View source for Nitrous oxide

{{Redirect|N2O}}
{{Distinguish|nitric oxide}}
{{Other uses}}
{{chembox
| Watchedfields = changed
| verifiedrevid = 269495247
| ImageFile = Nitrous-oxide-3D-vdW.png
| ImageSize = 150px
| ImageName = Nitrous oxide - space-filling model
| ImageFile1 = Nitrous-oxide-dimensions-3D-balls.png
| ImageSize1 = 200px
| ImageName1 = Nitrous oxide's bond lengths
| ImageFile2 = Nitrous-oxide-2D-VB.svg
| ImageSize2 = 250px
| ImageName2 = Nitrous oxide's canonical forms
| IUPACName = Dinitrogen monoxide
| OtherNames = Laughing gas
| Section1 = {{Chembox Identifiers
| CASNo_Ref = {{cascite}}
| CASNo = 10024-97-2
| CAS_Ref = {{cascite}}
| ChemSpiderID = 923
| PubChem = 948
| InChI = InChI=1/N2O/c1-2-3
| UNNumber = 1070 (compressed)<br/>2201 (liquid)
| RTECS = QX1350000
| MeSHName =
| ChEBI = 17045
| KEGG =
| ATCCode_prefix = N01
| ATCCode_suffix = AX13
}}
| Section2 = {{Chembox Properties
| Formula = N<sub>2</sub>O
| MolarMass = 44.013 g/mol
| Appearance = colorless gas
| Density = 1.977 g/L (gas)
| MeltingPt = –90.86 °C (182.29 K)
| BoilingPt = –88.48 °C (184.67 K)
| Solubility = 0.15 g/100 ml (15 °C)
| SolubleOther = soluble in [[alcohol]], [[ether]], [[sulfuric acid]]
| LogP = 0.35
| RefractIndex = 1.330
| VaporPressure = 5150 kPa (20 °C)
| HenryConstant =
| AtmosphericOHRateConstant =
 }}
| Section3 = {{Chembox Structure
| MolShape = linear, ''C''<sub>∞v</sub>
| Dipole = 0.166 [[Debye|D]]
 }}
| Section4 = {{Chembox Thermochemistry
| DeltaHf = +82.05 kJ/mol
| Entropy = 219.96 J&thinsp;K<sup>–1</sup>&thinsp;mol<sup>–1</sup>
 }}
| Section5 = {{Chembox Pharmacology
| AdminRoutes = [[Inhalation]]
| Bioavail =
| Metabolism = 0.004%
| HalfLife = 5 minutes
| ProteinBound =
| Excretion = [[Respiratory]]
| Legal_status = <!-- All U.S. states except for [[California]] allow nitrous oxide as an [[anesthetic]]. Also used in the [[United Kingdom]] and [[Australia]]. -->
| Legal_UK =
| Legal_AU =
| Legal_CA =
| PregCat =
| PregCat_AU =
| PregCat_US = C
 }}
| Section7 = {{Chembox Hazards
| ExternalMSDS = [http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc00/icsc0067.htm Ilo.org], ICSC 0067
| EUIndex = Oxidant ['''O''']
| EUClass =
| RPhrases =
| SPhrases =
| MainHazards =
| NFPA-H = 2
| NFPA-F = 0
| NFPA-R = 0
| NFPA-O = OX
| FlashPt = Non-flammable
| LD50 =
| PEL =
 }}
| Section8 = {{Chembox Related
| OtherFunctn = [[Nitric oxide]]<br/>[[Dinitrogen trioxide]]<br/>[[Nitrogen dioxide]]<br/>[[Dinitrogen tetroxide]]<br/>[[Dinitrogen pentoxide]]
| Function = [[nitrogen]] [[oxide]]s
| OtherCpds = [[Ammonium nitrate]]<br/>[[Azide]]
 }}
}}

'''Nitrous oxide''', commonly known as '''laughing gas''', is a [[chemical compound]] with the [[chemical formula|formula]] {{chem|N|2|O}}. It is an [[oxide]] of [[nitrogen]]. At room temperature, it is a colorless [[Flammability|non-flammable]] [[gas]], with a slightly sweet odor and taste. It is used in [[surgery]] and [[dentistry]] for its [[Anesthesia|anesthetic]] and [[analgesic]] effects. It is known as "laughing gas" due to the [[Euphoria|euphoric]] effects of inhaling it, a property that has led to its [[recreational drug use|recreational use]] as a [[dissociative]] [[anesthetic]]. It is also used as an [[Oxidizing agent|oxidizer]] in [[rocket]]ry and in [[Auto racing|motor racing]] to increase the power output of [[Piston engine|engines]]. At elevated temperatures, nitrous oxide is a powerful oxidizer similar to molecular oxygen. 

Nitrous oxide gives rise to NO on reaction with oxygen atoms, and this NO in turn reacts with [[ozone]]. As a result, it is the main naturally occurring regulator of [[stratosphere|stratospheric]] ozone. It is also a major [[greenhouse gas]] and [[air pollutant]]. Considered over a 100 year period, it has 298 times more impact per unit weight than [[carbon dioxide]].<ref>2007 IPCC Fourth Assessment Report (AR4) by Working Group 1 (WG1), [http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter2.pdf Chapter 2 "Changes in Atmospheric Constituents and in Radiative Forcing"] which contains information on [[global warming potential]] (GWP) of greenhouse gases.</ref>

