This has been in the back of my mind a while and just wanted to throw it out there to hopefully get some support for my answer to a problem.

 

The place I work at regularly receives shipments of hydrogen gas. One of the truck drivers insisted that after he unloads the hydrogen into our storage tanks that his truck is actually heavier. I disagreed with him.

 

I think that he imagines that hydrogen just magically floats and that he doesn't understand that hydrogen has mass (weight) but is buoyant in the heavier gases of our atmosphere. I reasoned with him that he is taking a large gas cylinder and taking some of the mass (hydrogen) out of it while the cylinder still displaces the same amount of atmosphere. The buoyant force acting on the cylinder is the same but the cylinder weighs less unloaded.

 

He just wouldn't accept my viewpoint. Hopefully you all agree that I was spot on but would you have any other ideas to express this concept? It's not like we got in a fight or that it really bothers me but I just really wanted him to understand.

you were quite correct.

You were right indeed, perhaps you could also note that hydrogen can also be a liquid that doesn't "magically" float precisely because it is too dense, which is exactly what buyoancy is about. I don't know how much that makes sense, perhaps you can gather something useful and more easily explainable at the Wikipedia article on buoyancy.

If the hydrogen were at less than ~15 atmospheres and the tank gets backfilled with air he'd be correct. But most small gas tanks I've seen are filled to at least 10x higher pressure, and I imagine larger tanks are similarly higher, and I don't imagine they get backfilled.