molybdenum to Mo(VI). A measured aliquot of the sample solution is added to a measured aliquot of previously analyzed ammonium molybdate solution. After thorough mixing, the solution is brought to pH 5 with ammonium acetate -acetic acid buffer, and 0.1 M Pb(NO, )2 solution is added to precipitate the molybdenum lead molybdate. The sample is centrifuged and the supernatant is discarded. The precipitate is dissolved in $ M HCl! and the solution is poured through a column packed with anion exchange resin (Dow Chemical Company Resin "Dowex A-1"'), previously treated with 9 M HCl. When all the active solution has passed through, the molybdenum is located in an adsorbed band at the top of the resin column. The following solutions are then passed in turn through the column to remove impurities: 0.1 MHC}; 1 mi. H,0; 10 milliliters (ml.) of 9 MHC1; 10 ml. of 5 ml. of 3 M NH,OH; l ml. H,0. The molybdenum is then removed from the resin by passing through 15 ml. of 4 M HNO,. A few drops each of sodium tungstate solution and silver nitrate solution are added to the eluate and the solutions mixed, then sufficient dilute hydrochloric acid is added to precipitate the added silver as silver chloride, The solution is digested in a hot-water bath to coagulate the mixed precipitates of tungstic acid and silver chloride and the precipitates are centrifuged off and discarded. The tungsten and silver precipitations are repeated. A small quantity of a so- lution containing Fe?}, La’, Tet# and zr*4 is then added to the supernatant and precipitated with NH,OH at pH 10 or higher for further decontamination. The precipitate is rejected. More Fe? and La? are added to the supernatant (which is ammoniacal) and the resulting precipitate rejected. The supernatant solution is then acidified with acetic acid to pH 5 and 0.1 M Pb (NO,), solution is added to precipitate the molybdenum as lead molybdate. is washed with water and acetone and dried. The precipitate . The dry precipitate is transferred to a weighed aluminum dish, the dish and contents are re-weighed, and the precipitate fixed in place by a few drops of diluted lacquer. difference. The weight of recovered lead molybdate is determined by The small dish is fastened with adhesive tape to a support suitable for insertion into the counting equipment and is counted once or twice daily for several days. The lacquer must be thoroughly dry before the counting is started, since the lacquer solvent exerts a pronounced effect on the counting rate. SUL GEE - 54 - &