THE MODERN FORM OF THE ALCHEMICAL QUEST OF THE ONE THING.
The study of the properties of the elements shows that these
substances fall into groups, the members of each of which are like one
another, and form compounds which are similar. The examination of the
properties and compositions of compounds has shown that similarity of
properties is always accompanied by similarity of composition. Hence,
the fact that certain elements are very closely allied in their
properties suggests that these elements may also be allied in their
composition. Now, to speak of the composition of an element is to
think of the element as formed by the union of at least two different
substances; it implies the supposition that some elements at any rate
are really compounds.
The fact that there is a very definite connexion between the values of
the atomic weights, and the properties, of the elements, lends some
support to the hypothesis that the substances we call, and are obliged
at present to call, elements, may have been formed from one, or a few,
distinct substances, by some process of progressive change. If the
elements are considered in the order of increasing atomic weights,
from hydrogen, whose atomic weight is taken as unity because it is the
lightest substance known, to uranium, an atom of which is 240 times
heavier than an atom of hydrogen, it is found that the elements fall
into periods, and the properties of those in one period vary from
element to element, in a way which is, broadly and on the whole, like
the variation of the properties of those in other periods. This fact
suggests the supposition--it might be more accurate to say the
speculation--that the elements mark the stable points in a process of
change, which has not proceeded continuously from a very simple
substance to a very complex one, but has repeated itself, with certain
variations, again and again. If such a process has occurred, we might
reasonably expect to find substances exhibiting only minute
differences in their properties, differences so slight as to make it
impossible to assign the substances, definitely and certainly, either
to the class of elements or to that of compounds. We find exactly such
substances among what are called the _rare earths_. There are
earth-like substances which exhibit no differences of chemical
properties, and yet show minute differences in the characters of the
light which they emit when they are raised to a very high
temperature.
The results of analysis by the spectroscope of the light emitted by
certain elements at different temperatures may be reasonably
interpreted by supposing that these elements are separated into
simpler substances by the action on them of very large quantities of
thermal energy. The spectrum of the light emitted by glowing iron
heated by a Bunsen flame (say, at 1200° C. = about 2200° F.) shows a
few lines and flutings; when iron is heated in an electric arc (say,
to 3500° C. = about 6300° F.) the spectrum shows some two thousand
lines; at the higher temperature produced by the electric
spark-discharge, the spectrum shows only a few lines. As a guide to
further investigation, we may provisionally infer from these facts
that iron is changed at very high temperatures into substances simpler
than itself.
Sir Norman Lockyer's study of the spectra of the light from stars has
shown that the light from those stars which are presumably the
hottest, judging by the general character of their spectra, reveals
the presence of a very small number of chemical elements; and that the
number of spectral lines, and, therefore, the number of elements,
increases as we pass from the hottest to cooler stars. At each stage
of the change from the hottest to cooler stars certain substances
disappear and certain other substances take their places. It may be
supposed, as a suggestive hypothesis, that the lowering of stellar
temperature is accompanied by the formation, from simpler forms of
matter, of such elements as iron, calcium, manganese, and other
metals.
In the year 1896, the French chemist Becquerel discovered the fact
that salts of the metal uranium, the atomic weight of which is 240,
and is greater than that of any other element, emit rays which cause
electrified bodies to lose their electric charges, and act on
photographic plates that are wrapped in sheets of black paper, or in
thin sheets of other substances which stop rays of light. The
_radio-activity_ of salts of uranium was proved not to be increased or
diminished when these salts had been shielded for five years from the
action of light by keeping them in leaden boxes. Shortly after
Becquerel's discovery, experiments proved that salts of the rare metal
thorium are radio-active. This discovery was followed by Madame
Curie's demonstration of the fact that certain specimens of
_pitchblende_, a mineral which contains compounds of uranium and of
many other metals, are extremely radio-active, and by the separation
from pitchblende, by Monsieur and Madame Curie, of new substances much
more radio-active than compounds of uranium or of thorium. The new
substances were proved to be compounds chemically very similar to
salts of barium. Their compositions were determined on the supposition
that they were salts of an unknown metal closely allied to barium.
Because of the great radio-activity of the compounds, the hypothetical
metal of them was named _Radium_. At a later time, radium was isolated
by Madame Curie. It is described by her as a white, hard, metal-like
solid, which reacts with water at the ordinary temperature, as barium
does.
