6. CHAPTER VI
THE AGE OF MODERN CHEMISTRY
§ 71. The Birth of Modern Chemistry.
Chemistry as distinct from Alchemy and iatro-chemistry commenced with
Robert Boyle (see plate 15), who first clearly recognised that its aim
is neither the transmutation of the metals nor the preparation of
medicines, but the observation and generalisation of a certain class of
phenomena; who denied the validity of the alchemistic view of the
constitution of matter, and enunciated the definition of an element
which has since reigned supreme in Chemistry; and who enriched the
science with observations of the utmost importance. Boyle, however, was
a man whose ideas were in advance of his times, and intervening between
the iatro-chemical period and the Age of Modern Chemistry proper came
the period of the Phlogistic Theory—a theory which had a certain
affinity with the ideas of the alchemists.
§ 72. The Phlogiston Theory.
The phlogiston theory was mainly due to Georg Ernst Stahl
(1660-1734), Becher (1635-1682) had attempted to revive the once
universally accepted sulphur-mercury-salt theory of the alchemists in a
somewhat modified form, by the assumption that all substances consist of
three earths—the
combustible, mercurial, and vitreous; and herein is to be found the germ
of Stahl's phlogistic theory. According to Stahl, all combustible
bodies (including those metals that change on heating) contain
phlogision, the principle of combustion, which escapes in the
form of flame when such substances are burned. According to this theory,
therefore, the metals are compounds, since they consist of a metallic
calx (what we now call the "oxide" of the metal) combined with
phlogiston; and, further, to obtain the metal from the calx it is only
necessary to act upon it with some substance rich in phlogiston. Now,
coal and charcoal are both almost completely combustible, leaving very
little residue; hence, according to this theory, they must consist very
largely of phlogiston; and, as a matter of fact, metals can be obtained
by heating their calces with either of these substances. Many other
facts of a like nature were explicable in terms of the phlogiston
theory, and it became exceedingly popular. Chemists at this time did not
pay much attention to the balance; it was observed, however, that metals
increased in weight on calcination, but this was "explained" on the
assumption that phlogiston possessed negative weight. Antoine Lavoisier
(1743-1794), utilising Priestley's discovery of oxygen (called
"dephlogisticated air" by its discoverer) and studying the weight
relations accompanying combustion, demonstrated the non-validity of the
phlogistic theory
1 and proved
combustion to be the combination of the substance burnt
with a certain constituent of the air, the oxygen. By this time Alchemy
was to all intents and purposes defunct, Boerhave (1668-1738) was the
last eminent chemist to give any support to its doctrines, and the new
chemistry of Lavoisier gave it a final death-blow. We now enter upon
the Age of Modern Chemistry, but we shall deal in this chapter with the
history of chemical theory only so far as is necessary in pursuance of
our primary object, and hence our account will be very far from
complete.
§ 73. Boyle and the Definition of an Element.
Robert Boyle (1626-1691) had defined an element as a substance which
could not be decomposed, but which could enter into combination with
other elements giving compounds capable of decomposition into these
original elements. Hence, the metals were classed among the elements,
since they had defied all attempts to decompose them. Now, it must be
noted that this definition is of a negative character, and, although it
is convenient to term "elements" all substances which have so far defied
decomposition, it is a matter of impossibility to decide what substances
are true elements with absolute certainty; and the possibility, however
faint, that gold and other metals are of a compound nature, and hence
the possibility of preparing gold from the "base" metals or other
substances, must always remain. This uncertainty regarding the elements
appears to have generally been recognised by the new school of chemists,
but this having been so, it is the more surprising that their criticism
of alchemistic art was not less severe.
§ 74. The Stoichiometric Laws.
With the study of the relative weights in
which substances combine, certain generalisations or "natural laws" of
supreme importance were discovered. These stoichiometric laws, as they
are called, are as follows:—
- 1. "The Law of Constant Proportion"—The same chemical
compound always contains the same elements, and there is a constant
ratio between the weights of the constituent elements
present.
- 2. "The Law of Multiple Proportions"—If two substances combine
chemically in more than one proportion, the weights of the one which
combine with a given weight of the other, stand in a simple rational
ratio to one another.
