You may be familiar with dry ice used for fog effects during Halloween, or perhaps for use keeping summer drinks cold in the summer season. Dry ice has many applications and is especially handy should your freezer break down. Carbon dioxide in solid form is known as dry ice, and as it melts, it returns to its normal state: colourless, odourless carbon dioxide gas. Dry ice can be used effectively for many purposes as long as you follow safety regulations when handling and storing.
Dry ice can lend a fun and spooky atmosphere to your Halloween festivities, but knowing how to use it is incredibly important. Dry ice is the frozen form of carbon dioxide, which is why, instead of melting into a liquid when heated, it turns into a gas. As it sits at a freezing temperature of -109.3°F, handling it correctly is a top priority.
Dry ice, when combined with hot tap water, can produce vigorous bubbling water and voluminous flowing fog. For example, with 5 pounds of Dry Ice in 4 to 5 gallons of hot water, the highest amount of fog will be produced the first 5 to 10 minutes. There will be far less fog for the next 5 to 10 minutes as the water cools down and the volume of Dry Ice diminishes. As the water cools, the fog becomes wispier. Dry ice makes fog because of its cold temperature, -109.3°F or -78.5°C, immersed in hot water, creates a cloud of real water vapour fog. When the water gets colder than 50°F, the Dry Ice stops making fog but continues to sublimate and bubble. The haze will last longer on a damp day than on a dry day.
Dry ice is frozen carbon dioxide, a regular part of our earth’s atmosphere. It is the gas that we exhale during breathing and the gas that plants use in photosynthesis. It is also the same gas commonly added to water to make soda water. This gas is often captured during industrial processes and recycled to make Dry Ice.
Dry ice is particularly useful for freezing, and keeping things frozen because of its freezing temperature: -109.3°F or -78.5°C. Dry ice is widely used because it is simple to freeze and easy to handle using insulated gloves. Dry Ice changes directly from a solid to a gas -sublimation- in normal atmospheric conditions without going through a wet liquid stage. Therefore it gets the name “dry ice.”
As a general rule, Dry Ice will sublimate at a rate of five to ten pounds every 24 hours in a typical ice chest. This sublimation continues from the time of purchase; therefore, pick up Dry Ice as close to the time needed as possible. Bring an ice chest or some other insulated container to hold the Dry Ice and slow the sublimation rate. Dry Ice sublimates faster than regular ice melts but will extend the life of regular ice.
It is best not to store Dry Ice in your freezer because your freezer’s thermostat will shut off the fridge due to the extreme cold of the Dry Ice! Of course, if the freezer is broken, Dry Ice will save all your frozen goods.
Commercial shippers of perishables often use dry ice even for non-frozen goods. Dry ice gives more than twice the cooling energy per pound of weight and three times the cooling energy per volume than regular water ice (H2O). It is often mixed with regular ice to save shipping weight and extend the cooling power of water ice. Sometimes dry ice is made on the spot from liquid CO2. The resulting dry ice snow is packed in the top of a shipping container offering extended cooling without electrical refrigeration equipment and connections.
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How to Make Dry Ice Fog
To create a fog effect with dry ice, you will need:
- A large container
- Hot water
- Dry ice
Make sure to follow all dry ice safe handling precautions.
Fill a metal or plastic container half full of hot water and add a few pieces of dry ice every 5-10 minutes. As the water cools, you will need to add more hot water to maintain the fog effect. As a rule of thumb, one pound of dry ice will create 2-3 minutes of fog effect—the warmer the water, the more fog, but the quicker sublimation of the dry ice.
For every 15 minutes put 5 to 10 pounds of Dry Ice into 4 to 8 gallons of hot water. This will make lots of fog depending upon the temperature of the water and the size of the pieces of Dry Ice. Warmer water will cause more fog. Boiling water will add its own rising steam to the vapour cloud. If there is no steam, the fog will flow downhill and in the direction of any air movement. A small fan can help control the direction. Smaller pieces of Dry Ice with more surface area produce a higher volume of fog and cool the water down much faster. In both cases, the result is more fog for a shorter amount of time. Keep the water hot with a hot plate, electric skillet, or some other heat source to produce mist for a longer time. Otherwise, when the water gets too cold, it must be replaced to continue the fog effects. If the container is filled with water, the fog will flow over the sides the best. But the Dry Ice sublimation will vigorously bubble the water and splash it out. Even a ¾ filled container will splash some so place the container where spilled water will not ruin anything. The water vapour fog will also dampen the area it flows across. Be careful because after some time floors do get slippery.