Since the discovery of radium compounds, many radio-active substances
have been isolated. Only exceedingly minute quantities of any of them
have been obtained. The quantities of substances used in experiments
on radio-activity are so small that they escape the ordinary methods
of measurement, and are scarcely amenable to the ordinary processes of
the chemical laboratory. Fortunately, radio-activity can be detected
and measured by electrical methods of extraordinary fineness, methods
the delicacy of which very much more exceeds that of spectroscopic
methods than the sensitiveness of these surpasses that of ordinary
chemical analysis.
At the time of the discovery of radio-activity, about seventy-five
substances were called elements; in other words, about seventy-five
different substances were known to chemists, none of which had been
separated into unlike parts, none of which had been made by the
coalescence of unlike substances. Compounds of only two of these
substances, uranium and thorium, are radio-active. Radio-activity is a
very remarkable phenomenon. So far as we know at present,
radio-activity is not a property of the substances which form almost
the whole of the rocks, the waters, and the atmosphere of the earth;
it is not a property of the materials which constitute living
organisms. It is a property of some thirty substances--of course, the
number may be increased--a few of which are found widely distributed
in rocks and waters, but none of which is found anywhere except in
extraordinarily minute quantity. Radium is the most abundant of these
substances; but only a very few grains of radium chloride can be
obtained from a couple of tons of pitchblende.
In Chapter X. of _The Story of the Chemical Elements_ I have given a
short account of the outstanding phenomena of radio-activity; for the
present purpose it will suffice to state a few facts of fundamental
importance.
Radio-active substances are stores of energy, some of which is
constantly escaping from them; they are constantly changing without
external compulsion, and are constantly radiating energy: all
explosives are storehouses of energy which, or part of which, can be
obtained from them; but the liberation of their energy must be started
by some kind of external shock. When an explosive substance has
exploded, its existence as an explosive is finished; the products of
the explosion are substances from which energy cannot be obtained:
when a radio-active substance has exploded, it explodes again, and
again, and again; a time comes, sooner or later, when it has changed
into substances that are useless as sources of energy. The
disintegration of an explosive, started by an external force, is
generally completed in a fraction of a second; change of condition
changes the rate of explosion: the "half-life period" of each
radio-active substance is a constant characteristic of it; if a gram
of radium were kept for about 1800 years, half of it would have
changed into radio-inactive substances. Conditions may be arranged so
that an explosive remains unchanged--wet gun-cotton is not exploded by
a shock which would start the explosion of dry gun-cotton--in other
words, the explosion of an explosive can be regulated: the explosive
changes of a radio-active substance, which are accompanied by the
radiation of energy, cannot be regulated; they proceed spontaneously
in a regular and definable manner which is not influenced by any
external conditions--such as great change of temperature, presence or
absence of other substances--so far as these conditions have been made
the subject of experiment: the amount of activity of a radio-active
substance has not been increased or diminished by any process to which
the substance has been subjected. Explosives are manufactured
articles; explosiveness is a property of certain arrangements of
certain quantities of certain elements: so far as experiments have
gone, it has not been found possible to add the property of
radio-activity to an inactive substance, or to remove the property of
radio-activity from an active substance; the cessation of the
radio-activity of an active substance is accompanied by the
disappearance of the substance, and the production of inactive bodies
altogether unlike the original active body.
Radio-active substances are constantly giving off energy in the form
of heat, sending forth _rays_ which have definite and remarkable
properties, and producing gaseous _emanations_ which are very
unstable, and change, some very rapidly, some less rapidly, into other
substances, and emit _rays_ which are generally the same as the rays
emitted by the parent substance. In briefly considering these three
phenomena, I shall choose radium compounds as representative of the
class of radio-active substances.
Radium compounds spontaneously give off energy in the form of heat. A
quantity of radium chloride which contains 1 gram of radium
continuously gives out, per hour, a quantity of heat sufficient to
raise the temperature of 1 gram of water through 100° C., or 100 grams
of water through 1° C. The heat given out by 1 gram of radium during
twenty-four hours would raise the temperature of 2400 grams of water
through 1° C.; in one year the temperature of 876,000 grams of water
would be raised through 1° C.; and in 1800 years, which is
approximately the half-life period of radium, the temperature of
1,576,800 _kilograms_ of water would be raised through 1° C. These
results may be expressed by saying that if 1 gram (about 15 grains) of
radium were kept until half of it had changed into inactive
substances, and if the heat spontaneously produced during the changes
which occurred were caused to act on water, that quantity of heat
would raise the temperature of about 15½ tons of water from its
freezing- to its boiling-point.
