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Speaker 1: now exclusively on iTunes. Hi Am Marshall Brain with today's question,
Speaker 1: how does dry ice work? Dry ice is frozen carbon dioxide.
Speaker 1: A block of dry ice has a surface temperature of
Speaker 1: minus a hundred nine degrees fahrenheit or minus seventy eight
Speaker 1: degrees centigrade. Dry ice also has the very nice feature
Speaker 1: of sublimation. As it breaks down, it turns directly into
Speaker 1: carbon dioxide gas, rather than ever becoming a liquid. The
Speaker 1: super cold temperature and the sublimation feature make dry ice
Speaker 1: great for refrigeration. For example, if you want to send
Speaker 1: something frozen across the country, you can pack it in
Speaker 1: dry ice. It'll be frozen when it reaches its destination
Speaker 1: and there won't be any messy liquid leftover like you
Speaker 1: would have with normal ice. Many people are familiar with
Speaker 1: liquid nitrogen, which boils at minus three hundred and twenty
Speaker 1: degrees fahrenheit. Liquid nitrogen is fairly messy and difficult to handle.
Speaker 1: So why is nitrogen a liquid while carbon dioxide is
Speaker 1: a solid. This difference is caused by the solid liquid
Speaker 1: gas features of nitrogen and carbon dioxide. We're all familiar
Speaker 1: with the solid liquid gas behavior of water. We know
Speaker 1: that at sea level, water freezes at thirty two degrees
Speaker 1: fahrenheit and boils at two hundred twelve degrees fahrenheit. Water
Speaker 1: behaves differently as you change the pressure. However, as you
Speaker 1: lower the pressure, the boiling point falls. If you lower
Speaker 1: the pressure enough, water will actually boil at room temperature.
Speaker 1: If you plot out the solid liquid gas behavior of
Speaker 1: a substance like water on a graph showing both temperature
Speaker 1: and pressure, you create what's called a phase diagram for
Speaker 1: the substance. The phase diagram shows the temperatures and pressures
Speaker 1: at which a substance changes between a solid, a liquid,
Speaker 1: and a gas. When you look at the phase diagram
Speaker 1: for carbon dioxide, what you can see is that at
Speaker 1: normal pressures, carbon dioxide moves straight between a gas and
Speaker 1: a solid. It's only at much higher pressures that you
Speaker 1: find liquid carbon dioxide. For example, a high pressure tank
Speaker 1: of carbon dioxide or a carbon dioxide fire extinguisher contains
Speaker 1: liquid carbon dioxide. To make dry ice, you start with
Speaker 1: a high pressure container full of liquid carbon dioxide. When
Speaker 1: you release the liquid carbon dioxide from the tank, the
Speaker 1: expansion of the liquid and the high speed of operation
Speaker 1: of carbon dioxide cools the remainder of the liquid down
Speaker 1: to the freezing point, where it turns directly into a solid.
Speaker 1: If you've ever seen a carbon dioxide fire extinguisher inaction,
Speaker 1: you've seen this carbon dioxide snow form in the nozzle.
Speaker 1: You compress the carbon dioxide snow to create a block
Speaker 1: of dry ice. Do you have any ideas or suggestions
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Speaker 1: at podcast at how stuff works dot com. For more
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