Phlogiston Theory four elements: earth, air, fire, and water. One early theory was that sulphur was the ingredient that caused combustion. (Principles of Earth) All matter contained a fatty substance that gives it definition. Becher and Stahl called it a mysterious, unknown substance "phlogiston"

During combustion, phlogiston is given off into the air: wood ---> calx (ash) + phlogiston (to the air) iron ---> calx (rust) + phlogiston (to the air) Wood ash is much lighter than the original wood. Iron rust seems much lighter than the original iron.

Charcoal is almost completely consumed when burned: charcoal ---> phlogiston (to the air) charcoal is almost pure phlogiston.

When wood burns in a sealed container, it will not burn to completion if there is not enough air. Thus it was deduced that any given amount of common air (as it was called) could hold only so much phlogiston. Common air that could hold no more phlogiston was called "phlogisticated air."

So: wood + common air ---> calx + phlogisticated air Some of this phlogisticated air would dissolve in water. Some of it would not. So there were now two kinds of air in this phlogisticated air. Neither of these two airs would support combustion.

The air which would dissolve in water was called "fixed air." The other air was theorized to be the actual phlogisticated air.

Joseph Priestley discovered another form of air. When mercury was heated in air, it formed a red substance, which became known as "the precipitate per se." This precipitate per se, when heated with no air at all, changed back into mercury and this new air.

This new air supported combustion much better than common air. Wood burned brighter, and more easily. Iron shavings actually burned rather than rusted. Common air was mostly composed of this impurity, which became known as "foul air" or "mephitic air."

And Priestley called his new air "dephlogisticated air": common air=foul air + dephlogisticated air phlogisticated air=dephlogisticated air + phlogiston wood + dephlogisticated air ---> calx (ash) + phlogisticated air

The mercury experiment was reversible: mercury + dephlogisticated air precipitate per se This precipitate per se would be a combination of a mercury calx and phlogiston.

Several metals can be produced from their calces by heating the calx with charcoal: calx + charcoal ---> metal + fixed air This is: calx + phlogiston ---> metal + phlogisticated air

Water was separated, by electrolysis, into two kinds of air, a new gas called "inflammable air" and dephlogisticated air: water ---> inflammable air + dephlogisticated air Inflammable air burns very easily, forming water: inflammable air + dephlogisticated air ---> (water) phlogisticated air=phlogiston + dephlogisticated air

To summarize water inflammable air (phlogiston) + dephlogisticated air metal (pure base + phlogiston) + dephlogisticated air ---> calx (pure base + water) charcoal (pure base + phlogiston) + dephlogisticated air ---> calx (fixed air + water) calx (pure base + water) + charcoal ---> metal (pure base + phlogiston) + fixed air metal (pure base + phlogiston) + water calx + inflammable air (phlogiston)

And we can now translate some of the archaic chemical words: an air=a gas (Common air was, of course, known to be a mixture of gasses from early on) fixed air=carbon dioxide (Charcoal is almost pure carbon) inflammable air=hydrogen dephlogisticated air=oxygen foul air (mephitic air)=nitrogen calx=oxide (iron rust and finery cinder are two different oxides of iron) precipitate per se=mercuric oxide