Editing Wilhelm Ostwald (section)

== Scientific contributions ==
=== Nitric acid process ===
Ostwald invented a process for the inexpensive manufacture of [[nitric acid]] by [[oxidation]] of [[ammonia]]. He was awarded patents for this process.<ref>W. Ostwald, "Process for Manufacturing Nitric Acid, [https://patentimages.storage.googleapis.com/93/97/63/d4b81eb9a5c399/US858904.pdf US858904], 2 July 1907.</ref> Ostwald's patent made use of a [[catalyst]] and described conditions under which the yield of nitric acid was near the [[Theoretical yield|theoretical limit]]. Aspects of the basic process had also been patented some 64 years earlier by [[Charles Frédéric Kuhlmann|Kuhlmann]].<ref>Note:

* Frédéric Kuhlmann, "Pour la fabrication de l'acide nitrique et des nitrates," French patent no. 11,331 (filed:  October 1838; issued:  22 December 1838).  Supplemental patent issued:  7 June 1839.  See:  ''Description des machines et procédés consignés dans les brevets d'invention,'' ... [Description of machines and methods recorded in the patents of invention, ... ] (Paris, France:  Madame Veuve Bouchard-Huzard, 1854), '''82''' :  [https://books.google.com/books?id=BppbAAAAcAAJ&pg=PA160 160.]
* Fréd. Kuhlmann (1838) [http://gallica.bnf.fr/ark:/12148/bpt6k29662/f1107.image.langEN "Note sur plusieurs réactions nouvelles déterminées par l'éponge de platine, et considérations sur les services que cette substance est appelée à rendre à la science"] (Note on several new reactions caused by platinum sponge, and reflections on the services that this substance is called to render to science), ''Comptes rendus'', '''7''' :  1107–1110.  From page 1109:  ''"1°. L'ammoniaque mêlée d'air en passant à une température de 300° environ sur de l'éponge de platine, est décomposée, et l'azote qu'il renferme est complétement transformé en acide nitrique, aux dépens de l'oxigène de l'air."'' (1. Ammonia mixed with air, upon passing at a temperature of about 300° over platinum sponge, is decomposed and the nitrogen that it contains is completely transformed into nitric acid, at the expense of the oxygen of the air.)
* John Graham Smith (1988)  "Frédéric Kuhlmann:  Pioneer of platinum as an industrial catalyst," ''Platinum Metals Review'', '''32''' (2) :  84–90.</ref> Kuhlmann's process did not become industrially significant, likely due to the lack of an inexpensive source of ammonia.  Shortly after Ostwald's finding, inexpensive ammonia became available as a result of [[Fritz Haber|Haber]] and [[Carl Bosch|Bosch's]] invention of a process for [[nitrogen fixation|nitrogen fixing]] [[Haber process|process]] (completed by 1911 or 1913) for ammonia synthesis. The combination of these two breakthroughs soon led to more economical and larger-scale production of [[fertilizer]]s and [[explosives]], of which Germany was in short supply during [[World War I]].<ref name="Haber process">{{cite web |last1=Louchheim |first1=Justin |title=Fertilizer History: The Haber-Bosch Process |url=https://www.tfi.org/the-feed/fertilizer-history-haber-bosch-process#:~:text=The%20solution%20soon%20came%20from,component%20in%20nitrogen%2Dbased%20fertilizers. |website=tfi.org |date=19 November 2014 |publisher=The Fertilizer Institute |access-date=16 June 2020}}</ref><ref name="Explosives">{{cite web |last1=Sutton |first1=Mike |title=Chemists at War |url=https://www.chemistryworld.com/features/chemists-at-war/7568.article#/ |website=chemistryworld.org |publisher=Royal Society of Chemistry |access-date=16 June 2020}}</ref> The process is often referred to as the [[Ostwald Process]].<ref name="Explosives" /> The process remains in widespread use in contemporary times for manufacture of nitric acid.<ref name="Catalysis" />
[[File:Van 't Hoff und Ostwald 01.jpg|left|thumb|300px|[[Jacobus Henricus van 't Hoff|Jacobus van 't Hoff]] (left) and Wilhelm Ostwald]]

