James Richard Fromm
In prehistoric times, earlier than perhaps 1000 BC, no distinction could be, or was, made between science and technology. Pure science did not exist. Although a great deal of applied science or technology was known and used by the Assyrian Empire, Pharaonic Egypt, or the early Greeks no natural philosophy, as distinguished from religious philosophy and from applied philosophy or technology, existed in the ancient world. In the history of Western civilization - and science as it is known today anywhere on earth is clearly of Western origin - the earliest efforts in natural philosophy or pure science trace back to Greece from about 700 BC onwards, culminating in the surviving works of Aristotle (384 - 322 BC). This, the first well-defined conceptual development of science, has had a profound influence on all of the later history and philosophy of science.
The Greek distinction between natural philosophy and technology is fundamentally different from our own. This is partially but not completely due to the distinction between scholars, or teachers, leaders, and philosophers, and craftsmen in the culture of ancient Greece. The craftsmen, or technologists, would teach their skills to their sons or apprentices but were not generally able to read and write and so taught by example rather than by book. Moreover, their skills were generally kept as "trade secrets" within the artisan group or groups, much as the mediaeval guilds kept their secrets in later centuries. They did no experiments, as such, because their interest lay not in understanding the nature of clay or gold or lead but in making better, cheaper, or more beautiful objects out of them. The scholars, who were teachers or philosophers, were skilled at observation but even more skilled in argument, debate and formal reasoning. Their skill lay in language and in logical systematic reasoning. The classical logic of hypothesis and syllogism and the logical beauty of Euclidean plane geometry are examples of this turn of mind and culture. The idea of resolving a dispute between theories by experiment rather than by debate would not have occurred to them. Even if it had, the technological ability to do the experiments was often absent; more important, perhaps, was the conceptual problem, because the concepts of their science were not clearly enough defined to suggest experiments that they could have carried out. It would be a mistake, however, to think that the Greeks could not make accurate measurements- they, or for that matter the priests of Pharaonic Egypt, could and did make quite accurate measurements of length (as in the construction of the Pyramids, in establishing boundary markers or surveying of fields, or even in estimating the size of the earth) or of mass (as in the weighing of silver and gold), or that they were not skilled in observation. It is the combination of controlled observation for the purpose of advancing understanding which we call an experiment which is missing from the natural philosophy of the ancient Greeks.
The period of classical history, which to us is this period of Greek theory and Roman practice, extended roughly from 700 BC to 600 AD. The important Greek thinkers were some of the philosophers, especially Plato of Athens (427 - 347 BC), who founded the Academy there, and his student and successor Aristotle of Stagira (384 - 322 BC). Aristotle was a great systematizer of Greek ideas and his writings had a profound influence on all subsequent Western thought. The last of the Greeks important to chemistry is Galen (129 - 199 AD), who was the leading systematizer of medicine in classical times. The works of Galen remained standard medical texts for centuries.
The nature of the chemical concepts which originated in the Greeks of the classical period remained, for almost 1500 years, the concepts through which chemistry was understood. We will take a closer look at two of them: the concept of the four elements, and the atomistic view of matter, held by two different philosophic schools of Greece.
The coherent picture of this concept dates back to Empedocles of Agrigentum (490 - 430 BC). This picture, somewhat elaborated and elegantly stated by Aristotle, was that all matter was made up of four elements: earth, air, fire and water. These four elements arise from the working of the two properties of hotness (and its contrary coldness) and dryness (and its contrary wetness) upon an original unqualified or primitive matter. The possible combinations of these two properties of primitive matter give rise to the four elements or elemental forms, as shown in the Figure below.
Perhaps only a culture whose leaders were involved with logic and geometry would put the concepts of chemistry in such a logical and geometric form. Fire and Water are obvious opposites, and so are Earth and Air. These opposites share no common properties. There are four properties, each shared by two non-opposite elements: fire and air share the property of hotness, water and air the property of wetness, and so on. Since the four elements are two pairs of opposite elements, so also are the four properties - hotness being the opposite of coldness and wetness the opposite of dryness. Each of the four elements was held to exist in an ideal pure form, which could not actually be found on earth. The real things around us were considered impure, or mixed, forms of these four ideal elements. Thus the different airs, or gases, were the form of air mixed with different proportions of the forms of fire or water; smoke was a mixture of the forms of air and earth with some of the form of fire added. But there was an ideal or pure form of earth, air, fire, and water, and the real ones which we see and use were not ideal but of lesser purity. In other words, the real or observed different kinds of the same element are due to different degrees of the same properties. The elements could be changed into one another by removal of one property and addition of another. Elements had a natural tendency to separate in space; fire moved outwards, away from the earth, and earth moved inwards, with air and water being intermediate. Matter, in whatever form, could be subdivided indefinitely in theory, although it was recognized that such subdivision might not be practically possible. Aristotle further held, against the atomistic philosophers, that void, or vacuum, did not exist.
