THE REIGN OF LAW--DALTON, JOULE
In the middle of the eighteenth century, when Lambert and Kant were
recognizing system and design in the heavens, little progress had been
made toward discovering the constitution of matter or revealing the laws
of the hidden motions of things. Boyle had, indeed, made a beginning,
not only by his study of the elasticity of the air, but by his
distinction of the elements and compounds and his definition of
chemistry as the science of the composition of substances. How little
had been accomplished, however, is evident from the fact that in 1750
the so-called elements--earth, air, fire, water--which Bacon had marked
for examination in 1620, were still unanalyzed, and that no advance had
been made beyond his conception of the nature of heat, the majority,
indeed, of the learned world holding that heat is a substance (variously
identified with sulphur, carbon, or hydrogen) rather than a mode of
motion.
How scientific thought succeeded in bringing order out of confusion and
chaos in the subsequent one hundred years, and especially at the
beginning of the nineteenth century, can well be illustrated by these
very matters, the study of combustion, of heat as a form of energy, of
the constituents of the atmosphere, and of the chemistry of water and of
the earth.
Reference has already been made to Black's discovery of carbonic acid,
and of the phenomena which he ascribed to latent heat. The first
discovery (1754) was the result of the preparation of quicklime in the
practice of medicine; the second (1761) involving experiments on the
temperatures of melting ice, boiling water, and steam, stimulated Watt
in his improvement of the steam engine. In 1766 Joseph Priestley began
his study of airs, or gases. In the following year observation of work
in a brewery roused his curiosity in reference to carbonic acid. In 1772
he experimented with nitric oxide. In the previous century Mayow had
obtained nitric oxide by treating iron with nitric acid. He had then
introduced this gas into ordinary air confined over water, and found
that the mixture suffered a reduction of volume. Priestley applied this
process to the analysis of common air, which he discovered to be complex
and not simple. In 1774, by heating red oxide of mercury by means of a
burning-glass, he obtained a gas which supported combustion better than
common air. He inhaled it, and experienced a sense of exhilaration. "Who
can tell," he writes, "but in time this pure air may become a
fashionable article in luxury? Hitherto only two mice and myself have
had the privilege of breathing it."
The Swedish investigator Scheele had, however, discovered this same
constituent of the air before 1773. He thought that the atmosphere must
consist of at least two gases, and he proved that carbonic acid results
from combustion and respiration. In 1772 the great French scientist
Lavoisier found that sulphur, when burned, gains weight instead of
losing weight, and five years later he concluded that air consists of
two gases, one capable of absorption by burning bodies, the other
incapable of supporting combustion. He called the first "oxygen." In his
_Elements of Chemistry_ Lavoisier gave a clear exposition of his system
of chemistry and of the discoveries of other European chemists. After
his studies the atmosphere was no longer regarded as mysterious and
chaotic. It was known to consist largely of oxygen and nitrogen, and to
contain in addition aqueous vapor, carbonic acid, and ammonia which
might be brought to earth by rain.
Cavendish obtained nitrogen from air by using nitric oxide to remove the
oxygen, and found that air consists of about seventy-nine per cent
nitrogen and about twenty-one per cent oxygen. He also by use of the
electric spark caused the oxygen and nitrogen of the air to unite to
form nitric acid. When the nitrogen was exhausted and the redundant
oxygen removed, "only a small bubble of air remained unabsorbed."
Similarly Cavendish had found that water results from the combination of
oxygen and hydrogen. Watt had likewise held that water is not an
element, but a compound of two elementary substances. Thus the great
masses,--earth, air, fire, water,--assumed as simple by many
philosophers from the earliest times, were resolving into their
constituent parts. At the same time other problems were demanding
solution. What are the laws of chemical combination? What is the
relation of heat to other forms of energy? To the answering of these
questions (as of those from which these grew) the great manufacturing
centers contributed, and no city more potently than Manchester through
Dalton and his pupil and follower Joule.