- 3. "The Law of Combining Weights"—Substances combine either in
the ratio of their combining numbers, or in simple rational multiples or
submultiples of these numbers. (The weights of different substances
which combine with a given weight of some particular substance, which is
taken as the unit, are called the combining numbers of such substances
with reference to this unit. The usual unit now chosen is 8 grammes of
Oxygen.)2
As examples of these laws we may take the few following simple
facts:—
- 1. Pure water is found always to consist of oxygen and hydrogen
combined in the ratio of 1.008 parts by weight of the latter to 8 parts
by weight of the former; and pure sulphur-dioxide, to take another
example, is found always to consist of sulphur and oxygen combined in
the ratio of 8.02 parts by weight of sulphur to 8 parts by weight of
oxygen. (The Law of Constant Proportion.)
- 2. Another compound is known consisting only of oxygen and
hydrogen, which, however, differs entirely in its properties from water.
It is found always to consist of oxygen and hydrogen combined in the
ratio of 1.008 parts by weight of the latter to 16 parts by weight of
the former, i.e., in it a definite weight of hydrogen is combined
with an amount of oxygen exactly twice that which is combined
with the same weight of hydrogen in water. No definite compound has been
discovered with a constitution intermediate between these two. Other
compounds consisting only of sulphur and oxygen are also known. One of
these (viz., sulphur-trioxide, or sulphuric anhydride) is found always
to consist of sulphur and oxygen combined in the ratio of 5.35 parts by
weight of sulphur to 8 parts by weight of oxygen. We see, therefore,
that the weights of sulphur combined with a definite weight of oxygen in
the two compounds called respectively "sulphur-dioxide" and
"sulphur-trioxide," are in the proportion of 8.02 to 5.35, i.e.,
3:2. Similar simple ratios are obtained in the case of all the other
compounds. (The Law of Multiple Proportions.)
- 3. From the data given in (1) above we can fix the combining
number of hydrogen as 1.008, that of
sulphur as 8.02. Now, compounds are known containing sulphur and
hydrogen, and, in each case, the weight of sulphur combined with 1.008
grammes of hydrogen is found always to be either 8.02 grammes or some
multiple or submultiple of this quantity. Thus, in the simplest
compound of this sort, containing only hydrogen and sulphur (viz.,
sulphuretted-hydrogen or hydrogen sulphide), 1.008 grammes of hydrogen
is found always to be combined with 16.04 grammes of sulphur,
i.e., exactly twice the above quantity. (The Law of Combining
Weights.)
Berthollet (1748-1822) denied the truth of the law of constant
proportion, and a controversy ensued between this chemist and Proust
(1755-1826), who undertook a research to settle the question, the
results of which were in entire agreement with the law, and were
regarded as completely substantiating it.
§ 75. Dalton's Atomic Theory.
At the beginning of the nineteenth century, John Dalton (see plate
15{sic should be 16}) put forward his Atomic Theory in explanation of
these facts. This theory assumes (1) that all matter is made up of
small indivisible and indestructible particles, called "atoms"; (2) that
all atoms are not alike, there being as many different sorts of atoms as
there are elements; (3) that the atoms constituting any one element are
exactly alike and are of definite weight; and (4) that compounds are
produced by the combination of different atoms. Now, it is at once
evident that if matter be so constituted, the stoichiometric laws must
necessarily follow. For the smallest particle of any definite compound
(now called a "molecule") must consist of a definite assemblage of
different atoms, and these
atoms are of definite weight: whence the law of constant proportion. One
atom of one substance may combine with 1, 2, 3 . . . atoms of some other
substance, but it cannot combine with some fractional part of an atom,
since the atoms are indivisible: whence the law of multiple proportions.
