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 BLACK
The 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 CAVENDISH
This 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 same air to supply the
place of that destroyed by the explosion, which was again fired,
and the operation continued till almost the whole of the mixture
was let into the globe and exploded. By this means, though the
globe held not more than a sixth part of the mixture, almost the
whole of it was exploded therein without any fresh exhaustion of
the globe."
At first this condensed matter was "acid to the taste and
contained two grains of nitre," but Cavendish, suspecting that
this was due to impurities, tried another experiment that proved
conclusively that his opinions were correct. "I therefore made
another experiment," he says, "with some more of the same air
from plants in which the proportion of inflammable air was
greater, so that the burnt air was almost completely
phlogisticated, its standard being one-tenth. The condensed
liquor was then not at all acid, but seemed pure water."
From these experiments he concludes "that when a mixture of
inflammable and dephlogisticated air is exploded, in such
proportions that the burnt air is not much phlogisticated, the
condensed liquor contains a little acid which is always of the
nitrous kind, whatever substance the dephlogisticated air is
procured from; but if the proportion be such that the burnt air
is almost entirely phlogisticated, the condensed liquor is not at
all acid, but seems pure water, without any addition
whatever."[2]
These same experiments, which were undertaken to discover the
composition of water, led him to discover also the composition of
nitric acid. He had observed that, in the combustion of hydrogen
gas with common air, the water was slightly tinged with acid, but
that this was not the case when pure oxygen gas was used. Acting
upon this observation, he devised an experiment to determine the
nature of this acid. He constructed an apparatus whereby an
electric spark was passed through a vessel containing common air.
After this process had been carried on for several weeks a small
amount of liquid was formed. This liquid combined with a solution
of potash to form common nitre, which "detonated with charcoal,
sparkled when paper impregnated with it was burned, and gave out
nitrous fumes when sulphuric acid was poured on it." In other
words, the liquid was shown to be nitric acid. Now, since nothing
but pure air had been used in the initial experiment, and since
air is composed of nitrogen and oxygen, there seemed no room to
doubt that nitric acid is a combination of nitrogen and oxygen.
This discovery of the nature of nitric acid seems to have been
about the last work of importance that Cavendish did in the field
of chemistry, although almost to the hour of his death he was
constantly occupied with scientific observations. Even in the
last moments of his life this habit asserted itself, according to
Lord Brougham. "He died on March 10, 1810, after a short
illness, probably the first, as well as the last, which he ever
suffered. His habit of curious observation continued to the end.
He was desirous of marking the progress of the disease and the
gradual extinction of the vital powers. With these ends in view,
that he might not be disturbed, he desired to be left alone. His
servant, returning sooner than he had wished, was ordered again
to leave the chamber of death, and when be came back a second
time he found his master had expired.[3]
JOSEPH PRIESTLEY
While the opulent but diffident Cavendish was making his
important discoveries, another Englishman, a poor country
preacher named Joseph Priestley (1733-1804) was not only
rivalling him, but, if anything, outstripping him in the pursuit
of chemical discoveries. In 1761 this young minister was given a
position as tutor in a nonconformist academy at Warrington, and
here, for six years, he was able to pursue his studies in
chemistry and electricity. In 1766, while on a visit to London,
he met Benjamin Franklin, at whose suggestion he published his
History of Electricity. From this time on he made steady
progress in scientific investigations, keeping up his
ecclesiastical duties at the same time. In 1780 he removed to
Birmingham, having there for associates such scientists as James
Watt, Boulton, and Erasmus Darwin.
Eleven years later, on the anniversary of the fall of the Bastile
in Paris, a fanatical mob, knowing Priestley's sympathies with
the French revolutionists, attacked his house and chapel, burning
both and destroying a great number of valuable papers and
scientific instruments. Priestley and his family escaped violence
by flight, but his most cherished possessions were destroyed; and
three years later he quitted England forever, removing to the
United States, whose struggle for liberty he had championed. The
last ten years of his life were spent at Northumberland,
Pennsylvania, where he continued his scientific researches.
