148 The Phosphates of America. 



hydrofluoric acids manufactured by Messrs. Schleicher & Schuell. 

 These filter rapidly, retain the finest precipitates, and leave an ash 

 which in the No. 590, of 9 cubic centimetres diameter, for example 

 mly amounts to 0.00008 gramme. 



Phosphoric Anhydride (P 2 O 6 ). 



Twenty-five c.c. of the filtrate from the siliceous matter, repre- 

 senting 0.50 gramme of the phosphate, are placed in a beaker with 10 

 grammes ammonium nitrate. The solution is heated over a Bun- 

 sen or other smokeless flame, and when quite warm is treated with 

 150 c.c. of molybdic solution and well stirred. After digesting for 

 one hour at 70 C., it is filtered and washed with water three or 

 four times. The beaker in which the precipitation was made is now 

 placed beneath the funnel ; a small hole is made in the bottom of 

 the filter-paper with the point of the stirring-rod, and the precipi- 

 tate is washed from the filter into the beaker by means of a hot 

 mixture of water and ammonia (5 : 1). If this washing is skil- 

 fully performed, the amount of liquid used will not exceed 75 c.c. 

 in order to remove all traces of the ammonium-phospho-molyb- 

 date. 



The filtrate having been nearly neutralized by the careful addi- 

 tion of hydrochloric acid until the yellow color only disappears 

 with difficulty, is allowed to cool, and there are then added to it 

 very slowly, in fact, drop by drop, 20 c.c. of magnesia mixture, stir- 

 ring with a glass rod all the time. Finally, there are poured in 

 about 50 c.c. of strong ammonia, the mixture is again stirred, and 

 then allowed to stand for four, hours. The precipitate is collected 

 on an ashless filter, and the beaker is very thoroughly washed 

 with dilute ammonia by means of a rubber tip on the glass rod. 

 When all the liquid has passed through the filter, the latter is 

 washed carefully twice, by blowing the dilute ammonia down its 

 sides in a fine stream, and is then placed in the drying-oven. 

 When quite dry, it is removed from the funnel, folded care- 

 fully in order to prevent loss of its contents, placed in a tared 

 porcelain crucible, and ignited, at first very gently, but finally over 

 the most intense obtainable flame, for ten minutes, in order that 

 the residue may become white. The crucible is now covered, 

 transferred with the tongs to the desiccator, allowed to become 

 quite cold, and weighed. The weight of this magnesium pyro- 

 phosphate (Mg 2 P 2 O 7 ) X .6396 X 2 = phosphoric anhydride (P 2 O 5 ) 

 in 1 gramme of the material. 



