During the dog days of summer, there's nothing quite like donning your swimsuit and doing a cannonball into a pool full of cool water. As you sink down to the bottom, the water surrounds you and refreshes you like no shower ever could!

If you spend a lot of time at the pool during the summer, you probably know how your skin can get dried out and your eyes can get red and irritated after hours in the pool. Why does that happen? It's because the pool probably has chemicals in it that keep the water fresh and bacteria-free.

One of the common chemicals found in most pools is chlorine. What you might not realize, though, is that chlorine is a gas, not a liquid!

Chlorine is a chemical element that is one of the most common substances on Earth. Pure chlorine is a yellow-green gas under standard conditions. Pure chlorine is very rare, though.

Pure chlorine gas is poisonous and can be lethal. In fact, it has been used in times of war as a chemical weapon. Fortunately, chlorine combines very easily with a wide variety of other elements to form many different compounds.

When combined with other elements, chlorine can be quite safe. For example, one of the most common substances that includes chlorine is sodium chloride, which you know as table salt!

Chlorine is used commercially to make many different products. Because of its bleaching and disinfectant properties, chlorine is an important part of many cleaning products. This is why chlorine is used in swimming pools. In pool water, chlorine kills bacteria and keeps the water clean and sanitary.

Swedish chemist Carl Wilhelm Scheele is given credit for discovering chlorine. He didn't realize it was an element at the time (he thought it was a combination of elements), but he nonetheless created pure chlorine gas when he mixed hydrochloric acid and the mineral pyrolusite.

Today, chlorine compounds, often in the form of hypochlorous acid, are used to purify drinking water. These compounds are added in water treatment plants to make drinking water safe for the public to drink.

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