Early in his scientific career Priestley began investigations
upon the "fixed air" of Dr. Black, and, oddly enough, he was
stimulated to this by the same thing that had influenced
Black--that is, his residence in the immediate neighborhood of a
brewery. It was during the course of a series of experiments on
this and other gases that he made his greatest discovery, that of
oxygen, or "dephlogisticated air," as he called it. The story of
this important discovery is probably best told in Priestley's own
words:
"There are, I believe, very few maxims in philosophy that have
laid firmer hold upon the mind than that air, meaning atmospheric
air, is a simple elementary substance, indestructible and
unalterable, at least as much so as water is supposed to be. In
the course of my inquiries I was, however, soon satisfied that
atmospheric air is not an unalterable thing; for that, according
to my first hypothesis, the phlogiston with which it becomes
loaded from bodies burning in it, and the animals breathing it,
and various other chemical processes, so far alters and depraves
it as to render it altogether unfit for inflammation,
respiration, and other purposes to which it is subservient; and I
had discovered that agitation in the water, the process of
vegetation, and probably other natural processes, restore it to
its original purity....
"Having procured a lens of twelve inches diameter and twenty
inches local distance, I proceeded with the greatest alacrity, by
the help of it, to discover what kind of air a great variety of
substances would yield, putting them into the vessel, which I
filled with quicksilver, and kept inverted in a basin of the same
.... With this apparatus, after a variety of experiments .... on
the 1st of August, 1774, I endeavored to extract air from
mercurius calcinatus per se; and I presently found that, by means
of this lens, air was expelled from it very readily. Having got
about three or four times as much as the bulk of my materials, I
admitted water to it, and found that it was not imbibed by it.
But what surprised me more than I can express was that a candle
burned in this air with a remarkably vigorous flame, very much
like that enlarged flame with which a candle burns in nitrous
oxide, exposed to iron or liver of sulphur; but as I had got
nothing like this remarkable appearance from any kind of air
besides this particular modification of vitrous air, and I knew
no vitrous acid was used in the preparation of mercurius
calcinatus, I was utterly at a loss to account for it."[4]
The "new air" was, of course, oxygen. Priestley at once
proceeded to examine it by a long series of careful experiments,
in which, as will be seen, he discovered most of the remarkable
qualities of this gas. Continuing his description of these
experiments, he says:
"The flame of the candle, besides being larger, burned with more
splendor and heat than in that species of nitrous air; and a
piece of red-hot wood sparkled in it, exactly like paper dipped
in a solution of nitre, and it consumed very fast; an experiment
that I had never thought of trying with dephlogisticated nitrous
air.
". . . I had so little suspicion of the air from the mercurius
calcinatus, etc., being wholesome, that I had not even thought of
applying it to the test of nitrous air; but thinking (as my
reader must imagine I frequently must have done) on the candle
burning in it after long agitation in water, it occurred to me at
last to make the experiment; and, putting one measure of nitrous
air to two measures of this air, I found not only that it was
diminished, but that it was diminished quite as much as common
air, and that the redness of the mixture was likewise equal to a
similar mixture of nitrous and common air.... The next day I was
more surprised than ever I had been before with finding that,
after the above-mentioned mixture of nitrous air and the air from
mercurius calcinatus had stood all night, . . . a candle burned
in it, even better than in common air."
A little later Priestley discovered that "dephlogisticated air .
. . is a principal element in the composition of acids, and may
be extracted by means of heat from many substances which contain
them.... It is likewise produced by the action of light upon
green vegetables; and this seems to be the chief means employed
to preserve the purity of the atmosphere."
