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Edited by S. CHAPMAN, M.A., D.Sc. 







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I. Parentage — Home Life — Early Education 
II. Needham Market — Nantwich — Warrington 

III. Leeds — Calnb 

IV. Birmingham and Experiments on Air 







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Joseph Priestley is probably one of the most interest- 
ing of the notable n>en of the eighteenth century. To 
his age he was perhaps most famous as a dauntless con- 
troversialist in politics and religion ; he himself regarded 
the study of Christian Religion and Theology as his life- 
work, while to-day his chief title to fame rests on his 
scientific work. 

Joseph Priestley was born at Fieldhead, a hamlet in- 
cluded in the parish of Birstall, which lies about six 
miles south-west of Leeds; the district is now closely 
dotted with the manufacturing towns which give the 
West Riding of Yorkshire its wealth and fame and un- 
. fortunately also its grime and murk. Leeds, Halifax, 
Wakefield, Hqddersfield, Bradford, are all within a com- 
paratively short distance of Birstall. Nevertheless in 
Priestley's day the district must have been a charming 
one; it is a gently undulating region, sufficiently far 
from the bleak moorlands of the Central Pennine Chain 
to be free from the grimness which so deeply influenced 
the lives and characters of the Bronte family, but yet 
sufficiently hilly to develop that sturdiness of character 
usually assumed to be lacking from the dwellers in 
flatter regions. Priestley was bom on 13th March, 1733, 
the eldest child of Jonas and Mary Priestley, and was 


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named after his grandfather, Joseph Priestley, a maker 
and dresser of woollen cloth, or after his maternal 
grandfather, Joseph Swift, a farmer and maltster of 
Shafton, a village situated about^ six miles south-east 
of Wakefield. Jonas Priestley, his father, was also a 
weaver and dresser of cloth; this occupation was of 
course carried on at home according to the custom of 
the period, and in the district may still be seen many old 
houses possessing the numerous small windows neces- 
sary to give light to the looms. The Priestleys were a 
sturdy, long-lived sto<ik with the evenness of tempera- 
ment that comes from generations of healthy ancestors. 
Priestley's mother died in 1740, soon after the birth 
of her youngest son. She had, in all, four sons and 
two daughters, and owing to the difficulty of looking 
aifter such a numerous and young family, Joseph and 
his brother Timothy were early committed to the care 
of their grandfather, Joseph Swift, with whom they re- 
mained almost uninterruptedly till their mother^s death. 
Of his mother Priestley says : " It is but little that I 
can recollect of my mother. I remember, however, 
that she was careful to teach me the Assembly's Cate- 
chism, and to give me the best instructions the little 
time I was at home. Once in particular, when I was. 
playing with a pin, she asked me where I got it ; and 
on telling her that I found it at my uncle's who lived 
very near to my father, and where I had been playing 
with my cousins, she made me carry it back again— no 
doubt to impress iny mind, as it could not fail to do, 
with a clear idea of the distinction of property and the 
importance of attending to it" As to his home life 
Priestley tells us : " My mother was a woman of exem- 
plary piety, and my father also had a strong ^ense of 

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religion, praying with his family morning and evening, 
and carefully teaching his children and servants the 
Assembly's Catechism, which was all the system of 
which he had any knowledge. In the latter part of his 
life he became very fond of Mr. Whitfield's writings, 
and X)ther works of a similar kind, having been brought 
up in the prihciples of Calvinism, and adopting them ; 
but without ever giving much attention to matters of 
speculation, and entertaining no bigoted aversion to 
those who differed from him on the subject" 

In 1742 Joseph was sent to stay with, and was appar- 
ently adopted by, his Aunt Sarah, the wife of a Mr. 
Keighley, " a man who had distinguished himself for 
his zeal for religion and for his public spirit ". Shortly 
after this. Priestley's uncle died, leaving his aunt a con- 
siderable fortune. " By this truly excellent and pious 
woman, who knew no other use of wealth, or of talents 
of any kind than to do good," Priestley was cared for 
as by a parent until her death in 1764. He was first 
sent to a school kept by a clergyman, Mr. Hague, under 
whose tuition. he learnt Latin and Greek. In the holi- 
days he learnt Hebrew from another minister, Mr. 
Kirkby, a rather formidable holiday task for a boy of 
twelve or thirteen to assume voluntarily. On t;he re- 
moval of Mr. Hague from his school Priestley went to 
one opened by the above Mr. Kirkby, and stayed there 
until it was closed. He was then about sixt*een and had 
acquired " a pretty good knowledge of the learned lan- 
guages ". While at school he also learned Dr. Annet's 
system of shorthand, and suggested to the author several 
improvements. This correspondence rapidly passed frona 
the subject of shorthand to that of free will and Chris- 
tianity, topics whose interest never failed for Priestley, 

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but whose discussion in the prefaces to bis non-theologi- 
cal works was often as little relevant as that of King 
Charles* head in the memorandum of a less talented 
writer. Apparently about this time he contracted a 
severe illness due to an " ulcer on the lungs " induced 
by bathing in an over-heated condition ; an act of im- 
prudence which at first ^eems strangely out of place in 
the youthful apologist The after-effects of this illness 
were so serious that Priestley was obliged to abandon 
his plan of entering the ministry, and began instead to 
study modern languages at home with a view to a com- 
mercial career. During this time he learnt, without a 
master, French, Italian and German, and apparently 
conducted the French and German correspondence of 
a merchant uncle. 

Thus for. two most important and formative years 
Priestle)^s education, secular and religious, was left 
almost entirely in his own hands ; unaided he attempted 
to solve theological questions difficult for a mature 
and trained intellect. He did not waste his time; 
under Mr. Haggerston, a local dissenting miniister and 
pupil of Maclaurin, he learnt ' geometry, algebra and 
othei' branches of mathematics ; he also studied logic 
and natural philosophy. During the same period he 
taught Hebrew to Mr. Thomas, a Baptist minister, and 
learned Chaldee and Syriac and began to read Arabic. 
At this time he had a great dislike for plays and 
.romances, so tl^at with the exception of "Robinson 
Crusoe," he had read no works of this character before he 
went to the Academy. He says : " I well remember 
seeing my brother Timothy reading a book of knight- 
errantry, and, with great indignation, I *snatched it out 
of his hands and threw it away ". • 

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Kept by his aunt to a close observance of the forms of 
religion, he says of this period : " By these means, not 
being disgusted with these strict forms of religion, as 
many persons of better health and spirits might have 
been, and on which account I am far from recommending 
the same strictness to others, I acquired in early life a 
serious turn of mind "• 

While still quite young he began to make notes of ^ 
sermons from memory, and soon did not trouble to re- 
thember more than the headings, trusting to his own 
powers of composition for the amplification. To this he 
attributed the facility with which his works were subse- 
quently composed. He was early thrown, at his aunt's 
house, into the company of unorthodox — or as he de- 
scribes them — "heretical" ministers of religion. PriesV 
ley from these men imbibed a number of unorthodox 
religious beliefs and was therefore refused" admission to 
membership of the Church which, with his aunt, he had 
always attended ; this did not prevent him from remem- 
bering later, with gratitude, the benefits which he bad 
received from that congregation. With one of the above- 
mentioned " heretical " ministers, Mr. Graham of Hali- 
fax, Priestley became very friendly, especially after his 
own entry into the Ministry ; they corresponded fre- 
quently in Latin, and Priestley dedicated to him his 
book "Disquisitions on Matter and Spirit". During 
this . period of physical weakness Priestley was much 
perturbed by religious doubts and distresses of mind, 
arising mainly from a confusion between theology and 
religion. He thus arrived at the age of eighteen " with 
sentiments of piety but vrithout bigotry " — and perhaps, 
it may be added, without stability, a Calvinist by training 
but luirdly by conviction. 

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A place was found for him in his uncle's counting- 
house at X.isbon, and a passage had actually been booked, 
when it was decided that he should resume his studies 
for the ministry owing to the favourable turn which his 
health had 'taken. Upon the recommendation of Mr. 
Kirkby, supported by his stepmother, it was decided 
that he should proceed to the academy of Dr. Doddridge 
at Daventry*. This proved impossible owing to the 
death of Dr. Doddridge in 1751^ and therefore in 1752 
Priestley took up residence at the academy of Mr., after- 
wards Dr. Ashworth, being the first pupil to enter there. 
Owing to the advanced state of his education he was 
excused all the studies of the first year and a great part 
df those of the second. 

Of the instruction at Dfiiventry we have more negative 
than positive information. We are told, by Priestley :• 
** There was then ijio provision made for teaching the 
learned languages. We had even no compositions or 
orations in Latin. Our course of lectures was also 
defective in containing no lectures on the Scriptures, 
or on ecclesiastical history, and by the students in 
general (and Mr. Alexander and myself were no ex- 
ceptions), commentators in general, and ecclesiastical 
history also were held in contempt" 

The Mr. Alexander mentioned above was a close 
friend who was in the same class* as, and during the first 
year shared the same room with Priestley. They read 
Greek tc^ether, but Priestley devoted more time to 
mathematical and philosophical studies. The students 
of Priestley's time were about equally divided upon all 
the usual questions of theological orthodoxy and hetero- 
doxy : Dr. Ashworth, the tutor, usually took the ortho- 
dox side of the discussions and the sub-tutor, Mr. Clark, 

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the heterodox. As both these tutors were young the 
lectures often assumed the character of informal dis- 

On the whole, the period of life spent at Daventry 
was pleasant rather than eventful. Priestley, although, 
argumentative and heterodox, appears to have been 
law-abiding, as he says : " Though Dr. Ashworth was 
earnestly desirous to make me as orthodox as possible, 
yet, as my behaviour was unexceptional, and as I 
generally took his part in some little things by which 
he often drew upon himself the ill-will of many of the 
students, I was upon the whole a favourite with hioi ^'. 

Priestley ever remained deeply attached to Daventry, 
his Alma Mater, ia spite* of its lack of tradition or 
splendour. Later in life he compared it favourably 
with, the ancient Universities: "Thus while your 
Universities resemble pools- of stagnant water; secured 
by dams and mounds, ours are like rivers which, taking 
their natural course, fertilise a whole country ". The 
whole of his studies at Daventry were consciously 
directed to one end, that of fitting him for the Christian 
ministry. He composed there, with the aid of Mr. 
Clark's advice, the " Institutes of Natural and Revealed 
Religion ". Owing to an impediment in his speech he 
was at times much discouraged but never for long ; he 
consoled himself with the remembrance of St. Paul's 
J' thorn in the flesh," and the reflection that perhaps this 
defect of stammering kept him from being too disputa- 
tious and thereby made him nfiore attentive to qualifica- 
tion3 of a superior kind. 

