Solution and Separation.—The compounds of uranium are soluble in acids. Powder the substance and evaporate with an excess of nitric acid. Take up with hydrochloric acid, dilute, pass sulphuretted hydrogen, and filter. Peroxidise the filtrate with a little nitric acid, add an excess of ammonic carbonate and some ammonium sulphide, and filter. Render the solution acid, boil; and precipitate the uranium by means of ammonia. Filter off, and wash it with dilute ammonic chloride. Ignite, and weigh as protosesqui-oxide, U3O8.
GRAVIMETRIC DETERMINATION.
The solution containing the uranium free from other metals is, if required, first peroxidised by boiling with nitric acid. Ammonia in slight excess is added to the nearly-boiling solution. A yellow precipitate is formed, which is filtered off hot and washed with a dilute solution of ammonium chloride. The precipitate is dried and ignited; and weighed as U3O8, which contains 84.8 per cent. of uranium.
VOLUMETRIC METHOD.
This is based on the precipitation of uranium as phosphate from acetic acid solutions and the recognition of complete precipitation by testing with potassic ferrocyanide; it is the converse of the process for the volumetric determination of phosphate.
The standard solution of phosphate is prepared by dissolving 29.835 grams of hydric sodic phosphate (Na2HPO4.12H2O) in water and diluting to 1 litre. 100 c.c. will be equivalent to 2 grams of uranium.
Take 1 gram of the sample (or, if poor in uranium, 2 grams) and separate the uranium as described. Dissolve the precipitate in nitric acid and evaporate to a small bulk, add 2 grams of sodium acetate, dilute with water to 100 c.c., and boil. Titrate the boiling solution with the sodium phosphate till it ceases to give a brown colouration with potassium ferrocyanide. Calculate the percentage in the usual way.
FOOTNOTES:
[78] MnO2 + 4HCl = MnCl2 + Cl2 + 2H2O.
[79] Provided a sufficiency of ammonic chloride is present.