Table I gives an estimate of the micrograms of other elements initially present with 0.01 <g of pe Only the elements listed above boron are expected to be present in equal or larger amount. Interference by quenching from calcium, manganese, lead, chromium and tron is not to be expected since their estimated amounts are too low by a factor of 10° for iron, 107 for calcium and still larger factors for the others. The emount of uranium in the individual sample is expected tc be about 100 ' g. . Table I Element “ g present/O.0l_ U (tracer) CF] mw oe a we At; Cf --. Fe (barge) 0.1 cl 9. Na 5. Mg 0.6 S 0.45 Ca 0.2 K U . 0.2 Br 0.035 C 0.015 Sr 0.006 B 0.0025 Si, PF, Al, Ru, Li <0.0012 P, Ba, ¢€ 0.00005 I, As, Fe Mn, Ca, Za, Fo, Se <0.000005 U (sea water) 0.000075 | Others >. Procedure for determinetion of Uranium a. Eveporetion Step. Take an accurately measured aliquot of the solution of the filter paper sample chosen to contain approximately 2 ~«g of Wc @ a