its activity is not yet told. It can not be told, for each year adds
information in regard to these activities, for there are thousands
of investigators at work. Another far-reaching manifestation is
this: the rays can separate the air or a gas into its constituent
particles, much as a strong electrical current separates water into
oxygen and hydrogen. They can communicate electrical charges to these
particles--positive and negative charges. The charged air-particles,
when forced through partitions of spun glass, does not give up their
electricity as they do when they are charged by an electrical machine.
This curious manifestation leads me to suspect that the electricity
and magnetism of the earth may be caused by an X-ray effect on our
atmosphere. The sun and the earth are separated like the terminals of
a Crooke’s tube--two conductors with a vacuum between. An electrical
excitation from the sun may cause an electrical discharge between it
and the earth. This discharge might consist of an X-ray effect which
could separate the upper layers of the atmosphere into positive and
negative charges. The velocity of the negatively charged particles is
greater than that of the positively charged ones, and the revolution
of the earth may cause such a movement of these electrified particles
that electrical currents may be generated which in circulation around
the earth could produce the observed magnetism of the north and south
poles, together with the auroral lights characteristic of those
regions. This, I am well aware, is an audacious theory. It is certainly
a vast extension of the laboratory experiments I have described, but
the electrical radiations developed in electrical discharges are as
competent to produce powerful magnetic whirls as the heat radiations
in our atmosphere to develop cyclones. In the lower regions of our
atmosphere the air is an insulator like glass to the passage of an
electrical current. A layer a foot thick can prevent the circulation of
the most powerful current which is now used to generate horse power.
When this air space is rarefied at a certain degree of rarefaction
the electrical current passes, especially, as we have seen, if it is
illuminated by the X rays. When, therefore, we ascend to a height of
ten or twenty miles the rarefied air becomes an excellent conductor of
electricity of high electro-motive force. To my mind the conditions
exist for developing an electrical state in the earth’s covering of
air, which is competent to explain the electrical manifestations of
the air, the auroral gleam, and the mysterious effect on the magnetic
needle which keeps it directed to the magnetic north. Can not we
conclude that the study of the X rays bids fair to greatly extend
our conceptions of the constitution of matter and of the action and
interaction of Nature’s forces?
* * * * *
A Himalayan explorer reported, a few years ago, that he had seen,
from one of the lofty summits of the Mount Everest district, a peak
which, beheld in the same view with Mount Everest, was evidently
higher than it. Nothing has been heard of the matter since then
till the recent appearance of Major L. A. Waddell’s book, Among
the Himalayas. This author, who has explored the same region,
represents that the Tibetans there say there is another mountain,
due north of Mount Everest, that exceeds that peak in height, thus
confirming the story of the former Alpinist. It appears that Mount
Everest is not called Gaurisankar or Deodunga, as some affirm,
but that the Tibetan name of the culminating peak of the group is
_Jomokang-kar_--“The Lady White Glacier.”
A HUNDRED YEARS OF CHEMISTRY.
BY F. W. CLARKE,
CHIEF CHEMIST, UNITED STATES GEOLOGICAL SURVEY.
It is hardly an exaggeration to say that chemistry, as a science, is
the creation of the nineteenth century. Chemical facts, indeed, were
known even in remote antiquity; some principles were dimly anticipated
long before the century began; Boyle had given the first rational
definition of an element; the principal gases had been discovered;
great foundations were laid, ready for the superstructure. But the
making of bricks is not architecture, nor does the accumulation
of details constitute a science. The scattered facts are needful
preliminaries, but only with the discovery of laws and the development
of broad generalizations does true science begin.
That truth can be born from error may seem paradoxical, but,
nevertheless, the statement is exact. False hypotheses stimulate
investigation, and so truth comes at last to light. In the history
of chemistry this principle is clearly illustrated. During the
eighteenth century the doctrine of phlogiston was generally accepted;
this led to exhaustive researches upon combustion, and from these the
science of chemistry received its present shape. Becher and Stahl
had taught that every combustible substance contained a combustible
principle--_phlogiston_--and that to the elimination of this principle
the phenomena of combustion were due. According to this theory, a metal
was regarded as a compound of its calx, or oxide, with phlogiston;
hydrogen became a compound of water with phlogiston, and so the truth
was curiously inverted. The doctrine was vigorously and ingeniously
defended, and, although it was overthrown by Lavoisier, it had
persistent supporters even after the present century began.
The weak point of the phlogistic theory was its practical disregard of
the phenomena of weight. That the calx weighed more than the metal was
well known, but quantitative considerations were subordinated to those
of quality, and the form of matter was studied rather than its mass.