John Dalton (1766-1844) was born in Cumberland, went to Kendal to teach
school at the age of fifteen, and remained in the Lake District of
England till 1793. In this region, where the annual rainfall exceeds
forty inches, and in some localities is almost tropical, the young
student's attention was early drawn to meteorology. His apparatus
consisted of rude home-made rain-gauges, thermometers, and barometers.
His interest in the heat, moisture, and constituents of the atmosphere
continued throughout life, and Dalton made in all some 200,000
meteorological observations. We gain a clue to his motive in these
studies from a letter written in his twenty-second year, in which he
speaks of the advantages that might accrue to the husbandman, the
mariner, and to mankind in general if we were able to predict the state
of the weather with tolerable precision.
In 1793 Dalton took up his permanent residence in Manchester, and in
that year appeared his first book, _Meteorological Observations and
Essays_. Here he deals, among other things, with rainfall, the formation
of clouds, evaporation, and the distribution and character of
atmospheric moisture. It seemed to him that aqueous vapor always exists
as a distinct fluid maintaining its identity among the other fluids of
the atmosphere. He thought of atmospheric moisture as consisting of
minute drops of water, or globules among the globules of oxygen and
nitrogen. He was a disciple of Newton's (to whom, indeed, Dalton had
some personal likeness), who looked upon matter as consisting of "solid,
massy, hard, impenetrable, movable particles, of such sizes and figures,
and with such other properties, and in such proportion, as most
conduced to the end for which God formed them." Dalton was so much under
the influence of the idea that the physical universe is made up of these
indivisible particles, or atoms, that his biographer describes him as
thinking _corpuscularly_. It is probable that his imagination was of the
visualizing type and that he could picture to himself the arrangement of
atoms in elementary and compound substances.
Now Dalton's master had taught that the atoms of matter in a gas
(elastic fluid) repel one another by a force increasing in proportion as
their distance diminishes. How did this teaching apply to the
atmosphere, which Priestley and others had proved to consist of three or
more gases? Why does this mixture appear simple and homogeneous? Why
does not the air form strata with the oxygen below and the nitrogen
above? Cavendish had shown, and Dalton himself later proved, that common
air, wherever examined, contains oxygen and nitrogen in fairly constant
proportions.
French chemists had sought to apply the principle of _chemical affinity_
in explaining the apparent homogeneity of the atmosphere. They supposed
that oxygen and nitrogen entered into chemical union, the one element
dissolving the other. The resultant compound in turn dissolved water;
hence the phenomena of evaporation. Dalton tried in vain to reconcile
this supposition with his belief in the atomic nature of matter. He drew
diagrams combining an atom of oxygen with an atom of nitrogen and an
atom of aqueous vapor. The whole atmosphere could not consist of such
groups of three because the watery particles were but a small portion of
the total atmosphere. He made a diagram in which one atom of oxygen was
combined with one atom of nitrogen, but in this case the oxygen was
insufficient to satisfy all the nitrogen of the atmosphere. If the air
was made up partly of pure nitrogen, partly of a compound of nitrogen
and oxygen, and partly of a compound of nitrogen, oxygen, and aqueous
vapor, then the triple compound, as heaviest, would collect toward the
surface of the earth, and the double compound and the simple substance
would form two strata above. If to the compounds heat were added in the
hope of producing an unstratified mixture, the atmosphere would acquire
the specific gravity of nitrogen gas. "In short," says Dalton, "I was
obliged to abandon the hypothesis of the chemical constitution of the
atmosphere altogether as irreconcilable to the phenomena."
He had to return to the conception of the individual particles of
oxygen, nitrogen, and water, each a center of repulsion. Still he could
not explain why the oxygen did not gravitate to the lowest place, the
nitrogen form a stratum above, and the aqueous vapor swim upon the top.
