lassaigne's nitrogen detection test

I was testing an organic dye for nitrogen today in lab.


First I added powdered ferrous sulfate (.2 g) and the mixture gave prussian blue precipitate. Then I boiled and cooled it. When I acidified the mixture using diluted sulfuric acid, the mixture cleared and only a few small blue crystals remained, when there should've been a bluish-green precipitate, ensuring the presence of nitrogen(organic dyes should contain nitrogen).


Where did it go wrong?