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The students of Daventry often amused themselves by 
speculations as to what the future held in store for 
them. Priestley never seems to have been ambitious 
.for place, and when his tutor suggested that he should 
apply for a vacant ministry at Needham Market he 
readily consented to do so. The town was a small one 
ini Suffolk, not far from Stowmarket and Ipswich, situ- 
ated in a countryside very different in character from 
that to which Priestley had been accustomed Here 
Priestley settled in 1755, going as assistant to Mr. 
Meadows, the superannuated minister, with a view to 
succeeding him when he died. 

The congregation numbered about one hundred per- 
sons. The salary promised was ;^40, but from various 
causes it rarely amounted to as much as £30, while 
Priestley found that the expenses of his board alone, 
generally exceeded ;^20. Under these conditions even 
bare subsistence would have been almost impossible 
but for an occasional five pounds procured for him 
from various religious charities. Many young men 
would have been embittered by these early struggles, 
especially men of the temperament of Priestley ; for al- 
though he was humble where worldly 'position was con- 
cerned he possessed a clear consciousness of his own 


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talents, and must often have contrasted ,at this 'time 
his actual position with that for which he felt himself 
fitted. We get a hint, but only a hint, of such feelings 
in his remark : " Visiting that country some years 
afterwards, when I had raised myself to some degree 
of notice in the world, and being invited to preach in 
that very pUlpit, the same people crowded to hear me, 
though my elocution was not much improved, and they 
professed to admire one of the same discourses they 
had formerly despised ". 

For the first six months the prospects of successful 
work seemed promising. Priestley's endeavours to im- 
plant his own pertinacious open-mindedness on religious 
matters in the hearts of his congregation led to his acquir- 
ing a reputation for heterodoxy which brought about an 
estrangement, between himself and most of his neigh- 
bours. In addition to this trouble he found his monetary 
position much more straitened owing to the failure of his 
aunt's remittances. His stammering at this time in- 
creased so much as to render his preaching painful, and 
he applied to his aunt for twenty guineas to defray the 
expenses of the treatment of Dr. Angier who promised 
to cure all defects of .speech. This led to his first visit 
to London. 

Forced by the straitened character of his circumstances^, 
Priestley, although extremely averse from the idea, at- 
tempted to open a school. He printed and distributed 
"proposals" to teach classics, mathematics, etc., but be- 
cause of his heterodoxy these efforts were fruitless. He 
next began to lecture on science, starting with a course 
of twelve lectures on the use of the globes. He obtained 
ten hearers whose fees just more than covered the expense 
of the apparatus. 

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Further perseverance upon these lectures was rendered 
unnecessary by his leaving Needham Market in 1758 in 
order to assume the pastorate of a church at Nantwich, 
near Chester. The congregation to which Priestley was 
now attached was very different from that at NeedlJam 
Market He found at Nantwich a good-natured, friendly 
people with whom he lived very happily for three*years. 
He remarks that as there were few children -in the con- 
gregation there was no scope for exertion with respect to 
his duty as a minister; this care for the young was 
characteristic of him. Under these conditions he confined 
his ministerial visits to those houses where there were 
young children, and did not scruple to preach again his 
old sermons made at Needham, where he composed at 
least one every week. 

If his ministerial duties were light, he assumed others 
which were much more onerous. He soon established a 
school to which he gave almost all his attention ; it con- 
'tained thirty boys and six girls. " Thus I was employed 
from seven in the morning until four in the afternpon 
without any interval except one hour for dinner, and I 
never gave a holiday on any consideration, the red letter 
days, as they are called, excepted." This reminds us of 
John Wesley's famous school where play was forbiddbtl ; 
it is doubtful whether the teachers or the taught would, 
protest more loudly if such a regimen were enforced to- 
day. After closing his own school for the day, Priestley 
went to private teaching in the house of a rich and eminent 
atto/ney, Mr. Tomlinson. These activities naturally left 
him very little leisure, but he was now free from the fear 
of debt which had been ever with him at Needham. He 
was able to purchase a few books and even some scientific 
instruments, such as an air pump, electrical machine, etc. 

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His oldest scholars were taught to. keep these in order 
and to perform small experiments with them. This 
appears to have been Priestley's introduction to practical, 
experimental science. 

At Nantwich he lived with Mr. Eddowes, a me^iber of 
his own congregation, who was a grocer and the most 
influential member of his church, and who, being himself 
a lover of music, persuaded Priestley to learn to play the 
English flute. 

In spite of the great demancls on his tinie he was able 
to compose, or rather re-compose, the " Observations on 
the Character and Reasonings of the Apostle Paul" 
which had already been submitted to, but not approved 
by, Dr. Lardner while Priestley was at Needham. 1 He 
ako wrote an ''English Grammar" for the use of his 
school. This was afterwards enlarged while he was a 
tutor at Warrington Academy and seems to have met 
with some success. 

In the year 1757, while Priestley was still at Need- 
ham Market, there had been instituted the " Warrington 
Academy for the education of young men of every religi- 
ous denomination for the Christian • ministry or as lay- 
men," ^nd Mr. Clark, of Daventry Academy, recommended 
Ibis old pupil Priestley for the post of tutor in languages. 
However, Mr. (afterwards Dr.) Aiken was preferred. 
Later when the tutor ,of divinity. Dr. Taylor, died, he 
was Succeeded by Mr. Aiken, and Priestley was offered 
the tutorship in languages. This he accepted, although 
it was less remunerative than his school at Nantwich and 
although he would hafe preferred to teach mathematics 
and natural philosophy. 

The Warrington Academy was for many years one of 
the chief Dissenting places of education in -Great Britaia 

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Sir T. E. Thorpe in his "Life of Joseph Priestley" 
describes it as " the centre of literary taste and activity, 
and of political liberalism of the district in which it was 
placed — the Areopagus of the Athens of Lancashire, as 
it was called '*. Several of its tutors were as erninent in 
their particular branches of knowledge as any men of 
their time. The poetess, Anna Laetitia Aiken, after- 
wards Mrs. Barbauld, was the daughter of the tutor in 

Priestley soon had more leisure than at Nantwich, and 
congenial society enabling him to make the best use of 
that leisure. During the first few months he was busy 
preparing his courses of lectures, a labour made more 
arduous because at that time he had no particular liking 
for the subjects which he was teaching. He continued 
to give lectures oh "The Theory of Language" and 
" Oratory and Criticism " as had been done by Mr. Aiken, 
and in connection with . these introduced weekly public 
declamations by his pupils. Finding the curriculum 
designed chiefly to train the students for the generally- 
called learned professions, whereas in fact most of those 
in residence intended to take up a civil or mercantile 
career, Priestley introduced courses which he thought 
would be more suitable for such men. He therefore 
introduced lectures on ''History and General Policy," 
on the " Laws and Constitutions of England," and on 
the "History of England". It was his intention later 
to publish these three courses of lectures, but the appear- 
ance of certain works by other authors . rendered un- 
necessary, in Priestley's opinion, the publication of two of 
these. It is interesting to note that the book which Super- 
seded his on the **Laws and Constitutions of England" 
was no other than the famous " Blackstone's Comment- 

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aries". The " Lectures on History and General Policy " 
were subsequently published with a dedication to Mr. 
Benjamin Vaughan, who had heard them as a student at 
Warrington and who later emigrated to America, having 
previously, in 1792, sat as Member of Parliament for 
Calne. In the preface Priestley condemns the general 
ignorance of the constitution and interests of the country. 
After reproving the growing spirit of faction and the taste 
for luxury and expense, he gives vent to an appeal that 
might be taken word for word from some regent leading 
article : " Of what unspeakable advantage might be 
one minister of state, one military commander, or even 
one single member of parliament, who thoroughly under- 
stood the interests of his country and who postponed 
every other interest and consideration to it ". Priestley, 
although desiring^ the spread of political knowledge, did 
not favour the idea of an educated democracy : " This 
is not teaching politics to low mechanics and manu- 
facturers, or encouraging the study of it among persons 
with whom it could be of no service to their country and 
often a real detriment to themselves ". Some of these 
. opinions were afterwards modified, but throughout his life 
Priestley, considering his own origin, was strangely con- 
temptuous in his references to the artisan class, their 
sufferings, and general mode of life. 

The lectures themselves covered a very wide field ; 
they did not. last very long, as Priestley's plan was to 
invite relevant interruptions and a general discussion. 
His views on certain matters, as for instance, criniinal 
punishment, seem to us now rather callous : ** The only 
proper use of torture is that of punishment for atrocious 
crimes**. For other crimes slavery is allowable as a 
punishment, although in a later lecture, slavery as an 


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institution, especially in America and the surrounding 
islands, is fiercely attacked He did not apparently 
approve of literature merely as literature, and thought 
that art had reached almost the limits of its develop- 
ment. Especially in regard* to poetry he considered that 
any further addition to its volume was undesirable, because 
much of what was added would be bad, and there was 
already in existence more good poetry than most people 
had leisure to read Other lectures dealt with Money 
and Prices, National Debts, Taxes, General Economics 
and the Government of Colonies, with especial reference 
tq America and Ireland. The latter problem is still un- 
solved, the former knot cut and not unravelled 

Besides these subjects Priestley also gave courses of 
lectures on elocution, logic and Hebrew. After a year 
or two he exchanged the latter two with Dr. Aik«n for 
lectures on civil law, and during one year he gave a 
course on anatomy. The students were encouraged by 
Priestley to write verses in order to give them a greater 
fecility in writing prose. He says : " I was myself far 
from having any pretension to the character of a poet, 
but in the early part of my life I was a great versifier, 
and this, I believe, as well as my custom of writing after 
preachers, as mentioned before, contributed to the ease 
with which I always wrote prose ". 

In defence of the system of studies which he intro- 
duced at Warrington, he composed art essay on "A 
Course of Liberal Education for Civil and Active Life," 
with syllabuses of the three new courses of lectures. 
Just at this time Dr. Brown published an educational 
scheme containing a recommendation for state control. 
Priestley therefore, on publishing his essay, added some 
" Remarks on his Treatise," asserting that state control 

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of education was "inimical to liberty and the natural 
rights of parents**. This led him to consider the whole 
subject of civil and political liberty, and his thoughts 
were embodied in an essay on " Government," subse- 
quently enlarged by reflections on church authority and 
further remarks on state education. 

At Warrington he drew up a " Chart of Biography," 
in which the lives of eminent men were represented by 
lines proportional to their length of years; thus by 
observing the lines intersected by any particular date, 
the eminent men living at that time would be known, 
and their ages, successors and predecessors read off. As 
a result of this work he was awarded the title of Doctor 
of Laws by the University of Edinburgh. Later, at 
Leeds, he published a ** Chart of History " on a similar 
plan ; this is much more involved in character. It 
appears to have been in fairly general use and is men- 
tioned in one of Maria Edgeworth's " Tales ". 

