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Joseph Priestley's recipe for carbonated water, for which he was elected to the French Academy of Sciences in 1772 and awarded a medal by the Royal Society a year later 

Thomas Jefferson, who became friendly with Joseph Priestley after Priestley emigrated to the United States

Joseph Priestley was born near Leeds in 1733. His father was a dyer and dresser of woollen cloth. The young Joseph was educated at a local grammar school in Leeds and later at Daventry Academy. While at school he became proficient in physics, philosophy, algebra, mathematics and a variety of ancient and modern languages, and devised an improved system of shorthand. In 1761 he published The Rudiments of English Grammar, in which he first expounded the view that is commonly held today, but which was virtually unknown then, that grammar is defined by common usage and should not be dictated by self-styled grammarians. The tolerant and liberal attitude he espoused was to remain rare until well into the twentieth century. 

Joseph Priestley was also one of the leading philosophers of his time. He held the view  that all humans were equal, and he backed this up by campaigning passionately against the evils of slavery, arguing that we should view all of mankind as brethren and neighbours, regardless of race or religion, and should work equally hard to relieve the distresses of all of them. As to the state, its function was to secure the greatest happiness of the greatest number of its citizens, who should enjoy both political liberty (in the shape of the right to vote) and civil liberty (to pursue as they wished those aspects of their life which were none of the state's business). Whilst few would dissent from these views today, in their time they were very radical indeed.

But his first interest was always in theology. His day job was that of minister in a succession of dissenting chapels  and much of his life was given up to re-examining doctrine, preaching and (frequently) changing his own religious opinions. Yet it is for his hobby as a scientist that he is chiefly remembered.

In 1765 he published his Chart of Biography, which won him a doctorate of laws from Edinburgh University. The following year he was elected a Fellow of the Royal Society in recognition of his experiments with electricity, which was followed in 1767 by the publication of The History and present State of Electricity, with original Experiments. He was encouraged in this work by Benjamin Franklin whom he met in London in 1776.  Franklin himself was interested in electricity (you'll recall the story about the kite) and the two men established a firm friendship.  

But his most important work was to be in the field of gases, which he called 'airs' (he would later chide James Keir for giving himself airs (oh dear!) by adopting the term 'gases' in his Dictionary of Chemistry, saying 'I cannot help smiling at his new phraseology'). Living, as he did at the time, next to a brewery, he noticed that the gas given off from the fermenting vats drifted to the ground, implying that it was heavier than air. Moreover, he discovered that it extinguished lighted wood chips. He had discovered carbon dioxide, which he called 'fixed air'. Devising a method of making the gas at home without brewing beer, he discovered that it produced a pleasant tangy taste when dissolved in water. By this invention of carbonated water, he had become the father of fizzy drinks!  

In 1772 he discovered the respiration of plants by placing a shoot of a green plant in a sealed container, in which he lit a candle that he left burning until it went out. Later, he discovered, the candle could be lit again. In the same year he invented a piece of apparatus that was to be of crucial importance in his experiments with gases. These experiments involved floating various materials on mercury inside a sealed glass container, which he then heated using a burning glass. 

With this apparatus he discovered nitrous oxide (laughing gas) in 1772 and then, in 1774 he made the discovery for which he is best known. Placing a piece of mercuric oxide in his apparatus, he discovered that a candle burned very brightly in the gas produced. After finding that mice survived quite happily in the gas he took a deep breath of it himself: 'The feeling of it to my lungs was not sensibly different from that of common air; but  I fancied that my breast felt particularly light and easy for some time afterwards. Who can tell but that, in time, this pure air may become a fashionable article in luxury? Hitherto only two mice and myself have had the privilege of breathing it.' He had discovered oxygen.

The problem was, he didn't know that was what he'd discovered. Priestley's mind was encumbered with some outdated and, as we now know, highly erroneous ideas. Along with his contemporaries, he believed that air, like water, was an element that could become polluted with  phlogiston as a result of fire or of animals' exhalations, and which (he discovered) could be restored to purity by agitating air in water or by the respiration of plants. He consequently thought that the oxygen he had isolated was dephlogisticated air - air with less phlogiston than ordinary air. In fact,  Priestley's report on his experiments with gases is a fascinating account of one man's struggle to make sense of what he had discovered, from which we can see that the leaps of imagination and understanding that would have been needed to truly appreciate the significance of his discovery were quite beyond him. (There is a brief extract in the right-hand panel.)

In 1780, whilst his experiments with gases were in full swing, Priestley came to Birmingham as a Unitarian minister at the New Meeting House. He joined the Lunar Society and besides enjoying the stimulating company he found there, he benefited  from the financial support for his scientific work that he received from his fellow Lunaticks, and from their advice and assistance. James Watt, in particular gave freely of his skill and experience in accurate measurement techniques. To add to his existing achievements, during this time Joseph Priestley discovered photosynthesis, and discovered and described the properties of ammonia, sulphur dioxide, hydrogen sulphide and carbon monoxide. 

