1772: Oxygen is discovered

Carl Wilhelm Scheele (1742-1786)

Oxygen was first described in 1740 by Alexander Ferguson, yet it wasn't discovered until 1772 by Carl Wilhelm Scheele.  He learned that candles burned brighter when he heated mercuric oxide and potassium titrate.

Because the gas he discovered made candles burn brighter, he referred to it as empyreal air, or fire air.

The problem for him was he waited until 1777 to publish his discovery in "Chemical Treatise on Air and Fire." By this time someone else had already received credit. (2, page 282)

Joseph Priestly (1733-1804)

Unaware of the works of Scheele, and unaware that a third man -- Antoine Lavoisier -- was doing similar research, (1) Joseph Priestly published a book in 1775 called "Observations on different kinds of Air."

Priestly described experiments he performed where he observed that blood placed in an atmosphere of hydrogen or nitrogen gave off a gas that he referred to as "dephlogisticated air." Due to the timeliness of his book, he is often given credit for the discovery of oxygen, despite the works of other men. (5, page 517)

So when Priestly burned mercury, he believed the gas emitted was the result of "phligoston," or impurities, being removed from the air and drawn into the mercury.  In this way, burning mercury purified the air.  This is why he referred to it as "dephlogisticated air." (5, page 476) (7 page 1680)

Antioine Lavoisier (1743-1794) 

The authors of a to a 1908 book called "Recent Advances in Physiology and bio-chemistry," said Priestly's...

...experiments were sound, but his views on respiration were erroneous, vitiated as they were by his belief in the old theory of "phlogiston" introduced by Stahl in 1697. Phlogiston was the material and principle of fire, not fire itself, and respiration, according to Priestley, was a phlogistic process, whereby the phlogiston absorbed by animals with their food was discharged. Venous blood was phlogisticated, arterial blood dephlogisticated; a clot of blood placed in "fixed" or phlogisticated air became very dark, but regained its red colour when it was transferred to oxygen or dephlogisticated air. This old theory was overthrown a few years later by Lavoisier, who extended and explained correctly the discoveries of Mayow, Black, and Priestley; he showed that there were differences in the so called phlogistic processes. (5, page 476)

Stephen Hales (1677-1761)

Priestly also observed that mice living in an environment with supplemental oxygen lived longer than mice who breathed normal air.  This was the first proof of the therapeutic benefits of supplemental oxygen.  (2)

After performing such experiments, he said he decided to try breathing it himself through a glass siphon.  He said:

The feeling of it to my lungs was not sensibly differentfrom that of common air; but I fancied that my breast felt peculiarly 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. (11, page 102)

Priestly then concluded the work of Michael Servetus, who noticed that the lungs changed the color of the blood and were the reason arterial blood was a brighter color than venous blood.  Priestly proved that oxygen is inhaled into the lungs and exchanged from the alveoli to the capillaries and then into the arteries.

Surely Priestly observed the possible therapeutic effects of oxygen, yet he also was concerned, and offered a warning regarding its use.  He said:

From the greater strength and vivacity of the flame of a candle, in this pure air, it may be conjectured, that it might be peculiarly salutary to the lungs in certain morbid cases, when the common air would not be sufficient to carry off the phlogistic putrid effluvium fast enough. But, perhaps, we may also infes from these experiments, that though pure dephlogisticated air might be very useful as a medicine, it might not be so proper for us in the usual healthy state of the body: for,, as a candle burns out much faster in dephlogisticated than in common air, so we might, as may be said, live out too fast and the animal powers be too soon exhausted in this pure kind of air. A moralist, at least, may say, that the air which nature has provided for us is as good as we deserve. (11, page 101)

In an 1866 paper, "Factitious Airs," Henry Cavendish described his discovery of hydrogen, or what he referred to as "inflammable air." He "exploded a mixture of hydrogen and oxygen and thus proved that water was not an element, but a compound of two gases." (4, page 194)

While the first gas was hydrogen, the second gas was oxygen, an element that Lavoisier would soon give a name to.

While Priestly is given credit for the discovery of oxygen, it was Lavoisier, in 1778, who disproved the "phlogostin" theory, thereby proving the substance that priestly had named "dephlogisicated air" was a chemical element, and he named it "oxygene," or "acid former." was the name that ultimately caught on. (8) (9, page 19)

This name for the element was chosen by Lavoisier because he believed it was the great 'acidifying principle in nature.' Oxygen is Greek for generator of acids.(1) (7, page 1680)

Lavoisier chose this name because he believed oxygen was acidic in nature due to some of the things it did. For instance, Lavoisier discovered that oxygen was involved in the rusting of metals, the formation of dew, as well as the respiration of animals and humans. Because it created such changes he believed it was an acid.

Lavoisier, working with Pierre-Simon Laplace, determined, in 1780, that the body's heat was a byproduct of combustion that takes place in the body.  So in this way he disproved Galen's theory that a body's heat was produced in the heart. He later determined this combustion took place both in the lungs and other places in the body. It was later proved by others that it was in the tissues that respiration occurs. (5, page 476)

Many years later it was learned that oxygen is present in most acids.  So for this reason the name "oxygen" really isn't an appropriate name for oxygen.  Yet the name stuck.  (1)

Regardless, this was the beginning of knowledge of respiratory exchange.

References:

1. Gray, Alonzo, "Elements of Chemistry:  Containing the Principles of the Science, both experimental and theoretical," 1840, Massachusetts, page 118
2. Brainbridge, William Seaman, "Oxygen in Medicine and Surgery -- a contribution with report of cases," New York State Journal of Medicine, 1908, Vol. 8, June, No. 6, pages 281-295
3. "Carbon Dioxide,"  Scienceclariied.com, http://www.scienceclarified.com/Ca-Ch/Carbon-Dioxide.html#b, observed the site on May 4, 2012 
4. Magner, Lois N., "History of Life Sciences," 2002, 3rd edition, New York, Marcel Dekker
5. Hill, Leonard, Benjamin Moore, Arthur Phillip Beddard, John James Rickard, etc., editors, "Recent Advances in Physiology and bio-chemistry," 1908, London, Edward Arnold
6. Fruto, Joseph S, "Proteins, Enzymes, Genes: The Interplay of Chemistry and Biology," 1999, New York, Yale University
7. Blakeman, Thomas C., "Evidence for Oxygen Use in the Hospitalized Patient: is more really the enemy of good," Respiratory Care, October, 2013, volume 58, number 10, pages 1679-1693
8. Grainge, CP, "Breath of Life: the evolution of oxygen therapy," Journal of the Royal Society of Medicine, October, 2004, 97 (10), pages 489-493
9. Heffner, JE, "The story of oxygen," Respiratory Care, January, 2013, volume 58, number 1, pages 18-30
10. Holzapple, GE, "The uses and effects of oxygen gas and nux vomica in the treatment of pneumonia," New York Medical Journal, September 3, 1887, volume 46, pages 264-267
11. Priestly, Joseph, "Experiments and Observations on Different Kinds of Air," volume 2, 1875, London, Printed for J. Johnson

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