Radium compounds send forth three kinds of rays, distinguished as
_alpha_, _beta_, and _gamma_ rays. Experiments have made it extremely
probable that the [alpha]-rays are streams of very minute particles,
somewhat heavier than atoms of hydrogen, moving at the rate of about
18,000 miles per second; and that the [beta]-rays are streams of much
more minute particles, the mass of each of which is about one
one-thousandth of the mass of an atom of hydrogen, moving about ten
times more rapidly than the [alpha]-particles, that is, moving at the
rate of about 180,000 miles per second. The [gamma]-rays are probably
pulsations of the ether, the medium supposed to fill space. The
emission of [alpha]-rays by radium is accompanied by the production of
the inert elementary gas, helium; therefore, the [alpha]-rays are, or
quickly change into, rapidly moving particles of helium. The particles
which constitute the [beta]-rays carry electric charges; these
electrified particles, each approximately a thousand times lighter
than an atom of hydrogen, moving nearly as rapidly as the pulsations
of the ether which we call light, are named _electrons_. The rays from
radium compounds discharge electrified bodies, ionise gases, that is,
cause them to conduct electricity, act on photographic plates, and
produce profound changes in living organisms.
The radium emanation is a gas about 111 times heavier than hydrogen;
to this gas Sir William Ramsay has given the name _niton_. The gas has
been condensed to a colourless liquid, and frozen to an opaque solid
which glows like a minute arc-light. Radium emanation gives off
[alpha]-particles, that is, very rapidly moving atoms of helium, and
deposits exceedingly minute quantities of a solid, radio-active
substance known as radium A. The change of the emanation into helium
and radium A proceeds fairly rapidly: the half-life period of the
emanation is a little less than four days. This change is attended by
the liberation of much energy.
The only satisfactory mental picture which the facts allow us to form,
at present, of the emission of [beta]-rays from radium compounds is
that which represents these rays as streams of electrons, that is,
particles, each about a thousand times lighter than an atom of
hydrogen, each carrying an electric charge, and moving at the rate of
about 180,000 miles per second, that is, nearly as rapidly as light.
When an electric discharge is passed from a plate of metal, arranged
as the kathode, to a metallic wire arranged as the anode, both sealed
through the walls of a glass tube or bulb from which almost the whole
of the air has been extracted, rays proceed from the kathode, in a
direction at right angles thereto, and, striking the glass in the
neighbourhood of the anode, produce a green phosphorescence. Facts
have been gradually accumulated which force us to think of these
_kathode rays_ as streams of very rapidly moving electrons, that is,
as streams of extraordinarily minute electrically charged particles
identical with the particles which form the [beta]-rays emitted by
compounds of radium.
The phenomena of radio-activity, and also the phenomena of the kathode
rays, have obliged us to refine our machinery of minute particles by
including therein particles at least a thousand times lighter than
atoms of hydrogen. The term _electron_ was suggested, a good many
years ago, by Dr Johnstone Stoney, for the unit charge of electricity
which is carried by an atom of hydrogen when hydrogen atoms move in a
liquid or gas under the directing influence of the electric current.
Some chemists speak of the electrons, which are the [beta]-rays from
radium, and the kathode rays produced in almost vacuous tubes, as
non-material particles of electricity. Non-material means devoid of
mass. The method by which approximate determinations have been made of
the charges on electrons consists in measuring the ratio between the
charges and the masses of these particles. If the results of the
determinations are accepted, electrons are not devoid of mass.
Electrons must be thought of as material particles differing from
other minute material particles in the extraordinary smallness of
their masses, in the identity of their properties, including their
mass, in their always carrying electric charges, and in the vast
velocity of their motion. We must think of an electron either as a
unit charge of electricity one property of which is its minute mass,
or as a material particle having an extremely small mass and carrying
a unit charge of electricity: the two mental pictures are almost, if
not quite, identical.
