nitric acid may be required to keep the reaction under control. As long as the addition of concentrated nitric acid produces noticeable nitrogen dioxide fumes, small additions are made periodically. e. When the reaction is complete, the mixture is fumed down to ap- proximately 20 ml, cooled, and 20 ml of 6 normal hydrochloric acid is added. The beaker walls are rinsed thoroughly with the hydrochloric acid and the solution diluted with one-half volume of water and cooled. f. The contents of the beaker are filtered through fine filter paper to remove any solids, and the filter paper washed with a few ml of 6N hydrochloric acid. g. The filter is transferred to the Vycor beaker and wet-ashed with 50 ml of concentrated nitric acid and 30 ml of concentrated perchloric acid. The solution is then evaporated until fuming begins. h. The solution plus any precipitate is transferred to the platinum crucible, and the beaker washed with 2N perchloric acid. Five ml of con- centrated hydrofluoric acid is added and the solution fumed to heavy fumes of perchloric acid for several minutes. hydrochloric acid is added. The solution is cooled, and 6N The solution is then transferred to a 40-ml centrifuge tube and centrifuged. i. Any residue remaining after this step (usually there is none) is subjected to a sodium carbonate fusion using 1 gram of sodium carbonate and fusing for 10 minutes at 900 - 950 °C. 4. Uranium Analysis of Filter Paper Samples a. Introduction, Since the observation by Nichols and Slattery in 19261! that small amounts of uranium fused in sodium fluoride give an intense yellow fluorescence, measurement of this property has been widely used for the quantitative determination of uranium, particularly in the 0.001 to 1 microgram range. Reference should be made to the reviews ro MY - ~ WS ~ 4 of Rodden, le and to the reasonably comprehensive article of Price, Ferreti and Schwartz 13 , ; Co ; er for detailed information in regard to this determination and ‘le. Nichols and M. K. Slattery, J. Opt. Soc. Amer. 12, 449 (1926). — I2C¢. J. Rodden and J. C. Warf, National Nuclear Energy Series, Div. Vill, 1, "Analytical Chemistry of the Manhattan Project'', McGraw-Hill, pp. 122-135 (1950), 3G. R. Price, R. J. Ferretti and S. Schwartz, Anal. Chem. 25, 322 (1953). ~ 43 -