Editing Creosote (section)

===Coal-tar creosote===
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|+ style="text-align:left; padding-left:5px; padding-bottom:10px; font-size:13.5px;" | Composition of a typical coal-tar creosote<ref name=melber11/><ref name=speight456/>
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! class="unsortable" style="text-align:left; padding-right:20px;" | [[Aromatic hydrocarbons]]
<span style="font-weight:normal>Polycyclic aromatic hydrocarbons ([[Polycyclic aromatic hydrocarbon|PAHs]]), alkylated PAHs, [[benzene]]s, [[toluene]]s, [[ethylbenzene]]s, and [[xylene]]s ([[BTEX]])</span>
| 75.0–90.0%
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! class="unsortable" style="text-align:left; padding-right:20px;" | [[Tar acids]] / [[phenol]]ics
<span style="font-weight:normal>Phenols, cresols, xylenols, and naphthols</span>
| 5.0–17.0%
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! class="unsortable" style="text-align:left; padding-right:20px;" | [[Tar bases]] / [[nitrogen]]-containing heterocycles
<span style="font-weight:normal>Pyridines, quinolines, benzoquinolines, acridines, indolines, and carbazoles</span>
| 3.0–8.0%
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! class="unsortable" style="text-align:left; padding-right:20px;" | [[Sulfur]]-containing [[heterocyclic compound|heterocycles]]
<span style="font-weight:normal>[[Benzothiophene]]s</span>
| 1.0–3.0%
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! class="unsortable" style="text-align:left; padding-right:20px;" | [[Oxygen]]-containing heterocycles
<span style="font-weight:normal>Dibenzofurans</span>
| 1.0–3.0%
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! class="unsortable" style="text-align:left; padding-right:20px;" | [[Aromatic amine]]s
<span style="font-weight:normal>Aniline, aminonaphthalenes, [[diphenylamine]]s, aminofluorenes, and aminophenanthrenes, cyano-PAHs, benz acridines</span>
|0.1–1.0%
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Coal-tar creosote is greenish-brown liquid, with different degrees of darkness, viscosity, and fluorescence depending on how it is made. When freshly made, the creosote is a yellow oil with a greenish cast and highly fluorescent, and the fluorescence is increased by exposure to air and light. After settling, the oil is dark green by reflected light and dark red by transmitted light.<ref name=allen366/> To the naked eye, it generally appears brown. The creosote (often called "creosote oil") consists almost wholly of [[aromatic hydrocarbon]]s, with some amount of bases and acids and other neutral oils. The flash point is 70&ndash;75&nbsp;°C and burning point is 90&ndash;100&nbsp;°C,<ref name=bateman50/> and when burned it releases a greenish smoke.<ref name=nickels615/> The smell largely depends on the naphtha content in the creosote. If there is a high amount, it will have a naphtha-like smell, otherwise it will smell more of tar.