Electrons are produced by sending an electric discharge through a
glass bulb containing a minute quantity of air or other gas, using
metallic plates or wires as kathode and anode. Experiments have shown
that the electrons are identical in all their properties, whatever
metal is used to form the kathode and anode, and of whatever gas there
is a minute quantity in the bulb. The conclusion must be drawn that
identical electrons are constituents of, or are produced from, very
different kinds of chemical elements. As the facts about kathode rays,
and the facts of radio-activity are (at present) inexplicable except
on the supposition that these phenomena are exhibited by particles of
extraordinary minuteness, and as the smallest particles with which
chemists are concerned in their everyday work are the atoms of the
elements, we seem obliged to think of many kinds of atoms as
structures, not as homogeneous bodies. We seem obliged to think of
atoms as very minute material particles, which either normally are, or
under definite conditions may be, associated with electrically charged
particles very much lighter than themselves, all of which are
identical, whatever be the atoms with which they are associated or
from which they are produced.
In their study of different kinds of matter, chemists have found it
very helpful to place in one class those substances which they have
not been able to separate into unlike parts. They have distinguished
this class of substances from other substances, and have named them
_elements_. The expression _chemical elements_ is merely a summary of
certain observed facts. For many centuries chemists have worked with a
conceptual machinery based on the notion that matter has a grained
structure. For more than a hundred years they have been accustomed to
think of atoms as the ultimate particles with which they have had to
deal. Working with this order-producing instrument, they have regarded
the properties of elements as properties of the atoms, or of groups of
a few of the atoms, of these substances. That they might think clearly
and suggestively about the properties of elements, and connect these
with other chemical facts, they have translated the language of
sense-perceptions into the language of thought, and, for _properties
of those substances which have not been decomposed_, have used the
more fertile expression _atomic properties_. When a chemist thinks of
an atom, he thinks of the minutest particle of one of the substances
which have the class-mark _have-not-been-decomposed_, and the
class-name _element_. The chemist does not call these substances
elements because he has been forced to regard the minute particles of
them as undivided, much less because he thinks of these particles as
indivisible; his mental picture of their structure as an atomic
structure formed itself from the fact that they had not been
decomposed. The formation of the class _element_ followed necessarily
from observed facts, and has been justified by the usefulness of it as
an instrument for forwarding accurate knowledge. The conception of the
elementary atom as a particle which had not been decomposed followed
from many observed facts besides those concerning elements, and has
been justified by the usefulness of it as an instrument for forwarding
accurate knowledge. Investigations proved radio-activity to be a
property of the very minute particles of certain substances, and each
radio-active substance to have characteristic properties, among which
were certain of those that belong to elements, and to some extent are
characteristic of elements. Evidently, the simplest way for a chemist
to think about radio-activity was to think of it as an atomic
property; hence, as atomic properties had always been regarded, in the
last analysis, as properties of elements, it was natural to place the
radio-active substances in the class _elements_, provided that one
forgot for the time that these substances have not the class-mark
_have-not-been-decomposed_.
As the facts of radio-activity led to the conclusion that some of the
minute particles of radio-active substances are constantly
disintegrating, and as these substances had been labelled _elements_,
it seemed probable, or at least possible, that the other bodies which
chemists have long called elements are not true elements, but are
merely more stable collocations of particles than the substances which
are classed as compounds. As compounds can be changed into certain
other compounds, although not into any other compounds, a way seemed
to be opening which might lead to the transformation of some elements
into some other elements.
The probability that one element might be changed into another was
increased by the demonstration of the connexions between uranium and
radium. The metal uranium has been classed with the elements since it
was isolated in 1840. In 1896, Becquerel found that compounds of
uranium, and also the metal itself, are radio-active. In the light of
what is now known about radio-activity, it is necessary to suppose
that some of the minute particles of uranium emit particles lighter
than themselves, and change into some substance, or substances,
different from uranium; in other words, it is necessary to suppose
that some particles of uranium are spontaneously disintegrating.
This supposition is confirmed by the fact, experimentally proved,
that uranium emits [alpha]-rays, that is, atoms of helium, and
produces a substance known as uranium X. Uranium X is itself
radio-active; it emits [beta]-rays, that is, it gives off electrons.
Inasmuch as all minerals which contain compounds of uranium contain
compounds of radium also, it is probable that radium is one of the
disintegration-products of uranium. The rate of decay of radium may be
roughly expressed by saying that, if a quantity of radium were kept
for ten thousand years, only about one per cent. of the original
quantity would then remain unchanged. Even if it were assumed that at
a remote time the earth's crust contained considerable quantities of
radium compounds, it is certain that they would have completely
disappeared long ago, had not compounds of radium been reproduced from
other materials. Again, the most likely hypothesis is that compounds
of radium are being produced from compounds of uranium.
