Subject: Why does a gas canister become cold when pressure is released?

I would like a more detailed answer than those I found posted.  One answer 
mentioned the ideal gas equation, since P decreases T must also.  Yet, wouldn't n 
be decreasing as well since gas is being discharged from the canister?  What I 
would really like is an explanation using kinetic theory.  Does the gas absorb 
energy when expanding (making the container cold), if so why?  On the otherhand, 
don't expanding gases lose kinetic energy when colliding with other particles and 
would this cool the container as well? Please straighten out which of these is 
happening (or something else) and which accounts for the drop in temperature of 
the container.  Thank you very much! 

Re: Why does a gas canister become cold when pressure is released?