What is chrorine?

   Back in 1774 a Swedish scientist heated a mixture of chemicals. Out of the mixture bubbled a greenish-yellow gas that had a suffocating odor. The scientist, Karl Wilhelm Scheele, thought he had made a new gas containing oxygen. Years later another scientist proved that Scheele had discovered chlorine.
   Chlorine is one of the simple substances called elements. In nature it is always joined with at least one other element. It is, we say, always in a compound. Salt is a compound made of chlorine and sodium.
   Although chlorine is a gas, it can be changed to a liquid. Great amounts of it are sold in liquid form.
   Chlorine is poisonous to breathe. In World War I it was used as a poison gas. Fortunately, it is poisonous to germs, too. Small amounts of it are dissolved in the water of swimming pools to kill germs. Many large cities use it to purify their drinking water, too.
  Chlorine is also used in bleaching solutions. These solutions help keep white cottons and linens white during washings.
   From their names it is easy to guess that carbon tetrachloride and chloroform have chlorine in them. Carbon tetrachloride can be used to put out fires. It is also a good cleaning fluid. Chloroform is sometimes used in hospitals as an anesthetic.
   Special chemicals are needed to produce the white smoke for skywriting. These special chemicals are chlorine compounds.