In 1801, however, Dalton hit upon the idea that gases act as _vacua_ for
one another, that it is only like particles which repel each other,
atoms of oxygen repelling atoms of oxygen and atoms of nitrogen
repelling atoms of nitrogen when these gases are intermingled in the
atmosphere just as they would if existing in an unmixed state.
"According to this, we were to suppose that atoms of one kind did _not_
repel the atoms of another kind, but only those of their own kind." A
mixed atmosphere is as free from stratifications, as though it were
really homogeneous.
In his analyses of air Dalton made use of the old nitric oxide method.
In 1802 this led to an interesting discovery. If in a tube .3 of an inch
wide he mixed 100 parts of common air with 36 parts of nitric oxide, the
oxygen of the air combined with the nitric oxide, and a residue of 79
parts of atmospheric nitrogen remained. And if he mixed 100 parts of
common air with 72 of nitric oxide, but in a wide vessel over water (in
which conditions the combination is more quickly effected), the oxygen
of the air again combined with the nitric oxide and a residue of 79
parts of nitrogen again resulted. But in the last experiment, if less
than 72 parts of nitric oxide be employed, there will be a residue of
oxygen as well as nitrogen; and if more than 72, there will be a residue
of nitric oxide in addition to the nitrogen. In the words of Dalton,
"oxygen may combine with a certain portion of nitrous gas [as he called
nitric oxide], or with twice that portion, but with no intermediate
portion."
Naturally these experimental facts were to be explained in terms of the
ultimate particles of which the various gases are composed. In the
following year Dalton gave graphic representation to his idea of the
atomic constitution of chemical elements and compounds.
( ) Hydrogen
(|) Nitrogen
(·) Oxygen
(*) Carbon
(|) (·) Nitric oxide
(·) (|) (·) Nitrous oxide
(·) (*) (·) Carbonic acid
Much against Dalton's will his method of indicating chemical elements
and their combinations had to yield to a method introduced by the great
Swedish chemist Berzelius. In 1837 Dalton wrote: "Berzelius's symbols
are horrifying: a young student in chemistry might as soon learn Hebrew
as make himself acquainted with them. They appear like a chaos of atoms
... and to equally perplex the adepts of science, to discourage the
learner, as well as to cloud the beauty and simplicity of the Atomic
Theory."
Meantime Dalton's mind had been turning to the consideration of the
relative sizes and weights of the various elements entering into
combination with one another. He argued that if there be not exactly the
same _number_ of atoms of oxygen in a given volume of air as of nitrogen
in the same volume, then the sizes of the particles of oxygen must be
different from those of nitrogen. His interest in the absorption of
gases by water, in the reciprocal diffusion of gases, as well as in the
phenomena of chemical combination, stimulated Dalton to determine the
_relative_ size and weight of the atoms of the various elements. Dalton
said nothing of the _absolute_ weight of the atom. But on the assumption
that when only one compound of two elements is known to exist, the
molecule of the compound consists of one atom of each of these elements,
he proceeded to investigate the relative weights of equal numbers of the
two sorts of atoms. In 1803 he pursued this investigation with
remarkable success, and taking hydrogen (the lightest gas known to him)
as unity, he arrived at a statement of the relative atomic weights of
oxygen, nitrogen, carbon, etc. Dalton thus introduced into the study of
chemical combination a very definite idea of quantitative relationship.
By him the atomic theory of the constitution of matter was made
definite and applicable to all the phenomena known to chemistry.
[Illustration: _Painting by Ford Madox Brown_ _By permission of the Town
Hall Committee of the Manchester Corporation_
JOHN DALTON COLLECTING MARSH GAS]
During the following months he returned to the study of those cases in
which the same elements combine to form more than one compound. We have
seen that oxygen unites with nitric oxide to form two compounds, and
that into the one compound twice as much nitric oxide (by weight) enters
as into the other. A like relation was found in the weight of oxygen
combining with carbon in the two compounds carbon monoxide and carbonic
acid. In the summer of 1804 he investigated the composition of two
compounds of hydrogen and carbon, marsh gas (methane) and olefiant gas
(ethylene), and found that the first contained just twice as much
hydrogen in relation to the carbon as the second compound contained. In
a series of compounds of the same two elements one atom of one unites
with one, two, three, or more atoms of the other; that is, a simple
ratio exists between the weights in which the second element enters into
combination with the first. This law of multiple proportions afforded
confirmation of Dalton's atomic theory, or chemical theory of definite
proportions.
