In 1774, in his small experimental laboratory, Swedish pharmacist Carl Wilhelm Scheele released a few drops of hydrochloric acid onto a piece of manganese dioxide. Within seconds, a greenish-yellow gas arose.
Although he had no idea at the time, he had just discovered chlorine.
The fact that the greenish-yellow gas was actually an element was only recognized several decades later by English chemist Sir Humphrey Davy. Davy gave the element its name on the basis of the Greek word khloros, for greenish-yellow. In 1810 he suggested the name "chloric gas" or "chlorine."
Represented by the chemical symbol "Cl," chlorine is number 17 on the Periodic Table of Elements, indicating each atom of chlorine contains 17 protons and 17 electrons. Chlorine is one of the five nonmetallic elements that make up the halogen or "salt-producing" group.
Chlorine is also one of the most useful chemical elements. Chlorine is known as a very reactive element—so reactive, in fact, that it is usually found combined with other elements in the form of compounds. More than 3,500 naturally occurring chlorinated organic (associated with living organisms) compounds alone have been identified.
Chlorine is produced from one of natureÕs most plentiful and inexhaustible minerals—common salt, sodium chloride—as well as potassium chloride. Chlorine is produced using the "chlor-alkali process." In this process, electricity is applied to a salt solution. The electricity separates sodium from chloride and produces chlorine gas, hydrogen gas and sodium hydroxide (caustic soda) solution.
Chlorine's chemical properties have been harnessed innovatively for good use. For example, this element plays an essential role in public health. Chlorine-based disinfectants are capable of destroying a wide variety of disease-causing germs in drinking water and wastewater as well as from hospital and food production surfaces. LIFE magazine even called drinking water filtration plus the use of chlorine "probably the most significant public health advancement of the millennium." Additionally, chlorine plays a critical role in the manufacturing of thousands of products we depend upon every day, from computer chips to crop-protection chemicals to cancer-fighting drugs. Some of these products contain chlorine, and others depend on chlorine chemistry for an intermediate step in their manufacturing. Chlorine is truly a workhorse chemical.