This recognition of the important part played by oxygen in the
atmosphere led Priestley to make some experiments upon mice and
insects, and finally upon himself, by inhalations of the pure
gas. "The feeling in my lungs," he said, "was not sensibly
different from that of common air, but I fancied that my
breathing felt peculiarly light and easy for some time
afterwards. Who can tell but that in time this pure air may
become a fashionable article in luxury? . . . Perhaps we may from
these experiments see that though pure dephlogisticated air might
be useful as a medicine, it might not be so proper for us in the
usual healthy state of the body."
This suggestion as to the possible usefulness of oxygen as a
medicine was prophetic. A century later the use of oxygen had
become a matter of routine practice with many physicians. Even in
Priestley's own time such men as Dr. John Hunter expressed their
belief in its efficacy in certain conditions, as we shall see,
but its value in medicine was not fully appreciated until several
generations later.
Several years after discovering oxygen Priestley thus summarized
its properties: "It is this ingredient in the atmospheric air
that enables it to support combustion and animal life. By means
of it most intense heat may be produced, and in the purest of it
animals will live nearly five times as long as in an equal
quantity of atmospheric air. In respiration, part of this air,
passing the membranes of the lungs, unites with the blood and
imparts to it its florid color, while the remainder, uniting with
phlogiston exhaled from venous blood, forms mixed air. It is
dephlogisticated air combined with water that enables fishes to
live in it."[5]
KARL WILHELM SCHEELE
The discovery of oxygen was the last but most important blow to
the tottering phlogiston theory, though Priestley himself would
not admit it. But before considering the final steps in the
overthrow of Stahl's famous theory and the establishment of
modern chemistry, we must review the work of another great
chemist, Karl Wilhelm Scheele (1742-1786), of Sweden, who
discovered oxygen quite independently, although later than
Priestley. In the matter of brilliant discoveries in a brief
space of time Scheele probably eclipsed all his great
contemporaries. He had a veritable genius for interpreting
chemical reactions and discovering new substances, in this
respect rivalling Priestley himself. Unlike Priestley, however,
he planned all his experiments along the lines of definite
theories from the beginning, the results obtained being the
logical outcome of a predetermined plan.
Scheele was the son of a merchant of Stralsund, Pomerania, which
then belonged to Sweden. As a boy in school he showed so little
aptitude for the study of languages that he was apprenticed to an
apothecary at the age of fourteen. In this work he became at
once greatly interested, and, when not attending to his duties in
the dispensary, he was busy day and night making experiments or
studying books on chemistry. In 1775, still employed as an
apothecary, he moved to Stockholm, and soon after he sent to
Bergman, the leading chemist of Sweden, his first discovery--that
of tartaric acid, which he had isolated from cream of tartar.
This was the beginning of his career of discovery, and from that
time on until his death he sent forth accounts of new discoveries
almost uninterruptedly. Meanwhile he was performing the duties of
an ordinary apothecary, and struggling against poverty. His
treatise upon Air and Fire appeared in 1777. In this remarkable
book he tells of his discovery of oxygen--"empyreal" or
"fire-air," as he calls it--which he seems to have made
independently and without ever having heard of the previous
discovery by Priestley. In this book, also, he shows that air is
composed chiefly of oxygen and nitrogen gas.
Early in his experimental career Scheele undertook the solution
of the composition of black oxide of manganese, a substance that
had long puzzled the chemists. He not only succeeded in this,
but incidentally in the course of this series of experiments he
discovered oxygen, baryta, and chlorine, the last of far greater
importance, at least commercially, than the real object of his
search. In speaking of the experiment in which the discovery was
made he says:
"When marine (hydrochloric) acid stood over manganese in the cold
it acquired a dark reddish-brown color. As manganese does not
give any colorless solution without uniting with phlogiston
[probably meaning hydrogen], it follows that marine acid can
dissolve it without this principle. But such a solution has a
blue or red color. The color is here more brown than red, the
reason being that the very finest portions of the manganese,
which do not sink so easily, swim in the red solution; for
without these fine particles the solution is red, and red mixed
with black is brown. The manganese has here attached itself so
loosely to acidum salis that the water can precipitate it, and
this precipitate behaves like ordinary manganese. When, now, the
mixture of manganese and spiritus salis was set to digest, there
arose an effervescence and smell of aqua regis."[6]
The "effervescence" he refers to was chlorine, which he proceeded
to confine in a suitable vessel and examine more fully. He
described it as having a "quite characteristically suffocating
smell," which was very offensive. He very soon noted the
decolorizing or bleaching effects of this now product, finding
that it decolorized flowers, vegetables, and many other
substances.