And these laws holding good, and the atoms being of definite weight, the
law of combining weights necessarily follows. Dalton's Atomic Theory
gave a simple and intelligible explanation of these remarkable facts
regarding the weights of substances entering into chemical combination,
and, therefore, gained universal acceptance. But throughout the history
of Chemistry can be discerned a spirit of revolt against it as an
explanation of the absolute constitution of matter. The tendency of
scientific philosophy has always been towards Monism as opposed to
Dualism, and here were not merely two eternals, but several dozen;
Dalton's theory denied the unity of the Cosmos, it lacked the unifying
principle of the alchemists. It is only in recent times that it has been
recognised that a scientific hypothesis may be very useful without being
altogether true. As to the usefulness of Dalton's theory there can be
no question; it has accomplished that which no other hypothesis could
have done; it rendered the concepts of a chemical element, a chemical
compound and a chemical reaction definite; and has, in a sense, led to
the majority of the discoveries in the domain of Chemistry that have
been made since its enunciation. But as an expression of absolute
truth, Dalton's theory, as is very generally recognised nowadays, fails
to be satisfactory. In the past, however, it has been the philosophers
of the materialistic school of thought,
rather than the chemists
quâ chemists, who have insisted on
the absolute truth of the Atomic Theory; Kekulé, who by
developing Franklin's theory of atomicity or valency
3 made still more definite the atomic view of
matter, himself expressed grave doubts as to the absolute truth of
Dalton's theory; but he regarded it as
chemically true, and thus
voices what appears to be the opinion of the majority of chemists
nowadays, namely, there are such things as chemical atoms and chemical
elements, incapable of being decomposed by purely chemical means, but
that such are not absolute atoms or absolute elements, and
consequently not impervious to all forms of action.
But of this more will be said later.
§ 76. The Determination of the Atomic Weights of the
Elements.
With the acceptance of Dalton's Atomic Theory, it became necessary to
determine the atomic weights of the various elements, i.e., not
the absolute atomic weights, but the relative weights of the various
atoms with reference to one of them as unit.4
We cannot in this place enter upon a
discussion of the various difficulties, both of an experimental
and theoretical nature, which were involved in
this problem, save to remark that the correct atomic
weights could be arrived at only with the acceptance
of Avogadro's Hypothesis. This hypothesis, which is
to the effect that equal volumes of different gases
measured at the same temperature and pressure
contain an equal number of gaseous molecules, was
put forward in explanation of a number of facts
connected with the physical behaviour of gases; but
its importance was for some time unrecognised, owing
to the fact that the distinction between atoms and
molecules was not yet clearly drawn. A list of those
chemical substances at present recognised as "elements,"
together with their atomic weights, will be
found on pp. 106, 107.
§ 77. Prout's Hypothesis.
It was observed by a chemist of the name of Prout, that, the atomic
weight of hydrogen being taken
as the unit, the atomic weights of nearly all the elements approximated
to whole numbers; and in 1815 he suggested as the reason for this
regularity, that all the elements consist solely of hydrogen. Prout's
Hypothesis received on the whole a very favourable reception; it
harmonised Dalton's Theory with the grand concept of the unity of
matter—all matter was hydrogen in essence; and Thomas Thomson undertook
a research to demonstrate its truth. On the other hand, however, the
eminent Swedish chemist, Berzelius, who had carried out many atomic
weight determinations, criticised both Prout's Hypothesis and Thomson's
research (which latter, it is true, was worthless) in most severe terms;
for the hypothesis amounted to this—that the decimals in the atomic
weights obtained experimentally by Berzelius, after so much labour, were
to be regarded as so many errors. In 1844, Marignac suggested half the
hydrogen atom as the unit, for the element chlorine, with an atomic
weight of 35.5, would not fit in with Prout's Hypothesis as originally
formulated; and later, Dumas suggested one-quarter. With this
theoretical division of the hydrogen-atom, the hypothesis lost its
simplicity and charm, and was doomed to downfall. Recent and most
accurate atomic weight determinations show clearly that the atomic
weights are not exactly whole numbers, but that, nevertheless, the
majority of them (if expressed in terms of O = 16 as the unit) do
approximate very closely to such. The Hon. R. J. Strutt has recently
calculated that the probability of this occurring, in the case of
certain of the commoner elements, by mere chance is exceedingly small
(about 1 in
1,000),
5 and several attempts to
explain this remarkable fact have been put forward. Modern scientific
speculations concerning the constitution of atoms tend towards a
modified form of Prout's hypothesis, or to the view that the atoms of
other elements are, in a manner, polymerides of hydrogen and helium
atoms. As has been pointed out, it is possible, according to modern
views, for elements of different atomic weight to have identical
chemical properties, since these latter depend only upon the number of
free electrons in the atom and not at all upon the massive central
nucleus. By a method somewhat similar to that used for determining the
mass of kathode particles (see § 79), but applied to positively
charged particles, Sir Joseph Thomson and Dr. F. W. Aston discovered
that the element neon was a mixture of two isotopic elements in unequal
proportions, one having an atomic mass of 20, the other (present only to
a slight extent) having an atomic mass of 22. Dr. Aston has perfected
this method of analysing mixtures of isotopes and determining their
atomic masses.
