Chlorine, a dense, greenish-yellow gas, was discovered in 1774. It has a choking smell and is very poisonous. It occurs as the chloride ion, Cl-, in sea water and salt lakes, from which sodium chloride is recovered by solar evaporation.

Commercially, chlorine is prepared by the electrolysis of aqueous sodium chloride obtained from seawater or salt deposits. Another process for the production of chlorine is the Chloralkali Process.

Common usage of chlorine includes:

It should be noted that manufacturers and suppliers of chemicals refer to solid hypochlorites and other chlorinating agents as "chlorine". Chlorine is a greenish-yellow gas, not a white powder.

Take a look at the Chlorine Chemistry Web site.

BCIT Chemistry Resource Center
http://nobel.scas.bcit.ca/resource/