It’s something that the average citizen of Maastricht sees almost every week, yet it links to something that they haven’t seen in over a century. And they connect through the now-mysterious medium of pneumatic chemistry.
Around 1600, Jan Baptiste van Helmont, a Flemish chemist, determined that there were vapors distinct from atmospheric air, which had previously been regarded as a primitive element, like earth and fire. He coined the word “gas”, sometimes thought to derive from the Dutch pronunciation of the word “chaos”, and linked "gas sylvestre", released by burning charcoal, to the unbreathable “fermenting mist” found in caves (both now known as carbon dioxide).
Soon, the study of gases, pneumatic chemistry, was taken up by many others, studying the physical properties and reactions of derived, isolated gases. A subspecies of ignitable gases, the Inflammable gases, previously known from studies of marsh vapors, were synthesized in the laboratory around 1726. The process involved heating coal, then purifying the vapor by bubbling it through water to remove the tars and through lime water to remove inert gases. The resulting Coal Gas consisted of hydrogen and methane: it could be stored in a sealed vessel called a gasometer, then transported or piped under pressure to fixtures where it could be burned for illumination.
Jean-Pierre Minkelers was a Professor of Natural Philosophy at the University of Louvain when commissioned by his patron (duc d’Arenberg) to investigate ballooning. The Montgolfier brothers made their first flight in a hot air balloon in 1783 using hot air, and Minckelers, well acquainted with pneumatic chemistry, set out to create balloons floated by inflammable air. He burned a wide variety of substances and filled envelopes with the vapors before settling on coal gas as the best solution.
And, somehow, this led Minckelers to the idea of illuminating his lecture halls with coal gas around 1785. He kept no notes of the process, and his invention is only known because two students recalled his pioneering demonstration of gaslight illumination in separate publications fifty years later. Minckelers had passed away in 1824, after fleeing an unhappy political situation in Louvain to arrive in Maastricht in 1794, where he was appointed professor of physics and chemistry at the Central School of Maastricht.
The city fathers in Maastricht honored his discovery with a statue in the Markt Square, where he still holds an eternal gaslight flame, surrounded by the pipes, pumps, flasks, and distillers that he used to make the first use of illuminating gas.
No balloons, though.
For the entire story, read The Origins of Gaslight Technology in Eighteenth-Century Pneumatic Chemistry (2009, Tomory).