The Discovery of Oxygen: Analyzing Joseph Priestley's Experiments

This report details Joseph Priestley's experiments and analysis that led to the discovery of oxygen in 1774. Priestley's methodology involved using an inverted container to capture gases produced during experiments, testing their ability to support life and sustain a flame. His experiments revealed that plants release oxygen, and he identified a gas he called "dephlogisticated air" that supported combustion more intensely than common air. The discovery challenged existing theories, particularly the phlogiston theory, and laid the groundwork for future investigations, including the isolation of carbon dioxide and further exploration of chemical reactions. The data collected focused on the duration a mouse could survive and the intensity of a flame in the presence of the discovered gas, confirming its unique properties. This report also proposes future research avenues related to Priestley's work. Access more solved assignments and study resources on Desklib.

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DISCOVERY OF OXYGEN
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a. Methodology
Priestley performed his experiments and analysis of the properties of different airs using an
inverted container that was placed on a raised platform. The apparatus therefore had the ability to
capture various gases as produced by the numerous experiments below it. The apparatus could
also be placed inside mercury or a pool of water, well-sealed. A gas would then be tested to
determine if can support life or sustain a flame. The results from the experiments showed that in
case a mouse died and a flame went off, that symbolized lack of air. When a green plant is put in
the jar and then exposed to sunlight, the mouse would breathe hence stay alive and the flame
would also burn. Priestley realized that the trouble that the animal undergoes is repaired by the
plant. He therefore witnessed that plants released oxygen into the air (Smith, 2011).
More experiments were done using a glass burning lens of width 12 inches. He focused light on a
lump of reddish mercuric oxide in an inverted glass container. The container was placed pool full
of mercury. From the experiment, he realized that the gas that was released was 5 or 6 times
better than the common air. More experiments were performed and the results was that the air
emitted enabled flame to burn intensely and also the mouse breathed it hence keeping it alive. He
also realized that the air kept the mouse alive and also maintained the burning flame at a rate up
to four times more than the common air. He named it dephlogisticated air given that it perfectly
supported combustion. The air also had no phlogiston and could therefore absorb the maximum
amount of it during burning.
b. Relevance of the investigation
Joseph Priestley performed several experiments which ultimately led to the discovery of oxygen
in 1774. The culmination of the experiments made Priestley discover that air is not just an

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elementary substance but a mixture or composition of several gases. Among the gases in the
mixture include a highly reactive and colorless gas which he called dephlogisticated air. The
name would later be changed by renowned chemist Antoine Lavoisier as Oxygen. Different
scholars have carried out studies and experiments aimed at discovering air. During his
experiments, Carl Wilhelm Scheele had also isolated a similar gas to the one Priestley achieved.
Carl called this gas fire air. This was because it could support combustion. The relevance of this
discoveries were made known later in the 18th century when there was need to find out what
really happens when a substance burns. Priestley discovery therefore acted as a basis for Antoine
Lavoisier to disprove the existence of phlogiston. The test for phlogiston would still follow
Priestley idea of putting a mouse in a container and measuring how long it lived.
c. Suitability of data collected
From the above experiments, it was realized oxygen is able to intensely support combustion and
is also required by plants and animals for breathing. The data collected was used to determine
how long a mouse can live in the container and how long a flame can burn. The information
revealed that a flame burnt longer and more intensely in the presence of oxygen as compared to
common air (Sternbach, & Varon, 2014).
Question 2: Future investigations.
The following related proposed investigations could also add to the work of Priestley;
i. Investigations into the existence of phlogiston.
ii. Isolation of carbon (IV) oxide.
iii. Chemical revolution

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References
Smith, W. D. A., (2011) A history of nitrous oxide and oxygen anaesthesia part I: Joseph
Priestley to Humphry Davy. 11th ed. London: British institute of Anaesthesia, 37(10),
pp.790-798.
Sternbach, G. L. and Varon, J., (2014) The discovery and rediscovery of oxygen. 20th century
Journal of emergency medicine, 28(2), pp.221-224.
International Historic Chemical Landmark, (2018, November 18). Discovery of oxygen.
Retrieved from https://www.brlsi.org/node/18153
American Chemical Society International Historic Chemical Landmarks, (2014, January 15)
Discovery of Oxygen by Joseph Priestley. Retrieved from
http://www.acs.org/content/acs/en/education/whatischemistry/landmarks/
josephpriestleyoxygen.
Experiments and Observations on different kinds of air, (2018, November 17) Joseph Priestley.
Retrieved from https://googleweblight.com/i?u=https://www.juliantrubin.com/bigten/
oxygenexperiments.html&hl=en-KE