DIY: Creepy Fog
TOOLS:
- CO2 fire extinguisher or CO2 canister from a bottling plant (beer / soda distributor)
- NOTE: CO2 Fire Extinguishers are explicitly marked. If it doesn't say CO2, it won't work
- Mesh Cloth (not a solid bag as you need to let the gas escape)
- Heavy Gloves
- Tape (optional)
PROCEDURE:
- Put on gloves
- Put the nozzle from the fire extinguisher in the bag
- Tape or clamp your hand around the bag and nozzle
- Discharge the extinguisher (or open the valve of the canister)
- Dry ice will begin collecting in the bag
CAUTION(s):
- Dry Ice Is Cold - At approximately -78.5C, dry ice can cause almost instantaneous frostbite
- Dry Ice Expands - As the solid sublimates into a gas, it can increase pressure. If you put it in a sealed container, the gas pressure may cause the container to burst.
THE SCIENCE:
Although arguably cheaper and quicker to buy dry ice in your local megamart, you would miss out on all the fun of a DIY project. Carbon Dioxide (gas) is compressed under pressure inside of either the extinguisher or canister and is generally stored as a liquid. When it is released, the rapid expansion cools some of the CO2 below the freezing point such that a solid is formed and captured in your bag. Conceptually, there are some similarities to the jet powered beer cooler.
Although there are some legitimate uses of dry ice in the cooling industry (it's fairly handy to have in case of a power outage to keep your fridge from spoiling), the special effects industry generally has a claim to its uses. At STP (standard temperature / pressure), dry ice sublimates (goes from a phase change of solid directly to gas, bypassing the liquid state). When you drop it in water, the cold CO2 causes the surrounding water vapor in the air to condense and form fog.
In case you are looking for some additional DIY fun, put a couple of chunks of dry ice into an empty aquarium. Since CO2 is heavier than air, in time, it will eventually fill up the container. After a few minutes though, you should be able to blow bubbles into the aquarium and they will hover at the CO2 / air line until they eventually freeze (remember I said that dry ice was cold?). At that point you can pick up the frozen bubble and play with it until it eventually thaws and pops.
And if your homemade dry ice wasn't enough to try all these cool things, as I mentioned before, you can likely pick it up at your local store. A 10lb brick is fairly cheap, and properly stored in a cooler, will last about 24 hours (don't put it in a working freezer or it could cause your thermometer to shut off your compressor).
NB:
As I define what these posts will ultimately be, I am going to try and do a DIY segment the first Thursday of each month to impart a little bit of structure and consistency here.