[bashbaliga]

In accordance with the forum rules i will tell you what i know, this is probably a noob question but the other day i saw a shopkeeper showing me a limestone rock and pouring water over it and it immediately disintegrated with white smoke coming out of it within seconds, the limestone was now something like a white powderish substance when touched by hand, I also know limestone is made out of crushed up sea shell and is a sedimentary rock, and was used for many constructional purposes,
My questions are
1) what does the limestone absorb ? Is it only carbon  di oxide and water ?
2) what was the white smoke ?
3)If this rock can be used to purify gases from co2 and moisture, how much limestone would it need ie how much mositure and co2 can a (say) 100g of limestone absorb.
4)I heard there are many huge limestone rocks in the nature, how is it not disintegrated when it rains.

Forgive me if i'm asking too much, have a nice day.

[Arkcon]

Briefly, the question isn't as simple as you'd expect.  However, some points:

1).  This isn't limestone, but instead quick lime, or slaked lime, or burnt limestone.  You can see more here: http://en.wikipedia.org/wiki/Limestone#Uses and read what the links there go to, and what those links go to, until you understand, at least, that this is pretty complicated.

2).  I don't know exactly what the white smoke is.  This sort of fumeing is pretty common, in diverse applications.  Briefly, the lime has gotten hot from reaction with water, some water has vaporized, and re-condensed like your breath on a cold humid day.  Also, some of the lime dust may be mixed in.

3).  Ah yes, here we are again, I've told you before -- we can determine how much the material can theoretically absorb, using stochiometry.  We need a balanced chemical reaction.  But if you're going to use it as an absorbent, there are more engineering concerns, for example, how to be sure the gas stream is piped so that the entire mass of solid is well exposed, but the gas still flows freely, and the outer surface of the solid isn't coated with reactant and then stops working.  So although the academic determination lakes a bit of work, I can't be certain that its practical.

4).  Again, limestone in nature isn't slaked or burnt lime.  In fact, then reaction with water and CO2 turn lime back into limestone.  Unrelated, but it is true that limestone is attacked by acids in the environment, that's why we have limestone caves, and sinkholes.