An antifreeze is a liquid that is added to water to keep it from freezing. When water freezes and turns to ice, it expands. The force of water expanding is so great that it will 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 freezes at the 0degC: the usual kind of antifreeze will not freeze until the temperature is 40degC below zero. A mixture of 5 parts of water and 4 parts of antifreeze will prevent freezing at 18degC below zero; 4 parts of water and 5 parts of antifreeze reduce this to 22degC below zero. Alcohol is a good antifreeze, but when the car is running it becomes hot and the alcohol boils away, so it must be replaced very often. Most people use antifreezes that do not boil away when the engine is running. There are several chemicals that do this. One of the most popular is called ethylene glycol , which is sold under various trade names such as Preston and Zerex. Antifreezes are useful in that they   _  .
keep the alcohol from boiling away can prevent ice from melting keep water liquid in cold weather can raise the freezing point of water