Charcoal metals 584 phlogiston

Metal calxes turn to metal when heated with charcoal because phlogiston transfers from the charcoal to calx. 

In 1772 Lavoisier was still a believer in the phlogistonic orthodoxy. But he had begun to doubt that this was all there was to combustion. He proposed towards the end of that year that metals take up ( fix ) air when calcined, and that the calx releases this fixed air when reduced back to metals with the agency of charcoal and heat. Hearing of Black s fixed air in 1773, he decided that this was what metals combine with to form a calx. That at least explained the gain in weight. It also weakened the need to invoke phlogiston at all. 

Let us examine briefly the logic of Lavoisier s model of the gaseous state. His earlier view, when he planned to collect and study the fumes emitted from heated metals, appears to have been that the fumes were no more than a simple physical vaporization, the combination of the solid body with the free fire of the direct heat. In his new view, however, the fire that liberates the air from the calx comes from the chemically fixed fire, phlogiston, in the charcoal. 

The majority of metallic calces are only reduced, that is to say, only return to the metallic condition, by immediate contact with a carbonaceous material, or with some substance containing what is called phlogiston. The charcoal that one uses is entirely destroyed during the... 

Plants absorb phlogiston from air and are rich in phlogiston. Plant substances can react with metal calces to restore the phlogiston and convert them to metals again. Charcoal is extremely rich in phlogiston and the most useful substance for this purpose. ... 

Figure 3.30 Georg Ernst Stahl (1660-1734), who formulated the phlogiston theory to explain combustion. He believed that all combustible substances and metals contained a common principle, phlogiston, which escaped on combustion or calcinations, but could be transferred from one substance to another, and restored to the metallic calx by heating with substances rich in phlogiston (such as charcoal, oil, etc.). (Published with permission from Deutsches Museum, Munich.)...

What should have been an obvious flaw with the phlogiston theory is that charcoal and other fuels lose weight when they burn, but metals gain weight when they rust or become a calx. If the theory of phlogiston were correct, these observations would imply that there must be two... 

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