1 00:00:00,560 --> 00:00:03,840 Speaker 1: Welcome to brain Stuff from houstuff works dot com where 2 00:00:03,880 --> 00:00:08,039 Speaker 1: smart happens. Join Josh and Chuck, the guys who bring 3 00:00:08,080 --> 00:00:10,240 Speaker 1: you stuff you should know, as they take a trip 4 00:00:10,280 --> 00:00:12,360 Speaker 1: around the world to help you get smarter in a 5 00:00:12,400 --> 00:00:16,000 Speaker 1: topsy turv economy. Check out the all new Superstuff Guide 6 00:00:16,040 --> 00:00:19,200 Speaker 1: to the Economy from how stuff Works dot Com, available 7 00:00:19,239 --> 00:00:25,880 Speaker 1: now exclusively on iTunes. Hi Am Marshall Brain with today's question, 8 00:00:26,320 --> 00:00:32,120 Speaker 1: how does dry ice work? Dry ice is frozen carbon dioxide. 9 00:00:32,520 --> 00:00:35,400 Speaker 1: A block of dry ice has a surface temperature of 10 00:00:35,640 --> 00:00:39,279 Speaker 1: minus a hundred nine degrees fahrenheit or minus seventy eight 11 00:00:39,280 --> 00:00:43,479 Speaker 1: degrees centigrade. Dry ice also has the very nice feature 12 00:00:43,520 --> 00:00:47,240 Speaker 1: of sublimation. As it breaks down, it turns directly into 13 00:00:47,320 --> 00:00:51,640 Speaker 1: carbon dioxide gas, rather than ever becoming a liquid. The 14 00:00:51,760 --> 00:00:55,760 Speaker 1: super cold temperature and the sublimation feature make dry ice 15 00:00:55,920 --> 00:00:59,400 Speaker 1: great for refrigeration. For example, if you want to send 16 00:00:59,480 --> 00:01:02,480 Speaker 1: something frozen across the country, you can pack it in 17 00:01:02,600 --> 00:01:06,280 Speaker 1: dry ice. It'll be frozen when it reaches its destination 18 00:01:06,440 --> 00:01:09,319 Speaker 1: and there won't be any messy liquid leftover like you 19 00:01:09,319 --> 00:01:12,920 Speaker 1: would have with normal ice. Many people are familiar with 20 00:01:12,959 --> 00:01:16,399 Speaker 1: liquid nitrogen, which boils at minus three hundred and twenty 21 00:01:16,440 --> 00:01:21,520 Speaker 1: degrees fahrenheit. Liquid nitrogen is fairly messy and difficult to handle. 22 00:01:22,000 --> 00:01:25,640 Speaker 1: So why is nitrogen a liquid while carbon dioxide is 23 00:01:25,680 --> 00:01:29,760 Speaker 1: a solid. This difference is caused by the solid liquid 24 00:01:29,840 --> 00:01:34,319 Speaker 1: gas features of nitrogen and carbon dioxide. We're all familiar 25 00:01:34,360 --> 00:01:37,440 Speaker 1: with the solid liquid gas behavior of water. We know 26 00:01:37,560 --> 00:01:41,080 Speaker 1: that at sea level, water freezes at thirty two degrees 27 00:01:41,120 --> 00:01:45,320 Speaker 1: fahrenheit and boils at two hundred twelve degrees fahrenheit. Water 28 00:01:45,400 --> 00:01:48,920 Speaker 1: behaves differently as you change the pressure. However, as you 29 00:01:48,960 --> 00:01:52,600 Speaker 1: lower the pressure, the boiling point falls. If you lower 30 00:01:52,640 --> 00:01:56,200 Speaker 1: the pressure enough, water will actually boil at room temperature. 31 00:01:56,640 --> 00:01:59,720 Speaker 1: If you plot out the solid liquid gas behavior of 32 00:01:59,760 --> 00:02:03,080 Speaker 1: a substance like water on a graph showing both temperature 33 00:02:03,200 --> 00:02:06,720 Speaker 1: and pressure, you create what's called a phase diagram for 34 00:02:06,760 --> 00:02:10,959 Speaker 1: the substance. The phase diagram shows the temperatures and pressures 35 00:02:11,000 --> 00:02:14,560 Speaker 1: at which a substance changes between a solid, a liquid, 36 00:02:14,560 --> 00:02:17,280 Speaker 1: and a gas. When you look at the phase diagram 37 00:02:17,320 --> 00:02:20,760 Speaker 1: for carbon dioxide, what you can see is that at 38 00:02:20,800 --> 00:02:25,200 Speaker 1: normal pressures, carbon dioxide moves straight between a gas and 39 00:02:25,280 --> 00:02:28,840 Speaker 1: a solid. It's only at much higher pressures that you 40 00:02:28,919 --> 00:02:33,280 Speaker 1: find liquid carbon dioxide. For example, a high pressure tank 41 00:02:33,360 --> 00:02:38,640 Speaker 1: of carbon dioxide or a carbon dioxide fire extinguisher contains 42 00:02:38,880 --> 00:02:42,800 Speaker 1: liquid carbon dioxide. To make dry ice, you start with 43 00:02:42,840 --> 00:02:46,480 Speaker 1: a high pressure container full of liquid carbon dioxide. When 44 00:02:46,520 --> 00:02:49,680 Speaker 1: you release the liquid carbon dioxide from the tank, the 45 00:02:49,800 --> 00:02:52,960 Speaker 1: expansion of the liquid and the high speed of operation 46 00:02:53,000 --> 00:02:56,160 Speaker 1: of carbon dioxide cools the remainder of the liquid down 47 00:02:56,200 --> 00:02:59,680 Speaker 1: to the freezing point, where it turns directly into a solid. 48 00:03:00,120 --> 00:03:03,480 Speaker 1: If you've ever seen a carbon dioxide fire extinguisher inaction, 49 00:03:03,919 --> 00:03:07,880 Speaker 1: you've seen this carbon dioxide snow form in the nozzle. 50 00:03:08,440 --> 00:03:12,000 Speaker 1: You compress the carbon dioxide snow to create a block 51 00:03:12,040 --> 00:03:15,920 Speaker 1: of dry ice. Do you have any ideas or suggestions 52 00:03:15,960 --> 00:03:18,880 Speaker 1: for this podcast? If so, please send me an email 53 00:03:18,919 --> 00:03:22,119 Speaker 1: at podcast at how stuff works dot com. For more 54 00:03:22,120 --> 00:03:24,360 Speaker 1: on this and thousands of other topics, go to how 55 00:03:24,400 --> 00:03:27,880 Speaker 1: stuff works dot com.