Paragraph 7 PRECIPITATION OF THE CALCIUM OXALATE

Add approximately 100 ml of water. Bring to the boil, add 8 to 10 drops of indicator solution (4.8) and, slowly, 50 ml of the hot ammonium oxalate solution (4.4), stirring constantly. If a precipitate forms, dissolve by adding a few drops of hydrochloric acid (4.1). Neutralise very slowly with ammonia solution (4.3) while stirring continuously to a pH of 4.4 to 4.6 (change of indicator (4.8) from green to blue). Place the beaker in a boiling hot water bath (5.2) for approximately 30 minutes.

Remove the beaker from the bath, leave standing for an hour and filter through the crucible (5.1).