MATT MEADOWS / SCIENCE PHOTO LIBRARY MATT MEADOWS / SCIENCE PHOTO LIBRARY
Sublimation of dry ice. A fog-like vapour spills out of a test tube containing dry ice, and pours into a glass beaker. Sublimation is the conversion of a solid directly to a vapour state by heating. Dry ice is solid carbon dioxide. Carbon dioxide is a colourless gas at room temperature but becomes a liquid under compression; if the liquid is allowed to expand rapidly to atmospheric pressure, it cools suddenly and freezes to dry ice. Dry ice sublimes (turns straight into a gas from the solid state) at -78.5 degrees Celsius (195 degrees Kelvin). If mixed with water it sublimes, as seen here, producing thick clouds of fog.
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