"Without such a theory," says Sir Henry Roscoe, "modern chemistry would
be a chaos; with it, order reigns supreme, and every apparently
contradictory discovery only marks out more distinctly the value and
importance of Dalton's work." In 1826 Sir Humphry Davy recognized
Dalton's services to science in the following terms: "Finding that in
certain compounds of gaseous bodies the same elements always combined
in the same proportions, and that when there was more than one
combination the quantity of the elements always had a constant
relation,--such as 1 to 2, or 1 to 3, or 1 to 4,--he explained this fact
on the Newtonian doctrine of indivisible atoms; and contended that, the
relative weight of one atom to that of any other atom being known, its
proportions or weight in all its combinations might be ascertained, thus
making the statics of chemistry depend upon simple questions in
subtraction or multiplication and enabling the student to deduce an
immense number of facts from a few well-authenticated experimental
results. Mr. Dalton's permanent reputation will rest upon his having
discovered a simple principle universally applicable to the facts of
chemistry, in fixing the proportions in which bodies combine, and thus
laying the foundation for future labors respecting the sublime and
transcendental parts of the science of corpuscular motion. His merits in
this respect resemble those of Kepler in astronomy."
In 1808 Dalton's atomic theory received striking confirmation through
the investigations of the French scientist Gay-Lussac, who showed that
gases, under similar circumstances of temperature and pressure, always
combine in simple proportions by _volume_ when they act on one another,
and that when the result of the union is a gas, its volume also is in a
simple ratio to the volumes of its components. One of Dalton's friends
summed up the result of Gay-Lussac's research in this simple fashion:
"His paper is on the combination of gases. He finds that all unite in
equal bulks, or two bulks of one to one of another, or three bulks of
one to one of another." When Dalton had investigated the relative
weights with which elements combine, he had found no simple arithmetical
relationship between atomic weight and atomic weight. When two or more
compounds of the same elements are formed, Dalton found, however, as we
have seen, that the proportion of the element added to form the second
or third compound is a multiple by weight of the first quantity.
Gay-Lussac now showed that gases, "in whatever proportions they may
combine, always give rise to compounds whose elements by volume are
multiples of each other."
In 1811 Avogadro, in an essay on the relative masses of atoms, succeeded
in further confirming Dalton's theory and in explaining the atomic basis
of Gay-Lussac's discovery of simple volume relations in the formation of
chemical compounds. According to the Italian scientist the _number_ of
molecules in all gases is always the same for equal volumes, or always
proportional to the volumes, it being taken for granted that the
temperature and pressure are the same for each gas. Dalton had supposed
that water is formed by the union of hydrogen and oxygen, atom for atom.
Gay-Lussac found that two volumes of hydrogen combined with one volume
of oxygen to produce two volumes of water vapor. According to Avogadro
the water vapor contains twice as many atoms of hydrogen as of oxygen.
One volume of hydrogen has the same number of molecules as one volume of
oxygen. When the two volumes combine with one, the combination does
not take place, as Dalton had supposed, atom for atom, but each
half-molecule of oxygen combines with one molecule of hydrogen. The
symbol for water is, therefore, not HO but H{2}O.
