the bottom, to facil itate the kindling of the kiln. Whenever the combustion was fairly commenced, the top, piled into a conical form, was covered in with sods, to render the calcin ation slow and regular. This method be ing found relatively inconvenient and in effectual, was succeeded by a permanent kiln built of stones or brickwork, in the shape of a truncated cone with the narrow end undermost, and closed at bottom by an iron grate. Into this kiln, the fuel and limestone were introduced at the top in alternate layers, beginning of course with the former ; and the charge was either al lowed to burn out, when the lime was altogether removed at a door near the bot tom, or the kiln was successively fed with fresh materials, in alternate beds, as the former supply sunk clown by the calcina tion, while the thoroughly burnt lime at the bottom was successively raked out by a side door immediately above the grate. The interior of the lime kiln has been changed of late years from the conical to the elliptical form ; and probably the best is that of an egg placed with its narrow end undermost, and truncated both above and below ; the ground plot or bottom of the kiln being compressed so as to give an elliptical section, with an eye or draft hole towards each end of that ellipse. A kiln thus arched in above gives a rever beratory heat to the upper materials, and also favors their falling down in propor tion as the finished lime is raked out be low ; advantages which the conical form does not afford. The size of the draft notes for extracting the quicklime, should be proportionate to the size of the kiln, in order to admit a sufficient current of air to ascend with the smoke and flame ; which is found to facilitate the ex trication of the carbonic acid. The kilns are called perpetual, because the operation is carried on continuously as long as the building lasts ; and draw-kilns, from the mode of discharging them by raking out the lime into carts placed against the draft-holes. Three bushels of calcined limestone, or lime-shells, are produced on an average for every bushel of coals con sumed. Such kilns should be built up against the face of a cliff, so that easy ac cess may be gained to the mouth for charging, by making a sloping cart road to the top of the bank.