Chlorine is a common element, recognized today as a pale green gas with the chemical symbol Cl and atomic number 17. The substance was first isolated in 1774 by Swedish chemist Carl Wilhelm Scheele. However, it took several more decades for the scientific community to correctly identify the gas as a unique, irreducible element.
The Groundbreaking Isolation in 1774
The first isolation of chlorine occurred in 1774, when Carl Wilhelm Scheele experimented with the mineral pyrolusite (manganese dioxide). He heated the mineral with hydrochloric acid, known as muriatic acid. Scheele observed the production of a dense, yellowish-green gas that possessed a distinctive, choking odor.
He recorded the properties of this new substance, noting its powerful chemical activity. He found that the gas possessed a strong bleaching effect, capable of turning litmus paper white and fading colored flowers. Scheele’s procedure produced the element we now know as chlorine.
Misunderstanding the New Substance
Despite isolating the gas, Scheele failed to recognize it as a new element, a misunderstanding rooted in the scientific theories of the time. Scheele was a proponent of the prevailing Phlogiston theory, which proposed that combustible materials contained phlogiston, released during burning.
Based on this framework, Scheele believed the gas was a compound, specifically “dephlogisticated muriatic acid air”. He reasoned that the manganese dioxide had removed phlogiston from the muriatic acid, leaving behind a modified acid. This interpretation, shared by many contemporaries, held that the gas was a substance containing oxygen and an unknown element.
Confirmation as a Unique Element
The true elemental nature of the gas was established in 1810 by the English chemist Humphry Davy. Davy conducted experiments, attempting to decompose the substance with heat and charcoal. His finding was that the gas could not be broken down into simpler components, which contradicted the contemporary belief that it was a compound containing oxygen.
Davy’s work proved that Scheele’s gas was an irreducible element. He announced his findings to the Royal Society, establishing the substance’s identity. Davy then proposed the name “Chlorine,” drawing from the Greek word chloros, meaning pale green, in reference to the gas’s visible color.
Immediate Practical Applications
The strong chemical properties of chlorine led to its first practical uses outside the laboratory. As early as 1785, the French chemist Claude Berthollet began applying the gas to the bleaching of textiles. He found that solutions containing chlorine compounds could rapidly whiten fabrics, an advantage over the slower, traditional methods of sun bleaching.
This discovery led to the industrial production of early bleaches, such as “Eau de Javel,” a weak solution of sodium hypochlorite. The powerful oxidizing properties of chlorine were also recognized for their potential in public health. Early disinfection efforts began in the late 19th century, with a bleach solution being used to sterilize a public water supply during a typhoid outbreak in Maidstone, England, in 1897. The regular chlorination of potable water in major cities, such as in Jersey City, New Jersey, in 1908, marked the beginning of its widespread use to combat waterborne diseases.