When you place dry ice into warm or hot water, clouds of white fog are created. This white fog is condensed water vapour, mixed in with the invisible CO2. The extreme cold causes the water vapour to condense into clouds. The fog is heavy, being carried by the CO2, and will settle to the bottom of a container. This can be poured out and produce enough mist to fill a medium-sized room with a pound or so of dry ice. Do not allow anyone (including pets) to lie in this fog because too much CO2 is toxic.
How does dry ice work?
Dry ice is frozen carbon dioxide. A block of dry ice has a surface temperature of -109.3 degrees Fahrenheit (-78.5 degrees C). Dry ice also has the very nice feature of sublimation — as it breaks down, it turns directly into carbon dioxide gas rather than a liquid. The super-cold temperature and the sublimation feature make dry ice great for refrigeration. For example, if you want to send something frozen across the country, you can pack it in dry ice. It will be frozen when it reaches its destination, and there will be no messy liquid leftover like you would have with regular ice.
Many people are familiar with liquid nitrogen, which boils at -320 degrees F (-196 degrees C). Liquid nitrogen is relatively messy and challenging to handle. So why is nitrogen a liquid while carbon dioxide is a solid? This difference is caused by the solid-liquid-gas features of nitrogen and carbon dioxide.
We are all familiar with the solid-liquid-gas behaviour of water. We know that at sea level, water freezes at 32 degrees F (0 degrees C) and boils at 212 degrees F (100 degrees C). Water behaves differently as you change the pressure, however. As you lower the weight, the boiling point falls. If you drop the pressure enough, water will boil at room temperature. If you plot out the solid-liquid-gas behaviour of a substance like water on a graph showing both temperature and pressure, you create what’s called a phase diagram for the material. The phase diagram shows the temperatures and pressures at which content changes between solid, liquid and gas.
This page shows the phase diagrams for water and carbon dioxide. What you can see is that, at normal pressures, carbon dioxide moves straight between gas and solid. It is only at much higher pressures than you find liquid carbon dioxide. For example, a high-pressure tank of carbon dioxide or a carbon-dioxide fire extinguisher contains dissolved carbon dioxide.
To make dry ice, you start with a high-pressure container full of liquid carbon dioxide. When you release the dissolved carbon dioxide from the tank, the expansion of the liquid and the rapid evaporation of carbon dioxide gas cools the remainder of the cash down to the freezing point, where it turns directly into a solid. If you have ever seen a carbon-dioxide fire extinguisher in action, you have seen this carbon-dioxide snow form in the nozzle. You compress the carbon-dioxide snow to create a block of dry ice.
Pool & Jacuzzi
50 to 100 pounds of Dry Ice dropped directly into a heated swimming pool will make fog for an hour or longer depending on the water temperature and the size of the Dry Ice pieces. Because of the Jacuzzi’s hot water, it makes the most fog the quickest. As long as the water is kept warm, it can take 50 to 100 pounds per hour. The Dry Ice will carbonate the water for several days. If possible, drain the Jacuzzi. The swimming pool will read more alkaline during this time so wait to add acid until the carbonation has dissipated. If the temperature of the water in a swimming pool, fountain, waterfall, or birdbath is too cold (less than 60°F), the Dry Ice will bubble but produce much less fog.
Add Dry Ice To Beverages
It is OK to put Dry Ice into beverages for drinking as long as the dry ice is food grade. Use 2 to 4 pounds of Dry Ice for each gallon of room temperature punch. Use large pieces of Dry Ice, not small pieces. The Dry Ice is denser than ice and will sink to the bottom. Do not use any regular ice! The Dry Ice will do the cooling and must not be eaten or swallowed. Too much Dry Ice will freeze the beverage so have extra standing by. It will bubble and give off the most fog when the drink is room temperature. When most of the Dry Ice has sublimated, it will surround itself with ice and float to the top. There is still a small piece of Dry Ice in the centre of these ice pieces, so do not serve or eat them. Carefully ladle the beverage into drinking glasses without any Dry Ice. Add regular ice to glasses for more refreshing drinks.