The question of who discovered the chemical composition of water, which at the time was still thought to be an element, is an intriguing one. In 1781 Darwin wrote to James Watt,  'Water is composed of aqueous gas, which is displaced from its earth by oil of vitriol.' At a Lunar Society meeting shortly afterwards, Priestley carried out an experiment in which he mixed inflammable air (ie, hydrogen) with dephlogisticated air (oxygen) in a flask, to which he applied an electric spark. The inside of the flask became covered with moisture. Learning of the finding, Henry Cavendish devised an improved version of the experiment, from which he concluded that 'almost all of the inflammable air, and about one fifth of the common air, are turned into pure water'. James Watt also experimented, concluding that 'water is pure air deprived of part of its latent heat and united to phlogiston'. Although Watt drafted a letter to the Royal Society, he held it back - a fatal mistake, because in the meantime Cavendish's secretary met Lavoisier in Paris and told him of the Lunar Society experiments. Immediately Laviosier repeated the experiment and registered the discovery that water was 'not ... an element, but can be decomposed and recombined' with the French Academy the next day. By the time the cautious Watt sent off his paper to the Royal Society over a year later, Cavendish had also placed the results of his experiments in the public domain. Whilst Priestley was philosophical about others claiming the credit for what was rightly a Lunar Society discovery and Darwin never sought recognition for the discovery, Watt was bitter in the extreme.

Although Joseph Priestley's years in Birmingham were the happiest and most productive of his life, they were to end in tragedy. He had a seemingly  irresistible tendency to controversy, which gained him a lot of enemies. (He had also made himself unpopular with the neighbours on account of the frequent explosions which emanated from his house during the course of his experiments.) The event that led to his downfall was a dinner held at Dadley's Hotel in Temple Row on 14th July 1781 to celebrate the second anniversary of the storming of the Bastille. A quantity of inflammatory, and egregiously inaccurate, propaganda was published in connection with this dinner - for example, it was alleged quite untruthfully that Priestley, who was not even at the dinner, had toasted ' the king's head on a plate'. Rumours had been circulating for days beforehand that there was to be a riot - and sure enough, the dinner proved the occasion, or at least the excuse, for a bout of rioting - the so-called Priestley riots - an efficiently organised and carefully targeted campaign, in which the houses of many of the Birmingham elite, Priestley's included, were looted, burnt down, or both.  Afraid for his life and the safety of his family, Joseph Priestley left for London, and although for a while he entertained hopes of returning, he finally accepted James Watt's advice against such a course. This enforced exile was a great loss to him. Years later he would write to James Watt, recalling 'the pleasing intercourse I have had with you and all my friends of the Lunar Society. Such another I can never expect to see - in fact, London cannot furnish it. I shall always think of you at the usual time of your meetings.'

In fact he became so traumatised that even in London he did not feel safe and in 1794 the Priestleys sailed for the United States, where he continued his experiments and became friendly with Thomas Jefferson, who described him as 'one of the few lives precious to mankind'. Joseph Priestley died aged 70 in 1804, in Northumberland, Pennsylvania. 



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'There are, I believe, very few maxims in philosophy that have laid firmer hold upon the mind than that air ... is a simple elementary substance, indestructible, and unalterable, at least as much so as water is supposed to be. In the course of my enquiries, I was, however, soon satisfied that atmospherical air is not an unalterable thing; for that the phlogiston with which it becomes loaded from bodies burning in it, and animals breathing it ... so far depraves and alters it as to render it altogether unfit for inflammation [or] respiration ... and I have discovered that agitation in water [and] the process of vegetation ... by taking out the superfluous phlogiston, restore it to its original purity. But I own I had no idea of the possibility of going any farther in this way, and thereby procuring air purer than the best common air. I might, indeed, have naturally imagined that such would be air that should contain less phlogiston than the air of the atmosphere; but I had no idea that such a composition was possible' 

One quotation will suffice to illustrate his attitude to English grammar: 'This may be said to be ungrammatical ... but custom authorises it, and many other departures from strict grammar, particularly in conversation.' 

 The following remark was seen as particularly inflammatory by Priestley's opponents:

'We are, as it were, laying gunpowder, grain by grain, under the old building of error and superstition, which a single spark may hereafter inflame, so as to produce an instantaneous explosion; in consequence of which that edifice, the erection of which has been the work of ages, may be overturned in a moment, and so effectually as that the same foundation can never be built upon again.'

'I consider my settlement at Birmingham as the happiest event of my life.'

'No single person ever discovered so many new and curious substances' Sir Humphrey Davy on Joseph Priestley 


Joseph Priestley's terminology seems very strange to those brought up on more modern notions. For instance, he called hydrogen 'inflammable air'; oxygen 'fire air' or 'dephlogisticated air'; carbon dioxide 'fixed air'; nitrogen 'phlogisticated air';  and sulphur dioxide 'vitriolic acid air'.


The Priestley riots dealt a severe blow to the ideals the Lunar Society was based on - concepts such as reason, science, learning, rationality and freedom. It was a blow for yobbishness and against intellectualism. With slogans like 'No philosophers' painted on Birmingham's walls, the Lunar Society found itself facing a newly hostile public mood. James Watt was moved to write, 'The Hellish miscreants who committed so many outrages here, by banishing Dr Priestley have almost broke up our Lunar Society'.

2001, 2002, 2003, 2005 Bob Miles