Bromine

Bromine and mercury are the only two elements that are liquid at 25 °C, and bromine is the only nonmetal among them: a heavy red-brown liquid at 3.1 g/cm³ that gives off a choking orange vapour. Antoine Balard isolated it in 1826 from the bitterns left after sea salt evaporation and the name comes straight from the Greek bromos, stench. Its most storied compound is far older: Tyrian purple, the dye reserved for Roman emperors, is 6,6′-dibromoindigo extracted from the glands of Murex sea snails at something like ten thousand animals per gram, which is why purple meant power. In the twentieth century bromine went into ethylene dibromide, the lead scavenger in leaded petrol, and then into brominated flame retardants; today it is drawn mainly from the Dead Sea and from Arkansas brines.