Uranium is a substance which, after being rightly classed with the
elements for more than half a century, because it had not been
separated into unlike parts, must now be classed with the radium-like
substances which disintegrate spontaneously, although it differs from
other radio-active substances in that its rate of change is almost
infinitively slower than that of any of them, except thorium.[12]
Thorium, a very rare metal, is the second of the seventy-five or
eighty elements known when radio-activity was discovered, which has
been found to undergo spontaneous disintegration with the emission of
rays. The rate of change of thorium is considerably slower than that
of uranium.[13] None of the other substances placed in the class of
elements is radio-active.
[12] The life-period of uranium is probably about eight
thousand million years.
[13] The life-period of thorium is possibly about forty
thousand million years.
On p. 192 I said, that when the radio-active substances had been
labelled _elements_, the facts of radio-activity led some chemists to
the conclusion that the other bodies which had for long been called by
this class-name, or at any rate some of these bodies, are perhaps not
true elements, but are merely more stable collocations of particles
than the substances called compounds. It seems to me that this
reasoning rests on an unscientific use of the term _element_; it rests
on giving to that class-name the meaning, _substances asserted to be
undecomposable_. A line of demarcation is drawn between _elements_,
meaning thereby forms of matter said to be undecomposable but probably
capable of separation into unlike parts, and _true elements_, meaning
thereby groups of identical undecomposable particles. If one names the
radio-active substances _elements_, one is placing in this class
substances which are specially characterised by a property the direct
opposite of that the possession of which by other substances was the
reason for the formation of the class. To do this may be ingenious; it
is certainly not scientific.
Since the time of Lavoisier, since the last decade of the eighteenth
century, careful chemists have meant by an element a substance which
has not been separated into unlike parts, and they have not meant
more than that. The term _element_ has been used by accurate thinkers
as a useful class-mark which connotes a property--the property of not
having been decomposed--common to all substances placed in the class,
and differentiating them from all other substances. Whenever chemists
have thought of elements as the ultimate kinds of matter with which
the physical world is constructed--and they have occasionally so
thought and written--they have fallen into quagmires of confusion.
Of course, the elements may, some day, be separated into unlike parts.
The facts of radio-activity certainly suggest some kind of inorganic
evolution. Whether the elements are decomposed is to be determined by
experimental inquiry, remembering always that no number of failures to
simplify them will justify the assertion that they cannot be
simplified. Chemistry neither asserts or denies the decomposability of
the elements. At present, we have to recognise the existence of
extremely small quantities, widely distributed in rocks and waters, of
some thirty substances, the minute particles of which are constantly
emitting streams of more minute, identical particles that carry with
them very large quantities of energy, all of which thirty substances
are characterised, and are differentiated from all other classes of
substances wherewith chemistry is concerned, by their spontaneous
mutability, and each is characterised by its special rate of change
and by the nature of the products of its mutations. We have now to
think of the minute particles of two of the seventy-five or eighty
substances which until the other day had not been decomposed, and were
therefore justly called elements, as very slowly emitting streams of
minuter particles and producing characteristic products of their
disintegration. And we have to think of some eighty substances as
particular kinds of matter, at present properly called elements,
because they are characterised, and differentiated from all other
substances, by the fact that none of them has been separated into
unlike parts.
The study of radio-activity has introduced into chemistry and physics
a new order of minute particles. Dalton made the atom a beacon-light
which revealed to chemists paths that led them to wider and more
accurate knowledge. Avogadro illuminated chemical, and also physical,
ways by his conception of the molecule as a stable, although
separable, group of atoms with particular properties different from
those of the atoms which constituted it. The work of many
investigators has made the old paths clearer, and has shown to
chemists and physicists ways they had not seen before, by forcing them
to think of, and to make use of, a third kind of material particles
that are endowed with the extraordinary property of radio-activity.
Dalton often said: "Thou knowest thou canst not cut an atom"; but the
fact that he applied the term _atom_ to the small particles of
compounds proves that he had escaped the danger of logically defining
the atom, the danger of thinking of it as a particle which never can
be cut. The molecule of Avogadro has always been a decomposable
particle. The peculiarity of the new kind of particles, the particles
of radio-active bodies, is, not that they can be separated into unlike
parts by the action of external forces, but that they are constantly
separating of their own accord into unlike parts, and that their
spontaneous disintegration is accompanied by the production of energy,
the quantity of which is enormous in comparison with the minuteness of
the material specks which are the carriers of it.
