Preparation of the solution for analysis
6.1 Weigh to the nearest 0.001 g, 5 g of the prepared sample and place it in a silica dish. Add 1 g calcium oxide (3.1)) moisten with water, mix thoroughly, evaporate the mixture to dryness and then transfer the crucible to a cold muffle furnace. Raise the temperature slowly to 450 ± 10°C and ignite for about 3 hours. Remove the crucible from the furnace, cool and add hydrochloric acid solution (3.4) until the resulting mixture is acid, then add 5 ml hydrochloric acid solution (3.4) in excess. Heat the mixture at 70°C for 15 minutes, cool and filter through a filter paper(1) into a suitable graduated flask washing both the dish and the filter with water. Make up to the mark with water and mix. Dilute an aliquot of this solution so that 3 ml contains between 5 and 25 kg of boron.
Whatman 42 or equivalent.