How Come My Balloon Doesn't Go Up Any More?

Last Updated (Tuesday, 29 April 2008 15:01) Written by Raymond Nakamura

The Pick Up Line "Daddy, would you like some bread?" my three-year-old asked me, as we neared a certain bakery that she knew and I knew always had an helium balloon for a cute little girl. On cue, the baker said, "Would you like a balloon?"And of course, my daughter said, "Yes, please." (Maybe the "please" is just wishful remembering) I went along with the scheme because I did want some bread and knew a balloon would keep my daughter amused the rest of the way home. A clever way to make some dough. The Let Down The next day, the prized balloon had come back down to Earth among the flotsam of her other toys. "How come my balloon doesn't go up any more?" she asked. "I think it ran out of gas," I said, off the top of my head. This seemed to satisfy her, but it got me wondering if that were indeed the case, or just so much hot air.

Gaps in My Knowledge
A cursory internet search reminded me that atoms are itsy bitsy teeny weeny things, and helium is second only to hydrogen in smallness. A helium balloon floats because it is less dense than air. As a gas, atoms bounce around worse than kids at a birthday party. The rubber in a balloon is made of large complicated molecules with relatively humongous with gaps between them, like open doors in the party room. So it's easy for the little heliums to escape.

Getting Down
It seemed to me, however, that the sunken balloon was not that much smaller than the floating one. Here are some possible explanations.

1. A balloon has to have a certain amount of helium to compensate for the mass of the balloon. So maybe it didn't need to lose that much gas before it sank if it wasn't that big to begin with.
2. My perception of size might be related to diameter. A small change in diameter could mean a significant change in volume.
3. "Balloon quality" helium is not pure helium. Air is mostly nitrogen, with some oxygen (even when you breathe out). These elements are bigger (especially because they have two atoms linked together), heavier and slower than helium, so they don't leak out as quickly. Apparently, the cost of helium is going up and up. Helium is a limited resource, extracted from natural gas deposits in only a few places in the world. If the helium does leak out first, leaving only air later, then what's leftover would not make your voice sound high if you inhaled it. Not that I'm recommending anyone try this, in case it is still helium and it works but you over do it and you pass out, or it's some other weird residual gas that makes you pass out.

Sealed with a Mist
The other thing I have noticed in the past is that some rubber balloons with helium have lasted several days. What was up with that?

I called a party supply store and Rick told me they use something called Hi-Float, a biodegradable, non-toxic, water-soluable plastic that coats the inside of the balloon to reduce leakage. Those shiny mylar balloons don't need that stuff because they are already less permeable to gas. And you can reinflate them when you run out of gas.

Speaking of running out of gas, this balloon question has lasted a lot longer than I expected and I'm starting to feel light-headed. I think I need a piece of toast.

I look forward to your thought balloons.

http://science.howstuffworks.com/helium2.htm
http://www.newscientist.com/article/mg16021608.600.html
http://www.madsci.org/posts/archives/2000-01/948894559.Ch.r.html#_jmp0_
http://www.wonderquest.com/Balloons.htm

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