Silver nitrate test for halogens. From left to right, these precipitates are silver chloride (AgCl), silver bromide (AgBr) and silver iodide (AgI). Chlorine, bromine and iodine are all halogens. The precipitates were formed by reacting silver nitrate (AgNO3) with solutions of halides (halogen ions). During the reactions the nitrate group becomes substituted with the halide forming a precipitate. The differences can be difficult to discern, but the use of dilute and then concentrated ammonia solution will progressively dissolve the chloride and then bromide precipitates.