4 Things You Can Do With Dry Ice (Besides Make Fake Fog)

Dry ice—or solid carbon dioxide, as it’s more specifically called—is a staple item in middle and high school science classes. But it’s also easily obtainable for anyone who wants to experiment with it in the comfort of his or her own home. While you still need to take precautions when handling it—don’t ever touch it with bare hands—it’s innocuous enough that it’s sold at most supermarkets.

[Image courtesy of Herkie's Flickr photostream]

So what can you do with dry ice? Sure, you can make artificial fog and other smoky special effects. But the possibilities certainly don’t end there. Here are just a few other things to do with solid carbon dioxide.

1. Power a rocket

If you mix dry ice with water, it will sublime—that is, change from a solid to a gas without existing in a liquid phase in between. If sublimation happens within an enclosed container, the carbon dioxide that’s produced will build up and this pressure will eventually cause a small explosion. With a few extra steps, you can use this same explosive reaction to send a basic rocket soaring.

There are dozens of ways to make dry ice rockets—and just as many YouTube demonstrations. But one of the simplest methods requires little more than a soda bottle and a cardboard box. (The guys in the above video didn't use a box; the box isn't necessary, but using one is a good way to ensure that you get the best possible launch.)

First, cut a hole in the base of the box that’s the same size as the bottle top; this is where you’ll put your projectile when you’re ready to launch it. Then cut or drill a small hole in the top of the bottle so that the gas can escape, and cover the hole with some Scotch tape.

Put enough water in the bottle so that it’s about 1/3 full and then add dry ice until it’s half full. Quickly close the bottle, stand it upside-down in the cardboard box, and wait—from a safe distance—for your rocket to take off. Just make sure to be careful; some dry ice rockets have a tendency to launch themselves horizontally.

2. Make root beer

Since dry ice is simply solid carbon dioxide—and carbon dioxide is what gives soda its fizz—you can use a chunk of the stuff to make your own carbonated beverage.

To make one gallon of root beer, take one gallon of water, two pounds of dry ice, and two ounces of root beer extract. Some recipes call for two cups of sugar as well; depending on what root beer extract you’re using, this might not be necessary.

Mix the water, extract, and sugar (if you’re using it) in a large container—one with a volume of at least four gallons and a sealable lid. Drop the dry ice, in chunks, into the liquid with tongs. Cover the container, but open it every so often in order to stir the solution and release some of the pressure building up inside so it doesn’t explode.

In about an hour, your root beer should be ready for consumption. Just make sure there are no solid chunks of dry ice remaining when you go to drink your concoction; while gaseous carbon dioxide can be consumed without concern, solid carbon dioxide can do serious damage to your internal organs. You can use this same procedure to make seltzer water if you omit the root beer extract.

3. Preserve your produce

Dry ice can be used to flash freeze food, and it’s a better way to freeze fruit and veggies than simply storing them in a conventional freezer. Produce that’s flash frozen will retain its initial texture and won’t get soggy when defrosted.

To flash freeze your food, get a seven to 10 pound bag of dry ice and put it in a large cooler. Place whatever fruits and veggies you want to freeze on a cookie sheet and then set the cookie tray on top of the dry ice. Close the cooler, and when your food is fully frozen, you can transfer it to your conventional freezer and save it for however long you like.

4. Protect yourself from pests

Mosquitoes and other insects are attracted to carbon dioxide gas; thus, dry ice can be used to lure these bugs away from their human targets. By hanging a cloth bag with a five-pound block of dry ice inside next to a mosquito lamp, you can significantly increase the trap’s efficacy. Strategically placed chunks of dry ice can be used to attract bed bugs as well.

Some people use dry ice to keep their terrariums free from unwanted bugs; removing the animals, placing a few cups of solid carbon dioxide and hot water in the base of the tank, then covering the tank and letting it sit for five minutes apparently works wonders. After five minutes passes, simply take out the cups, cover the tank, and let it stand for two or three hours before putting your animals back in.

The Surprising Reason Why Pen Caps Have Tiny Holes at the Top

If you’re an avid pen chewer, or even just a diehard fan of writing by hand, you’re probably well acquainted with the small hole that tops off most ballpoint pen caps, particularly those classic Bic Cristal pens. The reason it’s there has nothing to do with pen function, it turns out. As Science Alert recently reported, it’s actually designed to counter human carelessness.

