210 DETERMINATION OF ALKALIES IN MINERALS. 



sulphates the usual method must be adopted of throwing some 

 pulverized carbonate of ammonia into the platinum capsule or 

 crucible, and covering it up so as to have an ammoniacal 

 atmosphere around the salt, which will insure the volatilization 

 of the last traces of free sulphuric acid. The alkalies are now 

 in the state of pure sulphates, and may be weighed as such. 

 The manner of separating the alkalies from each other will be 

 mentioned further on. 



30. Thus far the mineral has been supposed to contain no 

 magnesia. If this alkaline earth be present, we take the res- 

 idue as found in the capsule (26), dissolve it in a little water, 

 then add sufficient pure lime-water* to render the solution 

 alkaline ; boil and filter ; the magnesia will in this simple way 

 be separated from the alkalies. The solution which has passed 

 through the filter is treated with carbonate of ammonia in the 

 manner alluded to (27), and the process continued and com- 

 pleted as described (28, 29). 



Summary.— Fuse one part of mineral with one of fluoride 

 of calcium and four to five of carbonate of lime ; dissolve out 

 the contents of the crucible with hydrochloric acid ; evaporate 

 to dryness and redissolve; precipitate with carbonate of am- 

 monia; filter, boil, and concentrate the filtrate; add nitric- 

 acid ; heat and evaporate to dryness ; dissolve the dry mass in 

 a little water and treat with carbonate of ammonia ; filter and 

 concentrate; then add sulphuric acid; boil for a little while; 

 pour in a platinum crucible, evaporate to dryness, and ignite. 

 If magnesia be present, treat with lime-water prior to the last 

 application of carbonate of ammonia. 



Conversion of the Sulphates into Chlorides. 



31. In continuation of the subject, the next point to be con- 

 sidered is the conversion of the sulphates of the alkalies into 

 chlorides. The method ordinarily adopted to accomplish this 

 change is to precipitate the sulphuric acid by means of chloride 

 of barium, care being taken to avoid the slightest excess of the 



* If lime-water be made, it is well to make it of lime of the best quality, 

 and the first two or three portions of distilled water shaken up should be 

 thrown away as containing the small amount of alkalies sometimes present 

 in lime. 



