"Nitrogen is an inert gas and is not chemically active."
"Air, freon, water, propane, oil, and so on and so on will react to changes in temp. My point is that nitrogen will not and makes a better gas to check for leaks."
Should have read that nitrogen is considered an inert gas and is not considered chemically active.
My second statement should have read that considered dry,nitrogen will not contract and expand as great to changes in temperature and makes a better gas to check for leaks.
In context of the original question, I considered original statements correct. I was relating nitrogen to the other gases available to a DIY (compressed air, propane, ands so forth). Outside of the question and I can see where my statements may have seemed slightly bold and partially incorrect and have adjusted accordingly.
If there is something better for pressurizing and leak testing piping that is easily accessible, please let me know.
Sorry about being so late to respond, reality is getting in the way of my fantasy.