Dry ice is available from both large grocery stores and chemical supply companies. Composed of frozen carbon dioxide, dry ice is often used to help keep foods refrigerated because it is much colder than water ice. Because of the unique properties of the chemical, carbon dioxide undergoes a process called sublimation when it warms up, a process in which a substance transitions directly from a solid to a gas.
The freezing point of carbon dioxide is minus 109 degrees Fahrenheit. Because it is so cold, it can cause frostbite or other damage to the skin when touched, so dry ice should not be handled carelessly or with bare hands. As the substance can be quite dangerous, restrictions often prevent its sale to minors.
Because it sublimates, dry ice creates no mess. However, the process of sublimation can cause pressure to build up in airtight containers of dry ice, which can potentially cause the container to explode. For this reason, it is important to ensure that containers that hold dry ice are well ventilated.
The sublimation of dry ice is visible, as the carbon dioxide forms a thin white or gray cloud. This is why many haunted houses and similar places use it to create fog.