shown that burning was not always accompanied by a loss of material, and a better theory was needed to account for this. Johann Joachim Becher In 1667, Johann Joachim Becher published his book , which contained the first instance of what would become the phlogiston theory. In his book, Becher eliminated fire and air from the classical element model and replaced them with three forms of the earth: , , and . was the element that imparted oily, sulphurous, or combustible properties. Becher believed that was a key feature of combustion and was released when combustible substances were burned. Becher did not have much to do with phlogiston theory as we know it now, but he had a large influence on his student Stahl. Becher's main contribution was the start of the theory itself, however much of it was changed after him. Becher's idea was that combustible substances contain an ignitable matter, the . Georg Ernst Stahl In 1703 Georg Ernst Stahl, a professor of medicine and chemistry at Halle, proposed a variant of the theory in which he renamed Becher's to phlogiston, and it was in this form that the theory probably had its greatest influence. The term 'phlogiston' itself was not something that Stahl invented. There is evidence that the word was used as early as 1606, and in a way that was very similar to what Stahl was using it for. The term was derived from a Greek word meaning inflame. The following paragraph describes Stahl's view of phlogiston: Stahl's first definition of phlogiston first appeared in his , published in 1697. His most quoted definition was found in the treatise on chemistry entitled in 1723. According to Stahl, phlogiston was a substance that was not able to be put into a bottle but could be transferred nonetheless. To him, wood was just a combination of ash and phlogiston, and making a metal was as simple as getting a metal calx and adding phlogiston. Soot was almost pure phlogiston, which is why heating it with a metallic calx transforms the calx into the metal and Stahl attempted to prove that the phlogiston in soot and sulphur were identical by converting sulphates to liver of sulphur using charcoal. He did not account for the increase in weight on combustion of tin and lead that were known at the time. J. H. Pott Johann Heinrich Pott, a student of