poisoned by these matches is also evident.
Fortunately, chemists have discovered a method of making a form of phosphorus which is not poisonous. When white phosphorus is gently heated for several hours in a closed vessel from which air is excluded, it slowly changes in color and the no-poisonous red phosphorus is formed. In addition to the fact that it is not poisonous, red phosphorus has other advantages. Its kindling temperature is much higher than that of the white variety, and this makes red phosphorus less dangerous to ship and to store. Another method of making phosphorus safe for use in matches is to combine it with sulphur. To do this, the two elements are mixed and heated in the absence of air. The phosphorus sulphide, which is formed, is not poisonous.
1. With the help of his brother, Prometheus succeeded in presenting fire to man.
2. Fire gave man an advantage over other animals.
3. Man learned to cook by accident.
4. In the Middle Ages even the palaces of the wealthy were cold because wood was much too expensive.
5. In striking a match, friction raises the phosphorus compound in the tip to the kindling temperature.
6. Red phosphorus is the only means of making phosphorus safe.
7. Fire has played an important role in the progress of civilization.
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