The continued study of the properties of the minute particles of
radio-active substances--a new name is needed for those most mutable
of material grains--must lead to discoveries of great moment for
chemistry and physics. That study has already thrown much light on the
phenomena of electric conductivity; it has given us the electron, a
particle at least a thousand times lighter than an atom of hydrogen;
it has shown us that identical electrons are given off by, or are
separated from, different kinds of elementary atoms, under definable
conditions; it has revealed unlooked-for sources of energy; it has
opened, and begun the elucidation of, a new department of physical
science; it has suggested a new way of attacking the old problem of
the alchemists, the problem of the transmutation of the elements.
The minute particles of two of the substances for many years classed
as elements give off electrons; uranium and thorium are radio-active.
Electrons are produced by sending an electric discharge through very
small traces of different gases, using electrodes of different metals.
Electrons are also produced by exposing various metals to the action
of ultra-violet light, and by raising the temperature of various
metals to incandescence. Electrons are always identical, whatever be
their source. Three questions suggest themselves. Can the atoms of all
the elements be caused to give off electrons? Are electrons normal
constituents of all elementary atoms? Are elementary atoms
collocations of electrons? These questions are included in the
demand--Is it possible "to imagine a model which has in it the
potentiality of explaining" radio-activity and other allied phenomena,
as well as all other chemical and physical properties of elements and
compounds? These questions are answerable by experimental
investigation, and only by experimental investigation. If experimental
inquiry leads to affirmative answers to the questions, we shall have
to think of atoms as structures of particles much lighter than
themselves; we shall have to think of the atoms of all kinds of
substances, however much the substances differ chemically and
physically, as collocations of identical particles; we shall have to
think of the properties of atoms as conditioned, in our final
analysis, by the number and the arrangement of their constitutive
electrons. Now, if a large probability were established in favour of
the view that different atoms are collocations of different numbers of
identical particles, or of equal numbers of differently arranged
identical particles, we should have a guide which might lead to
methods whereby one collocation of particles could be formed from
another collocation of the same particles, a guide which might lead
to methods whereby one element could be transformed into another
element.
To attempt "to imagine a model which has in it the potentiality of
explaining" radio-activity, the production of kathode rays, and the
other chemical and physical properties of elements and compounds,
might indeed seem to be a hopeless undertaking. A beginning has been
made in the mental construction of such a model by Professor Sir J.J.
Thomson. To attempt a description of his reasoning and his results is
beyond the scope of this book.[14]
[14] The subject is discussed in Sir J.J. Thomson's
_Electricity and Matter_.
The facts that the emanation from radium compounds spontaneously gives
off very large quantities of energy, and that the emanation can easily
be brought into contact with substances on which it is desired to do
work, suggested to Sir William Ramsay that the transformation of
compounds of one element into compounds of another element might
possibly be effected by enclosing a solution of a compound along with
radium emanation in a sealed tube, and leaving the arrangement to
itself. Under these conditions, the molecules of the compound would be
constantly bombarded by a vast number of electrons shot forth at
enormous velocities from the emanation. The notion was that the
molecules of the compound would break down under the bombardment, and
that the atoms so produced might be knocked into simpler groups of
particles--in other words, changed into other atoms--by the terrific,
silent shocks of the electrons fired at them incessantly by the
disintegrating emanation. Sir William Ramsay regards his experimental
results as establishing a large probability in favour of the assertion
that compounds of copper were transformed into compounds of lithium
and sodium, and compounds of thorium, of cerium, and of certain other
rare metals, into compounds of carbon. The experimental evidence in
favour of this statement has not been accepted by chemists as
conclusive. A way has, however, been opened which may lead to
discoveries of great moment.
Let us suppose that the transformation of one element into another
element or into other elements has been accomplished. Let us suppose
that the conception of elementary atoms as very stable arrangements of
many identical particles, from about a thousand to about a quarter of
a million times lighter than the atoms, has been justified by crucial
experiments. Let us suppose that the conception of the minute grains
of radio-active substances as particular but constantly changing
arrangements of the same identical particles, stable groups of which
are the atoms of the elements, has been firmly established. One result
of the establishment of the electronic conception of atomic structure
would be an increase of our wonder at the complexity of nature's ways,
and an increase of our wonder that it should be possible to substitute
a simple, almost rigid, mechanical machinery for the ever-changing
flow of experience, and, by the use of that mental mechanism, not
only to explain very many phenomena of vast complexity, but also to
predict occurrences of similar entanglement and to verify these
predictions.
