whats the purpose of the bubbling bottle in this procedure?
http://www.xinventions.com/main/pyro/hydrogen_balloons.htm

And how it realtes to a Makeshift Arsenal I will never know.

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You're in a laundry room, You're in a laundry room, the clue just came to you? Oh.

I know what these are dood!!! This kinda belongs in the back yard ballistics forum more though. There showing you one way to get hydrogen easily and fill balloons with it. What you do is hydrogen being even lighter than helium will float these balloons up nice and fast, unlike its boring (other than effect on vocal cords) relative helium hydrogen also posseses the wonderfull trait of being easily combustible so you attach a nice long fuse to the side of the balloon and light it and let the balloon rise up when teh fuse hits the balloon it ignites the hydrogen causing a small hydenburg recreation!

I think it's because the reaction is exothermic and you need to cool down the hydrogen so that it won't melt your baloon.