Phlogiston

Before the late 1700s air was believed to be a single substance, not a mixture of gases as we know it to be today. Without knowledge of the chemical composition of the gases in air, combustion (burning) was essentially impossible to understand, yet combustion reactions are among our most important chemical reactions. 

Alchemists believed that flammable materials contain a substance that they called phlogiston. Phlogiston was believed to be an actual material substance that had mass. 

Alchemists said that during combustion, phlogiston is released to the atmosphere. Similarly, alchemists beUeved that metals contain phlogiston. When a metal is extracted from its ore, phlogiston is gained in the process. Later, if the metal rusts, alchemists believed that phlogiston is released back to the atmosphere. 

In the case of combustion reactions, the theory of phlogiston was plausible. When wood bums, it turns into ash. Since the ash clearly weighs less than the wood did, it would seem that something was given off by the wood—phlogiston. 

It was the English minister and part-time chemist Joseph Priestley who provided an alternative to the theory of phlogiston. Priestley discovered oxygen gas, although, ironically, Priestly himself still continued to believe in the existence of phlogiston. 

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Stahl subsequently renamed the terra pingnis phlogiston, the motion of fire (or heat), the essential element of all combnstible materials. Thns the phlogiston theory was born to explain all combnstion and was widely accepted for most of the eighteenth centnry by, among others, such luminaries of chemistry as Joseph Priestley. 

In 1783 Lavoisier annonnced a basic reevalnation of the chemical theory, rejecting the phlogiston theory completely. At the same time, he elevated oxygen to a general explanatory principle (in a manner... 

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. 

A. L. Lavoisier recognized oxygen as an element, developed the modem theory of combustion, and demolished the phlogiston theory. 

Brsnnstoff, m. fuel, combustible Old Chem.) phlogiston, -aufwand, m. fuel consumption, ausnutzung, /. utilization of fuel, -chsmis, /. fuel chemistry, -vsrbrauch, m. fuel consumption. -wsrt, m. fuel value, -wirt-schaft, /. fuel economy, -zisgsl, m. fuel briquet. 

Historical Introduction and Perchlorates in General History. The early history of perchlorates and the perchlorate mdustryhas been thoroughly discussed (Refs 12 14, p 2), so it will be only briefly reviewed here. Early exptl work on chlorates and perchlorates was closely tied to the discovery and identification of Cl. Several workers, notably Priestly, Lavoisier, and Scheele reported the isolation of volat liqs and gases which probably were oxides or oxyacids of Cl, but they failed to identify and characterize the compds isolated. Scheele, for example, treated muriatic ac (HCl) with Mn dioxide and obtained a volat liq which he called muriatic ac derived of its phlogiston (Ref 14, p3). The first perchlorate definitely identified was the K salt which was prepd by Stadion in 1816 by the thermal decompn of K chlorate (Ref 2). From this he prepd a hydrate of perchloric ac by heating the K salt with sulfuric ac (Ref 3). Pure (anhyd) perchloric ac was first prepd by Roscoe in 1862 by distn of the hydrated ac (Ref 4)... 

Henry Cavendish (1731-1810) isolates and characterizes inflammable air , which he believes to be phlogiston... 

Freudenthal, Gad. "The problem of cohesion between alchemy and natural philosophy from unctuous moisture to phlogiston." In Alchemy revisited, ed. Z.R.W.M. von Martels, 107-116. Leiden Brill, 1990. 

Karl Hufbauer. The Formation of the German Chemical Community (1720-1795). Berkeley, CA University of California Press, 1982. Source for Lavoisier s burning phlogiston at the stake. 

Z. Jumps in knowledge arise from new theoretical concepts, such as the disproving of the phlogiston hypothesis ("the" paradigm shift) or the atom model of Dalton and the Periodic Table. An equally accelerating effect results from the discovery of new methods, such as electrochemistry, spectral analysis, and X-rays. 

As an example of the insufficiency of present usefulness and self-consistency as grounds for belief in a scientific construct, it may be in order to recall some scientific history. In our own field we have the familiar example of phlogiston and in astronomy the example of epicycles. By the use of epicycle superimposed on epicycle, the geocentric theory was able to give a self-consistent, popular, and accurate description of apparent planetary motions. The epicycle treatment is analogous to a Fourier analysis of the motions and its accuracy did not guarantee the physical reality of epicycles. 

The reasoning here is reminiscent of the negative mass that had to be postulated to support the phlogiston theory. 

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