UNCLASSIFIED 1S. Remove the silica from the filter paper and dry ina 110°C over overnight. Break up the aggregated material with a mortar and pestle, then transfer to a 250 mi platinum dish. 16. Moisten the silica with 10% H,S0,, then add about 100 ml of HF. 17. Evanorate on a sand bath to SO3 fumes to volatilize the silica. Cool and dilute with distilled water, transferring the result- ing solution to the original soil filtrate, and add 20 mg Sr** carrier. 18. Neutralize the filtrate with NaOH pellets until the pH is h-u.5. At this point add slowly, with stirring, 50 grams of NazCO3z and allow the precipitate to settle. Filter through No. 5 Whatman paper with suction and discard the filtrate. When the precipitate is dry, remove from the filter paper and transfer to the original beaker. Dissolve in 200 ml of concer~ trated HCl and evaporate slowly to dryness. Do not bake. 20. Now add 460 ml of distilled water and stir mechanically wmtil él. Add slowly, 1540 mi of 90% HNO, 226 Allow to settle until the supernatant is clear, then decant as much 75% HNOs as possible. the residue is completely dspersed. with continuous mechanical stir ring and allow to remain stirring for 1/2 hour. Transfer the precipitate and remaining acid to a 20 ml centrifuge bottle, centrifuge and decant, discarding the supernatant. Carry out another 75% HNO, separation using a volume of 200 ml. At this point the bulk of the calcium should be removed leaving strontium nitrate and insoluble material. Add 10° mi of hot distilled water to the precipitate, centrifuge and decant ints a 250 ml beaker. 26. Wash again with 50 ml of hot distilled water adding the suvernatant liquid to the beaker after centrifugation. The residue can now be discarded. C7. Evaporate the filtrate slowly to dryness. ma 57 UNCLASSIFIED