6 The results are of
great interest. The atomic weight of hydrogen, 1.008, is confirmed.
The elements helium, carbon, nitrogen, oxygen, fluorine, phosphorus,
sulphur, arsenic, iodine and sodium are found to be simple bodies with
whole-number atomic weights. On the other hand, boron, neon, silicon,
chlorine, bromine, krypton, xenon,
mercury, lithium, potassium and rubidium are found to be mixtures. What
is specially of interest is that the indicated atomic mass of each of
the constituents is a whole number. Thus chlorine, whose atomic weight
is 35.46, is found to be a mixture of two chemically-identical elements
whose atomic weights are 35 and 37. Some of the elements,
e.g.,
xenon, are mixtures of more than two isotopes.
It is highly probable that what is true of the elements
investigated by Dr. Aston is true of the remainder. It appears,
therefore, that the irregularities presented by the atomic weights of
the ordinary elements, which have so much puzzled men of science in the
past, are due to the fact that these elements are, in many cases,
mixtures. As concerns hydrogen, it is only reasonable to suppose that
the close packing of electrically charged particles should give rise to
a slight decrease in their total mass, so that the atomic weights of
other elements referred to H = 1 should be slightly less than whole
numbers, or, what is the same thing, that the atomic weight of hydrogen
referred to O = 16 should be slightly more than unity.
§ 78. The "Periodic Law".
A remarkable property of the atomic weights was discovered, in the
sixties, independently by Lothar Meyer and Mendeléeff. They found
that the elements could be arranged in rows in the order of their atomic
weights so that similar elements would be found in the same columns. A
modernised form of the Periodic Table will be found on pp. 106, 107. It
will be noticed, for example, that the "alkali" metals, Lithium, Sodium,
Rubidium and Cæsium, which
THE PERIODIC TABLE OF THE CHEMICAL ELEMENTS
| 0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
|
[Hydrogen
H=1°008]a |
|
|
|
|
|
Hydrogen
H=1°008 |
|
Helium
He=4°00 |
Lithium
Li=6°94 |
Glucinum
Gl=9°1 |
Boron
B=10°9 |
Carbon
C=12°005 |
Nitrogen
N=14.008 |
Oxygen
O=16°00 |
Flourine
F=19°0 |
|
Neon
Ne=20°2 |
Sodium
Na=23°00 |
Magnesium
Mg=24°32 |
Aluminium
Al=27°1 |
Silicon
Si=28°3 |
Phosphorus
P=31°04 |
Sulphur
S=32°06 |
Chlorine
Cl=35°46 |
|
Argon
A=39°9' |
Potassiumb
K=39°10 |
Calcium
Ca=40°07 |
Scandium
Sc=45°1 |
Titanium
Ti=48°1 |
Vanadium
V=51°0 |
Chromium
Cr=52°0 |
Manganese
Mn=54°93 |
Iron Fe=55°84c
Cobalt Co=58°97
Nickel Ni=58°68 |
|
Copper
Cu=63°57 |
Zinc
Zn=65°37 |
Gallium
Ga=70°1 |
Germanium
Ge=72°5 |
Arsenic
As=74°96 |
Selenium
Se=79°2 |
Bromine
Br=79°92 |
|
Krypton
Kr=82°92 |
Rubidium
Rb=85°45 |
Strontium
Sr=87°63 |
Yttrium
Y=89°33 |
Zirconium
Zr=90°6 |
Columbium
Cb=93°1 |
Molybdenum
Mo=96°0 |
? |
Ruthenium Ru=101°7
Rhodium Rh=102°9
Palladium Pd=106°7 |
|
Silver
Ag=107°88 |
Cadmium
Cd=112°40 |
Indium
In=114°8 |
Tin
Sn=118°7 |
Antimony
Sb=120°2 |
Tellurium
Te=127°5 |
Iodined
I (orJ)-
126°92 |
|
Xenon
Xe=130°2 |
Cæsium
Cs=132°81 |
Barium
Ba=137°37 |
Lanthanum
La=139°0 |
Ceriume
Ce=140°25 |
? |
? |
? |
? |
|
? |
? |
? |
? |
? |
? |
? |
|
| ? |
? |
? |
? |
? |
Tantalum
Ta=181°5 |
Tungsten
W=184°0 |
? |
Osmium Os=190°9
Iridium Ir=193°1
Platinum Pt=195°2 |
|
Gold
Au=197°2 |
Mercury
Hg=200°6 |
Thallium
Tl=204°0 |
Lead
Pb=207°20 |
Bismuth
Bi=208°0 |
Polonium
|
? |
|
Emanation
(Niton)222°0 |
? |
Radium
Ra=226°0 |
Actinium
? |
Thorium
Th=232°15 |
Ekatantalum
? |
Uranium
U=238°2 |
? |
? |
NOTES.
