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.
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.
It is manufactured by heating pitchblende with lime, treating the resulting calcium uranate with dilute sulphuric acid, and adding sodium carbonate in excess.