[Agent_4573]

I was reading the post about freezing the tank someone is sorely mistaken. Maybe you meant psi instead of lbs. If you put 70 lbs of air in a tank and then drop temp of the tank 50 degrees, there is still 70 lbs of air in the tank, the weight won't change at all. What will change is the psi on the tank. I'm going to give an example using the equation pv=nrt. where p=pressure, v=volume, n=number of moles of gas, r= universal gas constant=~.083, t=tempeture in kelvin=celcuis temp+273.

Were going to use the metric system too because it makes stuff so much easier.

So we start with a tank that holds 100 liters of air at STP(0 degrees celcius, 1 atm) according to pv=nrt; 1atm*100liters=n*.083*273. Therefore there are 4.41 moles of air. If we don't add any more air, there will always be 4.41 moles of air in the tank. We now drop the tempeture 100 degrees celcius and look for the new pressure on the tank.
pv=nrt p*100liters=4.41*.083*173, the new pressure on the tank is only .633 atm. Therefore you can put more cold air in at a lower tempeture. But the reason i wrote all this is to say that the number of moles, which is directly proportional to weight, doesn't change when you drop the tempeture. The only thing that will effect the poundage of the air tank is the volume of air you put in it. Cooling the tank only allows you to put more air in at a lower pressure.