Enough has been said to establish Dalton's claim to be styled a great
lawgiver of chemical science. His influence in further advancing
definitely formulated knowledge of physical phenomena can here be
indicated only in part. In 1800 he wrote a paper _On the Heat and Cold
produced by the Mechanical Condensation and Rarefaction of Air_. This
contains, according to Dalton's biographer, the first quantitative
statement of the heat evolved by compression and the heat evolved by
dilatation. His contribution to the theory of heat has been stated thus:
The volume of a gas under constant pressure expands when raised to the
boiling temperature by the same fraction of itself, whatever be the
nature of the gas. In 1798 Count Rumford had reported to the Royal
Society his _Enquiry concerning the Source of Heat excited by Friction_,
the data for which had been gathered at Munich. Interested as he was in
the practical problem of providing heat for the homes of the city poor,
Rumford had been struck by the amount of heat developed in the
boring-out of cannon at the arsenal. He concluded that anything which
could be created indefinitely by a process of friction could not be a
substance, such as sulphur or hydrogen, but must be a mode of motion. In
the same year the youthful Davy was following independently this line of
investigation by rubbing two pieces of ice together, by clock-work, in a
vacuum. The friction caused the ice to melt, although the experiment was
undertaken in a temperature of 29° Fahrenheit.
For James Prescott Joule (1818-1889), who came of a family of brewers
and was early engaged himself in the brewing industry, was reserved,
however, the distinction of discovering the exact relation between heat
and mechanical energy. After having studied chemistry under Dalton at
Manchester, he became engrossed in physical experimentation. In 1843 he
prepared a paper _On the Calorific Effects of Magneto-Electricity
and on the Mechanical Value of Heat_. In this he dealt with the
relations between heat and the ordinary forms of mechanical power,
and demonstrated that the mechanical energy spent "in turning a
magneto-electrical machine is _converted into the heat_ evolved by the
passage of the currents of induction through its coils; and, on the
other hand, that the motive power of the electro-magnetic engine is
obtained at the expense of the heat due to the chemical reactions of the
battery by which it is worked." In 1844 he proceeded to apply the
principles maintained in his earlier study to changes of temperature as
related to changes in the density of gases. He was conscious of the
practical, as well as the theoretical, import of his investigation.
Indeed, it was through the determination by this illustrious pupil of
Dalton's of the amount of heat produced by the compression of gases that
one of the greatest improvements of the steam engine was later effected.
Joule felt that his investigation at the same time confirmed the
dynamical theory of heat which originated with Bacon, and had at a
subsequent period been so well supported by the experiments of Rumford,
Davy, and others.
Already, in this paper of June, 1844, Joule had expressed the hope of
ascertaining the mechanical equivalent of heat with the accuracy that
its importance for physical science demanded. He returned to this
question again and again. According to his final result the quantity of
heat required to raise one pound of water in temperature by one degree
Fahrenheit is equivalent to the mechanical energy required to raise
772.55 pounds through a distance of one foot. Heat was thus demonstrated
to be a form of energy, the relation being constant between it and
mechanical energy. Mechanical energy may be converted into heat; if heat
disappears, some other form of energy, equivalent in amount to the heat
lost, must replace it. The doctrine that a certain quantity of heat is
always equivalent to a certain amount of mechanical energy is only a
special case of the Law of the Conservation of Energy, first clearly
enunciated by Joule and Helmholtz in 1847, and generally regarded as the
most important scientific discovery of the nineteenth century.
Roscoe, referring to the two life-sized marble statues which face each
other in the Manchester Town Hall, says with pardonable pride: "Thus
honor is done to Manchester's two greatest sons--to Dalton, the founder
of modern Chemistry and of the Atomic Theory, and the discoverer of the
laws of chemical combining proportions; to Joule, the founder of modern
Physics and the discoverer of the Law of the Conservation of Energy."
REFERENCES
Alembic Club Reprints, _Foundations of the Atomic Theory_.
Joseph Priestley, _Experiments and Observations on Different Kinds of
Air_.
Sir William Ramsay, _The Gases of the Atmosphere and the History of
their Discovery_.
Sir Henry E. Roscoe, _John Dalton_.
Sir E. Thorpe, _Essays in Historical Chemistry_.