While at Warrington Priestley formed the habit of 
spending one month of each year in London. His son 
adds : ** He saw and heard a great deal. He generally 
made additions to his library and chemical apparatus. 
A new turn was frequently given to his ideas. New 
and useful acquaintances were formed, and old ones 
confirmed." On the first of these visits he was intro- 
duced to several men who had a marked influence on 
his life : Dr. Price, Mr. Canton and Dr. Franklin. Dr. 
Price was then minister of Newington Green Chapel, and 
is famous for his work on morals and his writings on eco- 
nomics. John Canton, a schoolmaster, besides carrying 
out important physical work, also discovered the phos- 
phorescence of calcium sulphide — the so-called "Canton's 
Phosphorus". The cause of this phosphorescence is 

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still engaging the curiosity of chemists. Benjamin 
Franklin, by far the best known of the three, was at 
this time about dixty years of age and famous as a phy- 
sicist and statesman. His discoveries in electricity had 
been so important as to gain for him from the Royal 
Society — which had at first ridiculed his work — the dis- 
tinction of an honorary Fellowship although he was still 
a British subject. At the time when Priestley met him 
he was occupied in fighting the battles of the American 
Colonies against the Home Government His examina- 
tion before a committee of Parliament made him still 
more well known. 

Priestley has described to us how, on one day of the 
examination, he was enabled through the influence of 
Burke to be present, and has expressed his disapproval 
of the method of conducting the enquiry. The ac- 
quaintanceship now formed between the two men was 
strengthened during the next few years by their common 
• sufferings in the cause of liberty. But the friendship 
produced an almost immediate and very far-reaching 
effect. Priestley at this time had composed gH^ the 
lectures which he had to deliver, and having the necessary 
spare time he mentioned to Franklin a project of writing 
the history of discoveries in electricity, and said that 
he would undertake it provided that he could be furnished 
with the necessary books. Franklin readily agreed to 
provide these books, in which action he was assisted by 
other mutual friends of himself and Priestley, especially 
Mr. Michell, of Thornhill, near Leeds, the discoverer of 
the method of making artificial magnets. The book 
was published in 1767 under the title ** The History 
and Present State of Electricity. With Original Ex- 
periments illustrated with Copperplates.** It was well 

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received and ran through five editions in the author's 
lifetime. In the preface Priestley states that his idea 
was only to give a clear and methodical account of the 
present state of knowledge relating to electricity, con- 
cerning which he makes the following prophecy, rendered 
surprisingly true by recent research in radioactivity and 
electron theory : " Electricity, together with chemistry, 
and the doctrine of light and colour, seem to be giving 
us an inlet into their internal structure (/.^. of the 
various kinds of matter) on which all their sensible 
properties depend". His sources of information were 
mainly the " Transactions of the Royal Society/' which at 
that time published abstracts of foreign papers. Having 
a large electrical machine of his own Priestley was led 
to repeat many of the experiments which he described, 
and also to carry out research of his own. In the course 
of this work he discovered, amongst other things, the 
conducting power of charcoal and the phenomenon of 
the "Alternative path," or the tendency for a high. 
volGS^ge discharge, such as that of a battery of Leyden 
jars^ to take a short path of high resistance rather than 
a lengthy path of considerably lower resistance. His 
most important discovery in this connection was that 
of the. law of force for electrostatic attraction ; this law 
was inilppndently rediscovered by Coulomb in 1785, 
eighteen ybars after this date, and is generally known 
by his name. | These discoveries were remarkable in 
themselves but are made still more so by the circum- 
stances in which they were effected : " These experi- 
ments occupied a great portion of my leisure time ; and 
yet before the complete expiration of the year, in which 
I gave the plan of my work to Dr. Franklin, I sent 
binj a copy of it in print In the 3ame year, five houi:s 

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of every day were employed in lectures, public or private, 
and one two-months' vacation I spent chiefly at Bristol 
on a visit to my father-in-law." It was not only the 
speed with which the work" was completed that is re- 
markable, but also the thoroughness with which it was 
done. Of course it was hasty and imperfect in many 
particulars, but that it should have contributed so much 
to the real advancement of science more than compensates 
for its imperfections. Hasty workmanship was much 
more apparent in^someof Priestley's later publications, 
and to attacks on this ground he replied : " However, 
whether my publications have taken up more or less 
time, I am confident that more would not have con- 
tributed to their perfection, in any essential particular ; 
and about anything farther I have never been very 
solicitous. My object was not to acquire the character 
of a fine writer, but of an useful one." This excuse 
may be sound in particular cases, but it is extremely 
open to abuse. As a result of this experimental work 
in electricity Priestley was elected a Fellow of the Royal 
Society, being recommended by Dr. Franklin, Dr. 
Watson, Mr, Canton, and Dr. Price. 

Soon after taking up his residence at Warrington 
Priestley decided to become ordained, apparently in 
order to improve his qualifications in case he should 
again be obliged to re-enter the ministry as a means 
of obtaining his livelihood. It was not the highest 
motive, but common enough in an age in which, for 
instance, nearly all teaching was in the hands of or- 
dained ministers. In this, as in many other matters 
dealing with the application of spiritual principles to 
the conduct of life, Priestley showed an acceptance of 
tbe conventions of the day, rather out of place in one 

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who was, in so many other respects, a reformer and 

In 1762, shortly after his ordination, he married Mary 
Wilkinson, who was then about nineteen years of age. 
She was the daughter of Isaac Wilkinson, an iron master 
of Wrexham, with whose family Priestley had be- 
come acquainted through a younger sott, William, who 
attended his school at Nantwich. The marriage was 
a happy one. In Priestley's words: "This proved a 
very suitable and happy connection, my wife being a 
woman of excellent understanding, much improved by 
reading, of great fortitude and strength of mind, and of 
a teoiper in the highest degree affectionate and generous ; 
feeling strongly for others, and little for herself. Also, 
greatly excelling in everything relating to household 
affairs,, she entirely relieved me of all concern of that 
kind, which allowed me to give all my time to the pro- 
secution of my studies and other duties of my station." 
This last qualification was all the more important, be- 
cause directly after marriage she had the responsibility 
of looking after two of his pupils from the academy, 
Benjamin Vaughan, already mentioned, and his brother 
William. From his wife's brothers, Priestley, later in 
life, received much help ; the Wilkinsons were pioneers 
in works management and methods, and John Wilkinson 
ultimately built up a big industrial organisation, even 
coining his own monetary tokens. 4* 

With the other tutors Priestley was on very good 
terms; they usually met together every Saturday to 
drink tea and discuss the questions which interested 
them, questions generally relating to philosophy and 
religion. We g©t no hint that politics, national or 
international, formed a frequent subject for discussion, 

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although external events were portentous enough. 
They were all ** zealous necessarians," determinists as 
we should say now, and held similar theological views 

He used occasionally to stay at Liverpool with Mr. 
Bentley, afterwards partner with Wedgwood of pottery 
fame, and an extremely able man but an unbeliever in 
Christianity. Priestley therefore often discussed this 
subject with him, and it was perhaps remembrance of 
some long, well-fought arguments that made him 
write : ** We generally, and contrary to my usual custom, 
sat up late". He had also friends in Manchester, 
Bolton and other towns, but wherever he went, Priestley 
was not long in forming a circle of friends and acquaint- 
ances, and it is a tribute to his own character that often 
the friendships then made lasted long after he had left 
the locality. 

In spite of the zealous endeavours of the tutors the 
Warrington Academy did not flourish at this time. 
There were embittered differences of opinion among the 
trustees which caused many supporters of the scheme 
to withdraw. At the same time the health of Priestley's 
wife began to fail, and as he had by this time an infant 
daughter, Sarah, to provide for, he was ready to remove 
to tiny congenial post which offered him better remunera- 
tion, his salary at Warrington being ;^ioo per annum, 
and terms for boarders £1$ per annum. Thus he was 
"most laboriously employed for nothing more than a 
I bare subsistence ". 

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While at Warrington, Priestley, although under no ob- 
ligation to do so, continued to preach, and, as has already 
been mentioned, became ordained. His stammer still 
continued to hinder his preaching ; indeed, during the first 
two years at Nantwich it became so bad as almost to 
make him abandon preaching and confine himself wholly 
to his school. However, by dint of practice at reading 
slowly and loudly he to some extent overcame this defect, 
but throughout his life it continued to trouble him. His 
preaching in spite of this seems to have been effective, for 
in 1767 he received an invitation to take charge of the 
congr^ation at Mill Hill Chapel, Leeds, where he was 
already well known ; financially the change was not a 
great improvement, as he was to receive one hundred 
guineas per annum and a house. The chapel had been 
built in 1673, and the present building occupies the same 
site, in a corner of the city square in Leeds. Near to it 
are statues of Priestley, Watt and others. At Leeds 
Priestley continued for six years, on good terms with his 
congregation, whom he describes as ** liberal, friendly and 
harmonious ". Here he threw himself heart and soul into 
the work of a Christian minister ; work which he con- 
sidered as the most honourable of any, and in whose 
attendant and necessary studies he took the greatest 


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pleasure. This transference to Leeds was probably the 
cause of Priestley's henceforth devoting his main efforts 
to theological work. He at once resumed the studies in 
theology which had been interrupted by the business 
of teaching at Nantwich and Warrington, and it is char- 
acteristic of what he himself calls his ** disposition to 
precipitancy " that through the perusal of one book he 
became shortly after his arrival at Leeds a Socinian in 
theology. He next began the publication of the "Theo- 
logical Repository," an intermittent work to which he 
was the chief contributor. Three volumes were pub- 
lished at Leeds. For the use of his congregation he' 
published numerous tracts. 

Here at Leeds, Priestley began his career as a theolo- 
gical controversialist by a treatise in reply to some angry 
remarks on his " Discourse on the Lord's Supper ". It 
is said that the character of a controversialist was forced 
upon him, but if so he showed a surprising aptitude for 
the part and never shrank from the combat ; indeed, 
later, he wrote an annual " Defence of Unitarianism," 
until, as he somewhat ruefully remarks, it appeared to 
himself and his friends that his antagonists produced 
nothing to which it was of any consequence to reply. 
While at Leeds several pamphlets were also composed 
concerning the relations between Dissenters and the 
Government, and Priestley soon acquired the reputation 
of being one of the chief upholders of heterodox prin- 
ciples in religion and i advanced ideas in politics. The 
distinction is not merely verbal, because his heterodoxy 
in religion has made little progress on the whole, while 
in politics many of his hopes have been realised The 
success of John Wesley's preaching led to the composi- 
tion by Priestley of several pamphlets designed to com- 

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bat what he considered were errors in the tenets of 

Besides these theological publications Priestley also 
composed several other works of a general nature, in- 
cluding an "Essay on Grovernment," an "English 
Grammar," and a " Treatise on Perspective ": This last 
work he wrote in consequence of the difficulties he him- 
self had in obtaining correct rules for drawing his scien- 
tific apparatus ; in it there occurs the first printed 
reference to the use of india-rubber aS an eraser. En- 
couraged by the success of the " History of Electricity" 
he proposed to write histories of all the branches of 
experimental science, and next undertook and published 
a " History of Discoveries Relating to Vision, Light and 
Colours ". The sale, however, was not sufficiently prom- 
ising to warrant the further continuance of the plan, and 
Priestley's further scientific work consisted almost en- 
tirely of original experiments. 

