300 ASH. [CH. XV 



Phosphoric acid. 



A weighed quantity of the ash is dissolved in dilute 

 nitric acid and filtered. 



The phosphoric acid in the filtrate is precipitated with 

 ammonium molybdate. The precipitate is collected, 

 washed and dissolved in ammonia ; the phosphoric acid in 

 the ammonia solution may be estimated volumetrically by 

 a standard solution of uranium acetate, after precipitating 

 with magnesia mixture and dissolving the precipitate in 

 dilute acid. 



See Sutton, Volumetric Analysis, pp. 238 247. 



Alkalies. 



A weighed quantity of the ash is boiled with hydro- 

 chloric acid and filtered. The filtrate is evaporated till 

 nearly all free acid is removed, and baryta water added in 

 slight excess ; filter, after heating for some time on the 

 water-bath : the filtrate will only contain the alkalies and 

 barium salts as the other constituents are precipitated. 



Add sufficient ammonia and ammonium carbonate to 

 precipitate all the barium, let the precipitate subside and 

 filter : evaporate the filtrate to dryness in a platinum dish 

 and ignite till all ammonium salts are expelled. 



Weigh the residue (chlorides of sodium and potassium). 

 If it is desired to ascertain the amounts of sodium and 

 potassium the residue can be dissolved in water after 

 weighing, and the chlorine determined by standard solution 

 of silver nitrate. The weight of the two chlorides and of 

 the chlorine being determined the proportions in which 

 Na and K are present can be calculated. 



