An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments. Common antifreezes also increase the boiling point of the liquid, allowing higher coolant temperature. However, all common antifreeze additives also have lower heat capacities than water, and do reduce water's ability to act as a coolant when added to it.
Fluorescent green-dyed antifreeze is visible in the radiator header tank when car radiator cap is removed
Freezing-point depression
Freezing-point depression is a drop in the maximum temperature at which a substance freezes, caused when a smaller amount of another, non-volatile substance is added. Examples include adding salt into water, alcohol in water, ethylene or propylene glycol in water, adding copper to molten silver, or the mixing of two solids such as impurities into a finely powdered drug.
Workers spreading salt from a salt truck for deicing the road
Freezing point depression is responsible for keeping ice cream soft below 0°C.
Pre-treating roads with salt relies on the warmer road surface to initially melt the snow and make a solution; Pre-treatment of bridges (which are colder than roads) does not typically work.
Dissolved solutes prevent sap and other fluids in trees from freezing in winter.