There are several somewhat different forms of this Periodic Table.
This is one of the simplest, but it lacks certain advantages of some of
the more complicated forms. The atomic weights given are those of the
International Atomic Weights Committee for 1920-1. They are calculated
on the basis. Oxygen = 16. The number of decimal places given in each
case indicates the degree of accuracy with which each atomic weight has
been determined. The letter or letters underneath the name of each
element is the symbol by which it is invariably designated by chemists.
The number above each column indicates the valency which the
elements of each group exhibit towards oxygen. Many of the elements are
exceptional in this respect.
[a] The exact position of Hydrogen is in dispute.
[b] The positions of Argon and Potassium have been inverted in
order that these elements may fall in the right columns with the
elements they resemble; [d] 50 also have the positions of Tellurium and
Iodine.
[c] The whole of "Group 8" forms an exception to the Table.
[e] There are a number of ill-defined rare earth metals with
atomic weights lying between those of Cerium and Tantalum. They all
appear to resemble the elements of "Group 3," so that their positions in
the Table cannot be decided with accuracy.
resemble one another very closely, fall in Column 1; the "alkaline
earth" metals occur together in Column 2; though in each case these are
accompanied by certain elements with somewhat different properties. Much
the same holds good in the case of the other columns of this Table;
there is manifested a remarkable regularity, with certain still more
remarkable divergences (see notes appended to Table on pp. 106, 107).
This regularity exhibited by the "elements" is of considerable
importance, since it shows that, in general, the properties of the
"elements" are periodic functions of their atomic weights; and,
together with certain other remarkable properties of the "elements,"
distinguishes them sharply from the "compounds." It may be concluded
with tolerable certainty, therefore, that if the "elements" are in
reality of a compound nature, they are all, in general, compounds of a
like nature distinct from that of other compounds.
It is now some years since the late Sir William Crookes attempted
to explain the periodicity of the properties of the elements on the
theory that they have all been evolved by a conglomerating process from
some primal stuff—the protyle—consisting of very small particles. He
represented the action of this generative cause by means of a "figure of
eight" spiral, along which the elements are placed at regular intervals,
so that similar elements come underneath one another, as in
Mendeléeff's table, though the grouping differs in some respects.
The slope of the curve is supposed to represent the decline of some
factor (e.g., temperature) conditioning the process, which
process is assumed to be of a recurrent nature, like the swing of a
pendulum After the completion of one swing
(to keep to the illustration of a pendulum) whereby one series of
elements is produced, owing to the decline of the above-mentioned
factor, the same series of elements is not again the result as would
otherwise be the case, but a somewhat different series is produced, each
member of which resembles the corresponding member of the former series.
Thus, if the first series contains, for example, helium, lithium,
carbon, &c., the second series will contain instead, argon, potassium,
titanium, &c. The whole theory, though highly interesting, is, however,
by no means free from defects.
§ 79. The Corpuscular Theory of Matter.
We must now turn our attention to those recent views of the
constitution of matter which originated to a great extent in the
investigations of the passage of electricity through gases at very low
pressures. It will be possible, however, on the present occasion, to
give only the very briefest account of the subject; but a fuller
treatment is rendered unnecessary by the fact that these and allied
investigations and the theories to which they have given rise have been
fully treated in several well-known works, by various authorities on
the subject, which have appeared during the last few years.
7
When an electrical discharge is passed through a high-vacuum
tube, invisible rays are emitted from the kathode, generally with the
production of a greenish-yellow
fluorescence where they strike the glass walls of the tube. These rays
are called "kathode rays." At one time they were regarded as waves in
the ether, but it was shown by Sir William Crookes that they consist of
small electrically charged particles, moving with a very high velocity.