=== Ostwald's dilution law===
Ostwald also conducted significant research on dilution theory leading to his conceptualization of the [[law of dilution]] which at times is referred to as "Ostwald's Dilution Law". This theory holds that the behavior of a [[weak electrolyte]] follows the [[Law of mass action|principles of mass action]], being extensively dissociated at infinite dilution. This characteristic of weak electrolytes can be observed experimentally, such as by [[Electrochemistry|electrochemical determinations]].<ref name="Dilution Law">{{cite web |title=Ostwald's Dilution Law |url=https://www.sciencehq.com/chemistry/ostwalds-dilution-law.html |website=sciencehq.com |publisher=Rod Pierce DipCE BEng |access-date=11 June 2021 |url-status=dead |archive-url=https://web.archive.org/web/20210214005845/http://www.sciencehq.com/chemistry/ostwalds-dilution-law.html |archive-date=14 February 2021}}</ref>

===Catalysis===
Through his research on chemical reaction rates and velocities and his studies of acids and bases, Ostwald found that the concentration of acid or the concentration of base in a solution of certain chemical reactants can have a strong influence of the rate of chemical processes. He realized that this is manifestation of the concept of chemical catalysis first articulated by [[Berzelius]]. Ostwald articulated the idea that a catalyst is a substance that accelerates the rate of a chemical reaction without being a part of either the reactants or the products. Ostwald's advances in the understanding of chemical catalysis were widely applicable in biological processes such as enzymatic catalysis and also in many industrial processes. A catalyst is used in the nitric acid process that Ostwald invented.<ref name="Catalysis">{{cite journal |last1=Van Houten |first1=J. |title=A Century of Chemical Dynamics Traced through the Nobel Prizes |journal=Journal of Chemical Education |date=2002 |volume=79 |issue=2 |page=146 |doi=10.1021/ed079p146 }}</ref>

=== Crystallization ===
Ostwald studied the [[crystallization]] behavior of solids, especially those solids that are capable of crystallizing in different forms, in the phenomenon known as [[Polymorphism (materials science)|polymorphism]]. He discovered that solids do not necessarily crystallize in their most thermodynamically stable form but instead sometimes crystallize preferentially in other forms dependent on the relative rates of crystallization of each polymorphic form. Ostwald found that the relative rates were dependent on the surface tension between the solid polymorph and the liquid form. Many common materials exhibit this type of behavior, including [[minerals]] and various [[organic compounds]]. This finding came to be known as [[Ostwald's rule]].<ref name="Ostwald Rule">{{cite thesis |last1=Wang |first1=Tingting |title=Breakdown of the Ostwald step rule – The precipitation of calcite and dolomite from seawater at 25 and 40 °C |date=2013 |url=https://escholarship.mcgill.ca/concern/theses/sn00b224t }}</ref>

Ostwald realized that solid or liquid solutions can continue to evolve over time. While the a non-thermodynamically preferred polymorph may crystallize first, more thermodynamically stable forms can continue to develop as the solution ages. Often this results in large crystals forming, since they are more thermodynamically stable than are large numbers of small crystals. This phenomenon came to be known as Ostwald Ripening and is observed in many situations. An everyday example is the gritty texture that ice cream develops as it ages. On a [[geologic timescale]], many [[minerals]] exhibit Ostwald Ripening as their crystal forms evolve as the mineral ages.<ref name="Clay Minerals">{{cite journal |last1=Jahren |first1=J.S. |title=Evidence of Ostwald Ripening Related Recrystallization of Diagenetic Chlorites From Reservoir Rocks Offshore Norway |journal=Clay Minerals |date=1991 |volume=26 |issue=2 |page=169 |doi=10.1180/claymin.1991.026.2.02 |bibcode=1991ClMin..26..169J |citeseerx=10.1.1.604.4580 |s2cid=97430142 }}</ref>

