REAGENTS 183 



and then acid with acetic and then afterwards titrated with the 

 standard uranium solution. 



Conduct of the Uranium Method. The principle upon which 

 this method rests depends upon the fact, that uranium nitrate or 

 acetate precipitates uranium phosphate from solutions contain- 

 ing phosphoric acid and which contain no other free acid except 

 acetic. In the presence of ammonium salts the precipitate is 

 uranium ammonium phosphate having the formula PO 4 NH 4 UrO 2 . 

 The smallest excess of soluble uranium salt is at once detected 

 by the ordinary treatment with potassium ferrocyanid. 



Manipulation. In all cases the solution is first made slightly 

 alkaline with ammonia and then acid by a few drops of acetic 

 so that no free mineral acid may be present. 



1 i ) With liquids free of iron : 



If, on the addition of ammonium or sodium acetate, no tur- 

 bidity be produced, the liquid is free of iron and alumina. In 

 this case from 10 to 50 cubic centimeters of the solution con- 

 taining about one-tenth gram of phosphorus pentoxid are treated 

 with 10 cubic centimeters of sodium acetate, and afterwards 

 with a quantity of uranium solution corresponding, as nearly as 

 possible, to its supposed content of phosphorus pentoxid, and 

 heated to boiling. From the heated liquid, by means of a glass 

 rod, one or two drops are taken and placed upon a porcelain 

 plate and one drop of a freshly prepared solution of potassium 

 ferrocyanid allowed to flow on it. If no brown color be seen at 

 the point of contact of the two drops, additional quantities of the 

 uranium solution are added and, after boiling, again tested with 

 potassium ferrocyanid until a brown color is distinctly visible. 

 The quantity of the uranium solution thus having been deter- 

 mined, duplicate analyses can be made and the whole quantity 

 of the uranium solution added at once with the exception of the 

 last drops which are added as before. 



(2) Solutions containing iron and alumina. 



The solution is treated with the ammonium citrate solution of 

 Joulie, the magnesia mixture added slowly, and the precipitate 

 collected on a filter and washed with 2.5 per cent, ammonia. The 

 precipitate is then dissolved in nitric acid, made alkaline with 



