The discovery of oxygen by Scheele, Priestley and Lavoiser was happened at late 18th century. In 18th century, the chemical interest was concentrated on air and combustion, and development on new element was ongoing. The most dominate theory about air was Phlogiston, which described the property of combustion. Scheele and Priestly used the oxygen experiment as the supporting evidence of Phlogiston. Meanwhile, Lavoiser who had doubted the dominant theory used oxygen experiment for the refuting evidence. For now, the name ‘the first discoverer of oxygen’ is given to Lavoiser, who changed the big paradigm in history of Chemistry.
The first scientist who discovered oxygen among three of them was Scheele, the Swedish pharmacist and chemist born in 1742. He didn’t get enough attention compare to two other scientists eventhough he has a lot of achievements including oxygen experiment. His biography and results were reilluminated by A.E. Nordenskiöld at 19th century. Scheele’s research about oxygen started when he tried some chemical reactions in Uppsala. At first he was trying to react saltpeper(potassium nitrate) and acetic acid to generate nitrogen dioxide. By unclear reason, his interest was shifted to oxygen reaction using silver carbonate, manganese nitrate, manganese oxide, potassium nitrate, mercuric oxide and etc. He wrote that the oxygen has odorless, tasteless and it makes the combustion of candle to last longer. He named the gas as “feuerlift(fire-air) at 1775. His first experiment was 2 or 3 years earlier than Priestley’s, but the publishment was delay until 1775. Scheele blamed the publisher for the delay, but his tardy work process was also a reason of the postpone.
Priestley was a natural philosopher, chemist, educator, theologian born in England, 1733. He actively interaced with scientists, intellectuals and wealthy people and get opportunities for research and job. In 1773, he got offer from Earl of Shelburne to be a librarian, tutor for his offspring to get enough time for investigation. He used upside down glass bottle, mercury or water to seal the bottle and observed the change on flame and mouse. He found out that the flame goes out and mouse dies when they are sealed in the glass bottle for a while. He also discovered that the plant in the bottle will refresh the air under the sunlight, which is known as photosynthesis now. In 1774, he found out that the air came out from mercuric oxide experiment would make live mouse 5~6 times longer than the usual air. At first he thought it was Nitrogen dioxide, but soon after he named this gas as “dephlogisticate air”. He explained that this dephlogisticate air has insufficient phlogiston, hence it can absorb phlosiston while active combustion.
Lavoisier was a chemist born in 1743. By historical reference, he did not care about the oxygen until he got the mail from Scheele requesting for repeating his oxygen experiment. He also had dinner with Priestley and heard the oxygen experiment. At first, he used mercuric oxide to generate oxygen and focused on the acidity of the mysterious gas. After some experiments, he defined the gas as the oxygen(acid former), because a lot of acidic compound generated this same gas. With the results, he insisted that the source of acidity is in the part of air, which is related to combustion. In addition, he used the gas as a proof of refuting phlogiston theory.
As mentioned above, three chemists from three different countries contacted each other for same interest. Lavoisier and Priestley had met and talked about the oxygen experiment. In 1774, Scheele sent a letter saying that “I’ve got advise from Priestly, but the experimental result is suspicious, that I ask you for the conformation.” There is controversy over the fact whether Lavoisier got this letter or not(Some insists that his wife hid the letter to get the right for oxygen discovery), but it is certain that Scheele contacted Lavoisier and Priestley. After Scheele published his book “Chemical Treastise on Air and Fire”, he wrote the statement that he found the oxygen earlier than Priestly.
In his book “The Structure of Scientific Revolution”, Thomas Kuhn proposed who would be a real discoverer among 3 chemists. He said that Scheele doesn’t deserve for it because the publishment was late, so it is the choice between Priestley and Lavoisier. Priestley didn’t get the pure sample of oxygen, and he recognized the gas as the air without phlogiston. Lavoisier also recognized oxygen as the whole air or the cause of acidity. He didn’t focused on discovering a new gas but the theory about combustion. Kuhn insisted that from this oxygen case, it should be clear ‘what is the definition of oxygen’ and ‘which compound is oxygen’ to clarify the new discovery. The new discovery cannot occur at a certain time or by one scientist. For the new discovery is to be occurred, contain the consolidation of concept shoud be included, and the shift of paradigm might be needed. With the latter statement, Kuhn gives Lavoisier the authority for oxygen discovery. Two scientist had similar experiment and made same result, but only Lavoisier had doubt on the phlogiston theory. Only Lavoisier used the result to propose new paradigm, and became the leader of the Chemical Revolution.
Comparing three chemists’ experiment would be interesting, but it will be also helpful to think about the meaning of first discovery. Thomas Kuhn gave his standards for the first discovery, and the date of first experiment is not the only condition. For me, I thought it would be interesting to think who would be the first inventor of other theories.
“The Structure of Scientific Revolution”, Thomas Kuhn