In ammonium carbonate-nitrate solution, U (VI) forms an orange colored precipitate, {[Co(NH₃)₆]NO₃}₂UO₂(CO₃)₃, with hexamminecobalt (III) chloride. The precipitate dissolved in diluted hydrochloric acid gives orange coloration due to hexamminecobalt (III) ion. In neutral or acidic solution the complex salt decomposes with sodium sulfide and yields cobaltous sulfide precipitate which is extractable with nitric acid.
Utilizing these properties, the indirect colorimetric determination of 0.02510.0mg U (VI) in two different ways: measurement of absorbance at 473mμ for hexamminecobalt (III) ion and the colorimetric determination of Co (II) ion contained in the precipitate. For hexamminecobalt (III) photometry, disturbance of the method caused by the presence of Ca, Ni, Co, Cu, Pb, Cd, Fe, Bi and Th were studied. Furthermore, a radiometric determination was devised for the estimation of 0.0050.500mg U (VI) with the ⁶⁰Co tagged precipitant.