Warning: older versions of this answer incorrectly claimed that CO2
gas has no toxicity, and did not indicate that some grades of dry ice are unfit for human consumption. This should serve as a reminder not to put too much trust in any web site, including this one.
Dry ice is frozen carbon dioxide. It is special because it doesn't melt. Dry ice at atmospheric pressure goes straight from solid for to gas form. This is called sublimation. If you put dry ice in water, the carbon dioxide will turn to gas and then bubble out. The carbon dioxide gas itself is toxic if you breathe it in high concentrations (http://en.wikipedia.org/wiki/Carbon_dioxide#Toxicity
) and of course it is also very cold. Dry ice should be handled with gloves or tongs so as not to cause frostbite.
Adding dry ice to drinks is fine so long as
1. You use only 'food grade' dry ice, free of various contaminants in industrial grade material.
2.You are very careful not to ingest any of the frozen dry ice. http://www.dryiceinfo.com
gives some suggestions for use with, for example, large bowls of punch. The dry ice will make the punch give off a heavy fog (the cold carbon dioxide bubbles out of the punch, condenses water vapor, and sinks to the floor). This can be quite a lot of fun at Halloween parties, as your fruit punch can look like a seething witches' brew.
You should use 2-4 pounds of dry ice per gallon of liquid at room temperature. Use large chunks of dry ice instead of small ones. Dry ice is heavier than water, so it will sink to the bottom. This is a very important part, when the dry ice is almost gone, a layer of water will freeze around it. This chunk will float to the top. Inside the regular ice is still a piece of dry ice. This must be removed. NEVER ingest dry ice, even when it is coated with regular ice. This can cause frostbite inside your stomach! When ladling punch out of the punch bowl, do not include any dry ice, or even ordinary ice as it may have a piece of dry ice inside. Ordinary ice can be added later.
So if you have a cooler of regular ice and dry ice, most likely there is some dry ice embedded in the regular ice, and it is best not to eat the ice. Once it has all melted, there is no problem with the water -- it really is just plain, ordinary water, and the carbon dioxide goes into the air.
For more information about dry ice, check out www.dryiceinfo.com
Adam (modified by Mike W.)
(published on 10/22/2007)