Sir J. J. Thomson was able to determine the ratio of the charge carried
by these particles to their mass or inertia; he found that this ratio
was constant whatever gas was contained in the vacuum tube, and much
greater than the corresponding ratio for the hydrogen ion (electrically
charged hydrogen atom) in electrolysis. By a skilful method, based on
the fact discovered by Mr. C. T. R. Wilson, that charged particles can
serve as nuclei for the condensation of water-vapour, he was further
able to determine the value of the electrical charge carried by these
particles, which was found to be constant also, and equal to the charge
carried by univalent ions,
e.g., hydrogen, in electrolysis.
Hence, it follows that the mass of these kathode particles must be much
smaller than the hydrogen ion, the actual ratio being about 1:1700. The
first theory put forward by Sir J. J. Thomson in explanation of these
facts, was that these kathode particles ("corpuscles" as he termed them)
were electrically charged portions of matter, much smaller than the
smallest atom; and since the same sort of corpuscle is obtained whatever
gas is contained in the vacuum tube, it is reasonable to conclude that
the corpuscle is the common unit of all matter.
§ 80. Proof that the Electrons are not Matter.
This eminent physicist, however, had shown mathematically that a
charged particle moving with a very high velocity (approaching that of
light)
would exhibit an appreciable increase in mass or inertia due to the
charge, the magnitude of such inertia depending on the velocity of the
particle. This was experimentally verified by Kaufmann, who determined
the velocities, and the ratios between the electrical charge and the
inertia, of various kathode particles and similar particles which are
emitted by compounds of radium (see §§ 89 and 90). Sir J. J.
Thomson calculated these values on the assumption that the inertia of
such particles is entirely of electrical origin, and thereby obtained
values in remarkable agreement with the experimental. There is,
therefore, no reason for supposing the corpuscle to be matter at all;
indeed, if it were, the above agreement would not be obtained. As
Professor Jones says: "Since we know things only by their properties,
and since all the properties of the corpuscle are accounted for by the
electrical charge associated with it, why assume that the corpuscle
contains anything but the electrical charge? It is obvious that there is
no reason for doing so.
"The corpuscle is, then, nothing but a disembodied, electrical
charge, containing nothing material, as we have been accustomed to
use that term. It is electricity, and nothing but electricity. With this
new conception a new term was introduced, and, now, instead of speaking
of the corpuscle we speak of the electron."
8 Applying this modification to the above
view of the constitution of matter, we have what is called "the
electronic theory," namely, that the
material atoms consist of electrons, or units of electricity in rapid
motion; which amounts to this—that matter is simply an electrical
phenomenon.
§ 81. The Electronic Theory of Matter.
Sir J. J. Thomson has elaborated this theory of the nature and
constitution of matter; he has shown what systems of electrons would be
stable, and has attempted to find therein the significance of
Mendeléeff's generalisation and the explanation of valency.
There can be no doubt that there is a considerable element of truth in
the electronic theory of matter; the one characteristic property of
matter, i.e., inertia, can be accounted for electrically. The
fundamental difficulty is that the electrons are units of negative
electricity, whereas matter is electrically neutral. Several theories
have been put forward to surmount this difficulty. Certainly the
electron is a constituent of matter; but is it the sole constituent?
Recent research indicates that, as already pointed out, all atoms
consist of two distinct portions, a massive central nucleus, whose net
charge is positive, surrounded by a number of electrons, just sufficient
to neutralize this charge. The point of greatest interest is that the
indicated number of free electrons is exactly the number which expresses
the position of the element in the Periodic Table, reckoning helium as
2, lithium as 3, and so on; and it would seem that the chemical
properties of the elements are determined entirely by these electrons,
and are, therefore, not, strictly speaking, periodic functions of their
atomic weights, as was formerly thought (§ 78), but of their atomic
numbers. The exact nature of the nuclei of the various atoms has yet to
be
determined: in the case of the atoms heavier than helium they would
appear to be made up of the nuclei of hydrogen and (or) helium atoms
together with—in many cases—electrons insufficient in number to
neutralize the positive charges associated with these.
§ 82. The Etheric Theory of Matter.
