Elementary Knowledge - By Rens Van Der Sluijs
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Elementary Knowledge - By Rens Van Der Sluijs

Posted by ProjectC 
'Sixty years later, it was Faraday’s compatriot, Sir William Crookes (1832-1919), who followed up in earnest the suggestion of “Matter classed into four states – solid, liquid, gaseous, and radiant – which depend upon differences in the essential properties”. The term plasma was employed for the “radiant” or partly ionised gases by the Nobel-prize winning American chemist and physicist, Irving Langmuir (1861-1957), in 1928.'

Diagram showing the four elements, seasons and body types, based on an edition of Isidore of
Seville’s Liber de Responsione Mundi (6th or 7th century CE), Augsburg in 1472.
Courtesy Huntington Library.

Elementary Knowledge

By Rens Van Der Sluijs
May 31, 2010

A cornerstone of ancient Greek science was the theory of the four elements: Pythagoreans, Platonists, Aristotelians and Stoics alike subscribed to the idea that all visible matter is formed of earth, water, air and fire, varying only in concentration and mode of intermixture.

The 'four element theory' reached its standard form when Empedocles of Acragas (±492-432 BCE) synthesised earlier attempts to identify the prima materia, the primary or original substance from which all else was derived – historically as well as chemically.

During the formative period of Greek philosophy, Thales of Miletus (±624-547 BC) had argued that “the beginning and end of the universe was water”, while the Pythagorean Hippasus of Metapontum (±500 BCE), Heraclitus of Ephesus (±535-475 BCE) and Zeno of Elea (±490-±430 BCE?) all recognised fire as the first principle. Other opinions were voiced as well.

The notion of the four classical elements remained intact for centuries and was used to account for commonly observed physical processes, including weather and climate, as well as for cosmogonic theories. The only significant modification was Aristotle’s treatment of the ‘fire’ constituting stars and planets as a separate, fifth element called ‘aether’, an innovation which only the Aristotelians seem to have embraced. As one follower put it: “The substance of the heaven and the stars we call aether … it is an element different from the four elements, pure and divine.” The idea was that aethereal objects were perfectly immutable, while ‘fiery’ ones were prone to change and decay.

The theory fell out of favour with the rise of modern chemistry in the late 17th century. In 1669, the German physician and alchemist, Johann Joachim Becher, split the element of earth into three, corresponding to different degrees of viscosity and fluidity. During the same decade, the Irish alchemist, Robert Boyle, while pioneering chemical analysis, theorised that the traditional elements really were compounds and mixtures, consisting of smaller particles with a greater diversity.

As the infant science of chemistry progressed, the number of recognised elements rose from 33 in 1789 and 49 in 1818 to the 66 that Dmitri Mendeleyev incorporated in his periodic table in 1869. This further increased to the 118 elements that have been observed up until now, either in the laboratory, in space or in nature.

From this point of view, the ancient Greek notion of ‘four elements’ sounds hopelessly obsolete, but is it reasonable to view it as a precursor to the modern chemical definition of ‘elements’? Are ancient and modern ‘elements’ really the same thing? It is true that Platonists associated each of the four elements with one of the regular polyhedra, so as to make sense of their physical properties. But were these philosophers really so naïve as to imagine that all known physical behaviour is reducible to just four constituents?

A recurrent topic in the classical literature concerned the cycles according to which one ‘element’ would transform into another. In the modern sense of the word, elements jumping positions in the periodic table must be understood either in terms of alchemy or of nuclear chemistry, such as radioactive decay or nuclear fusion. Yet it is clear that this is not what Greek philosophers were preoccupied with. Heraclitus, for example, “called change the upward and the downward path, and held that the world comes into being in virtue of this.

When fire is condensed, it becomes moist, and when compressed it turns to water, water being congealed thus turns to earth, and this he calls the downward path. And, again, the earth is in turn liquefied, and from it water arises, and from that everything else; for he refers almost everything to the evaporation from the sea. This is the path upwards”. Clearly, speculations of this type do not involve chemical elements, but states of aggregation.

After the English natural philosopher, Joseph Priestley (1733-1804), successfully isolated different ‘airs’ or gases, including oxygen, three states of matter were widely recognised – solids, liquids, and gases. At a later date, one of the most significant fall-outs of the study of electromagnetism was the recognition of a fourth state. Its discoverer, the English scientist, Michael Faraday (1791-1867), dubbed it “radiant matter”:

“If now we conceive a change as far beyond vaporisation as that is above fluidity, and then take into account also the proportional increased extent of alteration as the changes rise, we shall perhaps, if we can form any conception at all, not fall far short of radiant matter … The simplicity of such a system is singularly beautiful, the idea grand, and worthy of Newton’s approbation.”

Sixty years later, it was Faraday’s compatriot, Sir William Crookes (1832-1919), who followed up in earnest the suggestion of “Matter classed into four states – solid, liquid, gaseous, and radiant – which depend upon differences in the essential properties”. The term plasma was employed for the “radiant” or partly ionised gases by the Nobel-prize winning American chemist and physicist, Irving Langmuir (1861-1957), in 1928.

The discovery of the plasma state allows a reappraisal of the ancient theory of elements. If the four ‘elements’ of the Greeks were really states of matter, the concept is no longer antiquated, but up to speed with current understanding. If ‘earth’ corresponds to solids, ‘water’ to liquids, ‘air’ to gases, and ‘fire’ to plasmas, the likes of Empedocles effectively anticipated Faraday by more than two millennia with their insight that fire and lightning represent an essentially different regime of matter than ordinary ‘air’. Faraday himself was acutely aware of this connection: “It was what the ancients believed, and it may be what a future race will realise.”

With remarkable prescience, Crookes, too, foresaw the immense scientific potential of the ‘radiant’ state as early as 1879:

“In studying this Fourth state of Matter we seem at length to have within our grasp and obedient to our control the little indivisible particles which with good warrant are supposed to constitute the physical basis of the universe. … We have actually touched the border land where Matter and Force seem to merge into one another, the shadowy realm between Known and Unknown which for me has always had peculiar temptations. I venture to think that the greatest scientific problems of the future will find their solution in this Border Land, and even beyond …”

Those at the forefront of plasma science today would agree that plasma constitutes “the physical basis of the universe” and that it can potentially solve “the greatest scientific problems”. Indeed, owing to its ubiquity in space, plasma has been promoted from being the ‘fourth’ state to the fundamental state of matter. And this, again, accords quite well with Heraclitus’ hoary adage: Tà dè pánta oiakízei keraunós – ‘Thunderbolt steers all things’.

Contributed by Rens Van Der Sluijs