Dry ice is the solid form of carbon dioxide (\(\text{CO}_2\)), used for cooling purposes. Unlike water ice, dry ice does not melt into a liquid; instead, it transitions directly into a gas at normal atmospheric pressure, a process known as sublimation. This phase change occurs at approximately \(-78.5^\circ\text{C}\) (\(-109.3^\circ\text{F}\)). Creating small batches of solid \(\text{CO}_2\) involves rapidly expanding compressed gas, a technique that can be performed safely at home with the correct supplies.
Necessary Supplies and Safety Gear
The primary requirement is a source of compressed, liquid carbon dioxide, typically a \(\text{CO}_2\) fire extinguisher or a large pressurized \(\text{CO}_2\) tank with an adapter. Confirm the extinguisher is specifically rated for \(\text{CO}_2\) and not a powder-based chemical agent. You will also need a heavy-duty cloth bag, such as a sturdy pillowcase or canvas sack, which serves as the collection chamber. This porous material allows the gas to escape while trapping the solid particles.
Safety is paramount, and the process should not be attempted without personal protective equipment. Insulated gloves, such as cryogenic or thick leather gloves, must be worn to prevent severe frostbite from contact with the dry ice or expanding gas. You must also wear safety goggles to shield your eyes from flying fragments or sudden blasts of gas. The entire operation needs to be conducted in a location with extreme ventilation, ideally outdoors, to prevent the buildup of carbon dioxide gas, which can displace oxygen.
Step-by-Step Procedure for Making Dry Ice
Once supplies and safety gear are secured, ready the collection bag by securing it tightly around the nozzle or discharge horn of the \(\text{CO}_2\) source. For an extinguisher, the bag must fully cover the plastic discharge horn. A strong clamp or heavy-duty tape can be used to create a tight seal around the nozzle neck, ensuring the expanding \(\text{CO}_2\) is directed entirely into the cloth bag.
With the bag secured, initiate the gas release; for a fire extinguisher, this involves removing the safety pin and depressing the handle. The rapid depressurization of the liquid carbon dioxide creates the dry ice through a process called adiabatic expansion. As the gas expands from the high-pressure container into the lower-pressure atmosphere within the bag, its thermal energy drops sharply. This sudden cooling causes a portion of the \(\text{CO}_2\) to convert directly into solid “snow.”
The discharge should be controlled and brief, typically lasting five to ten seconds, to avoid over-pressurizing the container or the collection bag. During the release, you will observe the cloth bag inflating and the \(\text{CO}_2\) gas escaping through the fabric. After the discharge is complete, carefully release the clamp or tape and gently remove the bag from the nozzle, taking care not to touch the extremely cold metal parts.
The result will be a white, snow-like residue—the dry ice—collected in the bottom of the cloth bag. Shake the bag to consolidate the powder. This solid carbon dioxide is ready to be transferred to a storage container, always using insulated gloves to handle the material. The success of this method relies on the gas escaping, which forces the rapid temperature drop necessary for the deposition of the solid phase.
Handling and Storage Guidelines
After the dry ice is created, proper handling is important to prevent injury. Never touch the solid \(\text{CO}_2\) with bare skin, as its temperature of \(-78.5^\circ\text{C}\) can cause severe cold burns or frostbite in seconds. Always use insulated gloves and non-metal scoops or tongs when manipulating the material.
For storage, dry ice must be placed in a well-insulated container, such as a Styrofoam chest or a cooler, to slow sublimation. Crucially, the container should never be completely airtight or fully sealed. As the solid \(\text{CO}_2\) sublimates into gas, it generates pressure, and an airtight container could rupture or explode.
Allowing the gas to vent safely is necessary, so a container with a loose-fitting lid is the correct choice. When disposal is needed, place the remaining material in a well-ventilated area, away from people and pets, and allow it to completely sublimate. Never dispose of dry ice in a drain, sink, or regular trash receptacle, as the extreme cold can damage plumbing and the gas release can be hazardous in confined spaces.