Quicklime
Or: The Sweet Smell of Desiccation
Add enough heat to limestone, and you end up with a white, soft lump of something that doesn't do what normal rocks should when you throw water on them.
It gets hotter.
Yes, But What Is It?
Limestone is a sort of rock, fairly uninteresting to speak to, though reportedly quite a good listener. It's mainly calcium carbonate with bits of other minerals and a spot of magnesium carbonate thrown in for flavor--a favorite ingredient amongst architects. But this is just the base.
When you put it to torch at about 18,000 degrees Farenheit--that's 10,000 Celsius, for those of you who feel your water should freeze at 0--it is calcined, and thus becomes a great deal more fun.
Feeling Hot, Hot, Hot
Calcined limestone--CaO/MgO, calcium oxide/magnesium oxide is better known as quicklime, and is characterized by the chemical reaction between it and water that releases comparatively large amounts of heat.
While it's doing that, by the way, the solid rapidly increases its volume. So stand back, and don't touch.
It's Not as Cool As Dry Ice, Is It?
No. Dry ice is much neater to play with. But quicklime is used for a wide variety of industrial applications, including:
And in olden times: