Bromination of alkenes with Br2. The upper picture is about the pure bromine and the bottom picture is from a dilute solution in chloroform.
Elemental bromine is a great reagent, it usually reacts well in most cases and due its intense color and odor it could be easily detected in the reaction mixture.
Long ago they also used it to find out, that is there an olefinic (double) bond in the organic molecule or not. The test was easy: add the organic substance to a dilute, but still visible bromine solution in an organic solvent and if the color fades, you have a double bond somewhere in the molecule. What happens? RCH=CHR’ + Br2 → RBrH2C-CHBrR’ where R and R’ is an alkyl, aryl, or any other organic group.