Bromine test for double bonds. Bromine solution can be used to detect for the presence of carbon-carbon double bonds within unsaturated organic molecules. Bromine atoms in the Br2 molecules are capable of adding across the double bonds. This type of addition is known as halogen-addition or halogenation. When this occurs, the orange-red colour of the bromine solution is decolourised. In this case, oleic acid (unsaturated fatty acid) undergoes addition with bromine solution.