Ice is just frozen water. But when you freeze water, different things could happen.
Water from different places have different minerals in it. That's why different ice tastes different to you.
Another difference is the density of the ice. When water freezes in
a freezer, a lot of air is frozen along with it. But there are also
glaciers, huge ice sheets hundreds of feet thick. They are so heavy
that a lot of that extra air has been pressed out. That makes the
glacial ice a little bit heavier than the ice from your freezer.
The biggest difference from one piece of ice to another is it's
structure. Ice is a crystal. A crystal is the name used when atoms and
molecules are formed into an organized shape. A good example is a brick
building. The bricks are laid so that they are in a pattern. However,
when a crystal (like ice) forms, it never works perfectly. Every
crystal has many defects in it. When you let the ice take a long time
to freeze, it will have fewer defects.
As for the last part of your question, anything warmer than 0
degrees C can melt ice. The warmer, the better. Another way to melt ice
is to cover it in salt. Regular water freezes at 32 Fahrenheit, but
salt water freezes at a much lower temperature. When you put salt on
top of ice, the salt causes the ice to melt since the salty water finds
it too warm to remain frozen. This is why they put salt on the roads
when it snows. The salt melts the ice (unless it's colder than about 0
Its an interesting fact that when you mix ice with salt in this
way, causing the ice to melt, the remaining ice and salt-water mixture
actually gets colder. This is because heat is required to melt the ice
that is touching the salt, and this heat is drawn out of the
surrounding ice. If you take a bucket of crushed ice and dump a bunch
of salt into it (and stir a bit) the remaining mixture will be much
colder that it started out being. Before freezers this was a common way
to get temperatures cold enough to make ice-cream.
(republished on 07/25/06)