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What is dry ice ?

Dry ice is formed by freezing carbon dioxide. Because the temperature of dry ice is extremely low, about -78.5 °C and is easy to produce, it is normally used as a coolant.

Scientists produce small quantities of dry ice by opening the valve of a tank filled with liquid carbon dioxide and placing a piece of cloth over the nozzle. When the escaping gaseous carbon dioxide condenses, dry ice is formed. This procedure is the most common way scientists create a small amount of dry ice for simple lab experiments.

When large quantities of dry ice is needed, the procedure used is evaporative cooling, wherein gaseous carbon dioxide is compressed to produce liquefied carbon dioxide. Since the temperature of substances increase when compressed, the gas form of the carbon dioxide is cooled to encourage liquid formation. The liquefaction starts when the pressure becomes 870 ppsi (pounds per square inch). A small quantity of liquid nitrogen is allowed to evaporate and in turn, allow molecules to escape. This causes temperature to decrease. Once enough heat evaporates, the liquid’s temperature drops below freezing point, wherein the transition phase occurs and solid carbon dioxide (dry ice) is formed.

Dry ice is stored on insulated containers, but once exposed to air, it begins to give off carbon dioxide gas instantly. This is due to the huge difference of temperature on the container and the environment. When fake fog is needed, for special effects on plays or movies, carbon dioxide is made to dissolve into vapor.

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