Apart from theological studies his chief 'occupation at 
Leeds was* the carrying out of experiments relating to 
e lectricity and the commencement of the work on gases 
which ultimately gained for him the title of the " Father 
of Pneumatic Chemistry". At Warrington Academy 
he had listened to lectures on chemistry by Dr. Matthew 
Turner, a physician of Manchester, but he knew very 
little of the subject when he began his experiments. 
He was led to the study of "fixed air" (carbon di- 
oxide) ovfing to the circumstance of the first house 
which he inhabited at Leeds being next to a brewery. 
By exposing water to the action of the gas — fixed air — . 
given off from the fermenting wort, he succeeded in 
obtaining a solution. But he soon found a more effect- 
ive and convenient method of obtaining this solution: 

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the gas was generated by the action of sulphuric aci'd 
upon chalk, passed through a bladder to allow of the 
deposition of moisture and then bubbled into water. 
He suggested that by the use of pressure the water 
might be more strongly impregnated with the gas. Priest- 
ley's first publication on gases appeared in 1772 and 
dealt with these experiments, the subject having some 
importance beside that of mere novelty, because it was 
hoped that the solution — now familiar as *Vsoda water" 
-^might be of use in preventing scurvy. The paper 
was considered by the College of Physicians and by them 
brought before the Lords of the Admiralty. For this 
work, published with additions in the "Philosophical 
Transactions of the Royal Society," Priestley was awarded 
the Copley Medal. In connection with these experi- 
ments Priestley devised the now well-known pneumatic 
trough, a crude form of which had been used by Hales, 
and a piece of apparatus so simple as almost to rank 
with the wheel or the lever, and like them important 
because commonplace. The first form used by Priestley 
was improvised from an earthenware trough used for 
washing linen. This' contained water below whose sur- 
face was fitted a shelf containing funnel-shaped perfora- 
tions with the narrow end upwards; the delivery tube 
from the apparatus generating any particular gas was 
placed below one of these openings and a tube or other 
vessel filled with water placed over it to collect the gas 
in the usual way. 

Already he had begun to acquire a reputation outside 
this country, for while at Leeds he was asked by the 
Grand Duke of Tuscany to procure for him the best 
electrical machine that could be made in England. The 
design for thia machiqe was drawn up by Priestley 

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himself, to whom was chiefly due the revival in the use 
of large electrical machines. Evidence of his reputation 
in British scientific circles was the proposal that he 
should accompany Captain Cook on his second voyage 
to the South Seas. Priestley consented to go and an 
assistant was appointed to take his place at Mill Hill. 
However, objections were raised at the last minute be- 
cause of Priestley's theological views — apparently a per- 
son of no principles would have been more acceptable 
than one of principles opposed to those. of the Board of 
Longitude, and the appointment was given to Dr. Forster. 
A far weightier objection to Priestley's appointment 
would have been his lack of knowledge of Natural 

During one of his London visits he made the acquain- 
tance of Mr. Lindsey, a friendship which, said he, " has 
been the source of more real satisfaction to me than any 
other circumstance in my whole life ". Mr. Lindsey was 
minister of the parish of Catterick, but in 1773, owing to 
a change in his views, he left his church and went to 
London, where he afterwards b^an to give services in 
the Essex Street Chapel, Priestley and Lindsey were at 
one in everything that they thought to be for the interest 
of Christianity ; and as they became more intimate, so 
great was Priestley's regard for the judg^nent of Lindsey 
and Mrs. Lindsey, that he published no theological 
work of any importance without first submitting it to 

In 1773 Priestley left Leeds in order to take up a 
position with Lord Shelbume, nominally as librarian. 
The Earl of Shelburne, an Irish nobleman, who had had 
a distinguished Parliamentary career, was at this time 
living in comparative retirement. He afterwards re- 

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entered public life, as Prime Minister concluded peace 
with the United States of America, and subsequently be- 
came Marquis of Lansdowne. Priestley had been re- 
commended to him by Dr. Price as a man suitable to 
be a literary companion. He carried out certain of the 
functions of a private secretary and of a librarian, but 
his actual position was rather indefinite. During the 
summer he lived with his family, now increased by two 
sons, at Calne, near to Bowood, the Earl of Shelburne's 
Wiltshire seat ; the greater part of the winter was spent 
in London. Priestley received ;f250 per annum to- 
gether with a house ; th^re was also to be, an allowance 
in case of death. In addition he received ;^40 per 
annum from Shelburne towards the expenses of his 
experiments on gases, etc., and ;f40 per annum from 
a group of subscribers who were sensible that many 
of these experiments were not carried to completion 
owing to lack of means. Shelburne often brought his 
guests, especially such as were foreigners, to witness 
Priestley's experiments. 

"^ In the autuihn of 1774 Priestley visited the Continent 
as the companion of Lord Shelburne. They made the 
tour of Flanders and Holland, and went as far as Stras- 
burg, returning to England via Paris where they spent a 
month. This first experience of foreign travel was very 
pleasing to Priestley ; he made the acquaintance of 
many men eminent in politics, literature or science. 

Apparently he soon wearied of Paris, for he left Lord 
Shelburne there and returned to England with a Mr. 
Magellan, a relative of the great navigator. While in 
Paris he met Lavoisier and other chemists, and from 
that circumstance arose the controversy as to the priority 
of the discovery of oxygen. Priestley's own words are 

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quite decided : " I frequently mentioned my surprise 
at the kind of air which I had got from this preparation 
(/.^. mercury oxide) to Mr. Lavoisier, Mr. Le Roy and 
several other philosophers who honoured me with their 
notice in that city, and who, I daresay, cannot fail to 
recollect the circumstance ". 

Priestley was not surprised to find that all the scientists 
to whom he was introduced in Paris were either agnostics 
or atheists, and adds : " As I chose on all occasions to 
appear as a Christian, I was told by some of them that 
I was the only person they had ever met with, of whose 
understanding they had any opinion, who professed Chris- 
tianity ". He soon found that their knowledge of Chris- 
tianity was very superficial, and that the same was the 
case with a great number of the company whom he met 
at Lord Shelburne's. This circumstance induced him 
while he was with Lord Shelburne to write the first part of 
his *' Letters to a Philosophical Unbeliever ". The second 
part was written at Birmingham, and the third part written 
on the ship that was taking him to America in 1794. 
They are written as to an anonymous friend in an easy con- 
versational style, and, apart from an occasional reference 
to Wilkes or the taxation of the American Colonies, might 
almost be the work of a much more modern apologist. 
Occasionally we light upon a compressed statement 
almost epigrammatic: "Something must have existed 
from all eternity, for otherwise nothing could have existed 
at all ; " or as when speaking of " the causes of infidelity 
in persons of a speculative turn of mind," he mentions the 
"affectation of being wiser than the rest of mankind" so 
that ** from a fondness for singularity he may be singularly 
in the wrong," a reminiscence of Lady Mary Wortley 
Montague's '* General conclusions are generally wrong". 

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In spite of the large amount of time which Priestley de- 
voted to experimental science, he yet managed to compose 
many theological and metaphysical works. Amongst 
these were : ** Lectures on Oratory and Criticism," de- 
dicated to Lord Fitzmaurice, Lord Shelburne's eldest 
son ; the third part of the " Institutes of Natural and 
Revealed Religion," and three " Pissertations on the 
Doctrine of Association of Ideas," in the preface to which 
he casually suggested that possibly the mental or sentient 
part of man might be merely a form of activity of the 
material body; the immortality of man he regarded as 
only possessing a basis in the Christian doctrine of the 
resurrection. These casual remarks were much mis- 
represented at the time and brought upon him the 
reputation of an atheist and an unbeliever in revelation. 
This merely incited Priestley to publish his " Disquisi- 
tions on Matter and Spirit ". Several of Lord Shelburne's 
friends unsuccessfully attempted to dissuade him from 
the publication of this work lest it should bring odium 
upon his patron. 

While with Lord Shelburne, Priestley carried out a 
number of experiments upon gases — his discovery of 
oxygen was made at this time — and published four 
volumes of his "Experiments on Air". 

Priestley's spending each winter in London led to 
a much closer acquaintance with Franklin ; they were 
members of the same club and were constantly together 
at this time. Their conversation related chiefly to the 
differences with America then arising. Of Franklin 
Priestley writes : " I can bear witness that he was so 
far from promoting, as was generally supposed, that he 
took every method in his power to prevent a rupture 
between the two countries. He urged so much the 

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doctrine of forbearance that, for some time, he was 
unpopular with the Americans on that account, as too 
much a friend to Great Britain/' Again he writes: . 
** He dreaded the war, and often said that, if the difference 
• should come to an open rupture it would be a war of 
ten yearsy and he should not live to see the end of it 
In reality the war lasted nearly eight years, but he did 
live to see the happy termination of it. That the issue 
would be favourable to America he never doubted." ,The 
last day that Franklin spent in England was in. the 
company of Priestley, reading' American newspapers, 
chiefly for their accounts of the reception of the ** Bostofi 
Port Bill". Franklin, who was an unbeliever in 
Christianity, acknowledged to Priestley that he had 
not given so much iattention to the study of the 
evidences of Christianity as the subject required, and 
asked to be reconimended a few treatises on the 
subject They continued to correspond occasionally for 
many years: in 1782 he wrote from France to tell 
Priestley of a meeting of the Academy of Science at 
which the Count du Nord (afterwards Emperor of Russia) 
was present, and where Lavoisier succeeded in melting 
platinum by burning charcoal in oxygen. In 1788 
Franklin, writing to M. Le Veillard, asks to be re- 
membered to that "honest heretic" Priestley whose 
" honesty has brought upon him the character of heretic ". 
Many other letters passed between them. * 

Priestley afterwards said of the time spent in the 
family of Lord Shelburne: " I can truly say that I was 
not at all fascinated with that mode of life. Instead 
of looking back upon it with regret, one of the greatest 
subjects of my present thankfulness is the change of 
that situation for the one in which I am now placed ; 


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and yet I was far from being unhappy there, much less 
so than those who are born to such a state and pass 
all their lives in it. These are generally unhappy from 
the want of necessary employment" 

During the last two years spent with Lord Shelbume 
Priestley was sensible of a strained character in their 
relations^ He discussed this with his friends; in 1780 
Franklin wrote from Passy advising him to continue 
^ with Lord Shelburne " under all the present disagreeable 
circumstances'* until the end of tlje agreed term: "all 
human situations have their inconveniences ; vf^feel those 
that we find in the present and we neither feel nor see 
those that exist in another ". At length Lord Shelburne 
himself proposed that they should part, ofTeting Priestley 
an establishment in Ireland This was refused, and the 
terms mutually agreed upon in 1773 were carried out 
Priestley received an annuity of ;£'i50 and took up his 
residence in London. Later in life Shelbume proposed 
to Priestley that he should return to his former position,' 
but this pflfi^r'wfits not acceptable, 

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While living at Calne, Priestley's expenses had increased 
to such an extent that fn spite of his augmented salary 
he was barely able to provide for the removal to London. 
In this situation he received much help from Mrs. Rayner,* 
one of the congregation of Mr. Lindsey, who by this time 
was in 'charge of a church in London. Priestley now 
proposed to set up a school and thus provide for himself, 
but Dr. Fothergill and others who had previously helped 
to provide for the expenses of his experiments now under- 
took to increase their allowance so that Priestley shoul3 
be under no necessity to undertake teaching. This offer 
Priestley accepted. Amongst those who made this 
annual allowance was Josiah • Wedgwood, the celebrated 
manufacturer of ppttery. Many others also helped, and 
it was from a desire to manifest his gratitude to these 
and other friends and benefactors that Priestley wrote his 
memoirs. Wedgwood also helped him considerably by 
gifts of apparatus from his pottery works : glass ap- 
paratus and the large burning lenses so necessarjf in 
many of his experiments were supplied by Mr. Parker 
of Fleet Street.. 

