18 Chemical Examination of American Minerals. 



rate the liquid which lias passed through the filter to dryness, 

 and re-dissolve the residual salt in water. A little carbonate 

 of magnesia will remain : the whole of the magnesia thus ob- 

 tained, is to be put into a platinum crucible, and exposed to 

 a strong red heat. It is now pure magnesia. 



When a mineral which contains a fixed alkali requires to 

 be heated with carbonate of soda, in order to render it solu- 

 ble in muriatic acid, the best way of proceeding, is to deter- 

 mine all the other constituents (except the alkali) by the 

 methods just described. To obtain the alkali proceed in 

 this manner. Twenty-five or thirty grains of the mineral are 

 reduced to an impalpable powder, and mixed intimately in a 

 platinum crucible, with a quantity of pounded fluor-spar, equal 

 in weight to 2i times the weight of the silica contained in the 

 mineral : this mixture is drenched with sulphuric acid, and 

 exposed for several hours to the heat of the sand bath. After 

 all evolution of fluosilicic acid is at an end, the crucible is 

 exposed for half an hour to a red heat, to drive ofi'the excess 

 of sulphuric acid, and to ensure a total decomposition of the 

 fluor spar. 



The dry matter is now digested in distilled water, till every 

 thing soluble is taken up. The solution after being mixed 

 with a solution of carbonate of ammonia, to throw down any 

 lime that may be taken up in the state of sulphate, and filter- 

 ed, is evaporated to dryness and heated to redness. What 

 remains is the alkali of the mineral united to sulphuric acid. 

 It is easy from the properties of the salt, to decide whether it 

 be sulphate of soda, or sulphate of potash. And the known 

 constitution of these salts, enables us at once to decide the 

 weight of alkali which the mineral contains. 



If the mineral contain magnesia, a portion of that earth in 

 the state of sulphate, may be mixed with the alkaline sulphate. 

 A good red heat will decompose this salt, and the magnesia 

 will remain when the alkaline sulphate is dissolved in water. 



