TITRATION OF SOLUTION OF URANIUM 141 



phoric acid is verified by evaporating a known volume, 50 cubic 

 centimeters, for example, with a solution of ferric hydroxid con- 

 taining a known quantity of ferric oxid. The mass having been 

 evaporated to dryness and ignited in a platinum crucible, gives 

 an increase in the weight of the iron oxid exactly equal to the 

 amount of anhydrous phosphoric acid contained therein, both the 

 nitric acid and ammonia being driven off by the heat. 



To prepare the solution of ferric hydroxid, dissolve 20 

 grams of iron filings in hydrochloric acid. The solution is filtered 

 to separate the carbon, and it is converted into ferric nitrate by 

 nitric acid ; then the solution is diluted with distilled water and the 

 ferric oxid precipitated by a slight excess of ammonia. The pre- 

 cipitate, washed by decantation with distilled water until the 

 wash-water no longer gives a precipitate with silver nitrate, is 

 redissolved in nitric acid and the solution is concentrated or di- 

 luted, as the case may be, to bring the volume to one liter. 



In order to determine the quantity of ferric oxid which it con- 

 tains, 50 cubic centimeters are evaporated to dryness, ignited, 

 and weighed. 



A second operation like the above is carried on by adding 50 

 cubic centimeters of the standard solution of phosphoric acid, 

 and the strength of the solution thus obtained is marked upon 

 the flask. 



If the operation has been properly carried on, three or four du- 

 plicates will give exactly the same figures. If there are sensible 

 differences, the whole operation should be done over from the 

 first. 



130. Titration of the Solution of Uranium. In a 150 cubic cen- 

 timeter flask marked at 75 cubic centimeters, are poured 10 

 cubic centimeters of the standard solution of phosphoric acid 

 measured with an exact pipette ; five cubic centimeters of the acid 

 sodium acetate are added, and distilled water enough to make 

 about 30 cubic centimeters, and the whole carried to the boil- 

 ing-point. The titration is then carried on by allowing the solu- 

 tion of uranium to fall into the flask from a graduated burette, 

 thoroughly shaking after each addition of the uranium, and try- 

 ing a drop of the liquor with an equal quantity of a 10 per cent. 