Mr. John Lee, of Leeds, one of the congregation of 
Dr. Lindsey, and through him a friend of Priestley's, pro- 
posed that he should receive a pension from the Civil 


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List. This was declined, as were also several subsequent 
repetitions of the proposal. 

Priestley had not decided to settle in London, and 
when his brother-in-law, John Wilkinson, proposed that 
he should come to live at Birmingham he assented and 
was there provided with a house. About three months 
after settling at Birmingham the minister of the New 
Meeting, Mr. Hjtwkes, resigned^ and Priestley took his 
place, with Mr. Blyth as colleague. Owing to the large 
amount of tim'e taken up by his scientific and theological 
work he confined his duties to the Sunday, leaving the 
work of the week days to be carried out by Mr. Blyth. 
He was there instrumental in opening one of the first 
Sunday Schools for children in the kingdom. 

Shortly after his settlement at Birmingham he published 
his ** History of the Corruptions of Christianity," an at- 
tempt to get back to the primitive basis of Christianity. 
It has been pointed out that his method of treatment 
in this and similar works marks him as "the genuine 
precursor of the properly historic treatment of biblical 
and theological questions ". This work caused him to 
be attacked by nearly all branches of the Christian 
Church,, and in defence of his opinions he published a 
"History of Early Opinions concerning Jesus Christ" 
and subsequently commenced a " General History of the 
Christian Church to the Fall of the Western Empire ". 

While at. Birmingham he composed the first part of 
his, Memoirs, which he concludes with some reflections of 
a personal nature. He was particularly thankful that he 
had inherited a happy temperament of mind and body. 
He never suffered from headaches or other complaints 
unfavourable to study. At all times of the day he could 
apply himself to mental work ; it was not even necessary 

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for him to retire from company, but many of his writings 
were composed 'by the fireside ^vith his wife and children 
round him. Nothing but uninterrupted reading or speak- 
ing disturbed him. Except for a short period while with 
Lord Shelburne his health had been uniformly good froni 
the age pf eighteen. His son states that he never slept . 
more than six Jiours. He rose at about six and gener- 
ally worked in his study until eight, when he breakfasted 
with his family. The morning was spdnt usually in his • 
study in literary work ; occasionally some time was spent 
in his laboratory. He dined at one, and contrary to the 
custom of the age. rarely drank wine or beer. In the 
afternoon he usually took a walk ; according to his son 
he walked very firmly and expeditiously. At eight he 
supped and generally spent the remaining time with his 
family, often in some game such as chess, backgammon 'or 
whist. Nothing ever depressed his mind for more than 
a short period. Frequently he observed that a few days 
?ifter some troublesome event hfe felt much less depressed 
than at any other time. The anticipation • of a similar 
reaction never failed to lessen the effect of any new 
cause of anxiety, and togethejr with his belief that all 
things were ordered for the best gave him considerable 
composure of mind throughout his life. When he wa^ a 
ypung author attacks on his writings p^tined him consider- 
ably, but later they produced hardly any effect. This 
was partially due to his resolution frankly to acknowledge 
any mistake into which he might realise that he h^d 
fallen : " That I have never been in the least backward to 
do this in matters of philosophy can never be denied ". 

His memory in certain respects was extremely bad, 
and perhaps it was this cause that rendered his theoreti- 
cal deductions from his own experiments so very feeble. 

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He often forgot entirely the substance of his own notes 
or even of the works which he had published On ac* 
count of this he used a variety of mechanical expedients 
to secure and arrange his thoughts, especially in the 
composition of his longer works. With characteristic 
ingenuousness he remarks: "As great excellences are 
often balanced by great, although not apparent, defects, 
so great and apparent defects are often accompanied by 
•great, though not apparent, excellences. Thus my de- 
fect in point of recollection, which may be owing to a 
want of sufficient coherence in the association of ideas 
formerly impressed, may arise from a mental constitution 
more favourable to new associations ; so that what -I 
have lost with respect to memory may havp been com-, 
pensated by what is called invention, or new and original 
combinations of ideas." 

At Birmingham Priestley was a meniber of the " Lunar 
Society". This was an informal association of men 
interested in science, especially in chemistry. It derived 
its name from the fact that it usually met at the time pf 
the full moon. The members dined together and then 
discussed some pre-arranged subject Many of Priest- 
ley's discoveries were. first announced at these meetings. 
Amongst its members were Dr. Withering, a physician 
and botanist ; James Watt, the celebrated engineer, and 
his partner Boulton ; and Dr. Erasmus Darwin, tlje author 
of " The Botanic Garden," and grandfather of the great 
Charles Darwin. 

In the period 1780-91, Priestley carried out numer- 
ous experiments on -gases and republished his ** Experi- 
ments on Air" in three volumes, dedicated to the Prince 
Regent. Priestley's reputation as a cheipist is derived 
chiefly from the work described in these three volumes. 

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The results of the investigations are throughout explained 
in terms of the Phlogistic Theory, to which Priestley re- 
mained a life-long adherent. 

The Phldgistic Theory owed its inception to the 
attempt of a German physician, J. J. Becher (1635-82), 
to explain the phenomena attending combustion and the 
calcination of metals in air. The changes attending 
these two processes had been r^arded throughout the 
middle ages as due to similar causes, and Becher ex- 
plained them by assuming the decomposition of the 
combustible substance or metal into a principle of 
combustibility — called ** terra pinguis*' — and a residjie. 
- Becher's hypothesis was extended*by Stahl (1660- 1734), 
who suggested that when a metal, such as iron, was 
heated in air it lo^t a volatile constituent, called by him 
" phlogiston" ; the residue, now known to be the oxide 
of .the metal, was cjescribed as the " calx '* from the Latin 
word for ashes. The escaping phlogiston . was as- 
sumed to be absorbed or taken up by the air in a 
manner somewhat resembling that in which a sponge 
takes up water; the mechanism of this side of the 
process was never clearly apprehended and described. 
A similar explanation was applied to the process of - 
combustion of such substances as sulphur, charcoal, 
. etc 

It followed from this hypothesis that substances burnt 
more readily according as they were richer in phlogis- 
ton and according as the gas in which they were 
heated was less saturated with phlogiston. The theory 
thus clearly .recognised the dependence of combus- 
tion upon the natu/e of the surrounding . gas, and it 
was also recognised that a given volume of air had only 
a limited power of supporting combustion. A gas which 

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could no longer support combustion was regarded as .hav- 
ing absorbed, or as containing its full amount of phlogis- 
ton and was described as " phlogi^ticated ". If on the 
other hand a gas previously incapable of supporting com- 
bustion, or capable of doing so only to a limited extent, 
were transformed to one well able to support combus- 
tion, then it was regarded as having become ** dephlc^is- 
ticated " ; some phlogiston had been removed, and so, 
like a wrung-out sponge, it could reabsorb. more. 

The mistake of assuming that combustion or ignition 
in air always resulted in the evolution of a volatile con- 
stituent was perhaps a. natural one when only the visible, 
phenomena attending tombustion were considered. The 
Phlogiston Theory received further support from the 
fact that on heating the calx of a metal with charcoal or 
sulphur the metal regenerated; the obvious 
explanation of this would be that the. charcoal gave up 
something to the " metallic calx ". Charcoal was itself 
readily combustible; i.e. rich in phlogiston, and there- 
fore its function was to replace tiie phlogiston Ibst by 
the mietal during calcination. Becher discovered that a 
similar process regenerated sulphur from sulphuric acid, 
and thus the Phlogiston Theory grouped together and 
explained the calcination of metals in air, the burning 
of such substances as sulphur to form acids — although 
the products of combustion in the two cases differ very 
widely in character — and the regeneration of the origi- 
nal substance by the action of charcoal. 

The Phlogiston Theory was also used to. explain 
the differences between, the solution pf metals and 
their calces (oxides) in acids. The metal dissolv.ed with 
the evolution of a combustible gas, the calx without 
such action. The calx was producecf, however, from 

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the metal by the loss of phlogiston, the combustible 
principle, so that the solution of the metal was regarded 
as taking place in two stages: (i) The loss of phlo- 
giston*" to form the calx, and (2) the* solution of the 
calx in the acid, as if the substance to be dissolved 
had otiginally been a calx ; the liberated phlc^iston, 
either by itself or united with a constituent of the acid, 
escaped as a gas, which was naturally combustible as it 
contained the phlogiston of the metal. 

The weakness of the Phlogistic Theory was phlogiston. 
The nature of this' substance or principle was never 
clearly defined; sometimes it was a " principle," some- 
tiAies a substance ; for a time it was identified with 
hydrogen. It was very difficult to explain, from the 
point of view of the Phlogistic Theory, the increase in 
weight that took place on the calcination of metals. 
Many of the chief facts which contributed to its over- 
throw were supplied by the researches of Priestley him- 
self. Nevertheless, the Phlogistic Theory had itself 
prepared the ground for the Oxygen Theory ; like the ' 
latter theory it correljated the phenomena of combustion, 
calcination and respiration, and explained the process of 
reduction. Wherever the Phlogistic Theory refers to 
" loss of phlogiston," the niodern view is arrived at by 
substituting the words " addition or absorption of oxy- 
gen"; and vice versa. The correlation of combustion, 
respiration, etc, remains as the lasting contribution of the 
• Phlogistic Theory to chemical science. 

