In its pure form, chlorine is a gas. It is one of the deadliest gases, but also one of the most useful! In nature, chlorine is part of compounds such as salt (natrium chloride).
Pure chlorine was originally prepared by a Swedish chemist called Karl Scheele in 1774. It is now made by passing a solution of salt through an electric current.
The first poison gas used in World War I was pure chlorine. The Germans used it on 22 April 1915. Then they and their allies used a variety of gases, all made from chlorine compounds.
During the Second World War, the Allies and their enemies had huge stockpiles of chlorine-based gases and other substances, but did not use them.
However, despite being so poisonous and dangerous, chlorine is useful to human health. Chlorine kills microbes and is an important part of antibacterials and disinfectants.
Most water purification systems contain chloride to kill any bacteria that survive the treatments. Only four-fifths chloride is used per 1,000,000 parts of water. This percentage is not harmful to humans, although the water may have a certain taste.
Chloride can be turned into a liquid by pressing or freezing. In its liquid form, chloride is transported in metal cylinders and also in tank-type machines.
Chlorine is used for bleaching and the preparation of bleaching powder. Under normal conditions, it is used in the papermaking process.
It is also used in the manufacture of dyes and, along with oxygen and potassium, is part of fireworks and some types of matches.
Carbon tetrachloride, a chloride derivative, is a non-explosive cleaning agent used in certain types of fire extinguishers. Chloride itself is also an important part of modern antiseptics.
