Alright, you real smart people answer me this...

[AKcharger]

Go to the flower store and look at that cylinder of Helium...weights 80-100lbs right? OK, if it can fill say 300 ballons that can each lift 1/2 pound (just for discussions sake) why doesn't the helium cylinder float away???

[bordin34]

Because the compressed helium is more dense?

[terrible one]

I would think a normal sized helium filled balloon would only lift a few grams . . . nowhere near a half pound. I know it was just a general example but at that rate it wouldn't contain nearly enough lifting power to float the 80 pound tank. 5 grams per balloon at 300 balloons is like 3 pounds of lifting force.

[DC_1]

This should answer some of your questions

http://www.chem.hawaii.edu/uham/lift.html

[squeakfinder]

 I would think with helium you would have to hold it at a high pressure because of it's extremely low boiling temperature. That would make it a liquid not a gas while it is held in a vessel?

[AKcharger]

I would think a normal sized helium filled balloon would only lift a few grams . . . nowhere near a half pound. I know it was just a general example but at that rate it wouldn't contain nearly enough lifting power to float the 80 pound tank. 5 grams per balloon at 300 balloons is like 3 pounds of lifting force.

I'm with ya' but the helium has the CAPABILTY to lift the weight of the tank...no doubt about that...but sydmore's link does provide the answer.

[AKcharger]

I went to a conference this weekend and spoke to an engineer from a company that's working on a hybrid airship. Truly fascinating discussion...an airship that can carry 500 TONS, really a neat idea. Oh, it's all about "displacement" of air, just like a ship in water that's how it can carry all that weight

http://www.defenseindustrydaily.com/aeros-dreaming-big-with-walrus-project-01898/

[Old Moparz]

Helium is not only a lighter gas, it's a fearful gas & why it floats upward when it's inside balloon. Think about why cats run away from small children. They don't want to have their tails pulled by a toddler, or be chased after, or teased. Helium reacts the same way when trapped inside a balloon that a kid is playing with. It uses natural instincts to get away & hide to avoid the chance of the balloon popping & dispersing the gas all over the atmosphere. When it's inside a metal cylinder it feels safe & remains in a calm state. This calm state allows the molecules to to settle closer together which in turn makes it too heavy & dense to lift the cylinder upward.

[Chad L. Magee]

There is a big difference in the weight of 300 unfilled rubber balloons vs. the weight of the steel tank by itself.  Helium gas is indeed lighter than air, but the tank would have to be made of a material that is much lighter for the gas to lift it while inside the tank.  Mythbusters did an episode to see if they could lift a person with just He balloons.  They got it to work, but they needed a lot of balloons to do so (way more than 300 if I remember right)..... 

[bull]

Oh, it's all about "displacement" of air, just like a ship in water that's how it can carry all that weight

That's what I would say. How else could you get a supercarrier, comprised of 70,000 long tons of steel, to float?

[Ponch ®]

There is a big difference in the weight of 300 unfilled rubber balloons vs. the weight of the steel tank by itself.  Helium gas is indeed lighter than air, but the tank would have to be made of a material that is much lighter for the gas to lift it while inside the tank.  Mythbusters did an episode to see if they could lift a person with just He balloons.  They got it to work, but they needed a lot of balloons to do so (way more than 300 if I remember right)..... 

I remember that episode. Kari looked smokin hot in that Bad Schoolgirl outfit...

[squeakfinder]

    ........

[last426]

Go to the flower store and look at that cylinder of Helium...weights 80-100lbs right? OK, if it can fill say 300 ballons that can each lift 1/2 pound (just for discussions sake) why doesn't the helium cylinder float away???

Same reason  a scuba tank floats when empty and sinks when full -- at least they used to.  Kim

[AKcharger]

There is a big difference in the weight of 300 unfilled rubber balloons vs. the weight of the steel tank by itself.  Helium gas is indeed lighter than air, but the tank would have to be made of a material that is much lighter for the gas to lift it while inside the tank.  Mythbusters did an episode to see if they could lift a person with just He balloons.  They got it to work, but they needed a lot of balloons to do so (way more than 300 if I remember right)..... 

Well I was thinking of that but what is they had one very large ballon as opposed to all the small ones, you'd displace much more air...it might work that way. Now picture using the ship hulll as an example, one huge 70,000 ton hull or a whole bunch of little steel hulls all taped togeter depending on the size/weight I bet they'd sink