LotR -- Book 4 - Chapter 03 - The Black Gate Is Closed

[lord of dor-lomin]

But thinking about it, how would Gollum know you COULD destroy the ring by throwing it in to the cracks of doom?

(come to think of it, how do gandalf and elrond know this - or was it an educated guess?)

I've always wondered this, too. Did Elrond take a sample from the Ring and toss it into the cracks? "Yep, it disolved, just like we thought."

How could they have possibly known for certain that Mt Doom would destroy it? Since Sauron can stoke Mt Doom's fire, isn't it possible that he got it hotter than it had ever been for the creation of the Ring, and that it would take his purposeful tinkering to get it that hot again, and that the Ring could only be destroyed in that way- Sauron doing it on purpose by turning the knob on Mt Doom to the "Ring-creation/destruction" temperature setting?