The Phlogistic Theory was iv>t the only faulty weapon 
in the armoury of the chemists of Priestley's age. There 
was considerable vagueness in the ideas with respect to 
elements and compounds. The doctrine of the four 
elements, earth, air, fire, and water, still lingered in the 

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minds of many teachers. Especially in regard to gases 
there was a distinct<inreadiness to regard various gaseous 
substances as other than modifications of some primordial 
gas, the modified properties being r^arded as cfue to 
admixed substances, just as water may be clear and 
sparkling or stagnant and fetid and still remain water. 
Quantitative work was very rarely carried out, and when 
attempted often gave erroneous results either from faulty 
manipula^tion or imperfect knowledge. Priestley's neglect 
of the iju^ntitative^side of chemistry led to his making 
many mistakes and missing many discoveries. This 
neglect was due, it would almost appear, to a complete 
lack of appreciation of the value of quantitative data. 
The state of mind is not so strange as would at first 
appear, seeing that, at the period in question, quantitative 
analysis was still in its infancy. Moreover, Priestley 
was not only an experimental but also a speculative 
philosopher and a theologian. His studies in other 
directions than experimental science would not be 
such as to lead him to attach weight to . quantitative 

In the original six volumes of the " Experiments on . 
Air " Priestley had arranged his work to a large extent 
in chronological order, a method necessitated by the fact 
that each volume. was generally published as soon as 
sufficient results had accumulated. In revising this Work 
and republishing it in three volumes, Priestley rearranged 
it so that the dironological order was no longer followed, 
but the data were classified* according to subjects. 

After a preface containing the usual references to 
theology and ethics Priestley described his experiments 
with fixed air (carbon dioxide). He found that the gas 
prepared by heating powdered limestone in a gun barrel 

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always contained a large proportion of** inflammable air," 
which he ascribed to the action of the iron. His " inflam- 
mable air" was in fact carbon monoxide, a gas which he 
several times isolated but never troubled to characterise ; 
its actual " discovery " was left to Cruikshank. He was 
then led to examine the effect of heat upon a number of 
substances, generally enclosing them in a gun barrel for 
the purpose and collecting the issuing gas. over water. 
Similar experitnents had already been carried out .by 
Hales. In this way by heating coal he obtained a gas 
of which he states that the first portions burnt with a 
white lambent flame and the last with a blue one. In 
this experiment he approximated very closely to the 
actual conditions used for manufacturing coal gas at a 
much later date. 

He tried numerous methods of making carbon dioxide, 
such as the action of nitric acid upon charcoal or ethyl 
alcohol, the action of charcoal on mercury oxide, etc * 
Some of his methods of preparation seem somewhat 
doubtful ; thus he says that iron and mercury oxide yield 
carbon dioxide, as ' do also phosphorus and oxygen, 
mercury and nitric acid, etc Many of these results are 
doubtless due to the lack of care exercised over his experi- - 
ments. We know that the water in his pneumatic trougn 
was often unchanged for month?, and the gases collected 
would include. carbon dioxide, carbon monoxide, impure 
hydrogen, etc^ ^ It is not to be wondered at that under 
such conditions carbon dioxide was formed in most of 
the reactions carried out. By passing the electric spark 
in carbon dioxide, he obtained carbon, ** inflammable air *' 
(carbon monoxide) and ** dephlbgisticated air " (oxygen). 
The " inflammable air " he confused with hydrogen. BJ^ 
heating iron in carbon dioxide by the sun's rays he 

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obtained an inflammable gas, probably carbon monoxide 
agaia . . 

His experiments on *' inflammable air" are full of 
useful information ; thus by sparking the vapours of 
certain oils he prepared hydrogen, a method which is 
now technically employed for the manufacture of this 
gas. By passing th« spark between mercury surfaces he 
proved that the effect was due entirely to the spark and 
not to the iron wire used as leads'. ' He also decomposed 
ammonia gas to hydrogen and nitrogen. In connection 
with these experiments he notes a fact, not then long 
discovered, that charcoal is capable of absorbing large 
volumes of gases and expelling them on heating. His 
experiments on "inflammable air" are to some extent 
spoilt by his lack of differentiation between various 
inflammable gases ; thus under the term ** inflammable 
air" he groups gases as widely different as hydrogen, 
hydrogen sulphide, carbon monoxide, methane, phos- 
phoretted hydrogen and coal gas. 

In the course of his investigations on " inflammable 
air," Priestley proved by a series of well-«xecuted ex- 
periments that water was essential to the production 
of hydrogen from iron. From these results Cavendish 
concluded that water was an essential constituent of 
** inflammable air," a conclusion to which Priestley as- 
sented. Speculations as to the composition of water 
itself were at this time occupying the minds of many 
chemists both in Great Britain and on the Continent 
Watt, the engineer, made the suggestion, stated thus 
in a letter of Priestley's :'** Mr.. Watt concluded from 
some experiments of which I gave an account to the 
Royal Society, and also from some observations of his 
own, that water consists of dephlogisticated-and inflam- 

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mable air, in' which Mr. Cavendish and M. Lavoisier 
concur with him ". The experiments of Priestley's 
referred to above were those, subsequently proved to 
be incorrectly interpreted, on. the "iconversion of water 
to air". - 

It is obvious that Priestley's view of the composition 
of " inflammable air " was incompatible with Watt's view 
of the composition of water, and many experiments were 
carried out by Priestley in order to throw light upon 
the two interrelated questions. By passing steam over 
heated . iron he produced " inflammable air " (hydrogen) 
and " iron calx " (iron oxide). This "inflammable air " 
when heated with " iron calx " regenerated iron and 
waten " Iron calx " was also produced when iron was 
heated in air or " dephlogisticated air " and was therer 
fore produced from iron by loss of phlogiston. In 
similar supposed accordance with this view was the fact 
thkt by heating " iron calx " with charcoal — a substance 
rich in " phlogiston "-r-iron was regenerated. 

The production of " inflammable air " from steam 
and iron was. then explained by Priestley on the as- 
sumption that the phlogiston given up by the iron 
combined with some 6f the steam, and that this compound 
of phlogiston and water constituted " inflammable air " 
or hydrogen. On passing this gas over ** iron calx " 
it naturally restored phlogiston to the calx and re- 
generated iron, while at the same time the water pre- 
viously combined with the phlogiston was liberated. 

Priestley found, however, that charcoal and ** iron calx" 
gave " inflammable air " ; this gas was really carbon 
monoxide, but Priestley — on very little evidence beyond 
the inflammability — assumed that the gas was identical 
with that -from iroq and acids, etc., t\e. hydrogen, and 

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was therefore a compound of phlogiston and water. 
The phlogiston necessary for its production by the 
method indicated above would come from the charcoal, 
but the wat6r must have come from the "iron calx" 
which was thus, according to Priestley, iron less its 
phlogiston and combined with water. 

This left Priestley with the difficulty of explaining 

. why. " iron calx," which contained water, could be 

^ prepared as well by the action. of air or " dephlogisti- 
cated air " as by steam. The explanation adopted was 
that " dephlogisticated air" contained water and that 
this water accounted for its action upon iron. He showed 

• further that steam passed ovet charcoal produced " in- 
flammable air " ; this was really a mixture of hydrc^en 
and carbon monoxide, and the process now serves for 
the commercial production of " Mond gas," used to-day 
in enormous quantities. But Priestley's conclusion was 
that the charcoal served to restore phlogiston to the 
water! and therefore the ** inflammable air" produced 
was a compound of phlogiston and water, thus con- 
firming previous results. 

At the suggestion of Cavendish, he examined the 
effect of copper upon nitric acid', and succeeded in pre- 
paring and identifying nitric 'oxide or "nitrous air". 
Hales had already prepared this gas and showed that 
when mixed with common air, it produced a reddish- 
brown g^s soluble in water ; to Priestley is due the 

/:redit of showing that this property of "nitrous air" 
may be made the basis ©f a method for the quantitative 
analysis of the atmosphere. He showed that common 
air. was diminished by about on^ fifth of its volume 
when it was mixed with " nitrous air," and exposed to 
the action of water. Cavendish obtained more accurate 

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but only slightly diflFerent results by the use of the same 

According to Priestley, ordinary air and " nitrous air " 
reacted in such a way that phlogiston was liberated from 
'the latter which was then converted back to nitric acid 
or " spirits of nitre ". Later he assented to the view of 
Dr. Metherie that " nitrous air " did not give up phlogis- 
ton to become nitric acid, but that the latter consisted 
of " nitrous air " united with " dephlogisticated air ". In 
connection with these experiments he suggested that 
nitric oxide was more soluble in water when mixed with 
nitrogen peroxide than when not so mixed. These ex- 
periments led also to a study of the properties of nitro- 
gen peroxide. He showed that on heating.this gas it 
became darker in colour. By the action of ** nitrous 
ait " upon olive oil, he produced -a solid, probably the 
stereoisomer whose existence was afterwards explained 
by the van 't Hoff theory of spatial configuration. The 
effect on turpentine and other oils was also examined. 
He. further found that nitrogen peroxide was soluble in 
a solution of ferrous sulphate and produced a character- 
istic deep brown coloration. He tested the antiseptic 
power of nitric oxide by preserving pigeons in it ; one 
which had been thus preserved from 28th April until 
4th JunlB was then cooked, and had a peculiar but not 
offensive taste ! • 

• It was found that nitric oxide exposed to the action 
of iron or," liver of sulphur" was diminished in volume, 
but the gas so produced was not examined until some 
two months after it was generated, a delay not un- 
common in Priestley's laboratory. This new gas was 
found to possess several surprising properties ; thus 
although nitric oxide did not Support combustion this 

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new gas was a better supporter of combustion than air 
itself although produced by a reaction which when ap- 
plied to air deprived i^ of the power of supporting com- 
bustion. The nfew gas was called " Dephlogisticated 
Nitrous Air " because it supported combustion, but by 
its method of preparation it should -have been "phlogis- 
ticated". Priestley showed that when this gas was 
heated it increased in vblume and became decomposed 
into ** phlogisticated air " (nitrogen) and '* dephlogisti- 
cated air " (oxygen). 

As early as 1771 he had heated nitre in a gun-barrel, 
and obtained a gas with a very enhanced power of sup- 
porting combustion. 0.f the actual discovery of oxygen 
in 1774, he writes: "The contents of this section will 
furnish a very striking illustration of the trutih of a re- 
mark which I have niore than once made in the- course 
of my philosophical writings and which can hardly be 
too often repeated, as it tends greatly to encourage philo- 
sophical investigations : viz. that more is owing to what 
we call chance, that is philosophically speaking, to the 
observation of events arising from unknown causes, than 
to any proper design or preconceived theory in the 
business". Happening to possess a "burning lens of 
considerable force " (it had a diameter of twelve and a 
focal' length of twenty inches), he tried the efiFect of heat 
on numerQUs substances. Hales and Boyle had used 
the same method of heating substances ; Boyle, by thus 
heating red lead contained in sealed glass tubes, had 
actually burst the tubes by -the pressure of the evolved 
gas. Priestley used " mercurius calcinatus per se *' (mer- 
curic oxide), and on ist August, 1774, prepared oxygen 
by heating this oxide over mercury. He collected the 
evolved gas and showed that it possessed a remarkable 

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power of supporting combustion, similar to that possessed n ' 
by oxide. 

