What Is Dry Ice?

Dry ice is the general term for solid carbon dioxide (CO), coined in 1925 by Long Island-based Prest Air Devices. Though originally a trademarked term, "dry ice" has become the most common way of referring to carbon dioxide in its solid, or frozen, state.

How Is Dry Ice Manufactured?

Carbon dioxide is "frozen" by compressing carbon dioxide gas to a high pressure to create dry ice. When it is released, as liquid carbon dioxide, it quickly expands and evaporates, cooling some of the carbon dioxide down to the freezing point (-109.3 F or -78.5 C) so that it becomes solid "snow." This solid can be compressed together into blocks, pellets, and other forms.

Such dry ice "snow" also forms on the nozzle of a carbon dioxide fire extinguisher when it is used.

Special Properties of Dry Ice

Under normal atmospheric pressure, dry ice undergoes the process of sublimation, transitioning directly from solid to gaseous form. In general, at room temperature and normal pressure, it sublimates at a rate of 5 to 10 pounds every 24 hours.

Because of the very low temperature of dry ice, it is used for refrigeration. Packing frozen food in dry ice allows it to remain frozen without the mess that would be involved with other cooling methods, such as water from melted ice.

Several Uses of Dry Ice

• Cooling materials—food, biological samples, perishable items, computer components, etc.
• Dry ice fog (see below)
• Cloud seeding to increase precipitation from existing clouds or decreasing cloud thickness
• Tiny pellets can be "shot" at surfaces to clean them, similar to sanding ... since it sublimates, the benefit is less residue to clean up
• Various other industrial uses

Dry Ice Fog

One of the most popular uses of dry ice is in special effects, to create fog and smoke. When combined with water, it sublimates into a cold mixture of carbon dioxide and humid air, which causes condensation of water vapor in the air, forming fog. Warm water speeds up the process of sublimation, producing more dramatic fog effects.

Such devices can be used to make a smoke machine, although simplified versions of this could be created by putting dry ice in water and using fans on low settings.

Safety Instructions

1. Do not taste, eat or swallow! Dry ice is very cold and can damage your body.
2. Wear heavy, insulated gloves. Since dry ice is cold, it can damage even your skin, giving you frostbite.
3. Do not store in sealed container. Because dry ice constantly sublimates into carbon dioxide gas, storing it in a sealed container will cause pressure to build up. If it builds up enough, the container could explode.
4. Use only in ventilated space. In a poorly ventilated area, the build up of carbon dioxide could create a suffocation hazard. This is a great danger when transporting the dry ice in a vehicle.
5. Carbon dioxide is heavier than air. It will sink to the floor. Keep this in mind when thinking about how to make the space ventilated.

Obtaining Dry Ice

You can buy dry ice at most grocery stores. You have to ask for it, though. Sometimes there might be an age requirement on buying dry ice, requiring someone age 18 or over. You can also make dry ice.

Edited by Anne Marie Helmenstine, Ph.D.