Experiments and Observations on Different Kinds of Air
Encyclopedia
Polymath
A polymath is a person whose expertise spans a significant number of different subject areas. In less formal terms, a polymath may simply be someone who is very knowledgeable...
Joseph Priestley
Joseph Priestley
Joseph Priestley, FRS was an 18th-century English theologian, Dissenting clergyman, natural philosopher, chemist, educator, and political theorist who published over 150 works...
which reports a series of his experiments on "airs" or gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
es, most notably his discovery of oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
gas (which he called "dephlogisticated air").
Airs
While working as a companion for Lord ShelburneWilliam Petty, 2nd Earl of Shelburne
William Petty-FitzMaurice, 1st Marquess of Lansdowne, KG, PC , known as The Earl of Shelburne between 1761 and 1784, by which title he is generally known to history, was an Irish-born British Whig statesman who was the first Home Secretary in 1782 and then Prime Minister 1782–1783 during the final...
, Priestley had a great deal of free time to engage in scientific investigations. The Earl even set up a laboratory for him. Priestley's experiments during his years in Calne
Calne
Calne is a town in Wiltshire, southwestern England. It is situated at the northwestern extremity of the North Wessex Downs hill range, a designated Area of Outstanding Natural Beauty....
were almost entirely confined to "airs" and from this work emerged his most important scientific texts: the six volumes of Experiments and Observations on Different Kinds of Air. These experiments helped repudiate the last vestiges of the theory of four elements
Classical element
Many philosophies and worldviews have a set of classical elements believed to reflect the simplest essential parts and principles of which anything consists or upon which the constitution and fundamental powers of anything are based. Most frequently, classical elements refer to ancient beliefs...
; as one early biographer writes: "taken collectively, [Priestley] did more than those of any one of his contemporaries to uproot and destroy the only generalisation by which his immediate predecessors had sought to group and connect the phenomena of chemistry", however "he was wholly unable to perceive this fact." Priestley's work on "airs" is not easily classified. As historian of science Simon Schaffer
Simon Schaffer
Simon Schaffer . He is a professor of the history and philosophy of science at the Department of History and Philosophy of Science at Cambridge University and was until recently editor of The British Journal for the History of Science.-Life:Schaffer was born in Southampton and attended Varndean...
points out, it "has been seen as a branch of physics, or chemistry, or natural philosophy, or some highly idiosyncratic version of Priestley's own invention." Also, the volumes were both a scientific and a political enterprise for Priestley; he argued in them that science could destroy "undue and usurped authority," writing that the government has "reason to tremble even at an air pump or an electrical machine."
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
and the discovery of several airs: "nitrous air" (nitric oxide
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...
, NO), "vapor of spirit of salt" (later called "acid air" or "marine acid air"; anhydrous hydrochloric acid, HCl), "alkaline air" (ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
, NH3), "diminished" or "dephlogisticated nitrous air" (nitrous oxide
Nitrous oxide
Nitrous oxide, commonly known as laughing gas or sweet air, is a chemical compound with the formula . It is an oxide of nitrogen. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic...
, N2O), and "dephlogisticated air" (oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, O2). Priestly also developed the "nitrous air test", which tested for the "goodness of air": using a "pneumatic trough", he would mix nitrous air with a test sample, over water or mercury, and measure the decrease in volume—the principle of eudiometry. After a small history of the study of airs, he explained his own experiments in an open and sincere style: "whatever he knows or thinks he tells: doubts, perplexities, blunders are set down with the most refreshing candour." He also invented and described cheap and easy-to-assemble experimental apparatus. His colleagues therefore believed that they could easily reproduce Priestley's experiments in order to verify them or to answer the questions that had puzzled him.
Although many of his results puzzled him, Priestley used phlogiston theory
Phlogiston theory
The phlogiston theory , first stated in 1667 by Johann Joachim Becher, is an obsolete scientific theory that postulated the existence of a fire-like element called "phlogiston", which was contained within combustible bodies and released during combustion...
to resolve the difficulties. This theory, however, led him to conclude that that there were only three types of "air": "fixed", "alkaline", and "acid". Priestley ignored the burgeoning chemistry of his day, indeed dismissing it in these volumes. Instead, he focused on gases and the "changes in their sensible properties", as had natural philosophers before him. He isolated carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
(CO) but seems not to have realized that it was a separate "air" from the others that he had discovered.
Discovery of oxygen
After the publication of the first volume of Experiments and Observations, Priestley undertook another set of experiments. In August 1774 he isolated an "air" that appeared to be completely new, but he did not have an opportunity to pursue the matter because he was about to tour Europe with Shelburne. While in Paris, however, Priestley managed to replicate the experiment for others, including Antoine LavoisierAntoine Lavoisier
Antoine-Laurent de Lavoisier , the "father of modern chemistry", was a French nobleman prominent in the histories of chemistry and biology...