Commercially this discovery of chlorine was of enormous
importance, and the practical application of this new chemical in
bleaching cloth soon supplanted the, old process of
crofting--that is, bleaching by spreading the cloth upon the
grass. But although Scheele first pointed out the bleaching
quality of his newly discovered gas, it was the French savant,
Berthollet, who, acting upon Scheele's discovery that the new gas
would decolorize vegetables and flowers, was led to suspect that
this property might be turned to account in destroying the color
of cloth. In 1785 he read a paper before the Academy of Sciences
of Paris, in which he showed that bleaching by chlorine was
entirely satisfactory, the color but not the substance of the
cloth being affected. He had experimented previously and found
that the chlorine gas was soluble in water and could thus be made
practically available for bleaching purposes. In 1786 James Watt
examined specimens of the bleached cloth made by Berthollet, and
upon his return to England first instituted the process of
practical bleaching. His process, however, was not entirely
satisfactory, and, after undergoing various modifications and
improvements, it was finally made thoroughly practicable by Mr.
Tennant, who hit upon a compound of chlorine and lime--the
chloride of lime--which was a comparatively cheap chemical
product, and answered the purpose better even than chlorine
itself.
To appreciate how momentous this discovery was to cloth
manufacturers, it should be remembered that the old process of
bleaching consumed an entire summer for the whitening of a single
piece of linen; the new process reduced the period to a few
hours. To be sure, lime had been used with fair success previous
to Tennant's discovery, but successful and practical bleaching by
a solution of chloride of lime was first made possible by him and
through Scheele's discovery of chlorine.
Until the time of Scheele the great subject of organic chemistry
had remained practically unexplored, but under the touch of his
marvellous inventive genius new methods of isolating and studying
animal and vegetable products were introduced, and a large number
of acids and other organic compounds prepared that had been
hitherto unknown. His explanations of chemical phenomena were
based on the phlogiston theory, in which, like Priestley, he
always, believed. Although in error in this respect, he was,
nevertheless, able to make his discoveries with extremely
accurate interpretations. A brief epitome of the list of some of
his more important discoveries conveys some idea, of his
fertility of mind as well as his industry. In 1780 he discovered
lactic acid,[7] and showed that it was the substance that caused
the acidity of sour milk; and in the same year he discovered
mucic acid. Next followed the discovery of tungstic acid, and in
1783 he added to his list of useful discoveries that of
glycerine. Then in rapid succession came his announcements of the
new vegetable products citric, malic, oxalic, and gallic acids.
Scheele not only made the discoveries, but told the world how he
had made them--how any chemist might have made them if he
chose--for he never considered that he had really discovered any
substance until he had made it, decomposed it, and made it again.
His experiments on Prussian blue are most interesting, not only
because of the enormous amount of work involved and the skill he
displayed in his experiments, but because all the time the
chemist was handling, smelling, and even tasting a compound of
one of the most deadly poisons, ignorant of the fact that the
substance was a dangerous one to handle. His escape from injury
seems almost miraculous; for his experiments, which were most
elaborate, extended over a considerable period of time, during
which he seems to have handled this chemical with impunity.
While only forty years of age and just at the zenith of his fame,
Scheele was stricken by a fatal illness, probably induced by his
ceaseless labor and exposure. It is gratifying to know, however,
that during the last eight or nine years of his life he had been
less bound down by pecuniary difficulties than before, as Bergman
had obtained for him an annual grant from the Academy. But it
was characteristic of the man that, while devoting one-sixth of
the amount of this grant to his personal wants, the remaining
five-sixths was devoted to the expense of his experiments.