This Greek set of chemical concepts was intended to, and did, explain something of the relationships between the qualitative properties of substances. It did not attempt to make any attempt to explain the quantitative results one can obtain in chemical operations. This was not because the Greeks or other ancients were incapable of making quantitative measurements - in their geometric work they made many - but because their chemical concepts were qualitative and they did not think of applying quantitative measurements to chemistry. The idea of making quantitative measurements of the most important chemical quantity, mass or weight, had to wait until the time of the French Revolution around 1790, despite the fact that balances capable of making the measurements necessary had been known, and in use by assay offices, coiners, jewellers, and merchants, for perhaps 5000 years.
The Greeks used this rather artificial-sounding theory of the four elements to explain many of the actions of nature. For example, a real fire was impure ideal fire. When a pot was placed over a fire, the bottom of the pot became black; this happened because the real fire was a mixture of ideal fire and ideal earth, and therefore when the fire entered the pot to give it more of the property of hotness some or all of the earth mixed with it was left behind on the bottom of the pot. When sea water was heated it absorbed the hotness of fire and moved away from water, becoming air; the impurity in real water, earth, then was left behind on the bottom of the pot as dry salt when the water finally had absorbed the hotness of enough fire and been completely converted into air. An air, when cooled, would condense droplets of water, as when cold metal was placed in contact with the air above a kettle of boiling water or in moist air. This occurred because the property of coldness, taken from the metal or earth, moved the air toward wetness and thus partially toward water.
Other Greek concepts of chemistry also reappeared, in slightly modified form, much later in history. Aristotle added a fifth element called quintaessentia to the four of Empedocles. This eternal and unchangeable element called the ether, or space, was a sort of pure form in which the other four elements existed. This concept, expressed as a luminiferous ether in which light waves were propagated just as water waves as propagated in oceans, rose to haunt physics until well after 1900 when experiments finally made its retention impossible. Another extension of the ideas of Empedocles, due to Plato of Athens, was the idea that each of the four elements existed in a particular geometric form and the properties of the element were therefore related to that form. So fire particles were believed to exist in the form of tetrahedrons, whose sharp points gave speed and burning sensations like arrows striking the flesh. Earth particles had the shapes of cubes, which accounted for their solidity; water particles had the smoother shape of an icosahedron, while those of air had the shape of an octahedron. Ether, being the highest of the elements, had the most complex geometry, that of a pentagonal dodecahedron. This idea, that each of the elements was made up of particles having a single definite shape, recurred again with considerable impact upon the developing modern definition of a chemical element in the seventeenth and eighteenth centuries.
Aristotle, like all the Greek scientific writers, paid comparatively little attention to chemical matters. The classical four elements are not "elements" in the modern, or Boyleian, sense. The states of earth, water, air and fire might now correspond to four physical states of matter - solid, liquid, gas, and plasma. Chemical processes involving water such as solution of salts, metabolic processes, and the release of waters of hydration on heating of minerals were undoubtedly known but were not distinguished from physical processes such as freezing, melting, condensation, and boiling. Aristotle comments on Anaxagoras' study of mixtures - the observation that when a white liquid is mixed drop-by-drop with a black one the color change is infinitesimally gradual, so these natural processes must be so minute as to escape the senses and can only be inferred, not observed. But his main concern is with the concept of change, which expressed in the twin concepts of "coming-into-being" and "passing-away". We may illustrate this with his comment on the burning of wood: "Now we do not speak of the wood as 'combined' with fire, not of its burning as a 'combining' either of its particles with one another or of itself with the fire; what we say is that the fire is coming-to-be but the wood is passing-away."
The concept of atoms appears to arise with Leucippus, of whom we know little, and his follower Democritus of Abdera (460? - 360 BC); in the form known to us it has become known through the criticism of Aristotle and the later writings of Epicurus of Samos (341 - 270 BC) and Titus Lucretius Carus (98 - 54 BC). The ideas of this school, in their fully-developed form, are as follows.