The analysis of matter has been carried a step further. A
philosophical view of the Cosmos involves the assumption of an
absolutely continuous and homogeneous medium filling all space, for an
absolute vacuum is unthinkable, and if it were supposed that the stuff
filling all space is of an atomic structure, the question arises, What
occupies the interstices between its atoms? This ubiquitous medium is
termed by the scientists of to-day "the Ether of Space." Moreover, such
a medium as the Ether is demanded by the phenomena of light. It appears,
however, that the ether of space has another and a still more important
function than the transmission of light: the idea that matter has its
explanation therein has been developed by Sir Oliver Lodge. The
evidence certainly points to the conclusion that matter is some sort of
singularity in the ether, probably a stress centre. We have been too
much accustomed to think of the ether as something excessively light and
quite the reverse of massive or dense, in which it appears we have been
wrong. Sir Oliver Lodge calculates that the density of the ether is far
greater than that of the most dense forms of matter; not that matter is
to be thought of as a rarefaction of the ether, for the ether within
matter is as dense as that without. What we call matter, however, is not
a continuous substance; it consists,
rather, of a number of widely separated particles, whence its
comparatively small density compared with the perfectly continuous
ether. Further, if there is a difficulty in conceiving how a perfect
fluid like the ether can give rise to a solid body possessed of such
properties as rigidity, impenetrability and elasticity, we must remember
that all these properties can be produced by means of motion. A jet of
water moving with a sufficient velocity behaves like a rigid and
impenetrable solid, whilst a revolving disc of paper exhibits elasticity
and can act as a circular saw.
10 It
appears, therefore, that the ancient doctrine of the alchemistic essence
is fundamentally true after all, that out of the "One Thing" all
material things have been produced by adaptation or modification; and,
as we have already noticed (§ 60), there also appears to be some
resemblance between the concept of the electron and that of the seed of
gold, which seed, it should be borne in mind, was regarded by the
alchemists as the common seed of all metals.
§ 83. Further Evidence of the Complexity of the Atoms.
There are also certain other facts which appear to demand such a
modification of Dalton's Atomic Theory as is found in the Electronic
Theory. One of the characteristics of the chemical elements is that each
one gives a spectrum peculiar to itself. The spectrum of an element
must, therefore, be due to its atoms, which in some way are able, at a
sufficiently high temperature, to act upon the ether so as to produce
vibrations of definite and characteristic wave-length. Now, in many
cases the number of lines of definite wavelength
observed in such a spectrum is considerable, for example, hundreds of
different lines have been observed in the arc-spectrum of iron. But it
is incredible that an atom, if it were a simple unit, would give rise to
such a number of different and definite vibrations, and the only
reasonable conclusion is that the atoms must be complex in structure. We
may here mention that spectroscopic examination of various heavenly
bodies leads to the conclusion that there is some process of evolution
at work building up complex elements from simpler ones, since the
hottest nebulæ appear to consist of but a few simple elements,
whilst cooler bodies exhibit a greater complexity.
§ 84. Views of Wald and Ostwald.
Such modifications of the atomic theory as those we have briefly
discussed above, although profoundly modifying, and, indeed,
controverting the philosophical significance of Dalton's theory as
originally formulated, leave its chemical significance practically
unchanged. The atoms can be regarded no longer as the eternal,
indissoluble gods of Nature that they were once supposed to be; thus,
Materialism is deprived of what was thought to be its scientific
basis.11 But the science of Chemistry
is unaffected thereby; the atoms are not the ultimate units out of which
material things are built, but the atoms cannot be decomposed by purely
chemical means; the "elements" are not truly elemental, but they are
chemical elements. However, the atomic theory has been subjected to
a far more searching criticism. Wald argues that substances obey the
law of definite
proportions because of the way in which they are prepared; chemists
refuse, he says, to admit any substance as a definite chemical compound
unless it does obey this law. Wald's opinions have been supported by
Professor Ostwald, who has attempted to deduce the other stoichiometric
laws on these grounds without assuming any atomic hypothesis
12; but these new ideas do not appear to
have gained the approval of chemists in general. It is not to be
supposed that chemists will give up without a struggle a mental tool of
such great utility as Dalton's theory, in spite of its defects, has
proved itself to be. There does seem, however, to be logic in the
arguments of Wald and Ostwald, but the trend of recent scientific theory
and research does not appear to be in the direction of Wald's views.
Certainly, however, it appears that, on the one hand, the atomic theory
is not necessitated by the so-called "stoichiometric laws"; but, on the
other hand, a molecular constitution of matter seems to be demanded by
the phenomenon known as the "Brownian Movement,"
i.e., the
spontaneous, irregular and apparently perpetual movement of microscopic
portions of solid matter when immersed in a liquid medium; such movement
appearing to be explicable only as the result of the motion of the
molecules of which the liquid in question is built up.
