THE
HISTORY
OF
CHEMISTRY.
BY
THOMAS THOMSON, M. D.
F.R.S. L. & E.; F.L.S.; F.G.S., &c.
REGIUS PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF GLASGOW.
IN TWO VOLUMES.
VOL. II.
LONDON:
HENRY COLBURN AND RICHARD BENTLEY,
NEW BURLINGTON STREET.
1831.
C. WHITING, BEAUFORT HOUSE, STRAND.
CONTENTS
OF
THE SECOND VOLUME.
CHAPTER I. Page
Of the foundation and progress of scientific chemistry in Great
Britain 1
CHAPTER II.
Of the progress of philosophical chemistry in Sweden 26
CHAPTER III.
Progress of scientific chemistry in France 75
CHAPTER IV.
Progress of analytical chemistry 190
CHAPTER V.
Of electro-chemistry 251
CHAPTER VI.
Of the atomic theory 277
CHAPTER VII.
Of the present state of chemistry 309
HISTORY OF CHEMISTRY.
CHAPTER I.
OF THE FOUNDATION AND PROGRESS OF SCIENTIFIC CHEMISTRY IN GREAT BRITAIN.
While Mr. Cavendish was extending the bounds of pneumatic chemistry,
with the caution and precision of a Newton, Dr. Priestley, who had
entered on the same career, was proceeding with a degree of rapidity
quite unexampled; while from his happy talents and inventive faculties,
he contributed no less essentially to the progress of the science, and
certainly more than any other British chemist to its popularity.
Joseph Priestley was born in 1733, at Fieldhead, about six miles from
Leeds in Yorkshire. His father, Jonas Priestley, was a maker and
dresser of woollen cloth, and his mother, the only child of Joseph
Swift a farmer in the neighbourhood. Dr. Priestley was the eldest
child; and, his mother having children very fast, he was soon committed
to the care of his maternal grandfather. He lost his mother when he
was only six years of age, and was soon after taken home by his father
and sent to school in the neighbourhood. His father being but poor,
and encumbered with a large family, his sister, Mrs. Keighley, a woman
in good circumstances, and without children, relieved him of all care
of his eldest son, by taking him and bringing him up as her own. She
was a dissenter, and her house was the resort of all the dissenting
clergy in the country. Young Joseph was sent to a public school in
the neighbourhood, and, at sixteen, had made considerable progress in
Latin, Greek, and Hebrew. Having shown a passion for books and for
learning at a very early age, his aunt conceived hopes that he would
one day become a dissenting clergyman, which she considered as the
first of all professions; and he entered eagerly into her views: but
his health declining about this period, and something like phthisical
symptoms having come on, he was advised to turn his thoughts to trade,
and to settle as a merchant in Lisbon. This induced him to apply to the
modern languages; and he learned French, Italian, and German, without a
master. Recovering his health, he abandoned his new scheme and resumed
his former plan of becoming a clergyman. In 1752 he was sent to the
academy of Daventry, to study under Dr. Ashworth, the successor of Dr.
Doddridge. He had already made some progress in mechanical philosophy
and metaphysics, and dipped into Chaldee, Syriac, and Arabic. At
Daventry he spent three years, engaged keenly in studies connected with
divinity, and wrote some of his earliest theological tracts. Freedom
of discussion was admitted to its full extent in this academy. The two
masters espoused different sides upon most controversial subjects, and
the scholars were divided into two parties, nearly equally balanced.
The discussions, however, were conducted with perfect good humour
on both sides; and Dr. Priestley, as he tells us himself, usually
supported the heterodox opinion; but he never at any time, as he
assures us, advanced arguments which he did not believe to be good,
or supported an opinion which he did not consider as true. When he
left the academy, he settled at Needham in Suffolk, as an assistant
in a small, obscure dissenting meeting-house, where his income never
exceeded 30_l._ a-year. His hearers fell off, in consequence of their
dislike of his theological opinions; and his income underwent a
corresponding diminution. He attempted a school; but his scheme failed
of success, owing to the bad opinion which his neighbours entertained
of his orthodoxy. His situation would have been desperate, had he not
been occasionally relieved by sums out of charitable funds, procured by
means of Dr. Benson, and Dr. Kippis.
Several vacancies occurred in his vicinity; but he was treated with
contempt, and thought unworthy to fill any of them. Even the dissenting
clergy in the neighbourhood thought it a degradation to associate
with him, and durst not ask him to preach: not from any dislike to
his theological opinions; for several of them thought as freely as
he did; but because the genteeler part of their audience always
absented themselves when he appeared in the pulpit. A good many years
afterwards, as he informs us himself, when his reputation was very
high, he preached in the same place, and multitudes flocked to hear the
very same sermons, which they had formerly listened to with contempt
and dislike.
