TYPICAL SOLUTION OF PHOSPHORIC ACID 139 



amount of acetic acid to cause this turbidity to disappear. The 

 volume is then completed to one liter with distilled water. 



The uranium nitrate often contains some uranium phosphate 

 and some ferric nitrate. It is important that it be freed from 

 these foreign substances. This is secured by dissolving it in dis- 

 tilled water and precipitating it by sodium carbonate, which re- 

 dissolves the uranium oxid and precipitates the iron phosphate 

 and oxid. 



The filtered liquor is saturated with nitric acid and the uranium 

 oxid reprecipitated by ammonia. It is washed with distilled water 

 by decantation and redissolved in nitric acid, as exactly as possi- 

 ble, evaporated, and crystallized. 



The crystals are taken up with ether, which often leaves behind 

 a little insoluble matter. The solution is filtered, and the ether 

 evaporated. The salt which remains is perfectly pure. 



It frequently happens when the uranium nitrate has not been 

 properly purified that the solution, prepared as has been indicated 

 above, deposits a light precipitate of phosphate w^hich alters its 

 strength and affords a cause of error. 



Only those solutions should be employed which have been pre- 

 pared some days in advance and which have remained perfectly 

 limpid. The solution of uranium thus obtained contains uranium 

 nitrate, a little ammonium nitrate, a very small quantity of ura- 

 nium acetate, some ammonium acetate, and a little free acetic 

 acid. Its sensibility is the more pronounced as the acetates pres- 

 ent in it are less in quantity. It is important, therefore, never to 

 prepare the solution with uranium acetate. 



127. Typical Solution of Phosphoric Acid. In order to titrate a 

 solution of uranium, it is necessary to have a standard solution 

 of phosphoric acid ; that is to say, a solution containing a precise 

 and known quantity of that acid in a given volume. This solu- 

 tion is prepared by means of acid ammonium phosphate, a salt 

 which is easily obtained pure and dry. Sometimes it may con- 

 tain a small quantity of neutral phosphate, which modifies the 

 relative proportions of phosphoric acid and ammonia, and it is 

 indispensable to have its strength verified. The titer of the typical 

 solution should be such that it requires for the precipitation of 