. After returning to Britain in January 1775, he continued his experiments and discovered vitriolic acid air (sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
, SO2). In March he wrote to several people regarding the new "air" that he had discovered several months earlier. One of these letters was read aloud to the Royal Society
Royal Society
The Royal Society of London for Improving Natural Knowledge, known simply as the Royal Society, is a learned society for science, and is possibly the oldest such society in existence. Founded in November 1660, it was granted a Royal Charter by King Charles II as the "Royal Society of London"...
, and he published a paper in Philosophical Transactions titled "An Account of further Discoveries in Air." Priestley called the new substance "dephlogisticated air" and described it as "five or six times better than common air for the purpose of respiration, inflammation, and, I believe, every other use of common atmospherical air." He had discovered oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
gas (O2). As revised for Experiments and Observations, his paper begins:
The contents of this section will furnish a very striking illustration of the truth of a remark which I have more than once made in my [natural] philosophical writings … that more is owing to what we call chance—that is, philosophically speaking, to the observations of events rising from unknown causes than to any proper design or preconceived theory in this business. … For my own part, I will frankly acknowledge that at the commencement of my experiments recited in this section I was so far from having formed any hypothesis that led to the discoveries I made in pursuing them that they would have appeared very improbable to me had I been told of them; and when the decisive facts did at length obtrude themselves upon my notice it was very slowly, and with great hesitation, that I yielded to the evidence of my senses. [emphasis Priestley's]
Priestley assembled his oxygen paper and several others into a second volume of Experiments and Observations on Air and published it in 1776. He does not emphasize his discovery of "dephlogisticated air" (leaving it to Part III of the volume) but instead argues in the preface how important such discoveries are to rational religion. His paper narrates the discovery chronologically, relating the long delays between experiments and his initial puzzlements. Thus, it is difficult to determine when exactly Priestley "discovered" oxygen. Such dating is significant as Lavoisier and Swedish pharmacist Carl Wilhelm Scheele
Carl Wilhelm Scheele
Carl Wilhelm Scheele was a German-Swedish pharmaceutical chemist. Isaac Asimov called him "hard-luck Scheele" because he made a number of chemical discoveries before others who are generally given the credit...
both have strong claims to the discovery of oxygen as well, Scheele having been first to isolate the gas (although he published after Priestley) and Lavoisier having been first to describe it as purified "air itself entire without alteration" (not "dephlogisticated air").
Scientific work on Airs
In this section, a list of all Priestley's scientific books on Airs has been compiled. The list doesnt include any of the several scientific papers, that he also wrote to various journals on the subject (see: List of works by Joseph Priestley).Books from 1772-1790:
- Directions for Impregnating Water with Fixed Air. London, 1772.
- Experiments and Observations on Different Kinds of Air, Vol.1. London, 1774.
- Experiments and Observations on Different Kinds of Air, Vol.2. London, 1775.
- Experiments and Observations on Different Kinds of Air, Vol.3. London, 1777.
- Experiments and Observations relating to various Branches of Natural Philosophy, Vol.1. [Experiments and Observations on Different Kinds of Air, Vol.4]. London, 1779.
- Experiments and Observations relating to various Branches of Natural Philosophy, Vol.2. [Experiments and Observations on Different Kinds of Air, Vol.5]. Birmingham, 1781.
- Experiments Relating to Phlogiston. London, 1784.
- Experiments and Observations relating to various Branches of Natural Philosophy, Vol.3. [Experiments and Observations on Different Kinds of Air, Vol.6]. Birmingham, 1786.
- Experiments and Observations on Different Kinds of Air, Vol.1-6. In 3 volumes, being the former 6 abridged and methodized, with many additions. Birmingham, 1790.
Books from 1791-1803:
- Experiments on the Generation of Air from Water; to which are prefixed, Experiments relating to the Decomposition of Dephlogisticated and Inflammable Air. London, 1793.
- Heads of Lectures on a Course of Experimental Philosophy; delivered at the New College in Hackney. [First 10 of 36 lectures are about Airs]. London, 1794.
- Considerations on the Doctrine of Phlogiston and the Decomposition of Water. Philadelphia, 1796.
- Experiments and Observations relating to the Analysis of Atmospherical Air; also farther Experiments relating to the Generation of Air from Water. [Red before the American Philosophical Society, Feb.5th and 19th in 1796, and printed in their Transacitons. To which are added, Considerations on the Doctrine of Phlogiston, and the Decomposition of Water, addressed to Messrs. Berthollet &c]. London, 1796.
- Considerations on the Doctrine of Phlogiston and the Decomposition of Water, Part II. Philadelphia, 1797.
- Doctrine of Phlogiston established and that of the Composition of Water refuted. Northumberland, 1800.
- Doctrine of Phlogiston established, with Observations on the Conversion of Iron into Steel, in a Letter to Mr. Nicholson. Printed in 1803.
External links
- The Discovery of Oxygen - background and experiments.