The specific gravity of propane is 0.495 at 25oC.
Used to make lots of different sorts of useful and essential plastics and skateboards
Comes from crude oil which is non-renewable.
try here!! http://www.youtube.com/watch?v=bpMS15kJyOY
If there is propane in the tank there will be pressue. It can't lose its pressure. If one has a propane tank that has "lost its pressure" even though there is propane in the tank, there is almost certainly a problem with the valve (assuming the individual attempting to use the tank knows how). There is an overfill valve inside the tank. It is a component entirely separate from the external valve that a user controls. Let a propane company sort it out. They're the experts, and they want you to come in so they can help. They live for stuff like this because they are professionals.