6.2 Place the flask (6.1) in a fume cupboard, add a small quantity of anti-bump granules (3.7) and then carefully add 25 ml sulphuric acid (3.9). Mix the contents of the flask and heat gently until boiling. Continue heating until dense white fumes of sulphuric acid are evolved for at least 15 minutes. Allow the mixture to cool and then carefully add 250 ml water. Allow to cool to room temperature and continue as described in 6.4.