Editing Conservation of mass (section)

===Discoveries in chemistry===
By the 18th century the principle of conservation of mass during chemical reactions was widely used and was an important assumption during experiments, even before a definition was widely established,<ref>{{Cite journal|last=Whitaker|first=Robert D.|date=1975-10-01|title=An historical note on the conservation of mass|journal=Journal of Chemical Education|volume=52|issue=10|pages=658|doi=10.1021/ed052p658|issn=0021-9584|bibcode=1975JChEd..52..658W}}</ref> though an expression of the law can be dated back to Hero of Alexandria’s time,<ref>{{cite book | url=https://books.google.com/books?id=dUQtlF6pDdQC&dq=Conservation+of+mass+dioptra&pg=PA2 | title=Rheology: An Historical Perspective | isbn=9780444829467 | last1=Tanner | first1=R. I. | last2=Walters | first2=K. | year=1998 | publisher=Elsevier }}</ref> as can be seen in the works of [[Joseph Black]], [[Henry Cavendish]], and [[Jean Rey (physician)|Jean Rey]].<ref>Robert D. Whitaker, "[https://eric.ed.gov/?id=EJ128341 An Historical Note on the Conservation of Mass]", ''[[Journal of Chemical Education]]'', 52, 10, 658-659, Oct 75</ref> One of the first to outline the principle was [[Mikhail Lomonosov]] in 1756. He may have demonstrated it by experiments and certainly had discussed the principle in 1748 in correspondence with [[Leonhard Euler]],<ref>{{cite book |last1=Pismen |first1=Len |title=The Swings of Science: From Complexity to Simplicity and Back |date=2018 |publisher=Springer |isbn=978-3-319-99777-3 |page=41 |url=https://books.google.com/books?id=Rvx9DwAAQBAJ&pg=PA41}}</ref> though his claim on the subject is sometimes challenged.<ref>{{Cite journal | volume = 10 | issue = 3 | pages = 119–127 | last = Pomper | first = Philip | title = Lomonosov and the Discovery of the Law of the Conservation of Matter in Chemical Transformations | journal = Ambix | date = October 1962| doi = 10.1179/amb.1962.10.3.119 }}</ref><ref>{{Cite book | publisher = [[Harvard University Press]] | last = Lomonosov | first = Mikhail Vasil’evich | others = [[Henry M. Leicester]] (trans.) | title = Mikhail Vasil'evich Lomonosov on the Corpuscular Theory | location = Cambridge, Mass. | year = 1970 | at = Introduction, p.&nbsp;25}}</ref> According to the Soviet physicist Yakov Dorfman:<blockquote>The universal law was formulated by Lomonosov on the basis of general philosophical materialistic considerations, it was never questioned or tested by him, but on the contrary, served him as a solid starting position in all research throughout his life. <ref>{{Cite book|last=Дорфман|first=Яков|title=Закон сохранения массы при химических реакциях и физические воззрения Ломоносова // Ломоносов М.В. Сборник статей и материалов, T.5|publisher=М.-Л.: Издательство АН СССР|year=1961|url=http://gidropraktikum.narod.ru/Lomonosov-Dorfman.djvu|pages=193}}</ref> </blockquote>A more refined series of experiments were later carried out by [[Antoine Lavoisier]] who expressed his conclusion in 1773 and popularized the principle of conservation of mass.<ref name=":0">{{Cite web |last1=Agnew |first1=Henry |last2=Alviar-Agnew |first2=Marisa |title=3.7 Conservation of Mass - There is No New Matter |url=https://chem.libretexts.org/Courses/Arkansas_Northeastern_College/CH14133%3A_Chemistry_for_General_Education/03%3A_Matter_and_Energy/3.07%3A_Conservation_of_Mass_-_There_is_No_New_Matter#:~:text=If%20you%20witness%20a%20300%20kg%20tree%20burn%20to%20the%20ground,%20there%20are%20only%20ashes%20left%20after%20the%20burn,%20and%20all%20of%20them%20together%20weigh%2010%20kg.%20It%20may%20make%20you%20wonder%20where%20the%20other%20290%20kg%20went.%20The%20missing%20290%20kg%20was%20released%20into%20the%20atmosphere%20as%20smoke,%20so%20the%20only%20thing%20left%20that%20you%20can%20see%20is%20the%2010%20kg%20of%20ash. |access-date=10 January 2024 |website=LibreTexts™ Chemistry|date=7 January 2020 }}</ref> The demonstrations of the principle disproved the then popular [[phlogiston theory]] that said that mass could be gained or lost in [[combustion]] and heat processes.

The conservation of mass was obscure for millennia because of the buoyancy effect of the Earth's atmosphere on the weight of gases. For example, a piece of wood weighs less after burning;<ref name=":0" /> this seemed to suggest that some of its mass disappears, or is transformed or lost. Careful experiments were performed in which chemical reactions such as rusting were allowed to take place in sealed glass ampoules; it was found that the chemical reaction did not change the weight of the sealed container and its contents. Weighing of gases using scales was not possible until the invention of the [[vacuum pump]] in the 17th century.

Once understood, the conservation of mass was of great importance in progressing from [[alchemy]] to modern chemistry. Once early chemists realized that chemical substances never disappeared but were only transformed into other substances with the same weight, these scientists could for the first time embark on quantitative studies of the transformations of substances. The idea of mass conservation plus a surmise that certain "elemental substances" also could not be transformed into others by chemical reactions, in turn led to an understanding of [[chemical element]]s, as well as the idea that all chemical processes and transformations (such as burning and metabolic reactions) are reactions between invariant amounts or weights of these chemical elements.

Following the pioneering work of Lavoisier, the exhaustive experiments of [[Jean Stas]] supported the consistency of this law in chemical reactions,<ref>Matthew Moncrieff Pattison Muir, [https://books.google.com/books?id=EwZZAAAAYAAJ ''The Elements of Chemistry''] (1904)</ref> even though they were carried out with other intentions. His research<ref>''Nouv. Recherches sur les lois des proportions chimiques'' (1865) 152, 171, 189</ref><ref>"Conservation of Mass in Chemical Changes"[https://books.google.com/books?id=bhQ3AAAAYAAJ ''Journal - Chemical Society, London'', Vol.64], Part 2 Chemical Society (Great Britain)</ref> indicated that in certain reactions the loss or gain could not have been more than 2 to 4 parts in 100,000.<ref>William Edwards Henderson, [https://archive.org/details/acourseingenera00hendgoog ''A Course in General Chemistry''] (1921)</ref> The difference in the accuracy aimed at and attained by Lavoisier on the one hand, and by [[Edward W. Morley]] and Stas on the other, is enormous.<ref>[[Ida Freund]], [https://archive.org/details/studychemicalco01freugoog ''The study of Chemical Composition'': an account of its method and historical development, with illustrative quotations] (1904)</ref>