An eye for an i #425 Children

It’s chlorine, not oxymuriatic acid

Portrait of Humphry Davy by artist Thomas Phillips.   | Photo Credit: National Portrait Gallery/ Wikimedia Commons

A chemical element is generally found to be useful if it exhibits at least one of the following two characteristics:

(1) It should be available abundantly or at least in sufficient quantities and

(2) It should exhibit properties that are extremely desirable.

Chlorine, which is one among approximately 100 natural chemical elements, satisfies both these conditions. Highly reactive, chlorine is naturally found throughout the Earth, bound with other elements. It is no wonder therefore that chlorine is considered one of the building blocks of our planet.

Scheele’s discovery

Even though some chlorine compounds were known (in other names and not as compounds of chlorine) through centuries, chlorine itself was first discovered, so as to say, only in 1774. German-Swedish chemist Carl Wilhelm Scheele is credited with the discovery. He discovered it when he dropped a few drops of hydrochloric acid with the mineral pyrolusite (manganese dioxide in its natural form). The greenish-yellow dense gas that resulted was chlorine, and Scheele noted that it had a choking smell, dissolved in water to give an acidic solution, bleached litmus paper, and decolourised leaves and flowers.

Even though Scheele had produced chlorine and had also noted many of its properties, he hadn’t identified it as a chemical element. The prevailing theory then identified what we now know as chlorine as a compound of oxygen. Famed French chemist Antoine Lavoisier believed that all acids must contain oxygen and that oxygen was the principle of acidity. Chlorine, therefore, was identified back then as oxymuriatic acid.

Davy does it

It took decades before these perceptions were corrected and the changes were widely accepted. The person who set these things right was English chemist Humphry Davy.

Davy began investigating this substance in the first decade of the 19th Century. He was able to show that oxygen wasn’t present in hydrochloric acid and also established the correct relation between chlorine and this acid. Proving this not only negated Lavoisier’s theory that all acids contained oxygen, but also showed that the name oxymuriatic acid cannot be applied to the substance in question.

<< Image shows the electron shell diagram for chlorine, which is the 17th element in the periodic table.

<< Image shows the electron shell diagram for chlorine, which is the 17th element in the periodic table.   | Photo Credit: Pumbaa (original work by Greg Robson)/ Wikimedia Commons

In a paper titled On a Combination of oxymuriatic Gas and Oxygene Gas, Davy presented what he called “extraordinary and novel results". He read this paper to the Royal Society on February 21, 1811. Davy went on to call the substance in question “chloros”, from the Greek word for greenish yellow, and updated it to chlorine later on.

Now used everywhere

Davy’s research on the substance allowed him to show that it was not only a simple substance, but was, in fact, a chemical element. He designed experiments to demonstrate that chlorine did not contain oxygen, explained chlorine’s bleaching action, and discovered two oxides of chlorine. His views on chlorine, however, were disputed for a number of years and it was almost another decade later that the larger scientific community accepted that chlorine truly was an element.

From not being considered an element, chlorine has come a long way as it is now elemental in our daily lives. Be it the salt in our foods or many of the life-saving drugs, chlorine forms an indispensable part of it. And these would be just the tip of the iceberg. We are all exposed to chlorine in more ways than one, and sometimes even in places where we least expect it to be.

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Printable version | Apr 11, 2021 12:19:17 AM | https://www.thehindu.com/children/its-chlorine-not-oxymuriatic-acid/article33822042.ece

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