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LIMESTONE. 



Genus I.— LIMESTONE. 



Pierre d chaux,- chaux carbonate, Fr. ; Ossicarbonato di calce It.; 



Kalkstelr. Cier. 



Lime exists abundantly in nature in combination with carbonic or 

 sulphuric acids, and not unfrequently with the fluoric and phos- 

 phoric acids. It is also frequently combined with magnesia, but 

 more sparingly with the other earths. The common compact 

 limestone, and the varieties comprehended under the term Car- 

 bonate of Lime, is so common in every country, as to render any 

 description of its characters and geographical distribution unneces- 

 sary. Lime, which is medicinally used, may be procured in a very 

 pure state from Calcareous Spar. 



Sp. 1. Calcareous Spar. — Chaux Carbonatee, Hauy. 

 Kalkspath, Werner.— Its usual colours are white, tinged with 

 yellow, and it is found of various shades of red, blue, green, grey, 

 brown, and greyish black. It occurs massive, and in a great variety 

 of external shapes, also very frequently chrystalized. The primi- 

 tive form is an obtuse rhomboid; the secondary forms far exceeds 

 that of any other mineral hitherto discovered: Bournon has 

 enumerated 642, and many more might be described. It is 

 scratched by fluor spar, and yields easily to the knife. It is rather 

 brittle, and breaks into rhomboidal fragments. The specific gravity 

 is about 2-50. It is translucent or transparent; that of Iceland, 

 Pl. XLV., fig. 1., known under the name of Iceland Spar, is 

 double refractive in a high degree. According to Woollaston, its 

 constituents arc lime 50, carbonic acid 44. It occurs in veins 

 and strata in almost every kind of rock. 



Pure lime is obtained by exposing limestone, or calcareous 

 spar, to a strong heat. It is of a fine white colour, and is 

 moderately hard; it requires an intense heat for its fusion, and 

 has an acrid alkaline taste. It is sparingly soluble in water; and the 

 solution is the form under which it has been exhibited medicinally. 

 "Lime-water, as it is named, is used with advantage in dyspepsia- 

 its beneficial effects arise principally from its tonic and astringent 



