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example, was composed of phlogiston and an element was much less
enigmatic, even if wrong, than the statement of the alchemist
that “metals are produced by the spiritual action of the three
principles, salt, mercury, sulphur”—particularly when it is
explained that salt, mercury, and sulphur were really not what
their names implied, and that there was no universally accepted
belief as to what they really were.
The metals, which are now regarded as elementary bodies, were
considered compounds by the phlogistians, and they believed that
the calcining of a metal was a process of simplification. They
noted, however, that the remains of calcination weighed more than
the original product, and the natural inference from this would
be that the metal must have taken in some substance rather than
have given off anything. But the phlogistians had not learned
the all-important significance of weights, and their explanation
of variation in weight was either that such gain or loss was an
unimportant “accident” at best, or that phlogiston, being light,
tended to lighten any substance containing it, so that driving it
out of the metal by calcination naturally left the residue
heavier.
At first the phlogiston theory seemed to explain in an
indisputable way all the known chemical phenomena. Gradually,
however, as experiments multiplied, it became evident that the
plain theory as stated by Stahl and his followers failed to
explain satisfactorily certain laboratory reactions. To meet
these new conditions, certain modifications were introduced from
time to time, giving the theory a flexibility that would allow it
to cover all cases. But as the number of inexplicable experiments
continued to increase, and new modifications to the theory became
necessary, it was found that some of these modifications were
directly contradictory to others, and thus the simple theory
became too cumbersome from the number of its modifications. Its
supporters disagreed among themselves, first as to the
explanation of certain phenomena that did not seem to accord with
the phlogistic theory, and a little later as to the theory
itself. But as yet there was no satisfactory substitute for this
theory, which, even if unsatisfactory, seemed better than
anything that had gone before or could be suggested.
But the good effects of the era of experimental research, to
which the theory of Stahl had given such an impetus, were showing
in the attitude of the experimenters. The works of some of the
older writers, such as Boyle and Hooke, were again sought out in
their dusty corners and consulted, and their surmises as to the
possible mixture of various gases in the air were more carefully
considered. Still the phlogiston theory was firmly grounded in
the minds of the philosophers, who can hardly be censured for
adhering to it, at least until some satisfactory substitute was
offered. The foundation for such a theory was finally laid, as
we shall see presently, by the work of Black, Priestley,
Cavendish, and Lavoisier, in the eighteenth century, but the
phlogiston theory cannot be said to have finally succumbed until
the opening years of the nineteenth century.
II. THE BEGINNINGS OF MODERN CHEMISTRY
THE “PNEUMATIC” CHEMISTS
Modern chemistry may be said to have its beginning with the work
of Stephen Hales (1677-1761), who early in the eighteenth century
began his important study of the elasticity of air. Departing
from the point of view of most of the scientists of the time, be
considered air to be “a fine elastic fluid, with particles of
very different nature floating in it” ; and he showed that these
“particles” could be separated. He pointed out, also, that
various gases, or “airs,” as he called them, were contained in
many solid substances. The importance of his work, however, lies
in the fact that his general studies were along lines leading
away from the accepted doctrines of the time, and that they gave
the impetus to the investigation of the properties of gases by
such chemists as Black, Priestley, Cavendish, and Lavoisier,
whose specific discoveries are the foundation-stones of modern
chemistry.
JOSEPH BLACKThe careful studies of Hales were continued by his younger
confrere, Dr. Joseph Black (1728-1799), whose experiments in the
weights of gases and other chemicals were first steps in
quantitative chemistry. But even more important than his
discoveries of chemical properties in general was his discovery
of the properties of carbonic-acid gas.
Black had been educated for the medical profession in the
University of Glasgow, being a friend and pupil of the famous Dr.
William Cullen. But his liking was for the chemical laboratory
rather than for the practice of medicine. Within three years
after completing his medical course, and when only twenty-three
years of age, he made the discovery of the properties of carbonic
acid, which he called by the name of “fixed air.” After
discovering this gas, Black made a long series of experiments, by
which he was able to show how widely it was distributed
throughout nature. Thus, in 1757, be discovered that the bubbles
given off in the process of brewing, where there was vegetable
fermentation, were composed of it. To prove this, he collected
the contents of these bubbles in a bottle containing lime-water.
When this bottle was shaken violently, so that the lime-water and
the carbonic acid became thoroughly mixed, an insoluble white
powder was precipitated from the solution, the carbonic acid
having combined chemically with the lime to form the insoluble
calcium carbonate, or chalk. This experiment suggested another.
Fixing a piece of burning charcoal in the end of a bellows, he
arranged a tube so that the gas coming from the charcoal would
pass through the lime-water, and, as in the case of the bubbles
from the brewer’s vat, he found that the white precipitate was
thrown down; in short, that carbonic acid was given off in
combustion. Shortly after, Black discovered that by blowing
through a glass tube inserted into lime-water, chalk was
precipitated, thus proving that carbonic acid was being
constantly thrown off in respiration.
