THE CHEMICAL PHILOSOPHY OF THE ANCIENTS
Speculations as to the origin and nature of matter, and as to the
conditions and forces which affect it, are to be found, more or less
imperfectly developed, in the oldest systems of philosophy of which
we have any record. These speculations are not based, in any real
sense, upon the systematic observation of natural phenomena. Still,
as they appealed to human reason, they must be held to be founded
upon experience, or at least not to be consciously inconsistent with
it: All the oldest cosmogonies regarded water as the fundamental
principle of things: from Okeanos sprang the gods—themselves deified
personifications of the “elements” or principles of which the world was
made.
In the course of time this doctrine of the origin and essential nature
of matter came to be more particularly associated with the name of
Thales of Miletus, who lived six centuries before our era, and who,
according to Tertullian, is to be regarded as the first of the race
of the natural philosophers—that is, the first of those who made it
their business to inquire after natural causes and phenomena. Thales
is known to have passed some years of his life in Egypt, and to have
been instructed in science by the priests of Thebes and Memphis; and it
is therefore possible that he may have been influenced by the Egyptian
teaching in the formulation of his cosmological theories.
It is significant of the tenacity with which the mind clings to
dogma and reveres authority that the teaching of Thales should have
survived through the space of twenty-four centuries. It can be shown
to have affected the course of chemical inquiry down to the close of
the eighteenth century. It influenced the experimental labours of
philosophers so diverse in character as Van Helmont, Boyle, Boerhaave,
Priestley, and Lavoisier—all of whom made attempts to prove or disprove
its adequacy. Van Helmont, indeed, was one of the most strenuous
supporters of the doctrine of Thales, and sought to establish it by
observations which, in the absence of all knowledge of the true nature
of air and water, seemed at the time irrefutable. Perhaps the one most
frequently cited is his observation on the growth of a plant which
apparently had no other form of sustenance than water. He describes how
he planted a willow weighing 5 lbs. in 200 lbs. of earth previously
dried in an oven. The plant was regularly watered, when at the end of
five years it was found to weigh 169 lbs. 3 oz., whereas the earth,
after redrying, had lost only 2 oz. in weight. Hence, 164 lbs. of
woody matter, leaves, roots, etc., had been produced seemingly from
water alone. More than a century had to elapse before any clue to the
true interpretation of Van Helmont’s experiment was gained. It was
first furnished by the observations of Ingenhousz and Priestley.
Although the idea of a primal “element” or common principle is to be
found in every old-world philosophical system, the ancient philosophers
were by no means in agreement as to its character. Anaximenes, who
lived _circa_ 500 B.C., taught that it was air, Herakleitos of Ephesus
that it was fire, and Pherekides that it was earth. The supposition
that a single primordial principle could be made to account for all
forms of matter and all the phenomena and manifestations of the
material world had its difficulties. Attempts to group qualities as
principles, and to construct from these principles the universe, were
indeed made even prior to the age of Thales. It was a comparatively
simple evolutionary step to regard these principles or “elements” as
mutually convertible. Anaximenes’ theory of the formation of rain was
an implicit admission of such convertibility. This philosopher taught
that rain came by the condensation of clouds, which in their turn
were formed by the condensation of air. Everything comes from air and
everything returns to air. That water might be converted by fire into
air was surmised from the earliest times. Such a supposition naturally
sprung from the circumstance that water was everywhere recognised to
disappear or to pass into the air under the influence of fire or solar
heat. The supposition had grown into a fixed belief in the Middle Ages.
Even Priestley, as late as the end of the eighteenth century, imagined
for a time that he had obtained proof of such a mutual conversion.
The possibility of the transmutation of water into earth was a belief
current through twenty centuries, and was only definitely and finally
disproved by Lavoisier in 1770. The conception of fire as the primal
principle has its germ in the fire- or sun-worship of the Chaldeans,
Scythians, Persians, Parsees, and Hindus, and it is not difficult to
trace, therefore, how heat came to be regarded either as antecedent
to, or as associated with, the other primal principles. Empedokles,
apparently, was the first whose name has come down to us to reintroduce
the definite conception of four primal elements—fire, air, water,
and earth. These he regarded as distinct, and incapable of being
transmuted, but as forming all varieties of matter by intermixture
in various proportions. These principles he deified, Zeus being the
personification of the element of fire, Here of air, Nestis of water,
and Aidoneous of earth.
The doctrine of the four elements was also adopted by Plato and
amplified by Aristotle, with whose name indeed it is commonly
associated. Aristotle, the greatest scientific thinker among the
Greeks, exercised an authority almost supreme in Europe during
nearly twenty centuries. His influence is to be traced throughout
the literature of chemistry long after the time of Boyle. It may be
detected even now. Probably few who write chemical memoirs to-day,
and who follow the time-honoured practice of prefacing their own
contributions to knowledge by a statement of what is already known
on the subject, are aware that in so doing they are obeying the
injunctions of Aristotle. His theory of the nature of matter is
contained in his treatise on _Generation and Destruction_. It mainly
differed from that of Empedokles in regarding the four “elements” as
mutually convertible. Each “element” or principle was regarded as being
possessed of two qualities, one of which was shared by another element
or principle.
