CHLORIDES OF POTASSIUM, SODIUM, ETC. 25 



sesquichloride of iron, and afterwards, with excess of 

 acetate of ammonia ; if the solution be now boiled for 

 some time, all the phosphoric acid and iron are pre- 

 cipitated, and the magnesia remains in solution. The 

 filtered liquid is evaporated, to dryness, the residue 

 heated till all ammoniacal salt is expelled and moistened 

 with sulphuric acid to convert the magnesia into sul- 

 phate. The excess of acid is expelled by heat, and the 

 residual salt gently ignited ; from the weight of this 

 residue. that of the magnesia, and consquently of the 

 phosphoric acid, is calculated. 



11. THE CHLORIDES OF POTASSIUM, SODIUM, AND 

 MAGNESIUM. 



In the analysis of minerals which are decomposed by 

 hydrochloric acid, there is .frequently obtained, after 

 the separation of the other constituents, a mixture of 

 the above-mentioned chlorides. The solution, if con- 

 taining, as is generally the case, ammoniacal salts, ^is 

 evaporated to dryness, and the mass gently ignited in 

 a platinum crucible until the latter are volatilized. The 

 magnesia and alkalies are then separated according to 

 one of the following methods : 



I. The mass is moistened with a concentrated solu- 

 tion of carbonate of ammonia, dried and ignited, during 

 which operation, a fragment of carbonate of ammonia 

 is held within the partially closed crucible. This pro- 

 cess is repeated until a constant weight is obtained. 

 A mixture of magnesia and alkaline chlorides is left, 

 from which the latter may be extracted by water. This 

 method is more difficult of execution in proportion as 

 more alkaline chlorides are present. 



II. The residue containing the three chlorides is 

 mixed in a platinum crucible, with some water and a 



3 