LAVOISIER AND THE FOUNDATION OF MODERN CHEMISTRY
The time was ripe for formulating the correct theory of chemical
composition: it needed but the master hand to mould the materials
into the proper shape. The discoveries in chemistry during the
eighteenth century had been far-reaching and revolutionary in
character. A brief review of these discoveries shows how
completely they had subverted the old ideas of chemical elements
and chemical compounds. Of the four substances earth, air, fire,
and water, for many centuries believed to be elementary bodies,
not one has stood the test of the eighteenth-century chemists.
Earth had long since ceased to be regarded as an element, and
water and air had suffered the same fate in this century. And
now at last fire itself, the last of the four "elements" and the
keystone to the phlogiston arch, was shown to be nothing more
than one of the manifestations of the new element, oxygen, and
not "phlogiston" or any other intangible substance.
In this epoch of chemical discoveries England had produced such
mental giants and pioneers in science as Black, Priestley, and
Cavendish; Sweden had given the world Scheele and Bergman, whose
work, added to that of their English confreres, had laid the
broad base of chemistry as a science; but it was for France to
produce a man who gave the final touches to the broad but rough
workmanship of its foundation, and establish it as the science of
modern chemistry. It was for Antoine Laurent Lavoisier
(1743-1794) to gather together, interpret correctly, rename, and
classify the wealth of facts that his immediate predecessors and
contemporaries had given to the world.
The attitude of the mother-countries towards these illustrious
sons is an interesting piece of history. Sweden honored and
rewarded Scheele and Bergman for their efforts; England received
the intellectuality of Cavendish with less appreciation than the
Continent, and a fanatical mob drove Priestley out of the
country; while France, by sending Lavoisier to the guillotine,
demonstrated how dangerous it was, at that time at least, for an
intelligent Frenchman to serve his fellowman and his country
well.
"The revolution brought about by Lavoisier in science," says
Hoefer, "coincides by a singular act of destiny with another
revolution, much greater indeed, going on then in the political
and social world. Both happened on the same soil, at the same
epoch, among the same people; and both marked the commencement of
a new era in their respective spheres."[8]
Lavoisier was born in Paris, and being the son of an opulent
family, was educated under the instruction of the best teachers
of the day. With Lacaille he studied mathematics and astronomy;
with Jussieu, botany; and, finally, chemistry under Rouelle. His
first work of importance was a paper on the practical
illumination of the streets of Paris, for which a prize had been
offered by M. de Sartine, the chief of police. This prize was not
awarded to Lavoisier, but his suggestions were of such importance
that the king directed that a gold medal be bestowed upon the
young author at the public sitting of the Academy in April, 1776.
Two years later, at the age of thirty-five, Lavoisier was
admitted a member of the Academy.
In this same year he began to devote himself almost exclusively
to chemical inquiries, and established a laboratory in his home,
fitted with all manner of costly apparatus and chemicals. Here he
was in constant communication with the great men of science of
Paris, to all of whom his doors were thrown open. One of his
first undertakings in this laboratory was to demonstrate that
water could not be converted into earth by repeated
distillations, as was generally advocated; and to show also that
there was no foundation to the existing belief that it was
possible to convert water into a gas so "elastic" as to pass
through the pores of a vessel. He demonstrated the fallaciousness
of both these theories in 1768-1769 by elaborate experiments, a
single investigation of this series occupying one hundred and one
days.
