218 DETERMINATION OF ALKALIES IN MINERALS. 



remains on the filter, except baryta and strontia, if they be 

 present in the mineral; but as these oxides are of rare occur- 

 rence in silicates no allusion will be made to them here. 



55. To the filtrate add carbonate of ammonia, and boil for 

 some time, when all the lime will be precipitated as carbonate; 

 add a few drops of a solution of carbonate of ammonia to the 

 hot solution, to be sure that all the lime is precipitated. Should 

 this be the case, filter; the filtrate will contain the chlorides 

 of the alkalies and chloride of ammonium. It is evaporated 

 to dryness over a water-bath in a small platinum capsule; the 

 capsule is carefully heated to expel the sal ammoniac, and 

 finally warmed up to 700 or 800° F. It is then weighted with 

 its contents, and the chlorides, if mixed, separated in the way 

 mentioned (45 and 46). The amount of sal ammoniac to be 

 expelled is quite small, not equaling the weight 'of mineral 

 originally employed. 



56. Nothing in analysis can be simpler or more speedy than 

 this process. Its constant accuracy still lacked some little to 

 render it perfect, as usually an amount of alkali remains be- 

 hind, represented by from two tenths to one per cent, of the 

 mineral used ; certainly a small amount, but still too much to 

 be omitted in an accurate analysis. This also must be arrived 

 at, and it can be accomplished in the following manner. 



57. After the fused mass has been treated with water filtered 

 and washed as in 54, the filter and its contents are dried ; the 

 latter are detached from the filter and rubbed up in a glazed 

 mortar with an amount of sal ammoniac equal to one half the 

 weight of the mineral, and reheated in a platinum crucible 

 exactly as in the first instance, treated with water, thrown on 

 a filter and washed, the filtrate added to that from the first 

 fusion, the whole treated with carbonate of ammonia, and com- 

 pleted as in 55. 



58. This second fusion complicates the method but little, 

 as the residue on the filter readily dries in a water-bath into 

 a powder that is easily detached from the filter, and the small 

 portion adhering to the latter may be disregarded, as the alka- 

 lies remaining rarely exceed more than one five-hundredth 

 of the whole mass, and in most instances not more than one 

 thousandth. In many analyses made one fusion sufficed for 

 the entire extraction of the alkalies; but as a few tenths would 



