Ultracold + water vapor = crystals ... otherwise known as snow!
That's the basic formula for this science experiment—created by physics professor Kenneth G. Libbrecht—that creates a snow crystal growth chamber (or diffusion chamber) right in your kitchen. Read on to find out how to do this experiment, taken from the book Try This Extreme.
WHAT’S GOING ON
Dry ice doesn’t melt, it sublimes. That is, it changes from a solid to a gas when it's warmed, producing carbon dioxide gas.
The bottle becomes a diffusion chamber, in which air is chilled at the bottom but warm at the top. This creates the perfect condition for crystals to grow.
The water evaporates from the sponge. The water vapor travels around the bottle, until the air inside it gets supersaturated, with humidity at more than 100 percent. Then vapor molecules attach to the string and form a crystal. The string provides a nucleation site where condensation can occur. In the atmosphere, dust crystals perform this purpose. There, supersaturated air condenses into water droplets if the temperature is above 32ºF (0ºC) and into ice crystals (snow) if the air temperature is below 32ºF.