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Reading Selection, Lesson 4

Deadly Density

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People in a chlorinated pool.

Chlorine is used to kill the microorganisms in swimming pools.

Have you heard about a substance called chlorine? If you have, you probably know that it is sometimes added to water. Chlorine is added to drinking water to kill harmful microorganisms.When you go swimming, you can smell the chlorine at the pool. That’s because chemicals that release chlorine are added to the water to keep it safe for swimming.

You may be surprised to learn that chlorine is a greenish yellow gas. It is also a very poisonous substance. This property is exploited when chlorine is used as a disinfectant to kill microorganisms. In small amounts, chlorine kills microbes but not larger organisms. However, chlorine has also been used to kill people.

In World War I (1914–1918), chlorine was used as a weapon. Most of the battles in this war were fought between lines of trenches that provided the soldiers with some protection against gunfire. On April 22, 1915, at the battle of Ypres, in France, the Germans used a new secret weapon. That weapon was chlorine.They released chlorine
Two world war one soldiers and their mules, all wearing gas masks.

To protect themselves against poisonous gases in World War I, these U.S. troops and their mules wore gas masks.

gas from their side of the lines. The chlorine was carried by the wind to the enemy trenches. Because chlorine is much denser than air, it stayed near the ground and poured into the trenches.Choked and blinded, the defenders were then overrun by German troops wearing gas masks. After this gas attack, soldiers on both sides were issued gas masks.


What are other properties and uses of chlorine? Use the library and Internet resources to find out more about chlorine.

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