yeah its rock salt, if you look in the November Freeze you can see the lifty of the month(Krissy) with a salt gun. Anyways rock salt is actually sold as driveway deicers, so dont put too much on your stuff or else its gonna just melt through.
It melts a top layer of snow, into water. The layers underneath though that are unaffected by the ice are still cool enough to refreeze the layer of water on top, freezing it into ice.
'Thanks for ripping off my friend. He has a magnum.' - SkogenJake
'I was like a 13 year old girl meeting a backstreet boy' - Ski@Jaypeak2 ... on meeting Glen Plake
Salt acts as an impurity to the water (in this case the snow) And so the interesting effect of any impurity is that it decreases the freezing point and raises the boiling point.
It does this because the Impurities dissolve into the water and mess up the packing arragments of the molecules which makes it harder for the water to freeze. This fucks up the freezing melting equlibrium and so as melting stays the same and freezing is slowed. You get an overall gain in melting. ie the snow melts.
Now this is where it gets important to add just the right amount of salt. Too much and the salt melts all the snow.
Just enough, and sufficient water is melted to reduce the concentration of the salt dissolved in the water so that refreezing can occur.
There you go. That is why salt melts ice. By the way any ionic compound will have the same effect! but salt is the cheapest to use.