In 1770 the scientific career of Lavoisier began, and the balance
became a chief instrument in chemical research. The constancy of
weight during chemical change was experimentally established, and
what had been a philosophical speculation--the increatability and
indestructibility of matter--became a doctrine of science, a datum
of knowledge instead of a hypothetical belief. In 1774 Priestley and
Scheele independently discovered oxygen, and with the aid of the
balance the phenomena of combustion were rendered intelligible. The
foundations of chemistry were laid, and upon them the nineteenth
century has built. Lavoisier, the greatest of the founders, fell a
victim to the guillotine; the judge who condemned him refused all
appeals for mercy, saying “the republic has no need for _savants_,”
but the necessity which judicial ignorance could not foresee presently
made itself felt. France, at war with all Europe, her ports closed to
supplies from without, fell back upon her own resources. Saltpeter
was needed for her guns, alkali for her industries, and the chemist
was called upon for help. The stress of continued warfare stimulated
intellectual activity, and one result was the creation of chemical
processes which revolutionized more than one industry. The dependence
of modern civilization upon science then began to be recognized--a
dependence which is, perhaps, the chief characteristic of the present
century.
With the opening of the new century a period of great activity began.
The constancy of matter was well established, and the fundamental
distinction between elements and compounds was clearly recognized; two
starting points for exact research had been gained. Only a small number
of elements, however, had been identified as such; of some substances
it was doubtful whether they were elementary or not, but the mine was
open and a rich body of ore was in sight. Furthermore, the utility of
research had become evident, so that intellectual curiosity received a
new stimulus and a new direction. Theory and practice became partners,
and have worked together to this day.
Between the years 1803 and 1808 one of the greatest advances, in
scientific chemistry was made, when John Dalton announced and developed
his famous atomic theory. In this we find a notable illustration of the
difference between metaphysics and science. The conception of matter as
made up of atoms, as discrete rather than continuous, was a commonplace
of philosophical speculation. It had been taught by Democritus and
Lucretius; it was the theme of wordy wrangles during centuries;
Swedenborg, Higgins, and other writers had sought to apply it to the
discussion of chemical phenomena; but it remained only a speculation,
unfruitful for discovery. Up to the time of Dalton it had led to
nothing but intellectual gymnastics.
A good scientific theory is never a product of the unaided imagination;
it must serve some purpose in the correlation of phenomena which
suggest it to the mind. This was the case with Dalton’s discovery,
which grew out of his observations upon definite and multiple
proportions. That every chemical compound has a fixed and definite
composition was recognized by Lavoisier, and by other chemists before
him; but the fact was disputed by Berthollet, and its verity was not
established until 1808. Dalton went a step further, and found that to
every element a definite combining number could be assigned, and that
when two elements united in more than one proportion even multiples of
that number appeared. Thus, taking the hydrogen weight as unity, oxygen
always combines with other elements in the proportion of eight parts
or some simple multiple thereof, and so on through the entire list of
elementary bodies. Each one has its own combining weight, and this was
the law for which Dalton sought an adequate explanation. Fractions of
the weights did not appear, fractional atoms could not exist; the two
thoughts were connected by Dalton. Chemical union, to his mind, became
a juxtaposition of atoms, whose relative weights were indicated by
their combining numbers, and so the atomic conception for the first
time was given quantitative expression. The facts were co-ordinated,
the special laws were combined in one general theory, and the mere
suppositions of other men were supplanted by a precise statement,
which is a corner stone of chemistry to-day. The doctrine led at once
to investigations, it rendered possible the discovery of new truth,
chemical formulæ and chemical equations were developed from it; without
its aid the growth of chemical science would probably have been
slow. The nature of the atoms may be in doubt, they may be divisible
or indivisible, but the value of the theory is independent of such
considerations. It gives adequate expression to known laws, and it can
only be set aside, if ever, by absorption into some wider and deeper
generalization.
The same year which saw the completion of Dalton’s theory (1807) was
also signalized by the remarkable discoveries of Sir Humphry Davy, who
decomposed the alkalies and proved them to be compounds of metals.
In 1810 chlorine, which was previously thought to be a compound, was
proved to be elementary, and this fact was emphasized a year later
by the discovery of iodine. These researches gave precision to the
conception of an element, and prepared the way for later investigations
upon many other oxides. All the so-called “earths”--lime, magnesia,
alumina, and so on--were now seen to be oxy-compounds of metals, and
an intelligent interpretation of all forms of inorganic matter became
possible. The first step in the chain of research was the discovery
of oxygen itself; from that, and from the teachings of Lavoisier, the
later discoveries logically followed.
While the investigations of Dalton and of Davy were still incomplete,
other chemists were actively studying the properties of gases and
exploring the fertile border-land between chemistry and physics. In
1805 Gay-Lussac and Humboldt determined the composition of water by
_volume_; in 1808 Gay-Lussac extended these observations, and found
that in all compound gases simple volumetric relations existed; and
in 1811 the entire subject was generalized into Avogadro’s law.