The effect of Black’s discoveries was revolutionary, and the
attitude of mind of the chemists towards gases, or “airs,” was
changed from that time forward. Most of the chemists, however,
attempted to harmonize the new facts with the older theories—to
explain all the phenomena on the basis of the phlogiston theory,
which was still dominant. But while many of Black’s discoveries
could not be made to harmonize with that theory, they did not
directly overthrow it. It required the additional discoveries of
some of Black’s fellow-scientists to complete its downfall, as we
shall see.
HENRY CAVENDISHThis work of Black’s was followed by the equally important work
of his former pupil, Henry Cavendish (1731-1810), whose discovery
of the composition of many substances, notably of nitric acid and
of water, was of great importance, adding another link to the
important chain of evidence against the phlogiston theory.
Cavendish is one of the most eccentric figures in the history of
science, being widely known in his own time for his immense
wealth and brilliant intellect, and also for his peculiarities
and his morbid sensibility, which made him dread society, and
probably did much in determining his career. Fortunately for him,
and incidentally for the cause of science, he was able to pursue
laboratory investigations without being obliged to mingle with
his dreaded fellow-mortals, his every want being provided for by
the immense fortune inherited from his father and an uncle.
When a young man, as a pupil of Dr. Black, he had become imbued
with the enthusiasm of his teacher, continuing Black’s
investigations as to the properties of carbonic-acid gas when
free and in combination. One of his first investigations was
reported in 1766, when he communicated to the Royal Society his
experiments for ascertaining the properties of carbonic-acid and
hydrogen gas, in which he first showed the possibility of
weighing permanently elastic fluids, although Torricelli had
before this shown the relative weights of a column of air and a
column of mercury. Other important experiments were continued by
Cavendish, and in 1784 he announced his discovery of the
composition of water, thus robbing it of its time-honored
position as an “element.” But his claim to priority in this
discovery was at once disputed by his fellow-countryman James
Watt and by the Frenchman Lavoisier. Lavoisier’s claim was soon
disallowed even by his own countrymen, but for many years a
bitter controversy was carried on by the partisans of Watt and
Cavendish. The two principals, however, seem. never to have
entered into this controversy with anything like the same ardor
as some of their successors, as they remained on the best of
terms.[1] It is certain, at any rate, that Cavendish announced
his discovery officially before Watt claimed that the
announcement had been previously made by him, “and, whether right
or wrong, the honor of scientific discoveries seems to be
accorded naturally to the man who first publishes a demonstration
of his discovery.” Englishmen very generally admit the justness
of Cavendish’s claim, although the French scientist Arago, after
reviewing the evidence carefully in 1833, decided in favor of
Watt.
It appears that something like a year before Cavendish made known
his complete demonstration of the composition of water, Watt
communicated to the Royal Society a suggestion that water was
composed of “dephlogisticated air (oxygen) and phlogiston
(hydrogen) deprived of part of its latent heat.” Cavendish knew
of the suggestion, but in his experiments refuted the idea that
the hydrogen lost any of its latent heat. Furthermore, Watt
merely suggested the possible composition without proving it,
although his idea was practically correct, if we can rightly
interpret the vagaries of the nomenclature then in use. But had
Watt taken the steps to demonstrate his theory, the great “Water
Controversy” would have been avoided. Cavendish’s report of his
discovery to the Royal Society covers something like forty pages
of printed matter. In this he shows how, by passing an electric
spark through a closed jar containing a mixture of hydrogen gas
and oxygen, water is invariably formed, apparently by the union
of the two gases. The experiment was first tried with hydrogen
and common air, the oxygen of the air uniting with the hydrogen
to form water, leaving the nitrogen of the air still to be
accounted for. With pure oxygen and hydrogen, however, Cavendish
found that pure water was formed, leaving slight traces of any
other, substance which might not be interpreted as being Chemical
impurities. There was only one possible explanation of this
phenomenon—that hydrogen and oxygen, when combined, form water.
“By experiments with the globe it appeared,” wrote Cavendish,
“that when inflammable and common air are exploded in a proper
proportion, almost all the inflammable air, and near one-fifth
the common air, lose their elasticity and are condensed into dew.
And by this experiment it appears that this dew is plain water,
and consequently that almost all the inflammable air is turned
into pure water.
“In order to examine the nature of the matter condensed on firing
a mixture of dephlogisticated and inflammable air, I took a glass
globe, holding 8800 grain measures, furnished with a brass cock
and an apparatus for firing by electricity. This globe was well
exhausted by an air-pump, and then filled with a mixture of
inflammable and dephlogisticated air by shutting the cock,
fastening the bent glass tube into its mouth, and letting up the
end of it into a glass jar inverted into water and containing a
mixture of 19,500 grain measures of dephlogisticated air, and
37,000 of inflammable air; so that, upon opening the cock, some
of this mixed air rushed through the bent tube and filled the
globe. The cock was then shut and the included air fired by
electricity, by means of which almost all of it lost its
elasticity (was condensed into water vapors). The cock was then
again opened so as to let in more of the
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