Further work on this gas was abandoned for some 
months, during which time Priestley visited Paris where 
he mentioned his discovery to M. Lavoisier and others ; 
during the same period he was also engaged in the 
investigation of sulphur dioxide, which he had not long 

On returning to the work on oxygen a chance experi- 
ment led him to recognise its peculiar power of support- 
ing combustion ; his own words are : " I cannot at this 
distance of time recollect what it was that I had in view 
in making this experiment, but I know I had no expecta- 
tion of the real issue of it Having acquired a consider- 
able degree of readiness in making experiments of this 
.kind, a very slight and evanescent motive would be 
sufficient to induce me to do it If, however, I had not 
happened, for some other purpose, to have had a lighted 
candle before me, I should probably never have made 
the trial ; and the whole train of my future experiments 
relating to this kind of air might have been prevented." 
The experiment referred to above is that in which 
Priestley found that the residue left after treating this 
new gas with a certain volume of nitric oxide was still 
capable of supporting combustion. He had already 
shown that ordinary air acted upon by a sufficient volume 
of nitric oxide left a residue quite incapable of supporting 
combustion.' This new gas appeared to leave no such 
residue. He showed that the gas was eminently fitted 
for respiration by testing it first on mice and then on 
himself, and suggested that it migHt thus be useful in 
some cases of illness or to increase the rate of combustion 
of charcoal so as to melt platinum, and to augment the 

4 ' 

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force of explosives. H6 rightly concluded that his new 
gas was the constituent which gave to ordinary air its 
power of supporting combustion, etc, but was misled by 
his phlogistic prejudices as to the composition of this gas 
and therefore of common air. He showed that this new 
gas would be produced by a variety of reactions, some 
of which, such as the action of heat upon calcium acetate, 
are rather doubtful sources of oxygen. 

Having shown that air owed its power of supporting 
combustion and respiration to the presence of oxygen, he 
concluded that most agents which impaired the quality 
of atmospheric air did so because they absorbed some of 
the oxygen. However, Priestley himself showed that air 
from different sources when analysed by means of pitric 
oxide showed no appreciable differences in the quantity 
of oxygen contained. 

He investigated the effect of fresh paint from this point 
of view and showed that it absorbed oxygen. Further 
work showed that turpentine alone when exposed to air 
absorbed it ; part of this absorbed air was simply dis- 
solved and was expelled under reduced pressure. 

By heating metals such as iron, tin, lead in air, he 
succeeded in absorbing part and leaving a residue of 
** phlogisticated air" (nitrogen), but failed to recognise 
the character of ^ the residue and so missed the discovery 
of nitrogen. . 

He was forced to collect certain gases over mercury 
because of their solubility in water, and this improvement 
in manipulation enabled him to make several discoveries : 
" marine acid air " (hydrochloric acid gas), " vitriolic acid 
air" (sulphur dioxide), "alkaline air" (ammonia), and 
" fluor acid air " (silicon fluoride). 

The discovery of hydrochloric acid gas was due to a 

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suggestion in a paper by CavendisL Priestley produced 
it first by heating copper with hydrochloric acid, later he 
found that hydrochloric acid alone yielded this gas, and 
was then naturally led to prepare it by the action of 
sulphuric acid upon salt The new gas was found to be 
extremely soluble in water and the solution then pos- 
sessed all the ordinary properties of hydrochloric acid. 
This led to the assumption that perhaps all acids were 
solutions of a corresponding gas in water and so to the 
discovery of sulphur dioxide. He tried the action of 
iron filings upon this "marine acid air," and fotind that 
it gave one half its volume of * * inflammable air ", Chalk 
was found to yield " fixed air *\ 

\ A similar attempt to prepare a gas by heating sul- 
phuric acid was unsuccessful, but some of the mercury 
in the trough sucked back into the hot acid and there 
readted with explosive violence, producing clouds of a 
very pungent smelling gas. This accident led to the 
discovery of sulphur dioxide) which Priestley imagined 
bore the same relation to sulphuric acid as hydrochloric 
acid gas did to hydrochloric acid. He showed that the 
gas was also formed when sulphuric acid was heated with 
olive oil or charcoal. He examined many of the pro- 
perties of sulphur dioxide, its power of liquefying cam- 
phor and of forming with water a solution which on 
freezing did not evolve its gas, as did a solution of 
carbon dioxide, but formed an " ice " which sank. 

His discovery of .Silicon fluoride arose from an attempt 
to repeat a preparation described by Scheele. Priestley 
showed that his new gas was decomposed by water 
yielding an acid solution and a stony film. Its pro- 
duction was due to the presence of silica in the calcium 
fluoride used. 

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By heating a solution of ammonia and collecting the 
gas over mercury, he next discovered "alkaline air" 
(ammonia), and showed that it could readily be prepared 
from sal ammoniac and slaked lime. The properties 
of ammonia were investigated, especially its reactions 
with the various other gases which he had discovered. 
With hydrochloric acid gas, he half expected to get 
common air, but recognised the product as sal ammoniac. 
He showed that carbon dioxide united with this gas to 
produce a crystalline, powdery solid. The majority 
Of these ammonium compounds were found to be 
volatile, but the gas united with sulphuric acid to pro- 
duce a non-volatile salt He next examined the effect 
of the electric spark on ammonia, and showed that its 
effect was due to the heat and not to the light of the 
spark, as by concentrating the sun's rays upon pieces 
of earthenware, etc., inside a vessel containing ammonia 
gas, he succeeded in bringing about a similar decom- 
position to th^it produced by the electric spark. A 
similar effect was produced by passing the gas through 
red-hot tubes. He showed that one of the products 
of decomposition was " inflammable air ". He observes 
naively : "'I by no means conclude that I •have dis- 
covered all the kinds of air that may exist in nature". 

Another accidental discovery which he made was that 
of " chamber ' crystals," or nitro-sulphuric acid. This 
compound was first observed in some sulphuric acid 
which had been impregnated with oxides of nitrogen 
and left by chance for about six months. 

He spent a great deal of time on the supposed con- 
version of water to " air," but himself proved that the 
air had diffused through the retort). He showed that 
the gas to which the water was "converted " depended 

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• % 


upon the gas surrounding the retort. The experiments 
by which he proved this were extremely well devised 
and thoroughly conclusive. He was^ at timc?s surpris- 
ingly inaccurate in measurement ; thus for the expansion 
of various gases by heat he obtained some extraordinary 
results, and quite missedi the discovery of the law after- 
wards recognised by Charles and .Gay Lussac. 

By acting upon lead oxide with " phosphoric acid " 
he produced^ a substance which when heated yielded, 
an inflamnaable gas. This was probably phosphuretted 
hydrogen, but Priestley apparently failed to distinguish 
it from hydrogen and so missed the discovery. 

He found that the intensity of sound in various gases 
depended entirely on the density of the gas and not on 

jjp chemical properties. 

One of the most important series of his experiments 
was devoted to the examination of the effect of vegeta- 
tion upon air. He had previously been somewhat sur- 
prised to find that a growing plant did not vitiate the 
surrounding air, but that a candle would burn very well 
in air in which plants had grown a long time : " Having 
had some reason to think, that there was something 
attending vegetation which restored air which had been 
injured by respiration, I thought it possible that the 
same process might also restqre the air that had been 
injured by the burning of candles. Acc6rdingly on 
the 17th of August, 1 77 1, I put a sprig of ijiint into a 
quantity of air, in which a wax candle had burned out, 
and found that, on the 27th of the same month, another 
candle burned perfectly well in it This experiment I 
repeated without the least variation in the event, not less 
than eight or ten times in the remainder of the summer." 

- He then showed that air which he bad him$elf breathed 

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until it would no longer support* combustion would do 
so after being exposed to the action of plants. He 
found that light was necessary for this effect and also 
. for the development of the green colour in certain algae. 
His experiments were important for their demonstration 
that the action of animals and plants upon air was not 
the same but opposed, or rather complementary. This 
was in direct opposition to the general opinion of his 
day ; even Scheele maintained that air was affected in 
the same way by vegetation as by the respiration of 
animals. Priestley not only showed that a growing 
plant restored vitiated air but succeeded in collecting 
" dephlogisticated air " (oxygen) from certain algal water- 
plants in sunlight and from the roots of ordinary plants. 
Some of his neatest and most conclusive experiments 
were carried out in connection with this work, which 
throughout exhibits him as an experimenter of a very 
high order. Just as much of the success of Emil Fischer 
in elucidating the constitution of the sugars depende4 
on his use of phenylhydrazine, so much of the success of 
Priestley's work on the respiration of plants ^was made 
possible by his use of nitric oxide as a reagent for detect- 
ing oxygen. 

The final conclusion niay be stated in his own words : 
" That plants are capable of perfectly restoring air injured 
by respiration, may, I think, be inferred with certaihty 
by the perfect restoration by this means, of air which 
had passed through my lungs, so that a candle would 
bum in it again, though it had extinguished flame before, 
and a part of the same original quantity of air still con- 
tinued to do so '*. ' , ' 

He carried out a number of experiments on the effect 
of oxygen, carbon iponoxide, hydrogen, etc., upon blood, 

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but these produced no very great advance on earlier 
WQrk. In connection with them he made some early, 
measurements of the oxygen absorbed and carbon dioxide 
evolved during respiration. 

His method of generating pure hydrogen by the solu- 
tion of iron in dilute acid was adversely criticised, and so 
he carried out some experiments on the subject. He* 
found that on solution of the iron a residue was left 
which gave "fixed air" (carbon dioxide) on combustion. 
This residue was least in quantity from malleable iron ; 
cast iron and steel were variable in their results. He 
also found that occasionally the "inflammable air" 
(hydrogen) generated from iron yielded carbon dioxide 
on combustion. All this is interesting in view of the 
modern work on the constitution of steel, wrought iron, 

Ip spite of the excellence of his experimental work 
and his success in discovering so many gases, his specu- 
lations, as to their composition were usually extremely 
unsound ; thus water was regarded as the probable basis 
of all gases. Although he still remained an adherent of 
the Phlogistic Theory, his views became very modified ; 
of the process of reduction he remarks : " The calx must 
part with the air as well as imbibe phlogiston in order 
to become a metal". Thus he recognised that "air" 
was taken up by a metal during calcination. 

