Although it's not exactly Mothra vs. Godzilla, the folks at Jefferson Lab -- in a segment for their YouTube series "Frostbite Theater" -- put dry ice and liquid nitrogen in the same container to see what would happen. Spoiler alert: The denser dry ice, which is about -110°F, sinks to the bottom of the container, and the liquid nitrogen, at about -321°F, begins to boil rapidly. Who knew dry ice was so hot? Well, in science, everything's relative.
Dry ice is solidified carbon dioxide gas. It's called "dry" ice because, unlike ice made from water, it sublimates at room temperature -- meaning that it goes directly from a solid to a gas, rather than melting into a messy puddle of liquid. These characteristics make dry ice valuable for keeping food cold without refrigeration, and for creating spooky foggy effects at Halloween.
Uses for Dry Ice
Beyond the ice cream cart and your punch bowl, however, dry ice is widely available and has many commercial uses. Medical facilities use it to keep specimens cold. Certain industries use dry ice -- in a method called "dry ice blasting," similar to sand blasting -- to clean equipment. For example, it is used in the oil fields to remove the sludge from the bottom of oil tanks. According to DryIceInfo.com, the commercial uses of dry ice range from cattle branding to meat processing to floor tile removal to gopher eradication. It's versatile stuff.
Liquid nitrogen is, as the name implies, nitrogen cooled to such an extent that it leaves the gaseous state and becomes liquid. As the folks at Jefferson Lab demonstrated, liquid nitrogen is much colder than dry ice. This makes it more dangerous to handle and therefore less available to the general public. Although some bars make cocktails with liquid nitrogen, in October 2012 this fad resulted in a teenager in the UK having emergency surgery to remove her stomach after she drank one. The bar quickly removed such drinks from its menu.
Uses for Liquid Nitrogen
Liquid nitrogen, handled safely, can be great fun in chemistry class. The Cornell University website lists many oddball uses for the stuff, including pouring about a cup of liquid nitrogen into a quart of bubble solution -- "Bubbles go everywhere!" -- and freezing a banana in liquid nitrogen and using it to hammer a nail. Silly, right? But these tricks reveal two of liquid nitrogen's most valuable properties: it expands quickly and freezes objects immediately.
The controversial process known as "fracking" takes advantage of liquid nitrogen's rapid expansion to fracture rock formations that contain natural gas. And liquid nitrogen's rapid and thorough cooling is put to use in many medical applications, for example in freezing -- and immediately destroying -- unwanted tissue, such as warts and small cancers.