A first-grade teacher gave me the best recipe for “witches brew”: 1 can Grape Juice. (Dark colour) One can Pineapple Juice. (Strange pulpy texture) 3-5 pounds of food-grade Dry Ice. (Do not use regular ice) Mix room temperature juices together. When ready for the special brew, add the Dry Ice. Do not touch Dry Ice directly, but use insulated gloves or tongs. Ladle juice into cups without any Dry Ice, and it will be perfectly safe. If you want more cooling drinks to add ice to the containers, not the punch bowl.
**(Food grade means the CO2 used to make the dry ice is the same quality CO2 as used for soda fountains, and also the dry ice can be used to transport food and produce.)
Using a fog machine or buckets of hot water and a fan, many shows are enhanced by adding flowing fog. I have seen it most often in the dance of the snowflake fairies in the Nutcracker Suite, and it is frequently used in Brigadoon and Oklahoma for their dream scenes.
A theatre fog machine is generally a 30 to 55-gallon metal or plastic water barrel with a 110-volt or a 220-volt hot water heater to keep the water warm. Dry ice is placed in a bucket with holes to allow hot water to enter. When the bucket is lowered into the boiling water, fog is instantly produced. The resulting water vapour fog is gently blown by a fan and directed to the desired area by an air duct tube. Fog stops whenever the bucket of Dry Ice is pulled out of the water. More new fog machines pump heated water over a trey holding the Dry Ice. All have a GFCI breaker for safety.
Garbage Disposal Volcano
A fantastic simulated volcano can be made in a sink with garbage disposal. Run hot water and put small one to two-pound pieces of Dry Ice into your garbage disposal one at a time. When you turn the disposal on it will make a spectacular eruption. Be sure to wear goggles as the hot water and ejected Dry Ice could be dangerous. Also, check out the Volcano in our “Science/ School Projects” section.
DANGER: If you put too much Dry Ice into the sink at one time it could burst the pipes. What happens when the heavy Dry Ice sinks to the bottom of the pipes or goes past u shape trap and when it sublimates back into its gas form the pressure could easily break the pipes. Only feed small amounts of Dry Ice at a time being sure to run enough hot water to turn it all into its gas form quickly.
Dry Ice “Firecrackers”
Small pieces of Dry Ice placed in an empty one-litre plastic soda bottle and then filled ¼ to ½ with hot water may explode 2 to 120 seconds after the top is tightly screwed on. It also may crack anywhere and just fizzle. Wear gloves and eye protection because the resulting explosion may dangerously push out pieces of the plastic bottle or the bottle top. A woman in Houston standing too close lost her eye from the ejected bottle top, so make sure no one is holding the bottle nor anyone is near it when it explodes. Although the explosion sprays mostly carbon dioxide gas and water, many municipalities classify them with more dangerous firecrackers and outlaw them. Southern Utah’s “Spectrum”, reports: “It’s a felony to drop a dry-ice bomb in Utah.” Sometimes these dry ice bombs are called “terrorist devices”, and people using them are arrested. In our area, several teenagers were jailed for three days for setting off these Dry Ice firecrackers. The logical defence explains there is no chemical reaction – only a change in the state of matter – from a solid to a gas. Unfortunately, there may be a high cost in lawyers fees to persuade a DA or judge of this fact. Therefore DO NOT DO THIS IF IT IS ILLEGAL IN YOUR COMMUNITY! For safety, DO NOT EVER ALLOW CHILDREN TO DO THIS. Always supervise children around Dry Ice. Of course, using anything other than plastic bottles is even more dangerous and by no means should ever be permitted!
Dry Ice Safety
If you ever have a chance to handle dry ice, you want to be sure to wear heavy gloves. The super-cold surface temperature can easily damage your skin if you touch it directly. For the same reason, you never want to taste or swallow dry ice, either.
Another critical concern with dry ice is ventilation. You want to make sure the area is well-ventilated. Carbon dioxide is heavier than air, and it can concentrate in low areas or enclosed spaces (like a car or a room where dry ice is sublimating). Healthy air is 78% nitrogen, 21% oxygen and only 0.035% carbon dioxide. If the concentration of carbon dioxide in the atmosphere rises above 5%, carbon dioxide can become toxic. Be sure to ventilate any area that contains dry ice, and do not transport it in a closed vehicle.