He would not admit that water consisted of hydrogen 
and oxygen, although by the reduction of mercury oxide 
in hydrogep he had himself produced water : " It must 
be acknowledged that substances possessed of very dif- 
ferent properties, may, as I have said, be composed by 
the same elements in different proportions, and different 
modes of combination. It cannot therefore be said to be 

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absolutely impossible that water may be composed of 
these two elements or of any other ; but then the sup- 
position should not be admitted without proof ; and if a 
former theory will sufficiently account for all the facts, 
there is no occasion to have recourse to a new one, 
attended with no peculiar advanitage." He was the first 
chemist to isolate and characterise as chemical individuals 
a number of gaseous substances without r^arding them 
all as mere modifications of one primordial " air ". ^ It 
was this lack of characterisation that prevented Hales, 
Priestley's predecessor, from anticipating many of these 

Priestley was usually a very bad theorist. He des- 
pised theories and hypotheses, they were to him mere 
opinions, to be repudiated without compunction, mere 
nine-pins put up to be knocked down. He rarely 
evolved a theory to correlate his results or worked in 
order to corroborate one. This was partly due to his 
lack of accurate quantitative data and partly to his 
method of working. Chemistry was really little more 
than a hobby to him, theology was his life-work. His 
chemical work was a series of experiments whose charm 
for him consisted in the actual manipulation and not so 
much in the scientific results achieved. A pretty experi- 
ment was often repeated many times, while an important 
discovery, such as that of oxygen, would be neglected 
for months. A bottle was sometimes left unlabdled and 
the nature of the contents forgotten ; a change in vol- 
ume would often be noted as " considerable " and not 
measured. All this merely means that Priestley was 
Priestley and not Cavendish ; he ^as a brilliant experi- 
.menter but poor at quantitative;, work or theoretical 

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speculation. Of his own hypotheses, he remarks : " The 
sketch that 1 shall now give may at least serve, like 
former theories, to amuse us when we look back upon 
it after having gained a more perfect knowledge of the 
subject." ' 

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In 1 79 1 Priestley was forced to leave Birmingham owing 
to an outbreak of disorder known as the " Birmingham 
Riots". For many years he had been r^arded as 
the protagonist of English Nonconformity and political 
Liberalism in an age in which the name . Nonconformist 
represented a legal fact, and in which political freedom 
was regarded as' having for its ultimate end the over- 
throw of the State. He had had theological controversies 
with most of the leading divines of his age of all schools 
of thought At Birmingham he participated in the 
demand for the repeal of the Test Act, and he had 
previously made himself obnoxious to the Court by 
a .pamphlet in support of Wilkes as well as by other 

When the French Revolution broke out he sympathised 
with it, and was to have been present at a dinner given on 
14th July, 1 79 1, to celebrate the anniversary of the taking 
of the Bastille. For some, days previous to this meeting 
rumours of intended violence had been rife, and it was 
almost decided to postpone it Instigated, it was be- 
lieved, by some of the leading citizens of the town, a 
large crowd assembled outside the hotel where the dinner 
was held, and after breaking the windows there, marched 
oflF to Priestley's church, the New Meeting, and sacked 


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and burnt it They next went to the Old Meeting and 
burnt that 

Some friends had by this time become aware of the 
danger to Priestley, and with his wife he was hurriecj off 
to the house of Mr. Rylands. This removal had only 
been effected a few hours, and William Priestley was still 
removing some valuable papers from his father's house, 
when the mob arrived and sacked it. On Friday, 15th 
July, they sacked three other houses, residences of those 
supposed to possess similar opinions to Priestley.^ .On 
Saturday no less than nine houses were sacked, most of 
them being burnt ; two of the houses attacked were the 
residences of ministers. On Sunday the attack on 
local churches was resumed, peiiiaps in deference to the 
day^ The Meeting House at Kingswood, seven miles 
away, was burned, 'together with several other build- 
ings. The riots came to an end with an attack on 
Edgbaston Hall which was interrupted by the arrival of 
the' military. 

Throughout the disturbances the rallying cry of the 
mob had been : " Church and King". King George III. 
made no secret of his satisfaction at the suffering inflicted 
on Priestley because of his opinions. There may be 
some faiqt respect for the demagogue who incites a mob 
to violence and then unflinchingly leads them in the 
attack, but one can feel nothing but contempt for the 
cowardly authors of this outrage upon Priestley. Not 
one of them was punished for inciting the rioters, but 
two of the mob were subsequently hanged for their share 
in the disturbances. The whole series pf events was 
thoroughly wretched. 

Priestley was hurried to London by friends, and there 
stayed for some time with Mr. William Vaughan. He 

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was advised to fly from the country but refused, and, on 
the contrary, as soon as he arrived in London made 
his ift^ival known to the Ministry and appealed for justice 
and indemnification. He claimed damages to the amount 
of ;f3628 and was awarded ;f2502 by the Court He 
received a great deal of help from his brothers-in-law and 
friends, especially from Wedgwood. 

Soon after his arrival in London he was invited to 
succeed Dr. Price at Hackney ; this invitation he accepted, 
and hoped that he would be able to settle in London. 
But public opinion was by this time too much inflamed 
to allow Priestley any respite from persecution. Threats 
of viQlence were openly made ; he. had difficulty even in 
finding a house in which to live, as owners of houses were 
afraid lest such a tenant might bring destruction upon 
their property; servants Would not take service with 
him for fear lest they should be involved in his destruc- 
tion. He was shunned by his old associates of the 
Royal Society. 

Before condemning those who treated him thus, we 
must remember the circumstances of the time. He held 
opinions similar to those held by the French at the 
commencement of their revolution. They had gone 
from liberty to licence, from freedom to lawlessness, 
and many in England who had s)anpathised with their 
preliminary struggles had been alienated l^ their sub- 
sequent excesses. Priestley had not been one of these ; 
he had maintained, rightly we may now judge, that 
licence is not the fruit borne of liberty, that the blood- 
red blossom of lawlessness is the flower not of the seed 
of freedom but of repression. The feelings of his op- 
ponents were too inflamed to allow them to estimate 

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the force of this argument, and Priestley, one of the 
least violent of men, was regarded as a supporter of 
any extreme of violence. His position was not helped 
by the receipt of several sympathetic addresses from 
France, and even invitations to a seat in the National 

He bore all these trials with a nobility and courage 
worthy of the highest 'praise. No excess either of 
temper or timidity marked his actions, not even while 
he listened to the blows with which the mob were de- 
molishing» his house. But it was borne in upon him 
that no useful work could now'be accomplished by him 
in England. His sons had left the country because 
in it there was no prospect of their obtaining a livelihood, 
and had sailed to America. He had tried to take up his 
old theological and scientific work and composed several 
publications. But it is pleasant to remember a mark 
of appreciation shown him at one of the older Uni- 
versities during this tinie when he was an object of 
popular execration ; on 19th December, 1793, he preached 
the sermon at the service for the commemoration of 
benefactors at Trinity College, Cambridge. But his 
mind was soon iriade up to leave the country, and on 
8th April, 1794, he sailed for New York. Thence he 
proceeded to Philadelphia and so On to Northumber- 
land, Pennsylvania, where it was proposed to found a 
settlement mainly composed of Englishmen who had 
left their native land because of the recent disturbances. 
This scheme was abandoned, "but, attracted by the beauty 
of the surrounding country, Priestley determined to 
settle there, and built himself a house on a hill-side 
overlooking the Susquehanna valley. 

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Soon after his arrival in America, he was offered the 
professorship of chemistry in the University of Philadel- 
phia, bi^ this he refused. Later in 1803 he was offered 
the position of principal of the college, but owing to his 
advanced age and other reasons he declined the pro- 

In America he resumed the work which for the pre- 
vious few years had been so much interrupted. Nothing 
of great scientific importance was discovered by him 
after leaving England ; he published some papers on 
Volta's pile, the analysis of atmospheric air, etc., and 
also a defence of tlie Phlogistic Theory. In addition 
he composed several theological works. He ndver 
^became a naturalised American, although at one time 
there was a danger of his being expelled from the 
country as an alien. He was at too advanced an ag^ 
to bear with complete equanimity the break with all 
his English associations, and in spite of at! outward 
appearance of settled calm it is doubtful whether he 
ever regarded himself as other than a stranger in a 
strange land. 

During the winter of 1803 his health began to fail 
rapidly; he experienced great difficulty in swallowing 
even liquid food — solid food he could not attempt to 
take. Nevertheless he continued to work as well as 
he was abl^. Occasionally h6 was unable to speak 
for several hours. He was busy at this time completing' 
the printing of a theological work, and whenever his 
strength allowed it would read over the proofs. The 
work was safely seen through the press and the publica- 
tion of several pamphlets proceeded with. On Monday, 
6th February, .1804, he dictated from his bed sevei:al 
alterations in the proofs, and concluded : " That is right, 

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I have now done". About half an hour afterwards he 

" Return unto thy rest, O my soul, for the Lord hath 
dealt bountifully with thee. I will lay me down in peace 
and sleep till I awake in the morning of the resurrec- 
tion." {Priestley's Epitaph.) 


English Men of Science : Joseph Priestley. Sir T. E. Thorpe. igo6. 

Nine Famous Birmingham Men: J. H. Muirhead (Editor). 1909. 

Cornish Brothers. 
Memoirs of Dr. Priestley, written by himself. 1904.. H. R; Alleiison. 
Joseph Priestley in Domestic Life. Madame Bellon. ' Oct., 1894. 

Contemporary Review. 


March 1733 Born. 

1752 Enters as student a( Daventry Academy. 

1755 Leaves Daventry and becomes minister to Independent 

Church, Needham Market . 

176% Marries Mary Wilkinson. 

1766 Elected Fellow of the Rdyal Society. 

1767 Leeds, minister of Mill Hill Chapel. 

177Z Starts his work on the effect of vegetation upon air.' 

1772 Publishes pamphlet on soda Water; his first publication 

dealing with chemistry. Discovers nitrous oxide, hydro- 
chloric acid gas, nitric oxide. 

1773 Becomes literary companion to Lord Shelburne. 

1774 Discovers oxygen, ammonia gas, sulphur dioxide. 

1775 Publishes first volume of " Experiments on Air ". Dis- 

covers silicon fluoride. 

1778 Discovers nitrosulphuric acid, ** chamber crystals *\ 

1779 Leaves Lord Shelburne. 

1780 Becomes minister at Birmingham. 

1791 Birmingham Riots; house wrecked; Priestley goes to 

1794 Sails for America. 
1804 Death. 


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Bdited by S. CHAPMAN, MlA., D.Sc. Bach with a Portrait. 7^ by 5. 
Paper cover, Is. ; cloth, 2s. net. 


By W. W. Bryant, F.R,A.S,, Royal Observatory, Greenwich. 


By J. A. Crowther, D.Sc. 


. The Story of a great Discoverer. By Lancelot T. HoobBn, 
P»A,, B.Sc. {Others tn preparation.) 


A Course of Six Lectures " adapted to a Juvenile Auditory " 
delivered at the Royal Institution at Christmas^ 1913. By 
H. H. Turner, D.Sc, D.C.L., F.R.S., Savilian Professor of 
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Naturb says : " We cordially recommend the book as being likely to give an in- 
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Explained in simple terms for the nonrtechnical reader. By 
J. A. Fleming, M.A., D.Sc., F.R.S., University Professor 
of Electrical Engineering in the University of London^ etc. 
With numerous Diagrams. Cloth boards, 48. net. 

Natvrb sajra: *' Dr. Fleming has undertaken a task which in many ways is more 
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use of mathematical or very technical language ". 


A Romance of Applied Science. By Raphael Meldola, 
F.R.S., F.I.C., sometime Professor of Chemistiy in Fins- 
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Cloth, 2s. Sd. net. 

The Olaboow Herald says: "The most romantic portion of the book to the 
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S. p. C. K., LONDON. 

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