What's -109 degrees Fahrenheit and dangerous to humans? If you guessed Wisconsin winters, you're close. The answer is frozen carbon dioxide, or, as it’s commonly known, “Dry Ice.”
When solid carbon dioxide was first developed, scientists couldn't control it in its snow-like form. It eventually melted into an extremely cold liquid. The scientists then decided to mix this liquid with other liquids that have low freezing temperatures, like alcohol. When mixed, the Dry Ice didn't melt; it vaporized.
Chemists have since found many helpful uses for Dry Ice. When shipping or storing perishable foods, it's very easy for them to go bad. One example is eggs, which go bad when carbon dioxide escapes through their shells. But, when they are refrigerated in Dry Ice, the carbon dioxide can't escape from the shell; therefore, the eggs last longer.
Dry Ice is also used as a preservative in florist shops. A florist can stop a rosebud from blooming for around three days if it is kept in an area with Dry Ice.
Dry Ice is a very interesting substance and helpful tool. But, never touch it with your hands; they'll get burned very badly!
[Source: The Big Book of Tell Me Why]