Related to solubility and crystallization was Ostwald's finding that dissolution of a solid depends on the size of the crystal. When the crystals are small, typically less than a [[micron]], the solubility of the solid in the solution phase is increased. Ostwald quantified this effect mathematically in a relationship that became known as the [[Ostwald-Freundlich equation]]. Ostwald first published his finding in 1900, and his mathematical equation was refined by German chemist [[Herbert Freundlich]] in 1909. This mathematical relationship also applies to the partial pressure of substance in the system. The Ostwald-Freundlich equation takes into account the surface tension of the particle in the system, in addition to curvature and temperature. The size dependence of solubility is sometimes utilized in the formulation of [[pharmaceuticals]] that have low solubility so as to enhance their uptake by the patient. The size dependence also has a role in Ostwald Ripening.<ref name="Freundlich eqn">{{cite journal |last1=Eslami |first1=Fatemeh |last2=Elliott |first2=Janet A. W. |title=Role of Precipitating Solute Curvature on Microdrops and Nanodrops during Concentrating Processes: The Nonideal Ostwald–Freundlich Equation |journal=Journal of Physical Chemistry B |date=2014 |volume=118 |issue=50 |pages=14675–86 |doi=10.1021/jp5063786 |pmid=25399753 |doi-access=free }}</ref>

[[File:Liesegang rings Saginaw Hill AZ.jpeg|left|thumb|Liesegang rings at Saginaw Hill, Arizona, USA]]
Collaborating with German chemist [[Raphael E. Liesegang]], Ostwald recognized that substances can crystallize in a periodic fashion wherein the crystallization behavior follows a spatial or temporal pattern. In certain circumstances, the result of this periodic crystallization behavior is easily visually observed, for example, in various [[geologic formations]]. Liesegang had previously investigated this phenomenon in specific laboratory experiments, showing his results to Ostwald. Ostwald then developed a mathematical model for the phenomenon that served to explain the observations and realized how widespread is the periodic crystallization behavior. These observations came to be known as [[Liesegang rings]].<ref name="Liesegang">{{cite web |title=A Short History of "Liesegang Rings" |url=https://www.insilico.hu/liesegang/history/history.html |website=insilico.hu |publisher=In Silico, Ltd. |access-date=7 August 2020}}</ref>

===Atomic theory===
[[File:Ostwald viscometer.jpg|thumb|Ostwald viscometer]]
Ostwald introduced the word [[Mole (unit)|mole]] into the [[lexicon]] of chemistry around 1900.  He defined one mole as the [[molecular weight]] of a substance in units of mass grams.  The concept was linked to the [[ideal gas]], according to Ostwald.  Ironically, Ostwald's development of the mole concept was directly related to his theory of [[energeticism]], in philosophical opposition to [[atomic theory]], against which he (along with [[Ernst Mach]]) was one of the last holdouts.  He explained in a conversation with [[Arnold Sommerfeld]] that he was convinced by [[Jean Perrin]]'s experiments on [[Brownian Motion|Brownian motion]].<ref>Nye, M., 1972, Molecular Reality: A Perspective on the Scientific Work of Jean Perrin, London: MacDonald.</ref><ref name="Gorin">{{cite journal |last1=Gorin |first1=George |title=Mole and Chemical Amount: A Discussion of the Fundamental Measurements of Chemistry |journal=Journal of Chemical Education |date=February 1994 |volume=71 |issue=2 |pages=114 |doi=10.1021/ed071p114|bibcode=1994JChEd..71..114G }}</ref>

In 1906 Ostwald was elected a member of the [[Commission on Isotopic Abundances and Atomic Weights|International Committee on Atomic Weights]]. As a consequence of [[World War I]], this membership ended in 1917 and was not resumed after the war.  The 1917 Annual Report of the committee ended with the unusual note: "Because of the European war the Committee has had much difficulty in the way of correspondence. The German member, Professor Ostwald, has not been heard from in connection with this report. Possibly the censorship of letters, either in Germany or en route, has led to a miscarriage".<ref name="Clark">{{cite journal | last=Clark | first=F.W. | year=1916 | title=Annual report of the international committee on atomic weights | journal=[[J. Am. Chem. Soc.]] | volume=38 | issue=11 | pages=2219–2221 | url=https://zenodo.org/record/1429080| doi=10.1021/ja02268a001}}</ref>

