3.1 Distilled Water - Water that has been distilled and passed through a 0.2 µm filter. Commercially available distilled water may be used. Water produced from Reverse Osmosis or ASTM Types I, II, III, or IV can also be used. Use fresh distilled water from stock for each use. Note: Distilled water of the required purity may be obtained from drug stores or grocery stores.
3.2 Reagent grade concentrated nitric acid (supplied as a 70% solution) or concentrated sulphuric acid (supplied as a 98% solution).
3.2.1 To prepare 35% nitric acid: mix one part distilled water and one part concentrated nitric acid. Caution: Always add acid to water slowly with continual mixing.
3.2.2 To prepare 25% sulphuric acid: mix one part concentrated sulphuric acid with three parts distilled water. Caution: Extreme heat will be generated. Always add acid to water slowly with continual mixing.
