| 摘要 |
<p>In obtaining ammonium sulphate crystals by evaporating solutions thereof or by forming ammonium sulphate (e.g. by reacting of ammonia and sulphuric acid) in a solution already saturated therewith, such solutions containing free acid and trivalent iron, aluminium or chromium ions, the shape of the crystals is controlled by the addition to the solution of oxalic acid or a salt thereof or substances giving rise to the same. Ammonium oxalate, sodium oxalate or calcium oxalate may be used as the additions. Preferably, the amount of oxalic acid or oxalate added is not more than is required to remove substantially the whole of the trivalent ions of iron, aluminium and chromium present in solution.</p> |