===Scientific measurements===
As part of Ostwald's investigations in to [[chemical equilibria]], [[chemical affinity]], and [[Acid-base balance|acid-base interactions]], he recognized that many established [[analytical methods]] disturb the chemical systems under investigation. He therefore turned to physical measurements as surrogate methods to understand these important basic phenomena. One such physical measurement is the measurement of the [[viscosity]], or resistance to flow, of a liquid. Ostwald invented a device for this purpose consisting of bulbs that act as reservoirs for a liquid with a capillary, or thin tube, in between the reservoirs.  The time that it takes for the liquid to flow through the capillary from one reservoir to the other is an indication of the viscosity of the liquid.  Using a reference solution, the viscosity of the liquid can be quantified. Ostwald typically used this device to study the behavior of [[solutes]] in water solutions. These devices came to be known as [[Ostwald viscometer]]s and are in widespread use in contemporary times for research and [[quality control]] purposes.<ref name="Sella">{{cite web |last1=Sella |first1=Andrea |title=Classic Kit: Ostwald's viscometer |url=https://www.chemistryworld.com/opinion/classic-kit-ostwalds-viscometer/3004929.article |website=chemistryworld.com |publisher=Royal Society of Chemistry |access-date=5 August 2020}}</ref>

Ostwald designed a pipette that could be used to transfer and measure liquids, especially [[serous fluid]]s. This design was later improved by [[Otto Folin]]. This type of pipette has a bulb at the lower end as a particular design feature. It became known as the [[Pipette#Ostwald–Folin pipette|Ostwald-Folin pipette]] and is widely used in contemporary times.<ref name="Pipette">{{cite web |title=Serological pipets |url=https://www.eppendorf.com/product-media/doc/en/308915/Liquid-Handling_Poster_Serological-Pipets.pdf |website=eppendorf.com |publisher=Eppendorf AG |access-date=11 August 2020}}</ref>

===Color science===
Following his 1906 retirement from academia, Ostwald became interested in the systematization of [[color]]s, which could be useful both scientifically and in the arts. He published ''The Color Primer'' and also ''The Color Atlas'' during the period of 1916–8. These publications established relationships between the various visual colors.<ref name="Ostwald Park" /> 
<gallery>
File:Die farbenfibel by Wilhelm Ostwald 1921 page 33.tif | ''The Color Primer'', <br/>page 33
File:Die farbenfibel by Wilhelm Ostwald 1921 page 44.tif | ''The Color Primer'', <br/>page 44
File:Die farbenfibel by Wilhelm Ostwald 1921 page 50.tif | ''The Color Primer'', <br/>page 50
File:Die farbenfibel by Wilhelm Ostwald 1921 page 56.tif | ''The Color Primer'', <br/>page 56
</gallery>

Ostwald represented these as a three dimensional representation of [[Ostwald color system|color space]] that is a [[Topological space|topological solid]] consisting of two cones.  One apex of the cone is pure white while the other is pure black. The eight primary colors are represented along the circumference or curved surfaces of the two cones. In this representation, each color is a mixture of white, black, and the eight primary colors. In this way, there are three [[degrees of freedom]] that represent each color.<ref name="Color science"/>

[[File:Ostwald Color.jpg|thumb|Ostwald color solid]]
This representation of colors was an important early step toward their systematization, replacing color perception by the human eye with an objective system.<ref name="Color science">{{cite web |last1=Nichols |first1=Kara |title=The Chemistry of Color |url=https://www.cooperhewitt.org/2018/05/09/the-chemistry-of-color/ |website=cooperhewitt.org |date=9 May 2018 |publisher=[[Smithsonian Design Museum]] |access-date=9 August 2020}}</ref> Much of Ostwald's work on systematization of color was done in collaboration with [[Deutscher Werkbund]], which was an association of painters and architects.<ref name="Kim" />