ALUMINA-ALUM. S3 



For the separation of baryta and strontia, neutral 

 chromate of potassa rnaj also be employed, which pre- 

 cipitates all the baryta as chromate; the latter is washed, 

 dried, ignited and weighed. It is necessary, however, 

 that the solution should be perfectly neutralized and 

 largely diluted. The strontia may afterwards be pre- 

 cipitated by neutral carbonate of ammonia. 



The neutral salts of lime, mixed with a solution of 

 arsenious acid, give with ammonia a precipitate of 

 arsenite of lime. The salts of strontia and baryta 

 treated in the same way do not form a precipitate. On. 

 the other hand, the presence of strontia in a salt of lirne 

 may be shown by a clear solution of sulphate of lime. 



16. ALUMINA-ALUM. 

 KO, S0 3 ; A1 2 3 , 3 S0 3 + 24 HO. 



A weighed quantity of the pure salt is dissolved in 

 water, and the sulphuric acid precipitated by chloride 

 of barium (see No. 3). 



From the solution filtered from the sulphate of ba- 

 ryta, the alumina is precipitated, together with the 

 excess of baryta which has been added, by a mixture 

 of carbonate of ammonia and free ammonia. After 

 gently heating for some time, the precipitate is filtered 

 off,. the solution evaporated, and the saline mass heated 

 till all the chloride of ammonium is volatilized. The 

 gently-ignited residue is chloride of potassium. 



The precipitate containing alumina and baryta is dis- 

 solved in dilute hydrochloric acid, and the baryta pre- 

 cipitated by sulphuric acid. 



From the solution filtered from the sulphate of 

 baryta, the alumina is precipitated by carbonate of 

 ammonia, or better, by sulphide of ammonium, either 

 of which effects a more complete precipitation than 

 caustic ammonia. 



