Editing Henry Cavendish (section)

==Chemistry research==
{{More citations needed|section|date=October 2024}}
[[Image:Cavendish hydrogen.jpg|thumb|Cavendish's apparatus for making and collecting hydrogen<ref name=pt/>]]
About the time of his father's death, Cavendish began to work closely with [[Charles Blagden]], an association that helped Blagden enter fully into London's scientific society. In return, Blagden helped to keep the world at a distance from Cavendish. Cavendish published no books and few papers, but he achieved much. Several areas of research, including [[classical mechanics|mechanics]], [[optics]], and [[magnetism]], feature extensively in his manuscripts, but they scarcely feature in his published work. Cavendish is considered to be one of the so-called [[pneumatic chemistry|pneumatic chemists]] of the eighteenth and nineteenth centuries, along with, for example, [[Joseph Priestley]], [[Joseph Black]], and [[Daniel Rutherford]]. Cavendish found that a definite, peculiar, and highly inflammable gas, which he referred to as "Inflammable Air", was produced by the action of certain [[acid]]s on certain [[metal]]s. This gas was [[hydrogen]], which Cavendish correctly guessed was proportioned two to one in water.<ref>{{cite book |title=Short History of Scientific Ideas to 1900 |last=Singer |first=Charles |publisher=Oxford at the Clarendon Press |year=1966 |location=[[Oxford University Press]] |pages=337–339 }}</ref>

Although others, such as [[Robert Boyle]], had prepared hydrogen gas earlier, Cavendish is usually given the credit for recognising its elemental nature. In 1777, Cavendish discovered that air exhaled by mammals is converted to "fixed air" ([[carbon dioxide]]), not "phlogisticated air" as predicted by Joseph Priestley.<ref name=Gil/> Also, by dissolving [[alkali]]s in acids, Cavendish produced carbon dioxide, which he collected, along with other gases, in bottles inverted over water or [[mercury (element)|mercury]]. He then measured their solubility in water and their [[specific gravity]], and noted their [[combustibility]]. He concluded in his 1778 paper "General Considerations on Acids" that respirable air constitutes acidity.<ref name=Gil/> Cavendish was awarded the Royal Society's [[Copley Medal]] for this paper. Gas chemistry was of increasing importance in the latter half of the 18th century, and became crucial for Frenchman [[Antoine-Laurent Lavoisier]]'s reform of chemistry, generally known as the [[chemical revolution]].

In 1783, Cavendish published a paper on eudiometry (the measurement of the goodness of gases for breathing). He described a new [[eudiometer]] of his invention, with which he achieved the best results to date, using what in other hands had been the inexact method of measuring gases by weighing them. Then, after a repetition of a 1781 experiment performed by Priestley, Cavendish published a paper on the production of pure water by burning hydrogen in "[[dephlogisticated]] air" (air in the process of combustion, now known to be [[oxygen]]).<ref name=Gil>{{cite book |last=Gillispie |first=Charles Coulston |author-link1=Charles Coulston Gillispie |title=The Edge of Objectivity: An Essay in the History of Scientific Ideas |year=1960 |publisher=Princeton University Press |isbn=0-691-02350-6 |pages=[https://archive.org/details/edgeofobjectivit00char/page/225 225–28] |url=https://archive.org/details/edgeofobjectivit00char/page/225 }}</ref><ref>[https://books.google.com/books?id=IPMHAAAAIAAJ&dq=history+of+chemistry&pg=PA1 A History of Chemistry] by [[Forris Jewett Moore|F. J. Moore]], New York: McGraw-Hill (1918) pp. 34–36</ref><ref name="Miller2004">{{cite book |author=David Philip Miller |title=Discovering water: James Watt, Henry Cavendish, and the nineteenth century 'Water Controversy' |url=https://books.google.com/books?id=orL4QRlvBfYC&pg=PA42 |year=2004 |publisher=Ashgate Publishing |isbn=978-0-7546-3177-4 |page=42|author-link=David Philip Miller }} Quoting from the monograph by [[James Riddick Partington]], ''The Composition of Water'', G. Bell and Sons, 1928, {{OCLC|3590255}}.</ref>
Cavendish concluded that rather than being synthesised, the burning of hydrogen caused water to be [[Condensation|condensed]] from the air. Some physicists interpreted hydrogen as pure [[phlogiston]]. Cavendish reported his findings to Priestley no later than March 1783, but did not publish them until the following year. The Scottish inventor [[James Watt]] published a paper on the composition of water in 1783; controversy about who made the discovery first ensued.<ref name=Gil/>

