How to Invent Everything: A Survival Guide for the Stranded Time Traveler

by Ryan North

dilute sulfuric acid reacts with iron to produce hydrogen gas.* Dilute sulfuric acid by (slowly) adding it to 3⅓ times its weight in water, put iron filings in a barrel, and pour your diluted acid on top of the iron filings in a 2:1 ratio by weight—meaning 2kg of acid gets poured on top of 1kg of iron. This will react to give you your hydrogen! You can then pass it through a second barrel filled with slaked lime (which you can make in Appendix C.4) to remove any acid carried over with the gas, which you’ll want to do because otherwise the gas you’re producing could eat through your balloon: historically, rarely a good thing. The sulfuric acid will exhaust itself before the iron does, so you can drain out the used-up acid from the first barrel and refill it with more until there’s no more iron left to react. Your hydrogen production apparatus will look like this: