CARBONATES. 387 



GENERAL CHARACTERS OF THE CARBONATES OF LIME. 

 a.) Do not scintillate, if pure. 



(a.) 

 (*0 



b.) Insoluble in pure water. 



c.) Effervesce with acids generally, but unequally.* 



d.) Become quick lime by a strong heat. 



e.) Sp. gr. under 3., generally not over 2.7. 



f.) Every variety of aggregation, from compact, and even earthy, 

 to perfect crystals, which are much diversified in form. 



(g.) The crystals of all pure calcareous carbonates, between 600 

 and 700 in number, have a rhomboidal nucleus, whose faces are 

 inclined at angles of 75 55' and 105 5'. 



3. CHEMICAL PROPERTIES. 



(a.) Caloric. Native crystallized carbonate decrepitates with 

 heat. Ignition separates the carbonic acid gas^ and the watery 

 vapor, and caustic lime remains. By strong ignition, it loses .44 or 

 .45 in weight, about .44 of which is acid. 



(b.) That the causticity of lime is owing to the loss of carbonic 

 acid, was discovered by Dr. Black in 1756. 



(c.) This gas in contact with caustic lime, renders it again mild 

 and effervescent,{ and restores the weight lost by the furnace. 



(d.) Not affected by air nor water. 



(e.) Soluble in liquid carbonic acid. If saturated with the acid, 

 water dissolves T jV f carbonate of lime. Lime water is a most 

 sensible test of carbonic acid, producing a milky appearance, and 

 carbonate of lime precipitates ; but if more carbonated water be ad- 

 ded, the precipitate is redissolved, and the fluid becomes again trans- 

 parent. 



(/.) If the excess of carbonic acid be saturated by more lime 

 water, or by ammonia, the carbonate of lime is again precipitated. 

 It is precipitated also bjr boiling, and by air pump exhaustion. 



(g.) The formation of stalactites, and stalagmites, and calcareous 

 incrustations of various forms, in caverns and veins, and of calcare- 

 ous petrifactions, and the precipitation of the carbonate in a crys- 

 talline or sub-crystalline form, as the water and gas evaporate, de- 

 pend upon the solution of limestone, by liquid carbonic acid. In 

 limestone countries, carbonate of lime is dissolved in the waters, usu- 



* Some carbonates, especially of earths, require to be finely pulverized. 



i Sir James Hall, by some very ingenious experiments, on carbonate of lime, as 

 to the effects of pressure in counteracting those of heat, succeeded in melting that 

 substance, and causing it to crystallize again, without losing its carbonic acid. Edin. 

 Trans. Vol. VI. part I. Nicholson's Jour. Vol. XIII, XIV. 



Mr. Bucholz also melted the carbonate of lime by the sudden application of a vio- 

 lent heat, without compression. Nicholson's Jour. XVII, and Henry, Vol. I, p. 

 588, 10th Ed. 



t The lime should be moist, or in the state of cream of lime, or least of the hy- 

 drate, as the gas is not readily absorbed by the dry earth. 