In 1771 he gave the first blow to the phlogiston theory by his
experiments on the calcination of metals. It will be recalled
that one basis for the belief in phlogiston was the fact that
when a metal was calcined it was converted into an ash, giving up
its "phlogiston" in the process. To restore the metal, it was
necessary to add some substance such as wheat or charcoal to the
ash. Lavoisier, in examining this process of restoration, found
that there was always evolved a great quantity of "air," which he
supposed to be "fixed air" or carbonic acid--the same that
escapes in effervescence of alkalies and calcareous earths, and
in the fermentation of liquors. He then examined the process of
calcination, whereby the phlogiston of the metal was supposed to
have been drawn off. But far from finding that phlogiston or any
other substance had been driven off, he found that something had
been taken on: that the metal "absorbed air," and that the
increased weight of the metal corresponded to the amount of air
"absorbed." Meanwhile he was within grasp of two great
discoveries, that of oxygen and of the composition of the air,
which Priestley made some two years later.
The next important inquiry of this great Frenchman was as to the
composition of diamonds. With the great lens of Tschirnhausen
belonging to the Academy he succeeded in burning up several
diamonds, regardless of expense, which, thanks to his
inheritance, he could ignore. In this process he found that a gas
was given off which precipitated lime from water, and proved to
be carbonic acid. Observing this, and experimenting with other
substances known to give off carbonic acid in the same manner, he
was evidently impressed with the now well-known fact that diamond
and charcoal are chemically the same. But if he did really
believe it, he was cautious in expressing his belief fully. "We
should never have expected," he says, "to find any relation
between charcoal and diamond, and it would be unreasonable to
push this analogy too far; it only exists because both substances
seem to be properly ranged in the class of combustible bodies,
and because they are of all these bodies the most fixed when kept
from contact with air."
As we have seen, Priestley, in 1774, had discovered oxygen, or
"dephlogisticated air." Four years later Lavoisier first
advanced his theory that this element discovered by Priestley was
the universal acidifying or oxygenating principle, which, when
combined with charcoal or carbon, formed carbonic acid; when
combined with sulphur, formed sulphuric (or vitriolic) acid; with
nitrogen, formed nitric acid, etc., and when combined with the
metals formed oxides, or calcides. Furthermore, he postulated the
theory that combustion was not due to any such illusive thing as
"phlogiston," since this did not exist, and it seemed to him that
the phenomena of combustion heretofore attributed to phlogiston
could be explained by the action of the new element oxygen and
heat. This was the final blow to the phlogiston theory, which,
although it had been tottering for some time, had not been
completely overthrown.
In 1787 Lavoisier, in conjunction with Guyon de Morveau,
Berthollet, and Fourcroy, introduced the reform in chemical
nomenclature which until then had remained practically unchanged
since alchemical days. Such expressions as "dephlogisticated" and
"phlogisticated" would obviously have little meaning to a
generation who were no longer to believe in the existence of
phlogiston. It was appropriate that a revolution in chemical
thought should be accompanied by a corresponding revolution in
chemical names, and to Lavoisier belongs chiefly the credit of
bringing about this revolution. In his Elements of Chemistry he
made use of this new nomenclature, and it seemed so clearly an
improvement over the old that the scientific world hastened to
adopt it. In this connection Lavoisier says: "We have,
therefore, laid aside the expression metallic calx altogether,
and have substituted in its place the word oxide. By this it may
be seen that the language we have adopted is both copious and
expressive. The first or lowest degree of oxygenation in bodies
converts them into oxides; a second degree of additional
oxygenation constitutes the class of acids of which the specific
names drawn from their particular bases terminate in ous, as in
the nitrous and the sulphurous acids. The third degree of
oxygenation changes these into the species of acids distinguished
by the termination in ic, as the nitric and sulphuric acids; and,
lastly, we can express a fourth or higher degree of oxygenation
by adding the word oxygenated to the name of the acid, as has
already been done with oxygenated muriatic acid."[9]
This new work when given to the world was not merely an
epoch-making book; it was revolutionary. It not only discarded
phlogiston altogether, but set forth that metals are simple
elements, not compounds of "earth" and "phlogiston." It upheld
Cavendish's demonstration that water itself, like air, is a
compound of oxygen with another element. In short, it was
scientific chemistry, in the modern acceptance of the term.
