WEBVTT - Why Does Ice Get Cloudy?

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<v Speaker 1>Welcome to brain stuff from how stuff works, Hey, brain stuff,

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<v Speaker 1>Lauren vocal bam here. When temperatures dip below freezing, it

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<v Speaker 1>adds a number of extra hazards to driving, but perhaps

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<v Speaker 1>none so tricksy as black ice. These are slick patches

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<v Speaker 1>of ice that blend in with the black pavement beneath

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<v Speaker 1>them because they're so transparent. When drivers blind to the

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<v Speaker 1>danger steer their cars over the ice, they can lose

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<v Speaker 1>traction and wind up in an accident. Other kinds of

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<v Speaker 1>ice are easier to see. You've no doubt noticed that

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<v Speaker 1>homemade ice cubes usually look cloudy in the little opaque

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<v Speaker 1>in the middle, like whitish blocks of cotton candy. That

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<v Speaker 1>stands in contrast to the frightening clarity of black ice.

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<v Speaker 1>So how come black ice is see through but the

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<v Speaker 1>cubes in your typical ice trays are not. Liquid water

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<v Speaker 1>appears to be clear. That's because the material neither absorbs

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<v Speaker 1>nor reflects most of the spectrum of visible light. Most

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<v Speaker 1>wavelengths in the spectrum pass right through it. And that's right,

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<v Speaker 1>I said. Most technical water is not colorless, although it

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<v Speaker 1>often looks that way. Believe it or not, The liquid

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<v Speaker 1>has a natural bluish tint, owing to the fact that

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<v Speaker 1>it absorbs red, yellow, and orange light more easily than

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<v Speaker 1>blue light. But our human eyes can only observe this

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<v Speaker 1>azure quality in deep bodies of water. This helps explain

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<v Speaker 1>why ocean water and glacial ice look blue to us,

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<v Speaker 1>while glassfuls of drinking water look transparent. Yet there is

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<v Speaker 1>a deceptive quality to water. No matter how fresh and

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<v Speaker 1>clear it may seem, it's never one pure. A sample

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<v Speaker 1>of H two O might contain floating bits of organic

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<v Speaker 1>matter like algae or plant remains, along with suspended sediments

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<v Speaker 1>a dust particles, or flexi minerals like calcium and lime.

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<v Speaker 1>It may also harbor lots of dissolved gases such as oxygen.

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<v Speaker 1>With outsid oxygen, fish wouldn't be able to breathe. Gases

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<v Speaker 1>and physical impurities are the key to understanding why those

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<v Speaker 1>ice cubes in your tray are so darn cloudy. When

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<v Speaker 1>water freezes, internal debris and air bubbles can become concentrated.

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<v Speaker 1>The class stirs impede light, causing all the differently colored

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<v Speaker 1>frequencies on the visible light spectrum to scatter. When this happens,

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<v Speaker 1>it makes the ice look white and clouded. But it

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<v Speaker 1>doesn't always happen. Let's take for a case study, a

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<v Speaker 1>YouTuber who once appeared to walk on water. Thomas Nunnock

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<v Speaker 1>filmed himself in a travel companion walking across vel k

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<v Speaker 1>Hankovo place So, a deep freshwater lake in the Slovakian Mountains.

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<v Speaker 1>His video went viral because it shows the two men

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<v Speaker 1>standing on some unbelievably clear ice. The lake bottom rocks

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<v Speaker 1>below them are pristinely visible through the frozen water. The

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<v Speaker 1>ice and Nunus video was so transparent that some viewers

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<v Speaker 1>assumed the footage had been faked, but the phenomenon is

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<v Speaker 1>very real, and when the lake freezes over, as it

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<v Speaker 1>often does, the surface ice can be crystal clear. An

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<v Speaker 1>ice sheet needs to be almost entirely free of both

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<v Speaker 1>air bubbles and debris in order to have this degree

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<v Speaker 1>of clarity. There are other requirements as well. Ice is

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<v Speaker 1>made up of crystals, and when water eases rapidly, those

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<v Speaker 1>crystals tend to be small and numerous. That makes the

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<v Speaker 1>ice look whider because each of those crystals have reflective surfaces,

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<v Speaker 1>so if there are more crystals, there will be more

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<v Speaker 1>reflection going on, which will help scatter incoming light on

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<v Speaker 1>the other hand, ice that's been slowly frozen is built

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<v Speaker 1>out of fewer and larger crystals, and those promote transparency.

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<v Speaker 1>So ice will only be see through and crystal clear

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<v Speaker 1>if it freezes slowly and doesn't have too many impurities

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<v Speaker 1>or crystals. Thomas knocks Now famous YouTube video is what

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<v Speaker 1>it looks like when all these conditions are met. On

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<v Speaker 1>the day of his trek, the lake was topped with

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<v Speaker 1>an icy blanket that was around two centimeters thick. That's

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<v Speaker 1>about three quarters of an inch. The water must have

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<v Speaker 1>frozen gradually during a tranquil period with no strong winds

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<v Speaker 1>to deposit debris in the lake or to churn up

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<v Speaker 1>the water. We see the same kind of thing happening

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<v Speaker 1>in roadway black ice, although not all of this stuff

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<v Speaker 1>comes from the same source. It can start out as fog, mist, drizzle,

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<v Speaker 1>or melted snow. It always freezes slowly during low wind periods.

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<v Speaker 1>It's consistently then, and it contains very few impurities. That's

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<v Speaker 1>why black ice is so transparent and frustrating to motorists,

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<v Speaker 1>but highway annoyances nonwithstanding, transparent ice isn't as common in

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<v Speaker 1>nature as the white clouded variety. There are a lot

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<v Speaker 1>of reasons why given ice chunk you find out in

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<v Speaker 1>nature might not be clear. Some ice is made up

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<v Speaker 1>of fallen snowflakes whose angular shapes and regular crystals scattered

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<v Speaker 1>light and sometimes temperatures drop rapidly, resulting in ice with

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<v Speaker 1>those smaller crystals. Artificial ice is subject to these same

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<v Speaker 1>physical laws. Most household ice trays are designed to freeze

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<v Speaker 1>little blocks of water from the outside. In doing so

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<v Speaker 1>has the side effect of driving impurities within the water

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<v Speaker 1>towards the center of each cube. The finished products therefore

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<v Speaker 1>look white and hazy in the middle. To get clearer,

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<v Speaker 1>more attractive cubes, some restaurants use expensive machines that freeze

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<v Speaker 1>water very gradually and exclusively from one side that lets

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<v Speaker 1>the impurities escape outward. Though if you want to make

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<v Speaker 1>clearer cubes at home, you can do it on cheap.

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<v Speaker 1>Try boiling the water first, thus ridding it of dissolved

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<v Speaker 1>gases before the freezing process starts, and just blood it

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<v Speaker 1>cool of it before you add it to your ice tray.

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<v Speaker 1>You wouldn't want to melt the plastic. Today's episode was

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<v Speaker 1>written by Mark Mancini and produced by Tyler Clay. Shop

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<v Speaker 1>for your favorite brainy companion in our online shop to

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<v Speaker 1>public dot com slash brain stuff, and of course, for

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<v Speaker 1>more on this and lots of other completely clear topics,

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<v Speaker 1>visit our home planet, how stuff Works dot com