MODIFIED METHOD 615 



and reprecipitated, and the magnesia in the filtrate added to that 

 in the first filtrate. 



. Iron. For iron another aliquot portion of the original solution 

 is used, acidified with sulfuric, evaporated to drive off hydro- 

 chloric acid, rediluted and passed through the Jones reductor. 

 The filtrate is titrated with potassium permanganate solution in 

 the usual manner. 



Alkalies. For the alkalies another aliquot portion is precipi- 

 tated while. hot with barium chlorid and barium hydrate, filtered, 

 and ammonia and ammonium carbonate added to remove the 

 excess of barium salt. Refilter, evaporate to dryness in a plati- 

 num dish, and ignite gently to expel all ammonia salts ; repeat 

 this operation after taking up with water and finally heat to 

 constant weight. The weight obtained represents a mixture 

 of potassium and sodium chlorids, with usually carbon derived 

 from impurities in the ammonia. A little magnesia is often 

 present. The potassium is estimated by means of platinum solu- 

 tion, and the potassium chlorid found deducted from the total 

 weight gives the sodium chlorid. The carbon is usually un- 

 weighable, though it often looks as if present in considerable 

 quantity. It may be estimated, however, by dissolving the mixed 

 chlorids in weak hydrochloric acid and filtering through a gooch 

 before making the potassium estimation. The estimation of the 

 magnesia remaining with the mixed chlorids may be effected by 

 evaporating the alcoholic solution remaining after the precipita- 

 tion of the potassium to dryness, redissolving in water, placing 

 the solution in a flask provided with gas tubulures, introducing 

 hydrogen, and placing in the sunlight. The platinum is soon re- 

 duced, leaving the liquid colorless. Heating facilitates the re- 

 action. Displace the hydrogen by a current of carbon dioxid, 

 filter, concentrate the solution and precipitate the magnesia by 

 sodium phosphate in the usual manner. 



Phosphoric Acid. It is best to determine the phosphoric acid 

 directly in an aliquot part of the first filtrate from the hydro- 

 chloric acid solution of the ash obtained as described under the 

 determinations of sand, silica and carbon. When there is not 

 enough of the material for this, the precipitate of ferric phosphate 



