An antifreeze is a liquid that is added to water to keep it from freezing. When water freezes and becomes into ice, it expands. The force of water of expanding is so great that it can break the hardest metal. Water is used in car engines to keep them cool while they run, and if this water is allowed to freeze in winter it can break the iron block of the engine. That is why antifreezes are necessary. Water freeze at zero centigrade the usual kind of antifreeze will not freeze until the temperature is 40℃ below zero. A mixture of five parts of water and four parts of antifreezes will prevent freezing at 18℃ below zero four parts of water and five parts of antifreeze reduce this to 22℃ below zero. Alcohol is a good antifreeze, but when the car is running it turns hot and the alcohol bums away, so it must be replaced very often. Most persons use antifreezes that do not boil away when the engine is running. There are many chemicals that do this. One of the most popular is called ethylene glycol, which is sold under various trade names such as Preston and Xerox. The text is written_________.