Polymerization

I would like to make the explosive polymerization with p-nitro aniline and sulfuric acid. I work in a laboratory and have access to the chemicals. I have seen several videos on Youtube and it looks awesome... When I try nothing happens, even after 10 minutes of heating. I have mixed 2 sp of the aniline and approximately 1 ml acid. I heat with a bunsen burner. Any good suggestions why it won't work? Best regards Jørgen