For much of the eighteenth century, chemists explained combustion, rusting, and respiration through the phlogiston theory, which held that combustible materials contained a substance called phlogiston, released into the air as the material burned. The theory had genuine explanatory reach: it accounted for why a candle burning in a sealed jar eventually extinguishes itself, since the enclosed air was said to become saturated with phlogiston and could absorb no more; it explained why charcoal, thought to be rich in phlogiston, could restore a calx, a metal that had been heated and reduced to a powdery residue, back to its original metallic form, the phlogiston supposedly passing from the charcoal into the calx. Georg Ernst Stahl and his followers considered the theory not a speculative sketch but a well-confirmed, unifying account of an entire family of chemical transformations, one that had organized decades of laboratory observation into a single coherent framework. The theory's undoing came from a measurement its proponents had largely set aside: when a metal is heated in open air and converted to a calx, the calx weighs more than the original metal, not less, even though phlogiston was supposedly departing during the process. Phlogiston's defenders proposed increasingly strained fixes, including the notion that phlogiston possessed negative weight, to preserve the theory against this anomaly. Antoine Lavoisier, working through a systematic series of weighed combustion experiments in the 1770s, argued instead that combustion was not a release of phlogiston but a combination of the burning substance with a distinct component of air, which he later named oxygen; the weight gained by a calx was simply the weight of the oxygen it had absorbed. Lavoisier's account required no negative-weight substance and matched the balance-scale evidence directly.