The results which have been obtained in the examination of
radio-activity, of kathode rays, of spectra at different temperatures,
and of phenomena allied to these, bring again into prominence the
ancient problem of the structure of what we call matter. Is matter
fundamentally homogeneous or heterogeneous? Chemistry studies the
relations between the changes of composition and the changes of
properties which happen simultaneously in material systems. The
burning fire of wood, coal, or gas; the preparation of food to excite
and to satisfy the appetite; the change of minerals into the iron,
steel, copper, brass, lead, tin, lighting burning and lubricating
oils, dye-stuffs and drugs of commerce; the change of the skins, wool,
and hair of animals, and of the seeds and fibres of plants, into
clothing for human beings; the manufacture from rags, grass, or wood
of a material fitted to receive and to preserve the symbols of human
hopes, fears, aspirations, love and hate, pity and aversion; the
strange and most delicate processes which, happening without
cessation, in plants and animals and men, maintain that balanced
equilibrium which we call life; and, when the silver cord is being
loosed and the bowl broken at the cistern, the awful changes which
herald the approach of death; not only the growing grass in midsummer
meadows, not only the coming of autumn "in dyed garments, travelling
in the glory of his apparel," but also the opening buds, the pleasant
scents, the tender colours which stir our hearts in "the spring time,
the only pretty ring time, when birds do sing, ding-a--dong-ding":
these, and a thousand other changes have all their aspects which it is
the business of the chemist to investigate. Confronted with so vast a
multitude of never-ceasing changes, and bidden to find order there, if
he can--bidden, rather compelled by that imperious command which
forces the human mind to seek unity in variety, and, if need be, to
create a cosmos from a chaos; no wonder that the early chemists jumped
at the notion that there must be, that there is, some _One Thing_,
some _Universal Essence_, which binds into an orderly whole the
perplexing phenomena of nature, some _Water of Paradise_ which is for
the healing of all disorder, some "Well at the World's End," a draught
whereof shall bring peace and calm security.
The alchemists set forth on the quest. Their quest was barren. They
made the great mistake of fashioning _The One Thing, The Essence, The
Water of Paradise_, from their own imaginings of what nature ought to
be. In their own likeness they created their goal, and the road to it.
If we are to understand nature, they cried, her ways must be simple;
therefore, her ways are simple. Chemists are people of a humbler
heart. Their reward has been greater than the alchemists dreamed. By
selecting a few instances of material changes, and studying these with
painful care, they have gradually elaborated a general conception of
all those transformations wherein substances are produced unlike those
by the interaction of which they are formed. That general conception
is now both widening and becoming more definite. To-day, chemists see
a way opening before them which they reasonably hope will lead them to
a finer, a more far-reaching, a more suggestive, at once a more
complex and a simpler conception of material changes than any of those
which have guided them in the past.
INDEX
Air, ancient views regarding, 129.
---- views of Mayow and Rey regarding, 129.
Alchemical account of changes contrasted with chemical account, 169.
---- agent, the, 64.
---- allegories, examples of, 41, 97.
---- classification, 59.
---- doctrine of body, soul, and spirit of things, 48.
---- doctrine of transmutation, 47, 74, 123, 170.
---- language, 36, 96, 101, 102.
---- quest of the One Thing, modern form of, 179.
---- signs, 105.
---- theory, general sketch of, 26.
Alchemists, character of, according to Paracelsus, 25.
---- made many discoveries, 87.
---- sketches of lives of some, 115.
---- their use of fanciful analogies, 31.
Alchemy, beginnings of, 23.
---- change of, to chemistry, 126.
---- contrasted with chemistry, 202.
---- general remarks on, 123.
---- lent itself to imposture, 106.
---- object of, 9, 26, 32, 105.
---- probable origin of word, 25.
---- quotations to illustrate aims and methods of, 11-14.
Alembic, 92.
Apparatus and operations of alchemists, 90.
Art, the sacred, 122.
Atom, meaning given to word by Dalton, 173.
Atomic theory of Greeks, 16.
---- additions made to, by Dalton, 21.
---- as described by Lucretius, 19.
Atomic weight, 174.
Atoms and electrons, 190, 198.
Bacon's remarks on alchemy, 95.
Balsamo, Joseph, 110.
Basil Valentine, his description of the three principles, 51.
---- his description of the four elements, 49.
---- some of his discoveries, 88.
Becquerel, his discovery of radiation of uranium, 181.