His friends being aware of the disagreeable nature of his situation
at Needham, were upon the alert to procure him a better. In 1758, in
consequence of the interest of Mr. Gill, he was invited to appear as a
candidate for a meeting-house in Sheffield, vacant by the resignation
of Mr. Wadsworth. He appeared accordingly and preached, but was not
approved of. Mr. Haynes, the other minister, offered to procure him a
meeting-house at Nantwich in Cheshire. This situation he accepted, and,
to save expenses, he went from Needham to London by sea. At Nantwich
he continued three years, and spent his time much more agreeably
than he had done at Needham. His opinions were not obnoxious to his
hearers, and controversial discussions were never introduced. Here he
established a school, and found the business of teaching, contrary
to his expectation, an agreeable and even interesting employment. He
taught from seven in the morning, till four in the afternoon; and after
the school was dismissed, he went to the house of Mr. Tomlinson, an
eminent attorney in the neighbourhood, where he taught privately till
seven in the evening. Being thus engaged twelve hours every day in
teaching, he had little time for private study. It is, indeed, scarcely
conceivable how, under such circumstances, he could prepare himself for
Sunday. Here, however, his circumstances began to mend. At Needham it
required the utmost economy to keep out of debt; but at Nantwich, he
was able to purchase a few books and some philosophical instruments, as
a small air-pump, an electrical machine, &c. These he taught his eldest
scholars to keep in order and manage: and by entertaining their parents
and friends with experiments, in which the scholars were generally the
operators, and sometimes the lecturers too, he considerably extended
the reputation of his school. It was at Nantwich that he wrote his
grammar for the use of his school, a book of considerable merit, though
its circulation was never extensive. This latter circumstance was
probably owing to the superior reputation of Dr. Lowth, who published
his well-known grammar about two years afterwards.
Being boarded in the house of Mr. Eddowes, a very sociable and sensible
man, and a lover of music, Dr. Priestley was induced to play a little
on the English flute; and though he never was a proficient, he informs
us that it contributed more or less to his amusement for many years. He
recommends the knowledge and practice of music to all studious persons,
and thinks it rather an advantage for them if they have no fine ear or
exquisite taste, as they will, in consequence, be more easily pleased,
and less apt to be offended when the performances they hear are but
indifferent.
The academy at Warrington was instituted while Dr. Priestley was at
Needham, and he was recommended by Mr. Clark, Dr. Benson, and Dr.
Taylor, as tutor in the languages; but Dr. Aiken, whose qualifications
were considered as superior, was preferred before him. However, on
the death of Dr. Taylor, and the advancement of Dr. Aiken to be tutor
in divinity, he was invited to succeed him: this offer he accepted,
though his school at Nantwich was likely to be more gainful; for the
employment at Warrington was more liberal and less painful. In this
situation he continued six years, actively employed in teaching and
in literary pursuits. Here he wrote a variety of works, particularly
his History of Electricity, which first brought him into notice as
an experimental philosopher, and procured him celebrity. After the
publication of this work, Dr. Percival of Manchester, then a student
at Edinburgh, procured him the title of doctor in laws, from that
university. Here he married a daughter of Mr. Isaac Wilkinson, an
ironmonger in Wales; a woman whose qualities he has highly extolled,
and who died after he went to America.
In the academy he spent his time very happily, but it did not flourish.
A quarrel had broken out between Dr. Taylor and the trustees, in
consequence of which all the friends of that gentleman were hostile
to the institution. This, together with the smallness of his income,
100_l._ a-year, and 15_l._ for each boarder, which precluded him
from making any provision for his family, induced him to accept an
invitation to take charge of Millhill chapel, at Leeds, where he had a
considerable acquaintance, and to which he removed in 1767.
Here he engaged keenly in the study of theology, and produced a great
number of works, many of them controversial. Here, too, he commenced
his great chemical career, and published his first tract on _air_.
He was led accidentally to think of pneumatic chemistry, by living
in the immediate vicinity of a brewery. Here, too, he published his
history of the Discoveries relative to Light and Colours, as the first
part of a general history of experimental philosophy; but the expense
of this book was so great, and its sale so limited, that he did not
venture to prosecute the undertaking. Here, likewise, he commenced and
published three volumes of a periodical work, entitled "The Theological
Repository," which he continued after he settled in Birmingham.
After he had been six years at Leeds, the Earl of Shelburne (afterwards
Marquis of Lansdowne), engaged him, on the recommendation of Dr.
