The precipitate, after having been collected and washed, is digested with a warm concentrated solution of ammonium carbonate, which dissolves the uranium as a yellow solution of ammonium uranate, while the hydrated oxide of iron, the alumina, &c., remain.
These are filtered off hot, and the filtrate is allowed to cool, when crystals of the uranate separate out.
The filtrate, on being boiled down, yields a second crop of uranate.
This uranate when ignited in a platinum crucible leaves a green oxide of the composition U308, i.e.
Sodium uranate, Na2U207, is used as a pigment for painting on glass and porcelain under the name of uranium yellow.