METHODS OF ANALYSIS. 29 



SULPHURIC ACID, POTASSIUM, SODIUM, AND LITHIUM. 



Another portion of the silica filtrate is precipitated while boiling 

 with hot dilute barium chlorid, and after standing it is filtered from 

 the precipitated barium sulphate, which is washed, dried, burned, and 

 finally weighed in the ordinary manner. 



The filtrate is evaporated to dryness and taken up with water. This 

 solution is precipitated with a solution of barium hydrate and filtered 

 off from the insoluble magnesium hydrate. The magnesium hydrate 

 precipitate is well washed and the combined filtrate and washings 

 treated with ammonia, ammonium carbonate, and a little ammonium 

 oxalate to precipitate calcium and barium. This precipitate is allowed 

 to stand over night, is filtered off, and well washed. The filtrate and 

 washings are evaporated to dryness on the steam bath, dried, and all 

 the ammonium salts driven off by a gentle heat. The residue is taken 

 up with water, filtered through a small filter, using as little wash 

 water as possible, evaporated to a small volume, and finally again pre- 

 cipitated with a drop of ammonia and two to three drops of ammonium 

 carbonate and oxalate. If any precipitate appears, which is not usu- 

 ally the case, it is filtered off and the same process repeated. In any 

 case the solution is filtered from the magnesium hydrate that precipi- 

 tates out on concentrating the solution. The filtrate is then evaporated 

 to dryness and all ammonium salts driven off by heating in platinum 

 to a little below redness. The residue is taken up with a little water 

 and filtered through a small filter, again using as little wash water as 

 possible, and is again heated in platinum to a point slightly below red 

 heat. By this time all of the magnesia should be removed. The 

 residue is then taken up with a little water, filtered into a weighed 

 platinum dish, treated with a few drops of hydrochloric acid, and 

 evaporated to dryness. This residue is thoroughly dried, heated to a 

 little below redness, cooled in a desiccator, and finally weighed as the 

 combined chlorids of potassium, sodium, and lithium. 



The determination of lithium is then made according to the method 

 of Gooch ; a i. e. , the combined chlorids are dissolved in water and 

 transferred to a small beaker, where they are again evaporated practi- 

 cally to dryness. About 30 cc of amyl alcohol are added and the con- 

 tents of the beaker boiled until the temperature rises to approximately 

 the boiling point of the amyl alcohol, showing that all of the water 

 has been driven off. . The liquid is cooled slightly and a drop of hydro- 

 chloric acid added to reconvert small amounts of lithium hydrate to 

 lithium chlorid. The boiling is then continued to again drive off all 

 water, until finally the liquid reaches a volume of about 15 cc. The 

 amyl alcohol is then filtered off in a weighed platinum dish and the 

 filter washed by running a little amyl alcohol into the dish. The amyl 



Amer. Chem. J., 9: 33. 