Price, to live with him as a kind of librarian and literary companion,
at a salary of 250_l._ a-year, with a house. With his lordship he
travelled through Holland, France, and a part of Germany, and spent
some time in Paris. He was delighted with this excursion, and expressed
himself thoroughly convinced of the great advantages to be derived
from foreign travel. The men of science and politicians in Paris were
unbelievers, and even professed atheists, and as Dr. Priestley chose
to appear before them as a Christian, they told him that he was the
first person they had met with, of whose understanding they had any
opinion, who was a believer of Christianity; but, upon interrogating
them closely, he found that none of them had any knowledge either of
the nature or principles of the Christian religion.--While with Lord
Shelburne, he published the first three volumes of his Experiments on
Air, and had collected materials for a fourth, which he published soon
after settling in Birmingham. At this time also he published his attack
upon Drs. Reid, Beattie, and Oswald; a book which, he tells us, he
finished in a fortnight: but of which he afterwards, in some measure,
disapproved. Indeed, it was impossible for any person of candour to
approve of the style of that work, and the way in which he treated Dr.
Reid, a philosopher certainly much more deeply skilled than himself in
metaphysics.
After some years Lord Shelburne began to be weary of his associate,
and, on his expressing a wish to settle him in Ireland, Dr. Priestley
of his own accord proposed a separation, to which his lordship
consented, after settling on him an annuity of 150_l._, according to a
previous stipulation. This annuity he continued regularly to pay during
the remainder of the life of Dr. Priestley.
His income being much diminished by his separation from Lord Shelburne,
and his family increasing, he found it now difficult to support
himself. At this time Mrs. Rayner made him very considerable presents,
particularly at one period a sum of 400_l._; and she continued her
contributions to him almost annually. Dr. Fothergill had proposed a
subscription, in order that he might prosecute his experiments to their
utmost extent, and be enabled to live without sacrificing his time to
his pupils. This he accepted. It amounted at first to 40_l._ per annum,
and was afterwards much increased. Dr. Watson, Mr. Wedgewood, Mr.
Galton, and four or five more, were the gentlemen who joined with Dr.
Fothergill in this generous subscription.
Soon after, he settled in a meeting-house in Birmingham, and continued
for several years engaged in theological and chemical investigations.
His apparatus, by the liberality of his friends, had become excellent,
and his income was so good that he could prosecute his researches to
their full extent. Here he published the three last volumes of his
Experiments on Air, and various papers on the same subject in the
Philosophical Transactions. Here, too, he continued his Theological
Repository, and published a variety of tracts on his peculiar opinions
in religion, and upon the history of the primitive church. He now
unluckily engaged in controversy with the established clergy of the
place; and expressed his opinions on political subjects with a degree
of freedom, which, though it would have been of no consequence at
any former period, was ill suited to the peculiar circumstances that
were introduced into this country by the French revolution, and to
the political maxims of Mr. Pitt and his administration. His answer
to Mr. Burke's book on the French revolution excited the violent
indignation of that extraordinary man, who inveighed against his
character repeatedly, and with peculiar virulence, in the house of
commons. The clergy of the church of England, too, who began about this
time to be alarmed for their establishment, of which Dr. Priestley
was the open enemy, were particularly active; the press teemed with
their productions against him, and the minds of their hearers seem to
have been artificially excited; indeed some of the anecdotes told of
the conduct of the clergy of Birmingham, were highly unbecoming their
character. Unfortunately, Dr. Priestley did not seem to be aware of
the state of the nation, and of the plan of conduct laid down by Mr.
Pitt and his political friends; and he was too fond of controversial
discussions to yield tamely to the attacks of his antagonists.
These circumstances seem in some measure to explain the disgraceful
riots which took place in Birmingham in 1791, on the day of the
anniversary of the French revolution. Dr. Priestley's meeting-house and
his dwelling-house were burnt; his library and apparatus destroyed,
and many manuscripts, the fruits of several years of industry, were
consumed in the conflagration. The houses of several of his friends
shared the same fate, and his son narrowly escaped death, by the care
of a friend who forcibly concealed him for several days. Dr. Priestley
was obliged to make his escape to London, and a seat was taken for him
in the mail-coach under a borrowed name. Such was the ferment against
him that it was believed he would not have been safe any where else;
and his friends would not allow him, for several weeks, to walk through
the streets.
He was invited to Hackney, to succeed Dr. Price in the meeting-house
of that place. He accepted the office, but such was the dread of his
unpopularity, that nobody would let him a house, from an apprehension
that it would be burnt by the populace as soon as it was known that he
inhabited it. He was obliged to get a friend to take a lease of a house
in another name; and it was with the utmost difficulty that he could
prevail with the landlord to allow the lease to be transferred to him.