In the process of coal-tar distillation, the distillate is collected into four fractions; the "light oil", which remains lighter than water, the "middle oil" which passes over when the light oil is removed; the "heavy oil", which sinks; and the "[[anthracene oil]]", which when cold is mostly solid and greasy, of a buttery consistence. Creosote refers to the portion of coal tar which distills as "heavy oil", typically between 230 and 270&nbsp;°C, also called "dead oil"; it sinks into water but still is fairly liquid. Carbolic acid is produced in the second fraction of distillation and is often distilled into what is referred to as "[[carbolic oil]]".<ref name=philips255/><ref name=martin416/><ref name=nelson204/><ref name=noller185/>
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[[File:Derivation of coal-tar creosote.svg|frameless|upright=2]]
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Commercial creosote contains substances from six groups.<ref name=melber11/> The two groups occur in the greatest amounts and are the products of the distillation process—the "[[tar acids]]", which distill below 205&nbsp;°C and consist mainly of phenols, cresols, and xylenols, including carbolic acid—and [[aromatic hydrocarbon]]s, which divide into [[naphthalene]]s, which distill approximately between 205 and 255&nbsp;°C, and constituents of an [[anthracene]] nature, which distill above 255&nbsp;°C.<ref name=ec531/> The quantity of each varies based on the quality of tar and temperatures used, but generally, the tar acids won't exceed 5%, the naphthalenes make up 15 to 50%, and the anthracenes make up 45% to 70%.<ref name=ec531/> The hydrocarbons are mainly aromatic; derivatives of benzene and related cyclic compounds such as [[naphthalene]], [[anthracene]], [[phenanthrene]], [[acenaphthene]], and [[fluorene]]. Creosotes from vertical-retort and low temperature tars contain, in addition, some paraffinic and olefinic hydrocarbons. The tar-acid content also depends on the source of the tar—it may be less than 3% in creosote from coke-oven tar and as high as 32% in creosote from vertical retort tar.<ref name=greenhow58/> All of these have antiseptic properties. The tar acids are the strongest antiseptics but have the highest degree of solubility in water and are the most volatile; so, like with wood-tar creosote, phenols are not the most valued component, as by themselves they would lend to being poor preservatives.<ref name=arbba287/> In addition, creosote contains several products naturally occurring in coal—nitrogen-containing heterocycles, such as acridines, carbazoles, and quinolines, referred to as the "[[tar bases]]" and generally make up about 3% of the creosote—sulfur-containing heterocycles, generally [[benzothiophene]]s<ref name=orr39/>—and oxygen-containing heterocycles, dibenzofurans.<ref name=speight77/> Lastly, creosote contains a small number of [[aromatic amine]]s produced by the other substances during the distillation process and likely resulting from a combination of [[thermolysis]] and [[hydrogenation]].<ref name=orr255/><ref name=bateman47/> The tar bases are often extracted by washing the creosote with aqueous mineral acid,<ref name=greenhow58/> although they're also suggested to have antiseptic ability similar to the tar acids.

Commercially used creosote is often treated to extract the carbolic acid, naphthalene, or anthracene content. The carbolic acid or naphthalene is generally extracted to be used in other commercial products.<ref name=mushrush115/> In the early 20th century, American-produced creosote oils typically had low amounts of anthracene and high amounts of naphthalene, because when forcing the distillate at a temperature that produces anthracene the soft pitch will be ruined and only the hard pitch will remain; this ruined it for [[Bituminous waterproofing|use in roofing purposes]] (which was common before widespread availability of cheap oil bitumen) and only left a product which wasn't commercially useful.<ref name=bateman47/>

====Historical uses====

=====Industrial=====
The use of coal-tar creosote on a commercial scale began in 1838, when a patent covering the use of creosote oil to treat timber was taken out by inventor [[John Bethell (inventor)|John Bethell]]. The "Bethell process"—or as it later became known, the [[full-cell process (wood processing)|full-cell process]]—involves placing wood to be treated in a sealed chamber and applying a vacuum to remove air and moisture from wood "cells". The wood is then pressure-treated to imbue it with creosote or other preservative chemicals, after which vacuum is reapplied to separate the excess treatment chemicals from the timber. Alongside the zinc chloride-based [[Sir William Burnett|"Burnett process"]], use of creosoted wood prepared by the Bethell process became a principal way of preserving railway timbers (most notably railway sleepers) to increase the lifespan of the timbers, and avoiding having to regularly replace them.<ref name=angier408/>

Besides treating wood, it was also used for lighting and fuel. In the beginning, it was only used for lighting needed in harbour and outdoor work, where the smoke that was produced from burning it was of little inconvenience. By 1879, lamps had been created that ensured a more complete combustion by using compressed air, removing the drawback of the smoke. Creosote was also processed into gas and used for lighting that way. As a fuel, it was used to power ships at sea and blast furnaces for different industrial needs, once it was discovered to be more efficient than unrefined coal or wood. It was also used industrially for the softening of hard pitch, and burned to produce [[lamp black]]. By 1890, the production of creosote in the [[United Kingdom]] totaled approximately 29,900,000 gallons per year.<ref name=nickels615/>

