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Robert Boyle
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The development of the Phlogiston Theory
Antoine Lavoisier and the demise of the Phlogiston Theory

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The Phlogiston Theory

The Natural Philosophers of Scheele's day adhered to the Phlogiston Theory. This theory that dated from 1667 stated that anything that could be combusted (burnt) contains an ethereal-like substance called phlogiston. When combustion was complete it meant that all the phlogiston had been released into the air. Phlogiston had no substance - as one proponent described it, it could not be 'put in a bottle'. However, the phlogiston theory seemed at odds with the fact that when a metal is heated in the air its calx (its oxide) is formed. This increase in weight did not seem to fit the theory but it was explained by assuming that phlogiston could have negative weight.



The cover of Scheele's book 'Chemical Treatise on Air and Fire'
published in 1777

A Summary of Scheele's achievements (by no means all!)

  • He identified 12 organic acids. These included lactic acid, tartaric acid, citric acid, oxalic acid, malice acid and gallic acid (some of these he discovered in n the last years of his life)

  • He discovered a process similar to pasteurization (1769)

  • First to isolate phosphorus from bone and found a way to mass produce phosphorus (leading to Sweden becoming the main supplier of matches) (1769)

  • Work with oxygen that he called "fire air" between 1770 and 1773
    Obtained oxygen in a variety of ways including - heating manganese IV oxide (manganese dioxide), heating metal nitrates, heating mercury II oxide

  • Discovered that "activated charcoal" (charcoal that has been chemically treated so that it is in the form of a very fine powder) absorbs gases (1773)

  • First to isolate chlorine gas from a sample of pyrolusite (black magnesia) - he treated the ore with hydrochloric acid and a yellow-green gas was given off that had a strong odour. The gas bleached litmus paper and flower petals. Scheele called this gas "dephlogisticated acid of salt" - we now know it as chlorine (1774)

  • Arguably the first to discover barium and manganese (1774)

  • Experimented with arsenic to produce copper arsenide that was pigmented. (1775)
    This pigment was known as Scheele's green and it was mass produced in Europe for use in dying cloth and wallpaper (1778)

  • He analysed kidney stones and produced an acid that he called lithic acid. The name was later changed to uric acid. (1776)

  • He isolated glycerine (1776)

  • He observed the reduction of silver salts to silver in sunlight - this later became important in photography (1777)

  • He made the difference between radiant heat (thermal radiation) from convection and conduction (1777)

  • He made daily records of the percentage of "fire air" (oxygen) in the atmosphere (1778)

  • He identified molybdenum from the mineral Molybdenite (1778)

  • He discovered new methods of producing calomel (mercury I chloride) and powder of algaroth (antimony oxychloride) (1778)

  • Plumbago (also known as 'black lead') was thought to be a type of lead. He proved that plumbago was mostly made of carbon (graphite). Scheele also identified two other black ores that were often mistaken for each other - molybdenum sulfide (molybdenite), lead II sulfide (galena) (1779)

  • He identified lactic acid as the chemical responsible for the souring of milk and produced mucic acid by boiling milk with nitric acid (1780)

  • He identified the components of a tungsten mineral as being mostly calcium tungstate (CaWO4).
    This ore is still an important source of tungsten and is known as scheelite (1781)

  • He conducted experiments to produce ether (1782)

  • He obtained the colouring matter Prussian blue from his work on prussic acid (hydrogen cyanide) (1783)

  • He distilled potassium ferrocyanide with sulfuric acid to produce hydrogen fluoride (1783)



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Carl Wilhelm Scheele (1742 - 1786)

Carl Wilhelm Scheele was born in Stralsund, Pomerania in a part of Germany that was under Swedish administration in 1742. Carl's father, Joachim Christian Scheele was a merchant dealing in grain and beer. Carl Scheele was the seventh in line of a total of eleven children. Both of his parents were German and German was Scheele's preferred language when writing his laboratory notes in later years.

As a child Scheele was educated until the end of middle school but he did not stay on at school to gain a high school diploma. Friends of the Scheele family were pharmacists (also termed apothecaries in the 18th century) and they taught Scheele how to read medical prescriptions and to how to interpret the chemical "symbols" of the day. At the age of fourteen Scheele moved to Gothenburg as an apprentice pharmacist. He was following in the steps of an older brother, Johann Martin, who had died three years before Scheele left home. Johann had also been an apprentice to the same pharmacist who was another family friend.

Scheele arrived in North Gothenburg in 1756 to train with Martin Anders Bauch at his Unicorn pharmacy. Even at this young age, Scheele spent the evenings and well into the nights reading books on pharmacy and chemistry. It is claimed that he had an eidetic memory and could literally remember everything once read. It is likely that Bauch possessed a good library and that Scheele would have had the opportunity to acquaint himself with the latest scientific publications, including those of George Ernst Stahl and his Phlogiston Theory (see left). During the eight years he spent in Gothenburg he is reported to have experimented with around seventy different chemicals. Apparently some of his experiments drew complaints from Bauch and his neighbours because they resulted in explosions!

In 1765, after Scheele had spent eight years in Gothenburg, Bauch decided to retire and sell the Unicorn pharmacy. Scheele found employment with Peter Magnus Kjellstrom in Malmö as a pharmacist's clerk. It was during the two years Scheele spent in Malmö that he met Anders Johann Retzius who was to become a good friend. Retzius had been a lecturer at the University of Lund and would later take up the position as Professor of Chemistry at the University of Stockholm.

