SpudFiles

Will Caulking around the fittings of my pneumatic potato cannon make it any more air tight and safe. I haven't done it yet I was just curious.

Well when you prime and cement a cannon together correctelly, it isn't glue that is holding the pipes together. A chemical reaction happens and the 2 pieces are actually fused (melted) together into 1 piece. So adding caulk and stuff don't really matter.

If your fittings are leaking then chances are when you put it together you didn't do a good enough primter/cement job. Also when you stick the fittings together your supposed to make about a quarter of a turn on the pipe to ensure they are sealed. I forgot to turn and had a great cement job one time and I had a small leak.

It's not a chemical change. It's a physical change. When you weld two pieces of metal together, you bond the metal, you don't alter the chemical structure.
That would be like saying ice melting was a chemical reaction.
The PVC is dissolved in solvent, and then rehardens. It basically liquifies, and then solidifies again, but this time, into one whole piece.

Sorry I meant what happens is a reaction happens from the primer/glue.

Either way, it's a damn good hold when done correctelly.