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

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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.

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iStock // Ekaterina Minaeva
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technology
Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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iStock
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Health
200 Health Experts Call for Ban on Two Antibacterial Chemicals
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iStock

In September 2016, the U.S. Food and Drug Administration (FDA) issued a ban on antibacterial soap and body wash. But a large collective of scientists and medical professionals says the agency should have done more to stop the spread of harmful chemicals into our bodies and environment, most notably the antimicrobials triclosan and triclocarban. They published their recommendations in the journal Environmental Health Perspectives.

The 2016 report from the FDA concluded that 19 of the most commonly used antimicrobial ingredients are no more effective than ordinary soap and water, and forbade their use in soap and body wash.

"Customers may think added antimicrobials are a way to reduce infections, but in most products there is no evidence that they do," Ted Schettler, science director of the Science and Environmental Health Network, said in a statement.

Studies have shown that these chemicals may actually do more harm than good. They don't keep us from getting sick, but they can contribute to the development of antibiotic-resistant bacteria, also known as superbugs. Triclosan and triclocarban can also damage our hormones and immune systems.

And while they may no longer be appearing on our bathroom sinks or shower shelves, they're still all around us. They've leached into the environment from years of use. They're also still being added to a staggering array of consumer products, as companies create "antibacterial" clothing, toys, yoga mats, paint, food storage containers, electronics, doorknobs, and countertops.

The authors of the new consensus statement say it's time for that to stop.

"We must develop better alternatives and prevent unneeded exposures to antimicrobial chemicals," Rolf Haden of the University of Arizona said in the statement. Haden researches where mass-produced chemicals wind up in the environment.

The statement notes that many manufacturers have simply replaced the banned chemicals with others. "I was happy that the FDA finally acted to remove these chemicals from soaps," said Arlene Blum, executive director of the Green Science Policy Institute. "But I was dismayed to discover at my local drugstore that most products now contain substitutes that may be worse."

Blum, Haden, Schettler, and their colleagues "urge scientists, governments, chemical and product manufacturers, purchasing organizations, retailers, and consumers" to avoid antimicrobial chemicals outside of medical settings. "Where antimicrobials are necessary," they write, we should "use safer alternatives that are not persistent and pose no risk to humans or ecosystems."

They recommend that manufacturers label any products containing antimicrobial chemicals so that consumers can avoid them, and they call for further research into the impacts of these compounds on us and our planet.

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