Question

Why is solid CO2 known as dry ice?

Answer 1

Dry ice is called dry ice because the solid turns to gas when heated, without turning into a liquid first. However, if we apply pressure and heat, we can turn it into a liquid, and sure, we can swim in it. We know this because of something called the phase diagram of carbon dioxide (the "stuff" of dry ice).

Answer 2

Solid carbon dioxide is known as dry ice. It sublimes at –78°C becoming an extremely cold gas. It is often used in theatres or nightclubs to produce clouds (looking a bit like smoke). Because it is denser than the air, it stays low. It cools the air and causes water vapour in the air to condense into tiny droplets – hence the clouds. 
 
It is also useful in the physics (and chemistry) laboratory. 
 
The Institute of Physics has kindly produced this video to explain how dry ice is formed.