Scheele's next appointment was as a pharmacist in the Old Town of Stockholm. He was disappointed with his working conditions in his new post; the pharmacy was only a small shop with no working laboratory and its proprietor, Johan Scharenberg, would only allow Scheele to prepare prescriptions. It was during his short tenure in Stockholm that Scheele submitted his first paper to the Swedish Academy of Science. Its subject was the discovery of tartaric acid that Scheele had prepared from Cream of Tartar. The paper was rejected by the Academy, probably because Scheele was relatively unknown in the research field at that time.


An image of Scheele (c 1768) aged twenty five taken from a miniature
original in the Swedish Academy


When Retzius took up his post in Stockholm in 1768 he worked on the tartaric acid paper, adding a few experiments of his own to make it weightier. This time it was accepted by the Academy and published in its journal in 1770. Retzius referenced all of Scheele's original work so that he was given due credit. With Retzius in Stockholm, Scheele had access to the university facilities. One of the two friends' joint investigations at this time provided the relationship of quicklime to calcium carbonate. Scheele was prolific in his investigations and discoveries. A list some of these, with approximate dates where known, are shown to the left.

After three years with Scharenberg Scheele left Stockholm for Uppsala, a town forty miles north of the capitol. His appointment was as Director of the Christian Ludwig Lokk pharmacy. This large pharmacy had a laboratory attached to it and this laboratory supplied chemicals to the University of Uppsala chemistry department. It was through this connection that Scheele met Torben Olaf Bergman, Professor of Chemistry and his assistant, Johann Gottlieb Gahn.

Bergman and Gahn had obtained a quantity of saltpeter (potassium nitrate) from the Lokk laboratory and were unable to explain the red fumes produced when acetic acid was added to molten saltpeter. Both scientists were impressed by Scheele's explanation of this reaction (an explanation based on the Phlogiston Theory). With these new collaborators Scheele now had access to the university laboratories and introductions to other leading scientists.

In the 1770s air was still considered to be an element. It was believed that air was essential for reactions to take place but that it played no part in these reactions. Scheele investigated the reaction that had puzzled Bergman and Gahn. He discovered that the 'red fumes' contained a gas that he named "fire air". Encouraged by Bergman, Scheele went on to produce "fire air" by heating a variety of chemicals (see left). He went even further in his study of air. Scheele's experimental results indicated that air was, in fact, made up of two components, "fire air" that supported respiration and "foul air" that did not.

Scheele exchanged letters Antoine Lavoisier in Paris about his results and it is reported that Joseph Priestley in England was influenced by Scheele's findings. Scheele had produced oxygen (his "fire air") in 1770, five years before Lavoisier's paper, known as the 'Easter Memoire' had been presented to the French Académie des Sciences. Unfortunately for Scheele, his own publication was held by the printer (one research source suggesting that the printer was waiting for the introduction which was to be written by Bergman) and his 'Chemical Treatise on Air and Fire' was not published until 1777.

Bergman nominated Scheele for the Swedish Academy of Science in 1774 and Scheele was admitted as a member in 1775. This was quite an honour since Scheele was only thirty three and he was still officially only a laboratory assistant since he had not, as yet, sat for his pharmacy exam. His admission to the Academy came with a yearly pension that helped to finance his future research.


One of Scheele's original illustrations from
'Chemical Treatise on Air and Fire' (1777)

By 1775 Scheele had made the decision to buy a pharmacy so that he could become more independent. He eventually found a suitable establishment in Köping, a village about 115 kilometres south west of Uppsala. Although, by this time, he had been offered various research opportunities from around Europe, Scheele preferred to remain in the business he knew would provide him with financial security. The pharmacy in Köping was owned by the widow of the precious pharmacist. They made a deal that Scheele would manage the pharmacy for twelve months with the option to buy after nine months. This deal almost went sour. The pharmacy was not as financially secure as Scheele had been led to believe and there was a complication with the tenancy. Scheele worked hard to make a success of the business and to balance the books. He became so popular as the local pharmacist that the 'tenancy problem' was eventually resolved with the support of the village residents.

It was only after his ownership of the pharmacy had been legally settled that Scheele travelled for the last time to Stockholm. During this visit he took his seat at the Science Academy (his one and only appearance) and sat his pharmacy exam that he passed with flying colours. Rejecting the offer of Director of the Berlin Academy, Scheele chose to spend the rest of his days in Köping. The widow of the previous owner of the pharmacy, Sara Margaretha Gonneman and one of Scheele's sisters lived with him acting as housekeepers. With the profits from the pharmacy and his pension from the academy, Scheele was able to build and equip a laboratory. He sent two or three papers every year to the Academy but never presented them in person. Those researchers who wished to meet him had to make their way to Köping.

Despite developing gout and rheumatism Scheele continued to experiment. During his research he had handled some very dangerous chemicals, such as cyanide and arsenic. His notes show that his observations included the taste and smell of the chemicals he made. It is very likely that this habit was responsible for his early demise. Scheele knew that he had not long to live when he married Sara Margaretha so that she could inherit the pharmacy along with the rest of his possessions. He died two days later, in 1786 and at only forty three years old.

Scheele was one of the most prolific experimenters of his generation and many of his investigations proved to be well before their time. His identification of organic acids, ether and glycerol was forty years before the discipline of organic chemistry came into being. Much of his work had to be 'rediscovered', such as his identification of what we now know as chlorine gas and his account of radiant heat. Considering that he was working with equipment far inferior to Antoine Lavoisier, Scheele's investigations were accurate and wide-ranging. Isaac Asimov famously referred to him as 'hard luck Scheele' for not having been credited with the discovery of oxygen. Scheele was buried in the Köping cemetery. The exact location of his grave was lost for some time until around 1865 when the silver plate from his coffin was found by workmen. A small monument was erected on the spot where the silver plate had been found.




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