13
[1.]
It should be noted, however, that if by the
term "phlogiston" we were to understand energy and not some form of
matter, most of the statements of the phlogistics would be true so far
as they go.
[2.]
In order that these laws may hold good, it is,
of course, necessary that the substances are weighed under precisely
similar conditions. To state these laws in a more absolute form, we can
replace the term "weight" by "mass," or in preference, "inertia"; for
the inertial of bodies are proportional to their weights, providing that
they are weighed under precisely similar conditions. For a discussion of
the exact significance of these terms "mass" and "inertia," the reader
is referred to the present writer's Matter, Spirit and the Cosmos
(Rider, 1910), Chapter I., "On the Doctrine of the Indestructibility of
Matter."
[3.]
The term "valency" is not altogether an easy
one to define; we will, however, here do our best to make plain its
significance. In a definite chemical compound we must assume that the
atoms constituting each molecule are in some way bound together (though
not, of course, rigidly), and we may speak of "bonds" or "links of
affinity," taking care, however, not to interpret such terms too
literally. Now, the number of "affinity links" which one atom can exert
is not unlimited; indeed, according to the valency theory as first
formulated, it is fixed and constant. It is this number which is called
the "valency" of the element; but it is now known that the "valency" in
most cases can vary between certain limits. Hydrogen, however, appears
to be invariably univalent, and is therefore taken as the unit of
valency. Thus, Carbon is quadrivalent in the methane-molecule, which
consists of one atom of carbon combined with four atoms of hydrogen; and
Oxygen is divalent in the water-molecule, which consists of one atom of
oxygen combined with two atoms of hydrogen. Hence, we should expect to
find one atom of carbon combining with two of oxygen, which is the case
in the carbon-dioxide—(carbonic anhydride)—molecule. For a development
of the thesis, so far as the compounds of carbon are concerned, that
each specific "affinity link" corresponds in general to a definite and
constant amount of energy, which is evolved as heat on disruption of the
bond, the reader is referred to the present writer's monograph On the
Calculation of Thermo-Chemical Constants (Arnold, 1909). The
phenomena of valency find their explanation in modern views concerning
the constitution of atoms (see § 81).
[4.]
Since hydrogen is the lightest of all known
substances, the unit, Hydrogen = 1, was at one time usually employed.
However, it was seen to be more convenient to express the atomic weights
in terms of the weight of the oxygen-atom, and the unit, Oxygen = 16 is
now always employed. This value for the oxygen-atom was chosen so that
the approximate atomic weights would in most cases remain unaltered by
the change.
[5.]
Hon. R. J. STRUTT: "On the Tendency of the
Atomic Weights to approximate to Whole Numbers," Philosophical
Magazine, [6], vol. i. (1901), pp.
311 et seq.
[6.]
F W. ASTON: "Mass-spectra and Atomic Weights,"
Journal of the Chemical Society, vol. cix. (1921), pp. 677 et
seq.
[7.]
We have found Prof. Harry Jones' The
Electrical Nature of Matter and Radioactivity (1906), Mr. Soddy's
Radioactivity (1904), and Mr. Whetham's The Recent Development
of Physical Science (1909) particularly interesting. Mention, of
course, should also be made of the standard works of Prof. Sir J. J.
Thomson and Prof. Rutherford.
[8.]
H. C. JONES: The Electrical Nature of Matter
and Radioactivity (1906), p. 21
[10.]
See Sir OLIVER LODGE, F.R.S.: The Ether of
Space (1909).
[11.]
For a critical examination of Materialism,
the reader is referred to the present writer's Matter, Spirit and the
Cosmos (Rider, 1910), especially Chapters I. and IV.
[12.]
W. OSTWALD: "Faraday Lecture," Journal of
the Chemical Society, vol. lxxxv. (1904), PP. 506 et seq. See
also W. OSTWALD: The Fundamental Principles of Chemistry
(translated by H. W. Morse, 1909), especially Chapters VI., VII. and
VIII.
[13.]
For an account of this singular phenomenon,
see Prof. JEAN PERRIN: Brownian Movement and Molecular Reality
(translated from the Annales de Chimie et de Physique, 8me
Séries, September, 1909, by F. Soddy, M.A., F.R.S., 1910).
