86 61. BASES AND ACIDS WITH REAGENTS. 



monia (Sp. Gr. = 0.96), wash out the filter wiih a mix- 

 ture of 3 parts of water and 1 of ammonin, and wash oif 

 what remams adhering to the walls of the beaker, in 

 Avhich the phospho-molybdate Avas precipitated, with a 

 little of the same ammonia water, or else collect this so- 

 lution of the whole precipitate in that beaker ; add di- 

 lute hydrochloric acid to the strong ammoniacal solution, 

 until the yellow precipitate, that appears with each drop 

 of the acid added, begins to dissolve again with some dif- 

 ficulty, showing that the ammonia is nearly neutralized, 

 then add the magnesia mixture as long as a precipitate is 

 produced, and the proper amount of the diluted ammonia, 

 and proceed as in a. 



Latschinow (JF'res. Zeitschrift 7, 215) asserts that this 

 precipitate of ammonio-magnesic phosphate must be fused 

 with potassic sodic carbonate, the fused mass extracted 

 Avith water, and this solution precipitated again with the 

 magnesia mixture in the usual manner, after addition of a 

 little citric acid. 



c. In the absence of at least all but small quantities of 

 iron and aluminium, phosphoric acid may be determined 

 with sufiicient accuracy for industrial purposes by a volu- 

 metric method, that depends upon the following reactions. 

 First, Avlien a solution of uranic salt is added to one of a 

 phosj^hate containing no other free acid than acetic, the 

 uranic oxide is immediately precipitated in combination 

 with phosphoric acid. Second, a solution containing the 

 least traces of uranic oxide gives a brown precipitate with 

 potassic ferrocyanide. 



Preparation of the standard sohitlo7is. 



1. Dissolve 12.6056 grms. of pure crystallized hydric 

 disodic phosphate, that does not show the least signs of 

 efliorescence, and has been thoroughly dried in powder 

 by pressure between folds of bibulous paper, in about 300 

 c.c. of water, and, when the temperature of the solution 

 is 15° C, make the volume up to exactly 500 c.c. with dis- 