In 1785, Cavendish investigated the composition of common (i.e. atmospheric) [[Atmosphere of Earth|air]], obtaining impressively accurate results. He conducted experiments in which hydrogen and ordinary air were combined in known ratios and then exploded with a spark of electricity. Furthermore, he also described an experiment in which he was able to remove, in modern terminology, both the oxygen and nitrogen gases from a sample of atmospheric air until only a small bubble of unreacted gas was left in the original sample. Using his observations, Cavendish observed that, when he had determined the amounts of phlogisticated air ([[nitrogen]]) and dephlogisticated air (oxygen), there remained a volume of gas amounting to 1/120 of the original volume of nitrogen.<ref>See page 382 of {{cite journal |author=Cavendish, Henry |title=Experiments on Air |journal=Philosophical Transactions of the Royal Society |year=1785 |volume=75 |pages=372–384 |bibcode=1785RSPT...75..372C |doi=10.1098/rstl.1785.0023|url=https://zenodo.org/record/1432276 |doi-access=free }} The same passage is on page 50 of the [https://books.google.com/books?id=-uEKAAAAIAAJ&q=Henry+Cavendish+air Alembic Club reprint] of the article.</ref><ref>A. Truman Schwartz, ''Chemistry: Imagination and Implication'', [https://books.google.com/books?id=oV3I0hNq6xIC&pg=PA96 p.96], Elsevier, 2012 {{ISBN|0323145116}}.</ref>
By careful measurements he was led to conclude that "common air consists of one part of dephlogisticated air [oxygen], mixed with four of phlogisticated [nitrogen]".<ref>See page 376 of {{cite journal |author=Cavendish, Henry |title=Experiments on Air |journal=Philosophical Transactions of the Royal Society |year=1785 |volume=75 |pages=372–384 |bibcode=1785RSPT...75..372C |doi=10.1098/rstl.1785.0023|url=https://zenodo.org/record/1432276 |doi-access=free }} The same passage is on page 44 of the [https://books.google.com/books?id=-uEKAAAAIAAJ&q=Henry+Cavendish+air Alembic Club reprint] of the article.</ref><ref>See also pages 261–262 of [https://books.google.com/books?id=EUoLAAAAIAAJ&pg=PA261 Cavendish] by Jungnickel and McCormmach (1996)</ref>

In the 1890s (around 100 years later) two British physicists, [[William Ramsay]] and [[John Strutt, 3rd Baron Rayleigh|Lord Rayleigh]], realised that their newly discovered [[Noble gas|inert gas]], [[argon]], was responsible for Cavendish's problematic residue; he had not made an error. What he had done was perform rigorous quantitative experiments, using standardised instruments and methods, aimed at reproducible results; taken the mean of the result of several experiments; and identified and allowed for sources of error. The balance that he used, made by a craftsman named Harrison, was the first of the precision balances of the 18th century, and as accurate as Lavoisier's (which has been estimated to measure one part in 400,000). Cavendish worked with his instrument makers, generally improving existing instruments rather than inventing wholly new ones.

Cavendish, as indicated above, used the language of the old phlogiston theory in chemistry. In 1787, he became one of the earliest outside France to convert to the new antiphlogistic theory of Lavoisier, though he remained sceptical about the nomenclature of the new theory.{{citation needed|date=August 2015}} He also objected to Lavoisier's identification of heat as having a material or elementary basis. Working within the framework of Newtonian mechanism, Cavendish had tackled the problem of the nature of heat in the 1760s, explaining heat as the result of the motion of matter.

In 1783, he published a paper on the temperature at which [[Mercury (element)|mercury]] freezes and in that paper made use of the idea of [[latent heat]], although he did not use the term because he believed that it implied acceptance of a material theory of heat. He made his objections explicit in his 1784 paper on air. He went on to develop a general theory of heat, and the manuscript of that theory has been persuasively dated to the late 1780s. His theory was at once mathematical and mechanical: it contained the principle of the conservation of heat (later understood as an instance of [[conservation of energy]]) and even included the concept (although not the label) of the [[mechanical equivalent of heat]].