Avogadro showed that equal volumes of gases, compared under equivalent
conditions, must contain equal numbers of molecules, and although the
force of his discovery was not fully appreciated until much later,
it is now recognized as one of the fundamental propositions of both
physics and chemistry. For the first time the distinction between atoms
and molecules was clearly stated, and from the density of a gas the
relative weight of its molecule could be calculated. Avogadro’s law
rounded out and completed the atomic theory, and to its application
much of the advance in organic chemistry is due. Equally striking, but
less far-reaching in its consequences, was the discovery announced by
Dulong and Petit in 1819, when it was shown that the specific heat of
an element was inversely proportional to its atomic weight. Otherwise
stated, this law asserts that the atoms of all the elements have the
same capacity for heat, and an important check upon determinations of
atomic weight was thus provided.
The next twenty years in the history of chemistry were years of
detail rather than of permanent generalizations. The multitudinous
verification of known laws, the development of experimental methods,
especially methods of analysis, the discovery of new elements, the
preparation of numberless new compounds, occupied the attention of most
workers. This period, which may be called the Berzelian period, was
enormously fruitful in results, although but few of the theories then
proposed have survived to the present day. During this period the name
and influence of Berzelius overshadowed all others, and his marvelous
researches, carried out in a laboratory which was hardly more than
a kitchen, were of almost incredible variety. For the crude symbols
of Dalton, Berzelius substituted a system of chemical formulæ which
could be used in chemical equations; in 1818 and 1826 he published
tables of atomic weights, determined with far greater exactness than
ever before; he discovered five new elements and a multitude of
compounds, devised methods of research, and proposed theories which,
though later to be overthrown, for many years dominated chemical
science. His electro-chemical experiments led him to his dualistic
theory of compounds, which interpreted each compound as made up of two
parts--one positive, the other negative. The electro-positive oxides
were basic, the electro-negative groups were acid; chemical affinity
was electrical attraction between the two opposites; chemical union
implied a neutralization of one by the other. These ideas were more
than speculation, for they rested upon experiment and led to further
experimental research; but they went too far, and therefore could
not last. The theory, however, contained much that was true, and the
formulæ developed by it gave the first general suggestion of what is
now known as chemical structure or constitution. The later study of
organic compounds led up to the modern views.
Although Berzelius and many other chemists did some work upon organic
compounds, their era was chiefly identified with inorganic researches.
Mineral chemistry received a great deal of attention, the relatively
simple acids, bases, and salts were studied, but the compounds of
carbon were thought to be more complex and received less consideration.
To-day, at the close of the century, nearly seventy thousand organic
compounds are known, and of these comparatively few were discovered
before the year 1830. Since then organic chemistry has been the
dominant line of investigation.
Among the earlier chemists of the nineteenth century it was commonly
supposed that organic and inorganic matter were radically different,
and that the former could only be produced by the operation of a
peculiar vital force. To this view there were some dissentients,
Berzelius among them, but experimental proof for their contention
was lacking. In 1827, however, Wöhler succeeded in transforming the
inorganic ammonium cyanate into the organic urea, and the barrier was
broken down. The era of synthetic chemistry had begun. Still earlier,
in 1823, Liebig had found that silver cyanate and silver fulminate
possessed the same percentage composition; in 1825 Faraday discovered
an isomer of ethylene; and Wöhler’s research now gave a third example
of the same kind. Two different substances could contain the same
elements in the same proportions, and to explain this fact Berzelius
inferred different arrangements of atoms within the molecule, and
suggested that their mode of union might be determined. A working
theory, however, was still lacking, and without it progress was
necessarily slow. The dualistic hypothesis explained the phenomena
only in part, and as the known facts increased in number it had to be
abandoned.
Two important investigations paved the way for an advance. In 1832
Liebig and Wöhler, studying benzoic acid, found that it and its
derivatives contained in common a group of atoms, not isolable by
itself, to which they gave the name of benzoyl. The conception of such
a group, a compound radicle, already existed, but it lacked clearness,
and now for the first time it became truly a scientific idea. The
search for, and the identification of, compound radicles began to
occupy the attention of chemists, and a definite line of attack upon
organic matter was recognized.
Two years later the second great step was taken. Dumas, studying the
action of chlorine upon acetic acid, showed that the chlorine could
replace hydrogen atom for atom, or volume for volume, and that his
observations explained other reactions which had been unintelligible
hitherto. This research led him to the famous theory of substitutions,
which at first was received with ridicule, but soon found general
acceptance. Electro-chemical conceptions, the Berzelian doctrines, were
then in vogue, and it seemed strange, even absurd, to suppose that
electro-negative chlorine could be substituted for electro-positive
hydrogen. But the facts were stronger than the preconceived ideas, and
the latter soon gave way. In this discovery by Dumas the first germs of
the modern theory of valence are to be found.