Thus: Fire is hot and dry; air is hot and wet; water is cold and wet;
earth is cold and dry.
In each primal “element” one quality prevails. Fire is more hot than
dry; air is more wet than hot; water is more cold than wet; earth is
more dry than cold. The relative proportion and mutual working of
these qualities determined the specific character of the “element.”
Thus, if the dryness of fire is overcome by the moisture of water,
air is produced; if the heat of air is overcome by the coldness of
earth, water is formed; if the moisture of water is overcome by the
dryness of fire, earth results. Ancient chemical literature contains
many illustrations or diagrams symbolising the convertibility or mutual
relations of the four “elements.”
It has been frequently stated that the influence of the Peripatetic
philosophy has been inimical to the development of science. But, in
reality, the founder of that school, a descendant of Esculapius, and
undoubtedly one of the greatest and most enlightened thinkers of
antiquity, was an ideal man of science. This is abundantly evident
from such of his works as can be proved to be genuine. Much of what
is called Aristotelianism is entirely foreign to the spirit of the
teaching of Aristotle. The Aristotelians of the Middle Ages were
mainly dialecticians, and almost wholly concerned with the formulæ of
syllogistic inference, and without real sympathy with, or knowledge
of, his system. Much, too, that was attributed to him, and which was
venerated accordingly, is undoubtedly spurious. The fame of the Master
has consequently suffered at the hands of those who, calling themselves
Peripatetics, were in no proper sense followers of his method or
interpreters of his dogma. Aristotle affirmed that natural science
can only be founded upon a knowledge of facts, and facts can only be
ascertained through observation and experiment. He illustrates this
particularly by a reference to astronomy, “which,” he says, “is based
on the observation of astronomical phenomena, and it is the case with
every branch of science or art.” It is erroneous and unjust, therefore,
to suppose that Aristotle’s philosophy, as he taught it, is opposed to
the true methods of science.
A knowledge of Aristotle’s works was transferred by Byzantine writers
to Egypt; and, when that land was overrun by the Arabs in the seventh
century, they adopted his system, spreading it abroad wherever their
conquests extended. In the eighth century they carried it into Spain,
where it flourished throughout their occupation of that country.
From the ninth to the eleventh century the greater part of Europe
was in a state of barbarism. The Moslem caliphate in Spain, under
the beneficent rule of Jusuf and Jaküb, alone preserved science from
extinction. Cordova, Seville, Grenada, and Toledo were the chief seats
of learning in Western Europe; and it was mainly through “the perfect
and most glorious physicist,” the Moslem Ibn-Roshd—better known as
Averroes—(1126–1198), that Christian scholiasts like Roger Bacon
acquired their knowledge of the philosophical system of Aristotle,
and mainly through the Moslems Geber and Avicenna that they gained
acquaintance with the science of the East.
The conception that matter is made up of particles or _atoms_, and
that these particles are in a state of ceaseless motion, is to be met
with in Hindu and Phœnician philosophy. It was taught by Anaxagoras,
Leukippos, and Demokritos to the Greeks, and by Lucretius to the
Romans. Leukippos and Demokritos explained the creation of the world as
due solely to physical agencies without the intervention of a creative
intelligence. According to their theories, the atoms are variable, not
only in size, but in weight. The smallest atoms are also the lightest.
Atoms are impenetrable; no two atoms can simultaneously occupy the same
place. The collision of the atoms gives them an oscillatory movement,
which is communicated to adjacent atoms, and these, in their turn,
transmit it to the most distant ones. Anaxagoras taught that every
atom is a world in miniature, and that the living body is a congeries
of atoms derived from the aliments which sustain it. Plants are living
things, endowed like animals with respiratory functions, and, like
them, atomically constituted. This philosopher was so far in advance
of his age that his countrymen accused him of sacrilege, and he only
escaped death by flight. Further, the assumption that these atoms
exert mutual attractions and repulsions is probably as old as the
fundamental conception itself. At least, so far as can be traced, the
conceptions of atoms and atomic motion are indissolubly connected. This
is not the place to develop the subsequent history of the doctrine of
the atom, nor need we now concern ourselves with the old metaphysical
quibble of its divisibility or indivisibility. It may be, as Lucretius
said, that the original atom is very far down. It may be that the
physical atom is something which _is_ not divided, not something that
_cannot_ be divided. This theory, dimly perceived in the mists of
antiquity, has grown and strengthened with the ages, and in its modern
application to the facts of chemistry has acquired a precision and
harmony unimagined even by the poets and thinkers of old. We shall
see later how the whole course of the science has been controlled,
illumined, and vivified by it. It is not too much to say that the
chemistry of to-day is one vast elaboration of this primeval doctrine.