Place 50 mg of powdered iron(II) sulfate (this is a large excess) in a
10 75-mm test tube, add 0.5 mL of the alkaline solution from the fusion,
heat the mixture gently with shaking to the boiling point, and then—without
cooling—acidify with dilute sulfuric acid (hydrochloric acid is unsatisfactory).
A deep-blue precipitate indicates the presence of nitrogen. If the coloration
is dubious, filter through a 2.5-cm funnel and see if the paper shows
blue pigment.