The members of the Royal Society, of which he was a fellow, declined
admitting him into their company; and he was obliged to withdraw his
name from the society.
When we look back upon this treatment of a man of Dr. Priestley's
character, after an interval of forty years, it cannot fail to strike
us with astonishment; and it must be owned, I think, that it reflects
an indelible stain upon that period of the history of Great Britain.
To suppose that he was in the least degree formidable to so powerful
a body as the church of England, backed as it was by the aristocracy,
by the ministry, and by the opinions of the people, is perfectly
ridiculous. His theological sentiments, indeed, were very different
from those of the established church; but so were those of Milton,
Locke, and Newton. Nay, some of the members of the church itself
entertained opinions, not indeed so decided or so openly expressed as
those of Dr. Priestley, but certainly having the same tendency. To be
satisfied of this it is only necessary to recollect the book which
Dr. Clarke published on the Trinity. Nay, some of the bishops, unless
they are very much belied, entertained opinions similar to those of
Dr. Clarke. The same observation applies to Dr. Lardner, Dr. Price,
and many others of the dissenters. Yet, the church of England never
attempted to persecute these respectable and meritorious men, nor did
they consider their opinions as at all likely to endanger the stability
of the church. Besides, Dr. Horsley had taken up the pen against Dr.
Priestley's theological opinions, and had refuted them so completely in
the opinion of the members of the church, that it was thought right to
reward his meritorious services by a bishopric.
It could hardly, therefore, be the dread of Dr. Priestley's theological
opinions that induced the clergy of the church of England to bestir
themselves against him with such alacrity. Erroneous opinions advanced
and refuted, so far from being injurious, have a powerful tendency to
support and strengthen the cause which they were meant to overturn.
Or, if there existed any latent suspicion that the refutation of
Horsley was not so complete as had been alleged, surely persecution
was not the best means of supporting weak arguments; and indeed it was
rather calculated to draw the attention of mankind to the theological
opinions of Priestley; as has in fact been the consequence.
Neither can the persecutions which Dr. Priestley was subjected to be
accounted for by his political opinions, even supposing it not to be
true, that in a free country like Great Britain, any man is at liberty
to maintain whatever theoretic opinions of government he thinks proper,
provided he be a peaceable subject and obey rigorously all the laws of
his country.
Dr. Priestley was an advocate for the perfectibility of the human
species, or at least its continually increasing tendency to
improvement--a doctrine extremely pleasing in itself, and warmly
supported by Franklin and Price; but which the wild principles of
Condorcet, Godwin, and Beddoes at last brought into discredit. This
doctrine was taught by Priestley in the outset of his Treatise on
Civil Government, first published in 1768. It is a speculation of so
very agreeable a nature, so congenial to our warmest wishes, and so
flattering to the prejudices of humanity, that one feels much pain
at being obliged to give it up. Perhaps it may be true, and I am
willing to hope so, that improvements once made are never entirely
lost, unless they are superseded by something much more advantageous,
and that therefore the knowledge of the human race, upon the whole,
is progressive. But political establishments, at least if we are to
judge from the past history of mankind, have their uniform periods of
progress and decay. Nations seem incapable of profiting by experience.
Every nation seems destined to run the same career, and the history
may be comprehended under the following heads: Poverty, liberty,
industry, wealth, power, dissipation, anarchy, destruction. We have no
example in history of a nation running through this career and again
recovering its energy and importance. Greece ran through it more than
two thousand years ago: she has been in a state of slavery ever since.
An opportunity is now at last given her of recovering her importance:
posterity will ascertain whether she will embrace it.
Dr. Priestley's short Essay on the First Principles of Civil Government
was published in 1768. In it he lays down as the foundation of his
reasoning, that "it must be understood, whether it be expressed or
not, that all people live in society for their mutual advantage; so
that the good and happiness of the members, that is the majority of
the members of any state, is the great standard by which every thing
relating to that state must be finally determined; and though it may be
supposed that a body of people may be bound by a voluntary resignation
of all their rights to a single person or to a few, it can never be
supposed that the resignation is obligatory on their posterity, because
it is manifestly contrary to the good of the whole that it should be
so." From this first principle he deduces all his political maxims.
Kings, senators, and nobles, are merely the servants of the public;
and when they abuse their power, in the people lies the right of
deposing and consequently of punishing them. He examines the expediency
of hereditary sovereignty, of hereditary rank and privileges, of the
duration of parliament, and of the right of voting, with an evident
tendency to democratical principles, though he does not express himself
very clearly on the subject.
