Hi All, I am currently designing a tethered balloon. The balloon is 36m3 and I was hoping to fill with hydrogen. The balloon will only be fully inflated at 400ft as I am aware of the risk of a hydrogen explosion. Unfortunately I live in Australia and 36m3 of hydrogen is USD$1800!! I am considering using a reaction of hydrochloric acid and aluminium as both substances are cheap here. (approx USD$120 for 200L 32% Hydrochloric acid technical grade, $20/kilo 200mesh aluminium powder[74micron particle size]) The system needs to be portable as I will be using it in outback Australia. Since I haven't studied chemistry in about 15years I am guessing I will need around 80L of hydrochloric acid to generate around 3.5kg of hydrogen gas. Firstly I need to know if I am correct in my calculations and how long the reaction would take? If you have any simpler/cheaper solutions to make hydrogen gas I am all ears!