Phlogiston hydrogen

In the days of alchemy and the phlogiston theory, no system of nomenclature that would be considered logical ia the 1990s was possible. Names were not based on composition, but on historical association, eg, Glauber s salt for sodium sulfate decahydrate and Epsom salt for magnesium sulfate physical characteristics, eg, spirit of wiae for ethanol, oil of vitriol for sulfuric acid, butter of antimony for antimony trichloride, Hver of sulfur for potassium sulfide, and cream of tartar for potassium hydrogen tartrate or physiological behavior, eg, caustic soda for sodium hydroxide. Some of these common or trivial names persist, especially ia the nonchemical Hterature. Such names were a necessity at the time they were iatroduced because the concept of molecular stmcture had not been developed, and even elemental composition was incomplete or iadeterminate for many substances. 

His name for hydrogen was inflammable air. However, he had no doubt that this gas he had discovered was phlogiston. In science, theory often determines what we observe. Cavendish was simply interpreting his results in terms of the accepted theory of his day. He was far from the only scientist who did so. For example, when Priestley discovered oxygen, he named it dephlogistated air. ... 

The scientific revolution that began when Lavoisier announced his new theory of combustion was far from over. Chemists stuck to the phlogiston theory and some of them continued to cling to the old four-element theory as well, objecting that Lavoisier hadn t really shown that water could be decomposed. The hydrogen, they said, could have come from the hot iron over which the steam had been passed. 

In the old Phlogiston Theory, phlogiston is equivalent to minus oxygen in the later theory it was sometimes assumed to be hydrogen (Cavendish, Kirwan, Priestley), or the matter of light (Macquer). Practically every chemist adopted the theory during the eighteenth century. 

Hydrogen sulfide was known to exist in water in the 15th century and was called sulfur water or sulfur vapors. Alchemists referred to H2S as aer hepaticus (hepatic air). Early chemists called it sulfuretted hydrogen, a term still used today. Carl Wilhelm Scheele (1742-1786) was the first chemist to prepare and describe hydrogen sulfide he considered it a combination of sulfur, phlogiston, and heat. Claude Louis Berthollet (1748-1822) determined the composition of H2S in 1789 and noted its acidic nature. 

By the action of marine acid on the black oxide of manganese, Scheele obtained chlorine gas and described its principal characteristic properties. He called it dephlo-gisticated marine acid. The name was reasonable from his point of view, since inflammable air (hydrogen) was conceived to be chiefly phlogiston and the above action deprived marine acid of its hydrogen. Chlorine was not conceived to be elementary in its nature even by Lavoisier Sir Humphry Davy, in 1810, was the discoverer of its elementary nature, and he it was who suggested the name chlorine. ... 

So immersed was Cavendish in the phlogiston of Becher that he did not know he had isolated, not the principle of fire, but pure, colorless, hydrogen gas. 

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