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Antoine Lavoisier and the demise of the Phlogiston Theory

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Johan Joachim Becher (1635 - 1682)

Becher

Johan Joachim Becher was a German alchemist who has also been labeled an 'adventurer'. A self-taught scholar, Becher is described as being haughty and as having a violent temper. After a tenure as Professor of Medicine at the University of Mainz, Becher moved around Europe, at least for part of the time as a special envoy for the Holy Roman Emperor. A natural philosopher, Becher turned his hand to amazingly diverse activities such as canal building, wool exporting and attempting to introduce a universal European language. Becher even claimed that he could make himself invisible!

He published his book Physica subterranae in 1669 while teaching in Mainz. In this book he developed the Greek 'four elements' theory by dividing 'Earth' into three sub-categories. It was during his time in Vienna that Becher believed that he had achieved transmutation (changing base elements into gold). He added silver to salts that he had taken from the banks of the Danube and heated them together. It was three centuries later that the gold was found to be present in the salt flats of the Danube located in the Vienna basin. Becher had not succeeded in transmuting silver to gold - gold was already there!

Becher made the journey to England in 1680. This was probably a way of escaping a public demonstration of transmutation that had been highly publicized in Holland, using beach sand (after the publication of his book Minera Arenaria that described the method of doing so). Once over the Channel he travelled the country, paying lengthy visits across the border to Scotland and as far south as Cornwall. Once in London in 1681, and under the patronage of Robert Boyle, Becher presented a paper to the Royal Society entitled De Arenania Perpetua where he unsuccessfully tried to take credit for the pendulum clock. Becher was also unsuccessful in his attempt to be made a member of the Royal Society although he did manage to convince Boyle to buy one of his furnaces for a staggering £12 (more than £1500 in today's money!)

Becher died in London in 1682. Although many sources describe Georg Ernst Stahl as Becher's pupil, it is highly unlikely that the two of them ever met. At the time of Becher's death in England, Stahl would have been twenty two and still a student in Germany.

 

Georg Ernst Stahl (1659 - 1734)

Stahl

Stahl studied medicine at University of Jena in Germany and later went on to teach. He was offered the Chair in Medicine at the University of Halle in 1694. By all accounts Stahl was not a pleasant character. He is described as 'critical and egotistical' and he considered his theories had their origins in 'divine intervention'. It is said that he made his lectures intentionally above the level of his students so that they were incomprehensible to the majority!

Stahl was very much influenced by the works of Becher, so much so that he had Physica subterranea republished in 1703. He published his own theories in his book Fundamenta Chymiae in 1723. In this book Stahl replaced Becher's 'terra pinguis' with 'Phlogiston'. However, Stahl cannot be credited with being the first to coin the word Phlogiston. Earlier alchemists, Nicolaus Niger Hapelius in 1606, Daniel Sennet in 1619 and Baptista van Helmont in 1625 had all used the word Phlogiston in much the same sense as Stahl.

 

HISTORY OF SCIENCE AND TECHNOLOGY

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The Phlogiston Theory

Ancient Greek Philosophers

Empedocles (495 BC - 430 BC)

Stated that all matter was made from four "elements". The amounts of any of the four "elements" in a substance would determine the qualities of that substance. The four "Elements" were;

  • water (representing liquids)

  • air (representing gases)

  • earth (representing solids)

  • fire (representing heat)

Aristotle (384 BC - 322 BC) added a fifth "element"

  • æther (representing the divine, spirituality)

 

In the 16th century

Paracelsus (1493 - 1541) a Swiss philosopher and alchemist, introduced iatrochemistry (an early form of medical chemistry). He proposed that three "elements" played a part in disease;

  • sulfur (the combustible element that represented the soil)

  • mercury (the fluid element that represented the spirit)

  • salt (the solid and permanent element that represented the body)

 

In the 17th century

Johann Joachim Becher (1635 - 1682) A German alchemist (see left) adapted the four "element" theory of Empedocles.

He considered "air" and "fire" to be agents of chemical change (so they 'helped' chemical change to happen) but they were not, themselves, "elements".

"Water" and "earth" he considered more important than "air" and "fire". He subdivided the "earth" element into three sub-categories (that resembled Paracelsus's "salt", "mercury" and "sulfur"). He published his theory in his book Physica Subterranea (1669) describing the three sub-categories of the "earth" element as;

  • terra lapidea: represented the original hard, stony earth

  • terra fluida: represented volatility, gaseous and flowing states

  • terra pinguis: "sulphur-like", present in combustible matter, grease and fat - it was released on combustion

 

First half of the 18th century

George Earnst Stahl (1659 - 1734) was influenced by Becher's Physica subterranea and had it republished in 1703. Stahl published his treatise Fundamenta Chymiae in 1723 (see left).

Stahl replaced Becher's terra pinguis with "Phlogiston" (from the Greek plagios, meaning to inflame).

 

Phlogiston

When a combustible substance burns it is reduced to ash. A mysterious "element" called phlogiston escapes. The flames of the fire are not phlogiston but they are an indication that phlogiston has been released. When all the phlogiston has escaped, ash remains.

Carbon is almost pure phlogiston since it burns away leaving a small amount of ash.

equation01

 

Metals that do not burn but form ashy calx (or, as we know it, metal oxide) also contain phlogiston

equation02

 

Calx, for example lead calx, was regarded as a metal from which all the phlogiston had escaped. Therefore, is a calx is heated together with carbon, the metal should be produced.

equation03

 

The phlogiston present in the carbon has been transferred to the metal.

(N.B. Metals were considered to be compounds of the metal calx plus phlogiston. In other words, when a metal is heated it decomposes to the metal calx and phlogiston escapes. The calx was already present in the metal.)

Stahl's phlogiston theory could be put to the test in the laboratory. Experiments were carried out on other substances, such as phosphorus and sulfur.

The phlogiston theory was held to be true for over a century. There was one obvious problem with the theory that scientists were well aware of - quantitative chemistry showed that metals gained weight (mass) when they were heated, even though phlogiston had been lost. This was explained away by assuming that phlogiston could have negative mass.

Even pre-phlogiston researchers, such as Boyle and Becher, had been aware that metal calx were heavier than the original metal. Becher's explanation was that 'fiery, igneous particles' had moved through the container from the flames and had joined with the metal inside.

 

Continued: Antoine Lavoisier and the demise of the Phlogiston Theory

 

 

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