This is the first segment in a series on Dry Ice Experiments.
Science is awesome. But when we 'try this at home', we must remember that safety comes first. This is especially true when it comes to dry ice (solid-state carbon dioxide).
Dry ice is formed by compressing gaseous carbon dioxide until it liquefies. This takes an amazing amount of pressure—870 psi! When the pressure is released, some of the carbon dioxide evaporates which cools the remaining carbon dioxide to a temperature of approx. -109° F (-79°C) and results in a solid.
A solid that's really stinkin' cold.
This means that if you (or your child) touches it, it will cause immediate frostbite. Though that might be educational in itself, it is probably best to avoid such an experience. It is very important to avoid touching the dry ice with your hands (do I even need to say 'don't eat it'?). Use heavy gloves, tongs, or both together to move and position the dry ice. Constantly remind yourself and your children of this. As experiments get rambunctious, it is easy to forget the safety rules.
Never place dry ice directly on the counter top, and be careful which plates and pans you use to hold it. We used metal cookie sheets, plastic bowls, and plastic and wooden tables, but I would make certain to use non-favorite ones, just in case it warps or cracks.
Solidified carbon dioxide does not return to a liquid state because of the pressure constraints of the normal atmosphere. Instead, it sublimates (skips the liquid phase) directly into a gaseous state. This gas is still pretty cold, and though it is colorless and you can't see it, it causes water vapor in the air to condense, creating the clouds and mist we are familiar with.
Carbon dioxide is a heavy gas, heavier than air. This is important to know because this means it will displace the air (and, therefore, oxygen) from the bottom of it's container (or room). In other words, you run the risk of suffocation if the room, car, wherever you are is not properly ventilated. Never have people or pets lie down in the area where you are working and move to fresh air immediately if you feel short of breath. When we were experimenting, we left the room's door to the outside open and placed a box fan in the doorway. It was also helpful to stop every so often and ask the children if they were feeling all right. Sometimes children get so excited that they don't notice they can't breathe—until it's too late.
Because the dry ice is sublimating, and the resulting gas takes up a larger volume than the solid block, any container in which it is placed must also be vented. Unventilated dry ice can make a container explode. That can be fun if it is planned for and anticipated, not so fun if it was the cooler in the trunk of your car or a glass jar. We kept the cooler vented with a wooden spoon until the blocks were needed.
Large blocks of dry ice can be broken up into pieces by using a hammer and chisel (I used a hammer and putty knife). Wear safety glasses to prevent pieces from flying into your eyes and make certain there is no one near you that could get hit by pieces.
When you are finished using dry ice, simply put it outside to sublimate or store it in a vented cooler. If you put it in your freezer, remember that it is colder than you usually keep your freezer, and it might burn the other items in it or cause the freezer to shut off completely.
DRY ICE SAFETY RULES
1. Never touch dry ice. Use heavy gloves or tongs.
2. Maintain proper ventilation.
3. Always vent the container.
4. Wear safety glasses when breaking up large blocks.
If these rules are followed, experimenting with dry ice is a fantastic learning experience!
Using sharp scissors (be careful, kids, don't run!), we cut a small (like in the lid. I then placed a small piece (1" long or less) piece of dry ice in the container and fill it with warm water. The lid was placed back on. That was cool enough because 
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