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Books and Other References
Check out the excellent book Serendipity: Accidental Discoveries in Science by Royston M. Roberts (1989, John Wiley and Sons).  This book describes Priestley's life and discoveries in great detail.  This is a fascinating book.

The New York Times has three good articles on Priestley:

  • Chemists at Sesquicentennial Will Honor Joseph Priestley: Famous Scientist, Who Discovered Oxygen and Invented Soda Water, Was Called a Heretic (September 5, 1926, Section VIII, page 14, cloumn 5).
  • Priestley and Oxygen (Editorial: March 13, 1933, page 12, column 3).
  • Topics of The Times: An Early Visitor (June 4, 1954, page 22, column 4).
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The king of serendipity.

Joseph Priestley was one of those tinkerers that happened to stumble across some of the most important scientific discoveries of all time.  That's a picture of him below. 

Joseph PriestlyPriestley was born near Leeds in England on March 13, 1733 (you're absolutely correct if you've concluded that he has long passed away).  He was raised in a strict Calvinist family.  While studying to become a minister, he found that his strong liberal beliefs conflicted with his church's teachings.  As as result, in 1767, Priestley became a pastor in a small dissenting church in Leeds. 

Note that Priestley had no real interest in the sciences.  In fact, he never took a single formal science course during his entire lifetime. 

This all changed when he met the one and only Benjamin Franklin, one of the most prominent scientists of the day, while on a trip to London in 1766.  Franklin's specialty was electricity (remember the famous, but often exaggerated, kite experiment?).  Franklin awakened Priestley's interest in science and they were to become lifelong friends.  As a result of this encounter, Priestley began to dabble in the field of  electricity. 

In 1767 (just one year after meeting Franklin), Priestley made his first major discovery - that graphite can conduct electricity.  This may not sound like a big deal, unless you realize that carbon is the main ingredient in modern electrical resistors.  That same year he published The History of Electricity

Now, remember that Priestley also became a pastor in Leeds at the same time.  He lived next to a brewery and was intrigued by the "air" that floated over the fermenting grain. 

Priestley didn't know it at the time, but he was about to become one of the most famous chemists of all time. 

From his first experiment, he was able to show that this brewery gas extinguished lighted wood chips.  He also noticed that this gas drifted to the ground around the vat, implying that it was more dense (heavier) than normal air.  This gas would later be identified as carbon dioxide. 

He devised a method to produce the gas back in his home laboratory.  When the heavy gas, as he called it, was dissolved in water, he found that it had a very pleasant and tangy taste.  For this invention of soda water, he was elected to the French Academy of Sciences in 1772 and received a medal from the Royal Society in 1773. 

Yes, he invented soda pop.  (Should we blame him for the cola wars?) 

In 1772, Priestley made another important discovery.  He had placed a shoot of a green plant into a container of water.  He then covered the container and lit a candle in it until it completely burned out.  Later, Priestley was able to both burn the candle again and keep mice alive in the air (did they have lab mice back then?).  Priestley became the first person ever to observe the photosynthesis in plants - the fact that they take in carbon dioxide and release oxygen. 

Priestley continued to experiment with gases.  He devised a new apparatus that allowed him collect gases over mercury.  As you may recall from science classes years ago, mercury is a dense liquid at room temperature.  Due to this high density, mercury will not absorb gases as easily as water.  Priestley floated various materials on top of the mercury and sealed a glass vessel over the top.  He then heated the material with a burning lens (essentially a magnifying glass used to concentrate the sun's rays). 

One of his first experiments with this device (again in 1772) produced a new gas - nitrous oxide.  It didn't take long for people to discover that this gas had unusual effects on people - hence the name laughing gas. Eventually, nitrous oxide would become the first surgical anesthetic, but this discovery was many years away. 

In 1774, Priestley placed a piece of mercuric oxide into the same test chamber.  When he sampled the gas, he found that it had an unusual property - it would burn a candle brightly.  All the other gases that he had tested extinguished the flame. 

Priestley had just discovered what would later be known as oxygen.  He called the gas dephlogisticated air, based on the phlogiston theory (the idea that combustion was essentially the process of losing a hypothetical substance known as phlogiston) of the day. 

In his next experiment, he observed that the green plant material that had grown on the walls of his jars when exposed to sunlight produced a gas.  He quickly identified this unknown gas as the same gas that was released from the heated mercuric oxide.  Priestley had just documented the process of photosynthesis

Priestley told French chemist Antoine Lavosier of his discovery.  Lavosier repeated Priestley's experiments and eventually proved the phlogiston theory wrong.  Lavosier named the gas oxygen.  From these experiments, Lavosier summarized his findings into the famous law of conservation of matter - you know this one from high school science - that matter is neither created nor destroyed but is simply changed from one form to another

So, let's summarize to this point.  Priestley discovered that graphite was a conductor of electricity, isolated and described the properties of carbon dioxide, nitrous oxide, and oxygen, invented soda pop, identified the gases involved in plant respiration (unifying chemistry and biology), and observed photosynthesis for the first time. 

This list of accomplishments would guarantee anyone a position in the history books, but Priestley did not stop there.  He also isolated and described the properties of ammonia, sulphur dioxide, hydrogen sulphide, and carbon monoxide for the first time.  Added to this long list is the decomposition of ammonia by electricity in 1781. 

Yet, the discovery that he made on April 15, 1770 would prove to be the most useful to the common man.  On this date Priestley discovered that India gum could  be used to rub out lead pencil marks.  Yes, he had invented the eraser and gave the material its common name - rubber

Priestley's nonconformist religious and political views eventually ran him into big trouble.  His book History of Corruptions of Christianity (1782) was officially burned in 1785.  Due to his open support of both the American and French Revolutions, his Burmingham home and church  were burned to the ground by an angry mob in 1791.  He moved to London, but the persecution continued. 

Finally, in 1794, Priestley and his family hopped a boat for an eight week voyage and emigrated to the United States.  He was enthusiastically received by the scientific and civic bodies of his day.  He settled in Northumberland, Pennsylvania and retired to the peaceful life of his writings.  Joseph Priestley died quietly in his home on February 6, 1804. 

Many scientists feel that Priestley was not a real scientist - he was more of a dabbler in science.  He frequently did not see the importance of his discoveries.  His real downfall was his continued belief in the phlogiston theory until the day he died.  Yet, one cannot deny that his discoveries and research methodology provided the foundation for nearly all scientists that came after him. 

And to think that he did it all without a scientific education.  Maybe that was his advantage. 

Useless?  Useful?  I’ll leave that for you to decide.

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