Body, soul, and spirit of things, alchemical doctrine of, 48.
Boyle, on calcination, 128.
---- on combustion, 141.
---- on elements, 161.
---- on the "hermetick philosophers," 95.
---- on the language of the alchemists, 55.
---- on the natural state of bodies, 43.
Cagliostro, 110.
Calcination, 129, 132, 135, 140, 142, 151, 155.
Chaucer's _Canon's Yeoman's Tale_, 107.
Chemical conception of material changes, 177.
Chemistry, aim of, 9, 26, 160.
---- change from alchemy to, 126.
---- methods of, 10.
---- probable origin of word, 24.
Classification, alchemical methods of, 59.
Colours, Lucretius' explanation of differences between, 18.
Combustion, 141.
Compounds, chemical conception of, 171.
Conservation of mass, 164.
Curie, her discovery of radium, 182.
Dalton's additions to the Greek atomic theory, 21, 172.
Democritus, his saying about atoms, 15.
Dephlogisticated air, 147.
Destruction, thought by alchemists to precede restoration, 65, 127.
Electrons, 187-189, 197, 198.
Elements, alchemical, contrasted with chemical, 165;
radio-active substances contrasted with, 190-192.
---- the alchemical, 49, 54, 60.
---- the chemical, 61, 62, 161.
---- use of word, by phlogisteans, 133.
Essence, the alchemical, 32, 35, 49, 58, 72.
Fire, different meanings of the word, 53.
Gates, the alchemical, 69.
Gold, considered by alchemists to be the most perfect metal, 40, 45.
Greek thinkers, their atomic theory, 15.
Hermes Trismegistus, 37.
Kathode rays, 188.
Language of alchemy, 96.
---- purposely made misleading, 36.
Lavoisier on calcination, 153, 155.
---- his use of word _element_, 194.
---- his use of word _principle_, 163, _note_.
---- on object of chemistry, 160.
---- on oxygen, 155.
---- on systems in science, 163.
---- on the principle of acidity, 59, 155.
---- on the reactions of metals with acids, 158.
---- on the transmutation of water to earth, 152.
Lockyer, on spectra of elements, 181.
Lucretius, his theory of nature, 16.
Magic, characteristics of, 23, 24.
Material changes, Greek theory of, 15.
Metals, alchemical connexion between, and plants, 34.
---- compared by alchemists with vegetables, 33.
---- mortification of, 65.
---- seed of, 34.
---- their desire to become gold, 40.
---- transmutation of, 33, 39, 46.
Natural state of bodies, 39, 43.
Oxygen, 144, 145.
Paracelsus, his description of alchemists, 25.
---- his distinction between natural and artificial mortification, 65.
---- sketch of life of, 117.
Pelican, 92.
Perfection, alchemical teaching regarding, 27, 40.
Phlogistic theory, 133, 139.
Phlogiston, 126, 130, 137.
Priestley, his discovery of oxygen, 144.
Principles, the alchemical, 49, 51, 54, 60, 133.
---- Lavoisier's use of the word, 163, _note_.
Radio-active substances, are they elements? 191, 194, 195;
properties of, 185-187.
Radio-activity, characteristics of, 183, 184;
of radium, 186;
of thorium, 193;
of uranium, 193.
Radium, emanation of, 187;
heat from, 186;
rays from, 186.
Ramsay, on transmutation of elements, 199.
Regimens, the alchemical, 72.
Sacred art, the, 122.
Scientific theories, general characters of, 21, 150.
Seed, alchemical doctrine of, 56.
Seeds of metals, 34.
Simplicity, asserted by alchemists to be the mark of nature, 28, 38.
---- is not necessarily the mark of verity, 138.
Solids, liquids, and gases, atomic explanation of, 19.
Stahl, his phlogistic theory, 130.
Stone, the philosopher's, 32, 35, 49, 58, 72.
Thorium, radio-activity of, 183, 193.
Transmutation, alchemical doctrine of, 47, 74, 123.
---- character of him who would attempt, 63.
---- of metals, 33, 39, 46, 74.
---- of metals into gold, alchemical account of, 75.
---- of water to earth, 151.
Transmutations, apparent examples of, 82.
Uranium, radio-activity of, 183, 192;
relation of, to radium, 192, 193.
Vegetables compared with metals by alchemists, 33.
Water contains hydrogen and oxygen, examination of this phrase, 167.
Water, different meanings of the word, 53, 167.