For the study of inorganic substances, however, the dualistic theory
was long retained, with the result that inorganic chemistry degenerated
to a great extent into analysis and compound making, without any
general conceptions which could stimulate scientific advance. It
became a science of details rather than of principles, and was soon
overshadowed by the organic branch. In the latter, theory after theory
sprang up, flourished, and died away, each one having partial truth,
but none being exhaustive and final. Still, the intellectual activity
led to discoveries, and the warfare between doctrines, unlike the
warfare between men, was productive of good instead of destruction.
From the conflict of ideas the truth gradually emerged, and a new
system of chemical philosophy was developed. The theory of compound
radicles, the nucleus theory, the theory of types, the conception of
conjugated compounds, followed rapidly one after the other, until in
the discovery of valence all discrepancies were reconciled, structural
chemistry came into existence, and a single doctrine, applicable alike
to organic and inorganic substances, had possession of the field.
The theory of valence was a logical outgrowth from its predecessors,
whose valuable features it included in a wider generalization, but it
was the work of no one master mind. Many chemists contributed to its
up-building, Frankland and Kekulé being among the leaders; but its
foundations are to be detected in the atomic theory itself, from which
it is legitimately derived. To understand its full significance we must
take a step backward in history, and trace the change in atomic weights
from their first form to the modern system.
In the early days of the atomic theory, in the determinations by
Wollaston, Berzelius, and others, attention was chiefly paid to
the atomic weights in their aspect of combining numbers. They were
primarily of use as factors in chemical calculations, and chemists
naturally sought for their simplest expressions, with little regard to
theoretical considerations. The laws of Avogadro, of Dulong and Petit,
had, indeed, been announced, but the adjustment of the atomic weights
to meet their requirements was long neglected. The importance of the
adjustment was not realized, for it was obscured by the prevailing
dualistic theory, but without it the deeper general relations of the
atoms could not appear. Accordingly, a system of chemical formulæ grew
up which was based upon a deceptive apparent simplicity of ratios,
and by which the theory of valence could not be even suggested. The
old formula for water, HO, expressed only its composition by weight,
ignoring its composition by volume; it failed, therefore, to accord
with Avogadro’s law or to give the slightest hint as to the relations
which are now covered by the conception of chemical structure. A part
of the existing knowledge was accurately symbolized, but the larger
part was ignored, a state of affairs which could not last, although the
change came about but slowly.
The incentive to reform came from two sources. Physics, in the
kinetic theory of gases, gave a new demonstration of the truth of
Avogadro’s law, and led chemists to realize more clearly than before
the distinction between atoms and molecules. Soon it was seen that the
molecule was the smallest particle of matter which could exist as such,
while the atom was the smallest particle which could take part in any
chemical change. The metaphysical atom was really the modern molecule;
the chemical atom was a new conception, due to the discoveries of
chemistry alone. This distinction was found to hold good even for
elementary bodies, and it became evident that free hydrogen or oxygen
must contain two atoms to the molecule, while phosphorus and arsenic
contained four. With mercury the atom and the molecule are identical,
but in most cases the greater complexity exists, and the elements as
we see them are compounds of like atoms with each other. That hydrogen
can unite with hydrogen, oxygen with oxygen, carbon with carbon, is a
conception to which the early chemists never attained, but which is a
necessary consequence of Avogadro’s law in its application to observed
phenomena.
The second impulse toward change originated in the study of organic
compounds, and gained its force from the struggle between contending
theories. The advocates of each theory sought for evidence in its
favor, and so innumerable discoveries were made, compound radicles
were recognized in great numbers, and the mass of data became so
overwhelming that for a while chaos reigned. Classification of
compounds became imperatively necessary, and to that all speculation
was subordinated. In 1842 Schiel found that the alcohols formed a
regular series, with progressive variation in their properties; Dumas
observed a similar relation among the fatty acids, and so something
like order began to appear.
In 1843 Charles Gerhardt proposed to use the law of Avogadro as a basis
for the determination of atomic weights. This involved the doubling of
many existing values, especially the atomic weights assigned to oxygen,
carbon, and sulphur. At first the proposition was violently opposed,
and even ridiculed, but by slow degrees it managed to make its way,
although it was not until after 1858 that it began to find anything
like general acceptance. In that year Cannizzaro put forth his revision
of the atomic weights, adjusted to accord with physical laws, and a
new era in chemistry began. The modern theories of chemistry became
possible, and the many researches in which they had been foreshadowed
received a clearer meaning. Cannizzaro did not stand alone; his work
was but the capstone of a structure which had long been growing;
Liebig, Dumas, Laurent, Gerhardt, Wurtz, Graham, Williamson, and
Frankland were among the builders. But at last chemical and physical
evidence were brought into full convergence, and each gave emphasis to
the other.