Such were his political principles in 1768, when his book was
published. They excited no alarm and drew but little attention;
these principles he maintained ever after, or indeed he may be said
to have become more moderate instead of violent. Though he approved
of a republic in the abstract; yet, considering the prejudices and
habits of the people of Great Britain, he laid it down as a principle
that their present form of government was best suited to them. He
thought, however, that there should be a reform in parliament; and that
parliaments should be triennial instead of septennial. He was an enemy
to all violent reforms, and thought that the change ought to be brought
about gradually and peaceably. When the French revolution broke out he
took the side of the patriots, as he had done during the American war;
and he wrote a refutation of Mr. Burke's extraordinary performance.
Being a dissenter, it is needless to say that he was an advocate for
complete religious freedom. He was ever hostile to all religious
establishments, and an open enemy to the church of England.
How far these opinions were just and right this is not the place to
inquire; but that they were perfectly harmless, and that many other
persons in this country during the last century, and even at present,
have adopted similar opinions without incurring any odium whatever,
and without exciting the jealousy or even the attention of government,
is well known to every person. It comes then to be a question of some
curiosity at least, to what we are to ascribe the violent persecutions
raised against Dr. Priestley. It seems to have been owing chiefly to
the alarm caught by the clergy of the established church that their
establishment was in danger;--and, considering the ferment excited
soon after the breaking out of the French revolution, and the rage
for reform, which pervaded all ranks, the almost general alarm of the
aristocracy, at least, was not entirely without foundation. I cannot,
however, admit that there was occasion for the violent alarm caught by
Mr. Pitt and his political friends, and for the very despotic measures
which they adopted in consequence. The disease would probably have
subsided of itself, or it would have been cured by a much gentler
treatment. As Dr. Priestley was an open enemy to the establishment,
its clergy naturally conceived a prejudice against him, and this
prejudice was violently inflamed by the danger to which they thought
themselves exposed; their influence with the ministry was very great,
and Mr. Pitt and his friends naturally caught their prejudices and
opinions. Mr. Burke, too, who had changed his political principles,
and who was inflamed with the burning zeal which distinguishes all
converts, was provoked at Dr. Priestley's answer to his book on the
French revolution, and took every opportunity to inveigh against him
in the house of commons. The conduct of the French, likewise, who made
Dr. Priestley a citizen of France, and chose him a member of their
assembly, though intended as a compliment, was injurious to him in
Great Britain. It was laid hold of by his antagonists to convince the
people that he was an enemy to his country; that he had abjured his
rights as an Englishman; and that he had adopted the principles of
the hereditary enemies of Great Britain. These causes, and not his
political opinions, appear to me to account for the persecution which
was raised against him.
His sons, disgusted with this persecution of their father, had
renounced their native country and gone over to France; and, on the
breaking out of the war between this country and the French republic,
they emigrated to America. It was this circumstance, joined to the
state of insulation in which he lived, that induced Dr. Priestley,
after much consideration, to form the resolution of following his sons
and emigrating to America. He published his reasons in the preface
to a Fast-day Sermon, printed in 1794, one of the gravest and most
forcible pieces of composition I have ever read. He left England in
April, 1795, and reached New York in June. In America he was received
with much respect by persons of all ranks; and was immediately offered
the situation of professor of chemistry in the College of Philadelphia;
which, however, he declined, as his circumstances, by the liberality
of his friends in England, continued independent. He settled, finally,
in Northumberland, about 130 miles from Philadelphia, where he built
a house, and re-established his library and laboratory, as well as
circumstances permitted. Here he published a considerable number of
chemical papers, some of them under the form of pamphlets, and the rest
in the American Transactions, the New York Medical Repository, and
Nicholson's Journal of Natural Philosophy and Chemistry. Here, also,
he continued keenly engaged in theological pursuits; and published, or
republished, a great variety of books on theological subjects. Here he
lost his wife and his youngest and favourite son, who, he had flattered
himself, was to succeed him in his literary career:--and here he died,
in 1804, after having been confined only two days to bed, and but a
few hours after having arranged his literary concerns, inspected some
proof-sheets of his last theological work, and given instructions to
his son how it should be printed.
During the latter end of the presidency of Mr. Adams, the same kind of
odium which had banished Dr. Priestley from England began to prevail
in America. He was threatened with being sent out of the country
as an alien. Notwithstanding this, he declined being naturalized;
resolving, as he said, to die as he had lived, an Englishman. When his
friend Mr. Jefferson, whose political opinions coincided with his own,
became president, the odium against him wore off, and he became as much
respected as ever.
