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