Inflating balloon. Historical artwork of the inflation of a gas balloon. The balloon is suspended from a wire stretched between two poles. Diluted sulphuric acid is mixed with iron filings in the barrels to produce hydrogen gas, which is piped off and pumped into the balloon to fill it. Gas balloons were more popular than hot air balloons during the 1800s. Published in A system of aeronautics, comprehending its earliest investigations, and modern practice and art, Philadelphia, 1850.