S ° Wash the silica wita approximately 50 ml of hot 1:9 HNOz followed by several washes With distilled water. 13. Discard the precipitate. Transfer the filtrate to a 3 liter beaker and adjust the volume to approximately 1.5 liters with distilled water. 1h. Add 50 ems of oxalic acid with magnetic stirring until the salt is completely dissoived. 156 Adjust the pH to 5.5 - 6.0 with NH,OH. (If the brown color of iron (III) hydroxide persists, add more oxalic acid and readjust the pH.) Repeat if necessary. The optimum condition is an excess of oxalic acid in solution without causing crystallization of ammonium oxalate upon cooling. 16. Allow to stand for several hours, stir and filter with suction through @ 15 cm No. 2 Whatman paper. lf. Discard the filtrate. Transfer the precipitate and paper to an appropriate size nickel or platinum dish and dry overnight at 110°C. 18. Ignite the oxalate precipitate in a muffle furnace at 400-500 degrees C for 2 hours. Raise the temperature to~700 degrees C and continue heating for 2 hours. (Spattering is minimized by ignition in this manner. ) 19. | Cool the precipitate and transfer to an appropriate size beaker. Dissolve in a minimm of 1:9 ENOz.« 20. Cool to room temperature. Gently heat to boiling. Filter through the smallest convenient size glass fiber filter using suction, to remove the insoluble material. Discard the residue. ele Pour th: solution into a suitable size beaker and evaporate to dryness. Tat evatoration mizt be done slowly to avoid spattering. = 26 -