As to the character of Dr. Priestley, it is so well marked by his
life and writings, that it is difficult to conceive how it could
have been mistaken by many eminent men in this kingdom. Industry was
his great characteristic; and this quality, together with a facility
of composition, acquired, as he tells us, by a constant habit while
young of drawing out an abstract of the sermons which he had preached,
and writing a good deal in verse, enabled him to do so much: yet, he
informs us that he never was an intense student, and that his evenings
were usually passed in amusement or company. He was an early riser,
and always lighted his own fire before any one else was stirring: it
was then that he composed all his works. It is obvious, from merely
glancing into his books, that he was precipitate; and indeed, from
the way he went on thinking as he wrote, and writing only one copy,
it was impossible he could be otherwise: but, as he was perfectly
sincere and anxious to obtain the truth, he freely acknowledged his
mistakes as soon as he became sensible of them. This candour is very
visible in his philosophical speculations; but in his theological
writings it was not so much to be expected. He was generally engaged
in controversy in theology; and his antagonists were often insolent,
and almost always angry. We all know the effect of such opposition; and
need not be surprised that it operated upon Dr. Priestley, as it would
do upon any other man. By all accounts his powers of conversation
were very great, and his manners in every respect very agreeable. That
this must have been the case is obvious from the great number of his
friends, and the zeal and ardour with which they continued to serve
him, notwithstanding the obloquy under which he lay, and even the
danger that might be incurred by appearing to befriend him. As for his
moral character, even his worst enemies have been obliged to allow that
it was unexceptionable. Many of my readers will perhaps smile, when I
say that he was not only a sincere, but a zealous Christian, and would
willingly have died a martyr to the cause. Yet I think the fact is of
easy proof; and his conduct through life, and especially at his death,
affords irrefragable proofs of it. His tenets, indeed, did not coincide
with those of the majority of his countrymen; but though he rejected
many of the doctrines, he admitted the whole of the sublime morality
and the divine origin of the Christian religion; which may charitably
be deemed sufficient to constitute a true Christian. Of vanity he seems
to have possessed rather more than a usual share; but perhaps he was
deficient in pride.
His writings were exceedingly numerous, and treated of science,
theology, metaphysics, and politics. Of his theological, metaphysical,
and political writings it is not our business in this work to take any
notice. His scientific works treat of _electricity_, _optics_, and
_chemistry_. As an electrician he was respectable; as an optician,
a compiler; as a chemist, a discoverer. He wrote also a book on
perspective which I have never had an opportunity of perusing.
It is to his chemical labours that he is chiefly indebted for the
great reputation which he acquired. No man ever entered upon any
undertaking with less apparent means of success than Dr. Priestley
did on the chemical investigation of _airs_. He was unacquainted with
chemistry, excepting that he had, some years before, attended an
elementary course delivered by Mr. Turner, of Liverpool. He was not in
possession of any apparatus, nor acquainted with the method of making
chemical experiments; and his circumstances were such, that he could
neither lay out a great deal of money on experiments, nor could he
hope, without a great deal of expense, to make any material progress
in his investigations. These circumstances, which, at first sight,
seem so adverse, were, I believe, of considerable service to him, and
contributed very much to his ultimate success. The branch of chemistry
which he selected was new: an apparatus was to be invented before any
thing of importance could be effected; and, as simplicity is essential
in every apparatus, _he_ was most likely to contrive the best, whose
circumstances obliged him to attend to economical considerations.
Pneumatic chemistry had been begun by Mr. Cavendish in his valuable
paper on carbonic acid and hydrogen gases, published in the
Philosophical Transactions for 1766. The apparatus which he employed
was similar to that used about a century before by Dr. Mayow of
Oxford. Dr. Priestley contrived the apparatus still used by chemists
in pneumatic investigations; it is greatly superior to that of
Mr. Cavendish, and, indeed, as convenient as can be desired. Were
we indebted to him for nothing else than this apparatus, it would
deservedly give him high consideration as a pneumatic chemist.
His discoveries in pneumatic chemistry are so numerous, that I must
satisfy myself with a bare outline; to enumerate every thing, would
be to transcribe his three volumes, into which he digested his
discoveries. His first paper was published in 1772, and was on the
method of impregnating water with carbonic acid gas; the experiments
contained in it were the consequence of his residing near a brewery in
Leeds. This pamphlet was immediately translated into French; and, at
a meeting of the College of Physicians in London, they addressed the
Lords of the Treasury, pointing out the advantage that might result
from water impregnated with carbonic acid gas in cases of scurvy at
sea. His next essay was published in the Philosophical Transactions,
and procured him the Copleyan medal. His different volumes on air were
published in succession, while he lived with Lord Shelburne, and while
he was settled at Birmingham. They drew the attention of all Europe,
and raised the reputation of this country to a great height.