Though it’s arguably unwise—not to mention unhygienic—to chomp or suck on a plastic pen cap all day, plenty of people do it, especially kids. And inevitably, that means some people end up swallowing their pen caps. Companies like Bic know this well—so they make pen caps that won’t impede breathing if they’re accidentally swallowed.

This isn’t only a Bic requirement, though the company’s Cristal pens do have particularly obvious holes. The International Organization for Standardization, a federation that sets industrial standards for 161 countries, requires it. ISO 11540 specifies that if pens must have caps, they should be designed to reduce the risk of asphyxiation if they’re swallowed.

It applies to writing instruments “which in normal or foreseeable circumstances are likely to be used by children up to the age of 14 years.” Fancy fountain pens and other writing instruments that are clearly designed for adult use don’t need to have holes in them, nor do caps that are large enough that you can’t swallow them. Any pen that could conceivably make its way into the hands of a child needs to have an air hole in the cap that provides a minimum flow of 8 liters (about 2 gallons) of air per minute, according to the standard [PDF].

Pen cap inhalation is a real danger, albeit a rare one, especially for primary school kids. A 2012 study [PDF] reported that pen caps account for somewhere between 3 and 8 percent of “foreign body aspiration,” the official term for inhaling something you’re not supposed to. Another study found that of 1280 kids (ages 6 to 14) treated between 1997 and 2007 for foreign body inhalation in Beijing, 34 had inhaled pen caps.

But the standards help keep kids alive. In that Beijing study, none of the 34 kids died, and the caps were successfully removed by doctors. That wasn’t always the case. In the UK, nine children asphyxiated due to swallowing pen caps between 1970 and 1984. After the UK adopted the international standard for air holes in pen caps, the number of deaths dropped precipitously [PDF]. Unfortunately, it’s not foolproof; in 2007, a 13-year-old in the UK died after accidentally swallowing his pen cap.

Even if you can still breathe through that little air hole, getting a smooth plastic pen cap out of your throat is no easy task for doctors. The graspers they normally use to take foreign bodies out of airways don’t always work, as that 2012 case report found, and hospitals sometimes have to employ different tools to get the stubbornly slippery caps out (in that study, they used a catheter that could work through the hole in the cap, then inflated a small balloon at the end of the catheter to pull the cap out). The procedure doesn’t exactly sound pleasant. So maybe resist the urge to put your pen cap in your mouth.

[h/t Science Alert]

Mark Ralston/AFP/Getty Images
Big Questions
What Causes Sinkholes?
Mark Ralston/AFP/Getty Images
Mark Ralston/AFP/Getty Images

This week, a sinkhole opened up on the White House lawn—likely the result of excess rainfall on the "legitimate swamp" surrounding the storied building, a geologist told The New York Times. While the event had some suggesting we call for Buffy's help, sinkholes are pretty common. In the past few days alone, cavernous maws in the earth have appeared in Maryland, North Carolina, Tennessee, and of course Florida, home to more sinkholes than any other state.

Sinkholes have gulped down suburban homes, cars, and entire fields in the past. How does the ground just open up like that?

Sinkholes are a simple matter of cause and effect. Urban sinkholes may be directly traced to underground water main breaks or collapsed sewer pipelines, into which city sidewalks crumple in the absence of any structural support. In more rural areas, such catastrophes might be attributed to abandoned mine shafts or salt caverns that can't take the weight anymore. These types of sinkholes are heavily influenced by human action, but most sinkholes are unpredictable, inevitable natural occurrences.

Florida is so prone to sinkholes because it has the misfortune of being built upon a foundation of limestone—solid rock, but the kind that is easily dissolved by acidic rain or groundwater. The karst process, in which the mildly acidic water wears away at fractures in the limestone, leaves empty space where there used to be stone, and even the residue is washed away. Any loose soil, grass, or—for example—luxury condominiums perched atop the hole in the ground aren't left with much support. Just as a house built on a weak foundation is more likely to collapse, the same is true of the ground itself. Gravity eventually takes its toll, aided by natural erosion, and so the hole begins to sink.

About 10 percent of the world's landscape is composed of karst regions. Despite being common, sinkholes' unforeseeable nature serves as proof that the ground beneath our feet may not be as solid as we think.

A version of this story originally ran in 2014.


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