Lavoisier's observations on combustion are at once important and
interesting: "Combustion," he says, ". . . is the decomposition
of oxygen produced by a combustible body. The oxygen which forms
the base of this gas is absorbed by and enters into combination
with the burning body, while the caloric and light are set free.
Every combustion necessarily supposes oxygenation; whereas, on
the contrary, every oxygenation does not necessarily imply
concomitant combustion; because combustion properly so called
cannot take place without disengagement of caloric and light.
Before combustion can take place, it is necessary that the base
of oxygen gas should have greater affinity to the combustible
body than it has to caloric; and this elective attraction, to use
Bergman's expression, can only take place at a certain degree of
temperature which is different for each combustible substance;
hence the necessity of giving the first motion or beginning to
every combustion by the approach of a heated body. This necessity
of heating any body we mean to burn depends upon certain
considerations which have not hitherto been attended to by any
natural philosopher, for which reason I shall enlarge a little
upon the subject in this place:
"Nature is at present in a state of equilibrium, which cannot
have been attained until all the spontaneous combustions or
oxygenations possible in an ordinary degree of temperature had
taken place.... To illustrate this abstract view of the matter by
example: Let us suppose the usual temperature of the earth a
little changed, and it is raised only to the degree of boiling
water; it is evident that in this case phosphorus, which is
combustible in a considerably lower degree of temperature, would
no longer exist in nature in its pure and simple state, but would
always be procured in its acid or oxygenated state, and its
radical would become one of the substances unknown to chemistry.
By gradually increasing the temperature of the earth, the same
circumstance would successively happen to all the bodies capable
of combustion; and, at the last, every possible combustion having
taken place, there would no longer exist any combustible body
whatever, and every substance susceptible of the operation would
be oxygenated and consequently incombustible.
"There cannot, therefore, exist, as far as relates to us, any
combustible body but such as are non-combustible at the ordinary
temperature of the earth, or, what is the same thing in other
words, that it is essential to the nature of every combustible
body not to possess the property of combustion unless heated, or
raised to a degree of temperature at which its combustion
naturally takes place. When this degree is once produced,
combustion commences, and the caloric which is disengaged by the
decomposition of the oxygen gas keeps up the temperature which is
necessary for continuing combustion. When this is not the
case--that is, when the disengaged caloric is not sufficient for
keeping up the necessary temperature--the combustion ceases. This
circumstance is expressed in the common language by saying that a
body burns ill or with difficulty."[10]
It needed the genius of such a man as Lavoisier to complete the
refutation of the false but firmly grounded phlogiston theory,
and against such a book as his Elements of Chemistry the feeble
weapons of the supporters of the phlogiston theory were hurled in
vain.
But while chemists, as a class, had become converts to the new
chemistry before the end of the century, one man, Dr. Priestley,
whose work had done so much to found it, remained unconverted.
In this, as in all his life-work, he showed himself to be a most
remarkable man. Davy said of him, a generation later, that no
other person ever discovered so many new and curious substances
as he; yet to the last he was only an amateur in science, his
profession, as we know, being the ministry. There is hardly
another case in history of a man not a specialist in science
accomplishing so much in original research as did this chemist,
physiologist, electrician; the mathematician, logician, and
moralist; the theologian, mental philosopher, and political
economist. He took all knowledge for his field; but how he found
time for his numberless researches and multifarious writings,
along with his every-day duties, must ever remain a mystery to
ordinary mortals.
That this marvellously receptive, flexible mind should have
refused acceptance to the clearly logical doctrines of the new
chemistry seems equally inexplicable. But so it was. To the
very last, after all his friends had capitulated, Priestley kept
up the fight. From America he sent out his last defy to the
enemy, in 1800, in a brochure entitled "The Doctrine of
Phlogiston Upheld," etc. In the mind of its author it was little
less than a paean of victory; but all the world beside knew that
it was the swan-song of the doctrine of phlogiston. Despite the
defiance of this single warrior the battle was really lost and
won, and as the century closed "antiphlogistic" chemistry had
practical possession of the field.