LIMESTONE. 211 



drate or carbonate of baryta, and the process conducted 

 as in No. 80, the baryta and the other bases being pre- 

 cipitated from the solution by a mixture of ammonia 

 and carbonate of ammonia; after gently heating, the 

 precipitate is filtered off, the solution evaporated, and 

 the residue ignited, when chloride of potassium and 

 chloride of sodium are left. Or the analysis may be 

 made with a mixture of hydrofluoric acid and hydro- 

 chloric acid. 



112. COMMON LIMESTONE, HYDRAULIC LIMESTONE, 

 MARL. 



Carbonates of CaO, MgO, FeO, MnQ, with Clay con- 

 taining alkali, and sometimes 3 CaO, PO 5 . 



I. For the detection of the alkali, large fragments of 

 the mineral, when it contains carbonate of lime in pre- 

 dominating quantity, are placed in a charcoal fire, and 

 heated for half an hour to whiteness, when the clay, 

 which contains the alkali, is decomposed. 



The ignited mass is carefully freed from adhering 

 ash, powdered, exhausted with water, the solution mixed 

 with some carbonate of ammonia, evaporated, the pre- 

 cipitated carbonate of lime filtered off, the solution 

 acidified with hydrochloric acid, evaporated todryness, 

 and the residual chloride of potassium or sodium 

 heated to dull redness. If both salts be present, they 

 are separated by bichloride of platinum. 



II. From a portion of the mineral which has been 

 dried at 100 and weighed, the water is expelled by 

 ignition in a glass tube, and its quantity determined 

 by collecting it in a weighed chloride-of-calcium tube. 



III. The carbonic acid may be expelled from ano- 

 ther portion of the mineral by nitric acid in the appa- 

 ratus employed for testing potashes, and its amount 

 determined directly by the loss of weight. (Fig. 24.) 