The first of his discoveries was _nitrous gas_, now called _deutoxide
of azote_, which had, indeed, been formed by Dr. Hales; but that
philosopher had not attempted to investigate its properties. Dr.
Priestley ascertained its properties with much sagacity, and almost
immediately applied it to the analysis of air. It contributed very much
to all subsequent investigations in pneumatic chemistry, and may be
said to have led to our present knowledge of the constitution of the
atmosphere.
The next great discovery was _oxygen gas_, which was made by him on
the 1st of August, 1774, by heating the red oxide of mercury, and
collecting the gaseous matter given out by it. He almost immediately
detected the remarkable property which this gas has of supporting
combustion better, and animal life longer, than the same volume of
common air; and likewise the property which it has of condensing into
red fumes when mixed with nitrous gas. Lavoisier, likewise, laid
claim to the discovery of oxygen gas; but his claim is entitled to
no attention whatever; as Dr. Priestley informs us that he prepared
this gas in M. Lavoisier's house, in Paris, and showed him the method
of procuring it in the year 1774, which is a considerable time before
the date assigned by Lavoisier for his pretended discovery. Scheele,
however, actually obtained this gas without any previous knowledge of
what Priestley had done; but the book containing this discovery was not
published till three years after Priestley's process had become known
to the public.
Dr. Priestley first made known sulphurous acid, fluosilicic acid,
muriatic acid, and ammonia in the gaseous form; and pointed out easy
methods of procuring them: he describes with exactness the most
remarkable properties of each. He likewise pointed out the existence
of carburetted hydrogen gas; though he made but few experiments to
determine its nature. His discovery of protoxide of azote affords
a beautiful example of the advantages resulting from his method of
investigation, and the sagacity which enabled him to follow out
any remarkable appearances which occurred. Carbonic oxide gas was
discovered by him while in America, and it was brought forward by him
as an incontrovertible refutation of the antiphlogistic theory.
Though he was not strictly the discoverer of hydrogen gas, yet his
experiments on it were highly interesting, and contributed essentially
to the revolution which chemistry soon after underwent. Nothing,
for example, could be more striking, than the reduction of oxide of
iron, and the disappearance of the hydrogen when the oxide is heated
sufficiently in contact with hydrogen gas. Azotic gas was known before
he began his career; but we are indebted to him for most of the
properties of it yet known. To him, also, we owe the knowledge of the
fact, that an acid is formed when electric sparks are made to pass
for some time through a given bulk of common air; a fact which led
afterwards to Mr. Cavendish's great discovery of the composition of
nitric acid.
He first discovered the great increase of bulk which takes place
when electric sparks are made to pass through ammoniacal gas--a fact
which led Berthollet to the analysis of this gas. He merely repeated
Priestley's experiment, determined the augmentation of bulk, and the
nature of the gases evolved by the action of the electricity. His
experiments on the amelioration of atmospherical air by the vegetation
of plants, on the oxygen gas given out by their leaves, and on the
respiration of animals, are not less curious and interesting.
Such is a short view of the most material facts for which chemistry
is indebted to Dr. Priestley. As a discoverer of new substances, his
name must always stand very high in the science; but as a reasoner or
theorist his position will not be so favourable. It will be observed
that almost all his researches and discoveries related to gaseous
bodies. He determined the different processes, by means of which the
different gases can be procured, the substances which yield them, and
the effects which they are capable of producing on other bodies. Of
the other departments of chemistry he could hardly be said to know any
thing. As a pneumatic chemist he stands high; as an analytical chemist
he can scarcely claim any rank whatever. In his famous experiments on
the formation of water by detonating mixtures of oxygen and hydrogen
in a copper globe, the copper was found acted upon, and a blue liquid
was obtained, the nature of which he was unable to ascertain; but Mr.
Keir, whose assistance he solicited, determined it to be a solution of
nitrate of copper in water. This formation of nitric acid induced him
to deny that water was a compound of oxygen and hydrogen. The same acid
was formed in the experiments of Mr. Cavendish; but he investigated
the circumstances of the formation, and showed that it depended upon
the presence of azotic gas in the gaseous mixture. Whenever azotic
gas is present, nitric acid is formed, and the quantity of this acid
depends upon the relative proportion of the azotic and hydrogen gases
in the mixture. When no hydrogen gas is present, nothing is formed
but nitric acid: when no azotic gas is present, nothing is formed
but water. These facts, determined by Cavendish, invalidate the
reasoning of Priestley altogether; and had he possessed the skill, like
Cavendish, to determine with sufficient accuracy the proportions of the
different gases in his mixtures, and the relative quantities of nitric
acid formed, he would have seen the inaccuracy of his own conclusions.
