Tried making ice-cream at home? All
that ice and salt makes such a mess, doesn't it? What if there was a dry kind
of ice, that didn't melt into a mess? Well, there is - it's called dry ice.
The trouble with
water ice
Ice is anything
that is frozen, though we commonly use the word for frozen water. Dry ice is
frozen carbon dioxide. Carbon dioxide goes from being a gas to a solid at
-78.5°C. Its a lot more useful than ice for freezing some kinds of foods.
Water ice can
cause a few problems. When it melts, the water can make a sticky and dirty
mess. It helps bacteria and fungi to grow, spoiling the food. It can also cause
crystal formation, ruining the texture of some water-containing foods.
Whats good about
dry ice?
Dry ice doesnt
melt, but becomes gas immediately (this is called sublimation). Also, it stays
solid much longer, because a lot of heat is needed to sublime it completely.
Therefore, theres no mess being created, for the sublimed dry ice will simply
waft into the air. And carbon dioxide acts as a preservative, killing bacteria
and fungi. And it doesnt help crystal formation.
So next time you
make ice cream at home, try dry ice!
Artificial fog
Seen a horror or
thriller film, in which theres a lady in white walking on a lonely road,
surrounded by cold fog? The fog is made of dry ice!
You keep big
blocks of dry ice on the film sets. They slowly sublime into carbon dioxide.
This is a dense gas, heavier than air. So it hangs low, looking like fog. There
are other ways to make artificial fog, but using dry ice is safer. Thats
because you need no chemical other than carbon dioxide.
So next time you
see a thriller film, you can point out the secret of the fog to your friends!
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