In 1854, [[Alexander McDougall]] and [[Robert Angus Smith]] developed and patented a product called [[McDougall's Powder]] as a sewer deodorant; it mainly consisted of [[phenol|carbolic acid]] derived from creosote. McDougall, in 1864, experimented with his solution to remove [[entozoa]] parasites from cattle pasturing on a sewage farm.<ref name=brock91/> This later led to widespread use of creosote as a cattle wash and [[sheep dip]]. External parasites would be killed in a creosote diluted dip, and drenching tubes would be used to administer doses to the animals' stomachs to kill internal parasites.<ref name=salmon7/>

[[File:Wood Pavers (36011657806).jpg|thumb|Wooden street pavers in Chicago]]
Creosoted wood blocks were a common road-paving material in the late 19th and early 20th centuries, but ultimately fell out of favor because they did not generally hold up well enough over time.<ref>{{cite web |title=Ames Street Paving |publisher=Ames History Museum |location=Ames, Iowa |url=https://ameshistory.org/content/ames-street-paving |access-date=2023-01-25}}</ref><ref>{{cite journal |title=(untitled advertisement) |journal=The Town Crier |volume=10 |issue=32 |page=7 |location=Seattle |date=1915-08-07 |url=https://commons.wikimedia.org/wiki/File:The_Town_Crier,_v.10,_no.32,_Aug._7,_1915_-_DPLA_-_9f439e1283fe9793c210a74b8e85dc66_(page_7).jpg |access-date=2023-01-25}}</ref><ref>{{cite web |last1=Reed |first1=Ryan J. |title=The Creosoted Wood Block: One Step in the Evolution of St. Louis Paving |publisher=Landmarks Association of St. Louis, Inc. |location=St. Louis, Missouri |url=https://www.landmarks-stl.org/news/the_creosoted_wood_block_one_step_in_the_evolution_of_st_louis-paving/ |access-date=2023-01-25}}</ref><ref>{{cite web |title=Historic Wood Paver from Galveston's Market Street |publisher=Rosenberg Library Museum |location=Galveston, Texas |url=https://www.rosenberg-library-museum.org/treasures/historic-wood-paver-from-galvestons-market-street |access-date=2023-01-05}}</ref>

Two later methods for creosoting wood were introduced after the turn of the century, referred to as [[empty-cell process]]es, because they involve compressing the air inside the wood so that the preservative can only coat the inner cell walls rather than saturating the interior cell voids. This is a less effective, though usually satisfactory, method of treating the wood, but is used because it requires less of the creosoting material. The first method, the "Rüping process" was patented in 1902, and the second, the "Lowry process" was patented in 1906. Later in 1906, the "Allardyce process" and "Card process" were patented to treat wood with a combination of both creosote and zinc chloride.<ref name=angier408/> In 1912, it was estimated that a total of 150,000,000 gallons were produced in the US per year.

=====Medical=====
Coal-tar creosote, despite its toxicity, was used as a stimulant and [[escharotic]], as a [[corrosive substance|caustic]] agent used to treat ulcers and malignancies, cauterize wounds, and prevent infection and decay. It was particularly used in dentistry to destroy tissues and arrest necrosis.<ref name=farrar412/><ref name=farrar1/><ref name=pease/>

====Current uses====

=====Industrial=====
Coal-tar creosote is the most widely used wood treatment today; both industrially, processed into wood using pressure methods such as "full-cell process" or "empty-cell process", and more commonly applied to wood through brushing. In addition to toxicity to fungi, insects, and marine borers, it serves as a natural [[water repellent]]. It is commonly used to preserve and waterproof [[railroad tie]]s, pilings, telephone poles, power line poles, marine pilings, and fence posts. Although suitable for use in preserving the structural timbers of buildings, it is not generally used that way because it is difficult to apply. There are also concerns about the environmental impact of the [[#Release into environment|leaching of creosote into aquatic ecosystems]].

Due to its [[carcinogen]]ic character, the European Union has regulated the quality of creosote for the EU market<ref name=cec2001/> and requires that the sale of creosote be limited to professional users.<ref name=cec2007/><ref name=hse2011/> The [[United States Environmental Protection Agency]] regulates the use of coal-tar creosote as a wood preservative under the provisions of the [[Federal Insecticide, Fungicide, and Rodenticide Act]]. Creosote is considered a restricted-use pesticide and is only available to licensed pesticide applicators.<ref name=creosotecouncil/><ref name=ibach141/>