He was a firm believer in the existence of phlogiston; but he seems,
at least ultimately, to have adopted the view of Scheele, and many
other eminent contemporary chemists--indeed, the view of Cavendish
himself--that hydrogen gas is phlogiston in a separate and pure state.
Common air he considered as a compound of oxygen and phlogiston.
Oxygen, in his opinion, was air quite free from phlogiston, or air in
a simple and pure state; while _azotic gas_ (the other constituent of
common air) was air saturated with phlogiston. Hence he called oxygen
_dephlogisticated_, and azote _phlogisticated air_. The facts that
when common air is converted into azotic gas its bulk is diminished
about one-fifth part, and that azotic gas is lighter than common air or
oxygen gas, though not quite unknown to him, do not seem to have drawn
much of his attention. He was not accustomed to use a balance in his
experiments, nor to attend much to the alterations which took place in
the weight of bodies. Had he done so, most of his theoretical opinions
would have fallen to the ground.
When a body is allowed to burn in a given quantity of common air, it is
known that the quality of the common air is deteriorated; it becomes,
in his language, more phlogisticated. This, in his opinion, was owing
to an affinity which existed between phlogiston and air. The presence
of air is necessary to combustion, in consequence of the affinity which
it has for phlogiston. It draws phlogiston out of the burning body,
in order to combine with it. When a given bulk of air is saturated
with phlogiston, it is converted into azotic gas, or _phlogisticated
air_, as he called it; and this air, having no longer any affinity for
phlogiston, can no longer attract that principle, and consequently
combustion cannot go on in such air.
All combustible bodies, in his opinion, contain hydrogen. Of course
the metals contain it as a constituent. The calces of metals are those
bodies deprived of phlogiston. To prove the truth of this opinion, he
showed that when the oxide of iron is heated in hydrogen gas, that gas
is absorbed, while the calx is reduced to the metallic state. Finery
cinder, which he employed in these experiments, is, in his opinion,
iron not quite free from phlogiston. Hence it still retains a quantity
of hydrogen. To prove this, he mixed together finery cinder and
carbonates of lime, barytes and strontian, and exposed the mixture to a
strong heat; and by this process obtained inflammable gas in abundance.
In his opinion every inflammable gas contains hydrogen in abundance.
Hence this experiment was adduced by him as a demonstration that
hydrogen is a constituent of finery cinder.
All these processes of reasoning, which appear so plausible as Dr.
Priestley states them, vanish into nothing, when his experiments are
made, and the weights of every thing determined by means of a balance:
it is then established that a burning body becomes heavier during its
combustion, and that the surrounding air loses just as much weight as
the burning body gains. Scheele and Lavoisier showed clearly that the
loss of weight sustained by the air is owing to a quantity of oxygen
absorbed from it, and condensed in the burning body. Cruikshank first
elucidated the nature of the inflammable gas, produced by the heating
a mixture of finery cinder and carbonate of lime, or other earthy
carbonate. He found that iron filings would answer better than finery
cinder. The gas was found to contain no hydrogen, and to be in fact
a compound of oxygen and carbon. It was shown to be derived from the
carbonic acid of the earthy carbonate, which was deprived of half its
oxygen by the iron filings or finery cinder. Thus altered, it no longer
preserved its affinity for the lime, but made its escape in the gaseous
form, constituting the gas now known by the name of carbonic oxide.
Though the consequence of the Birmingham riots, which obliged Dr.
Priestley to leave England and repair to America, is deeply to be
lamented, as fixing an indelible disgrace upon the country; perhaps
it was not in reality so injurious to Dr. Priestley as may at first
sight appear. He had carried his peculiar researches nearly as far
as they could go. To arrange and methodize, and deduce from them the
legitimate consequences, required the application of a different
branch of chemical science, which he had not cultivated, and which his
characteristic rapidity, and the time of life to which he had arrived,
would have rendered it almost impossible for him to acquire. In all
probability, therefore, had he been allowed to prosecute his researches
unmolested, his reputation, instead of an increase, might have
suffered a diminution, and he might have lost that eminent situation as
a man of science which he had so long occupied.
With Dr. Priestley closes this period of the History of British
Chemistry--for Mr. Cavendish, though he had not lost his activity, had
abandoned that branch of science, and turned his attention to other
pursuits.