This plate illustrates the parts and mechanism of the faucet used to control the gas in the first hydrogen-filled balloon, launched from the Champs de Mars in Paris on August 27, 1783. In the illustration on Plate 3, this faucet connects the neck of the balloon to the barrel in which hydrogen gas is being produced by a reaction between sulfuric acid and iron filings.
Faujas-de-St.-Fond, cit. (Barthélemy). “Plate 1: Robinet.” In Description Des Expériences De La Machine Aérostatique De MM. De Montgolfier. Paris, France: Cuchet, 1783. https://digital.sciencehistory.org/works/2z10wq262.