158 § 93. SPECIAL METHODS OF ANALYSIS. 



taining excess of ammonia, let the precipitate settle, filter, 

 evaporate to dryness, and ignite ; dissolve the residue in 

 water, and precipitate again with ammonia and ammonic 

 carbonate, filter, evaporate to dryness, and ignite; and re- 

 peat tliis operation as long as these reagents cause any 

 turbidity ; finally, ignite gently, weigh the alkaline chlo- 

 rides thus obtained, and determine potassium and sodium 

 in the mixture by the indirect process (§ 46 d)^ or, if greater 

 accuracy is desired, precipitate potassium with platinic 

 chloride (§ 46 h), 



(2.) Precipitate the SO3 in the boiling solution with 

 baric chloride in slightest possible excess, if this has not 

 already been done, evaporate the mixture on the water- 

 bath until most of the free acid is removed, add some wa- 

 ter and then ammonia and ammonic carbonate as long: as 

 a precipitate is formed, and finally a little ammonic oxa- 

 late, digest on the water-bath, filter, and wash the contents 

 of the filter carefully. Evaporate the filtrate and wash- 

 ings to dryness (§ 37), ignite the residue to expel ammo- 

 niacal salts, weigh roughly, and add a quantity of a con- 

 centrated solution of pure oxalic acid thixt contains enough 

 of the acid to make quadroxalate with an amount of po- 

 tassa equivalent to all the bases present, evaporate to dry- 

 ness, and ignite again. By this process, magnesia and 

 traces of lime, baryta, ferric oxide, etc., that may possibly 

 be present, are rendered insoluble in Avater. Treat the ig- 

 nited residue with a small quantity of boiling water, throw 

 it on a filter, wash it with several small portions of boiling 

 water, as long as anything is dissolved, add hydrochloric 

 acid in slight excess to the filtrate and washings, evaporate 

 to dryness, and ignite the residue of alkaline chlorides 

 gently, weigh, and determine potassium and sodium by 

 the indirect process (§ 46 d), or with platinic chloride 

 (§ 46 h). 



If, when these chlorides are dissolved in water, a clear 

 solution is not obtained, or if the solution has a basic re- 



