Common use of Heavy Metals Clause in Contracts

Heavy Metals. Place 2.0 g of NM441 in a porcelain crucible, cover loosely with a lid, and carbonise by gentle ignition. After cooling, add 2 mL of nitric acid and 5 drops of sulphuric acid, heat cautiously until white fumes no longer are evolved, and incinerate by ignition between 500°C and 600°C. Cool, add 2 mL of hydrochloric acid, evaporate to dryness on a water bath, moisten the residue with 3 drops of hydrochloric acid, add 10 mL of hot water, and warm for 2 minutes. Then add 1 drop of phenolphthalein TS, and add ammonia TS dropwise until the solution develops a pale red colour, add 2 mL of dilute acetic acid, filter if necessary, and wash with 10 mL of water. Transfer the filtrate and washings to a ▇▇▇▇▇▇▇ tube, and add water to make 50 mL. Designate it as the test solution. The control solution is prepared as follows: Evaporate a mixture of 2 mL of nitric acid, 5 drops of sulphuric acid and 2 mL of hydrochloric acid on a water bath, further evaporate to dryness on a sand bath, and moisten the residue with 3 drops of hydrochloric acid. Hereinafter, proceed as directed in the test solution, then add 2 mL of Standard Lead Solution and water to make 50 mL. Add 1 drop of sodium sulphide TS to each of the test solution and the control solution, mix thoroughly, and allow to stand for 5 minutes. Then compare the colours of both solutions by viewing the tubes downward or transversely against a white background. The test solution has no more colour than the control solution (not more than 10ppm). Reagents •