 gr.1.37, and heating the mass in a porcelain capsule until the chief part of the action is over, then distilling off in a retort two-thirds of the nitric acid ; three or four parts of nitric acid are afresh introduced into the retort, and the whole kept for two or three days at a temperature near to boiling point.After disengagement of gas has ceased, water is added to the residue, which forms a precipitate – the chrysammic acid.