First, matter is not capable of infinite subdivision. The ultimate and indivisible constituents of matter are extremely small and imperceptible particles called atoms. These, like matter itself, are eternal and indestructible. The differences between substances are due to the elements of which they are formed, which may differ from each other in the size, shape and arrangements of the atoms of which they are composed. The properties of a substance which we observe are not the properties of its atoms but properties which arise from the manner in which the atoms are combined.
Second, these atoms are constantly in motion and this motion is a property inherent in them, as motes of dust are seen to dance in a sunbeam. Combinations are due to coalescence of the particles or atoms as they collide.
Third, these atoms are separated from each other by void, or vacuum, in which the atoms move.
It is tempting to read more into the atomistic philosophers in the light of our modern knowledge of atoms than they actually did write. Like other Greek thought, theirs was based upon logic and argument rather than experiment. Nevertheless, the idea of atoms originating with them had, by 1750, been spread through the scientific community and was the foundation stone for the work of John Dalton.
Many of the pure substances available in the ancient world were metals, of which seven were then known: gold, silver, lead, tin, iron, copper, and mercury. The other pure substances known in the ancient world, in addition to naturally-occurring minerals, constitute rather a mixed group.
One of the earliest pure substances of commerce was common salt (NaCl, sodium chloride). This was obtained from salt water, either the sea or salt springs, by evaporation. The evaporation could take place in natural rock hollows or in specially built basins, and both were in use well before historical records begin. Salt was of great use in food preservation and is a necessary part of a human diet. Since dry salt is fairly easily transportable, a commerce in it flourished in ancient times. Another chemical, similar to salt but less useful, known to the ancient world was soda or natron
(Na2CO3, sodium carbonate) which was obtained from natural deposits such as those of the Wadi Natron in Egypt. It was used for cleansing and medicinal purposes.
Vinegar, used in the ancient world and now in cooking, was also used as a preservative. Wine, when exposed to air, goes sour and turns to vinegar. The sour taste is due to acetic acid,
CH3COOH, produced by air oxidation of the ethanol, CH3CH2OH, in the wine. A pure vinegar is a dilute solution of acetic acid.
Lime or quicklime (CaO, calcium oxide) was manufactured in the ancient world for use in cement; many Roman cement or concrete structures still stand. Lime was obtained by strong heating of limestone (CaCO3, calcium carbonate) which is abundant in nature.
Bitumen, or pitch, was obtained from natural seepages, primarily in the Middle East. It was used for calking of ships, tarring of roofs, and, in Greek fire, used as a weapon much like a modern flamethrower. It was not processed, as is done in a modern oil refinery, but it was shipped overseas in fairly large quantity.
Spices, obtained from plants, were also items of chemical commerce, as were medicinals - which covered everything used in medicine. Most of these were plant materials, although a few came from animals and some were naturally occurring minerals. Dye materials such as the blue dye woad obtained by the Welsh for the coloring of fabrics (and themselves!) were generally of plant origin. A few dyes such as Tyrian purple obtained from a species of mollusc growing near modern Lebanon, were of animal origin. One interesting material, used as a burn ointment, a pigment, and in putty, was white lead (2PbCO3.Pb(OH)2, basic lead carbonate) which was produced by a chemical manufacturing process.
In this process, lead metal was placed in earthen pots over sharp vinegar and after it had acquired some thickness of a kind of white rust, or crust, which it usually did in about ten days, the workers opened the vessels and scraped off this deposit. The lead was returned to the vessel over the vinegar again and the process was repeated over and over again until the lead was completely gone. The material scraped off was then beaten to powder and boiled with water for a long time. What at last settled to the bottom of the vessel was white lead. What happens in this process is that the lead is attacked by the acetic acid in the vinegar and forms lead acetate, Pb(CH3COO)2. On boiling in water the impure lead acetate is converted to 2PbCO3.Pb(OH)2, white lead, which is very insoluble in water and so it is left on the bottom of the vessel.
Few pure substances were known in the ancient world other than those mentioned above, but the separation of mixtures was understood and employed in metallurgy and in medicine. The theory of the four elements was interpreted as indicating that all real substances were mixtures in any case, and separation of complex mixtures into simpler ones made eminent conceptual good sense even if it was difficult in practice. Only the techniques of smelting of metals and of crystallization from water were used for the deliberate purification of materials on any large scale in the ancient world, and it is doubtful that any other methods were understood.