One can associate chlorine with cubism’s style of simultaneously representing a subject from many viewpoints on the same canvas. In a way, it takes a cubist’s perspective to paint a complete picture of chlorine. A part of cellular electrolytes in the form of chloride, it’s a life-essential element. As part of an acid it initiates the digestion of protein in many animals. By isolating it we have been able to make disinfectants, one which keeps water free of contaminants between a water treatment plant and the tap at home. But others have used the elemental form as a weapon of war. Cl2 is an also intermediate in the production of a wide variety of industrial compounds, many of which are indispensable, while many others have turned out to be known or probable carcinogens.
Let us begin with how mankind first stumbled upon the element.
Chlorine was first prepared in 1774 by Swedish chemist Carl Wilhelm Scheele. He had produced the yellow-green gas by adding fuming muriatic acid or spiritus salis (fuming hydrochloric acid) to a fine powder of pyrulosite (a mineral containing manganese dioxide Figure 1). But a pair of flawed hypotheses prevented Scheele and others from realizing that the gas was a new element. The first idea that stood in the way was the phlogiston hypothesis.
Chemists at the time believed that metals, acids and combustible substances contained phlogiston, which was released in fires and corrosion. It was impossible not to notice the new gas(chlorine)’s suffocating odour and painful action on the lungs. It resembled dephlogisticated air (oxygen) by supporting combustion. The phlogiston hypothesis had proposed that in a closed space, a fire died out before the fuel was consumed because the air would become saturated with phlogiston. Dephlogisticated air had a greater capacity for phlogiston, which was their explanation for why oxygen was better than air at sustaining flames. Using the internal logic of the hypothesis, Scheele concluded that the pyrulosite had taken away the phlogiston from the acid, and so he called the gas “dephlogisticated muriatic acid”.
A few years later, after Lavoisier had refuted the phlogiston hypothesis by revealing the role of oxygen in combustion, a second idea stood in the way of understanding the nature of chlorine. Lavoisier had incorrectly proposed that all acids contained oxygen. Chemists who had accepted his views thought of muriatic acid as an oxygen-bound compound. Davy realized that when muriatic acid and water were added to potassium, the potassium was liberating hydrogen from the acid and then from water. Any oxygen that went into solution (as hydroxide) was coming from water, not from the muriatic acid. Since experiments that had tried to separate chlorine gas into other substances had all failed, Davy concluded that muriatic acid was a compound of only hydrogen and chlorine and that chlorine was a new element.
The above was an excerpt from the book Life’s Essential Elements (2019)