Chemistry, philosophical aspects of
Publié le 22/02/2012
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only in size or shape.
The processes we observe around us are the result of changing groupings or arrangements of
atoms; the qualitative aspects of experience are the results of their collisions with the atoms of our soul or mind.
However, Democritus is very explicit that we cannot expect to have knowledge of qualities.
By convention are sweet and bitter, hot and cold, by convention is colour; in truth are atoms and the void.
…There are two forms of knowledge, one genuine, one obscure.
To the obscure belong all of the following:
sight, hearing, smell, taste, touch.
(Kirk and Raven 1962: 422)
The atomistic tradition was continued by Plato who, in the Timaeus , gave an elaborate geometrical account of
atoms in terms of the five regular polyhedra ( Plato §16 ).
In The Nature of Things , Lucretius provided
speculative corpuscular explanations of everything from evaporation to sexual attraction, but in part because of its
historical connections to Epicurean moral philosophy, atomistic theorizing became theologically suspect and was
not further developed until the rise of modern science ( Epicureanism §§3, 12 ).
The dominant theory of matter was Aristotle 's sophisticated account of the four elements - earth, air, fire and water
(an account earlier developed by Empedocles).
Aristotle posited an underlying substratum of prime matter that
could neither be created nor destroyed.
On it were impressed various combinations of the four fundamental
qualities, the hot or the cold, the wet or the dry.
The four elements could be transmuted into each other.
For
example, by adding more warmth to water (formed from the cold and the wet) one could change it into air
(characterized as the hot and the wet) ( Matter §1 ).
In trying to explain the multiplicity of properties which we actually observe, Aristotle associated additional
qualities with each element.
Thus softness and ductility and a bland taste are characteristic of water.
Brittle
materials are earthy, while sour or spicy foods contain fire.
Not only do ordinary materials contain varying
proportions of the elements, they also differ in how intimately the parts are combined.
Although there are places where Aristotle seems to presuppose a sort of conservation law for his qualities, there
are also passages in which he says that the more potent properties can completely transform the weaker.
Thus if a
great quantity of water is added to wine, in the end the water will actually convert the wine into water.
In a similar
way, Aristotle says, living things can transform food into flesh and bone ( De generatione et corruptione I 5).
The
Aristotelian system thus provided the philosophical foundation for alchemy ( Alchemy ).
2 Corpuscles, forces and conservation
Greek atomism had postulated that all processes could be understood as the result of collisions between, and
regroupings of, invisible particles, but it had very little to say about how or why the atoms moved or what caused
them to cohere into relatively stable clusters.
Both of these deficiencies were addressed by the theories of motion
developed in the seventeenth century.
Although Descartes rejected the possibility of a vacuum, his programme of.
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