==History==
The gas was first synthesized by [[English people|English]] [[natural philosopher]] and chemist [[Joseph Priestley]] in 1772, who called it ''phlogisticated nitrous air'' (see [[phlogiston]]).<ref name="Nitrous Oxide pioneers">{{cite journal |url=http://journals.lww.com/anesthesiology/citation/1941/09000/The_Development_of_Anesthesia.8.aspx |author=Keys TE|title=The_Development_of_Anesthesia|work=Anesthesiology journal |year=1941|volume=2|pages=552–574}}</ref> Priestley published his discovery in the book ''Experiments and Observations on Different Kinds of Air (1775)'', where he described how to produce the preparation of "nitrous air diminished", by heating iron filings dampened with [[nitric acid]].<ref name="Joseph Priestley">{{cite web |url=http://www.erowid.org/chemicals/nitrous/nitrous_journal1.shtml|author=Priestley J|title=Experiments and Observations on Different Kinds of Air (vol.2, sec.3)|year=1776}}</ref>

===Early use (1794-1843)===
First important use of nitrous oxide, was made possible by [[Thomas Beddoes]] and the renowned engineer [[James Watt]], who worked together to publish the book ''Considerations on the Medical Use and on the Production of Factitious Airs (1794)''. This book was important for two reasons. First, James Watt had invented a novel machine to produce "Factitious Airs" (i.e. nitrous oxide) and a novel "breathing apparatus" to inhale the gas. Second, the book also presented the new medical theories by Thomas Beddoes, that [[tuberculosis]] and other lung diseases could be treated by inhalation of "Factitious Airs"<ref name="Drug discovery"/> (the word [[factitious]] means "artificial").

The machine to produce "Factitious Airs" comprised three parts: A furnace to burn the needed material, a vessel with water where the produced gas passed through in a spiral pipe (in order for impurities to be "washed off"), and finally the gas cylinder with a gasometer where the produced air could be tapped into portable air bags (made of airtight oily silk). The breathing apparatus comprised one of the portable air bags connected with a tube to a mouthpiece. With this new equipment being engineered and produced already in 1794, the way was now paved for [[clinical trial]]s, which began when [[Thomas Beddoes]] in 1798 established the ''"Pneumatic Institution for Relieving Diseases by Medical Airs"'' in [[Clifton, Bristol|Clifton (Bristol)]]. In the basement of the building, a large scale machine was producing the gases under the supervision of a young [[Humphry Davy]], who was encouraged to experiment with new gases for patients to inhale.<ref name="Drug discovery"/> The first important work of Davy was to examine the nitrous oxide, with the results being published in his book: ''Researches, Chemical and Philosophical (1800)''. In that publication, Davy notes the analgesic effect of nitrous oxide at page 465 and its potential to be used for surgical operations at page 556.<ref name="Humphry Davy">{{cite book |url=http://books.google.com/?id=jhUAAAAAQAAJ&printsec=frontcover&dq=Researches,+chemical+and+philosophical&cd=1#v=onepage&q |author=Davy H|title=Researches, chemical and philosophical –chiefly concerning nitrous oxide or dephlogisticated nitrous air, and its respiration|year=1800 |publisher=Printed for J. Johnson}}</ref>

Despite the valuable finding made by Davy, that inhalation of nitrous oxide could relieve a conscious person from pain, another 44 years would elapse before doctors attempted to use it for [[anaesthesia]]. The use of nitrous oxide as a [[recreational drug]] at "laughing gas parties", primarily arranged for the [[Social structure of Britain#Upper classes|British upper class]], became an immediate success beginning in 1799. While the effects of the gas generally make the user feel stuporous, dreamy and sedated, some people also "get the giggles" in a state of euphoria, and erupt in laughter and overall amusement.<ref name="Illicit drugs">{{cite web |url=http://www.druglibrary.org/schaffer/Library/studies/cu/CU43.html|author=Brecher EM|title=Consumers Union Report on Licit and Illicit Drugs, Part VI - Inhalants and Solvents and Glue-Sniffing|work=Consumer Reports Magazine|year=1972}}</ref>

===Anesthetic use===
The first time nitrous oxide was used as [[anesthetic]] drug in the treatment of a patient was when dentist [[Horace Wells]], with assistance by [[Gardner Quincy Colton]] and [[John Mankey Riggs]], demonstrated insensitivity to pain from a [[dental extraction]] in December 1844.<ref name="Discovery of Wells">{{cite web |url=http://ukpmc.ac.uk/picrender.cgi?artid=1703729&blobtype=pdf|author=Erving HW|title=The Discoverer of Anæsthesia: Dr. Horace Wells of Hartford|work=Yale Journal of Biology and Medicine, May 1933; v.5, n.5, p.421–430|year=1933}}</ref> In the following weeks, Wells treated the first 12-15 patients with nitrous oxide in [[Hartford]], and according to his own record only failed in two cases.<ref name="Horace Wells">{{cite book |url=http://books.google.com/?id=exNtlBi8T4EC&printsec=frontcover&dq=Horace+Wells#v=onepage&q|author=Wells H|title=A history of the discovery, of the application of nitrous oxide gas, ether, and other vapors, to surgical operations|year=1847 |publisher=J. Gaylord Wells}}</ref> In spite of these convincing results being reported by Wells to the medical society in [[Boston]] already in December 1844, this new method was not immediately adopted by other dentists. The reason for this was most likely that Wells, in January 1845 at his first public demonstration towards the medical faculty in Boston, had been partly unsuccessful, leaving his colleagues doubtful regarding its efficacy and safety.<ref name="Discovery of anaesthesia">{{cite web |url=http://www.ijaweb.org/text.asp?2007/51/6/472/61183|author=Desai SP, Desai MS, Pandav CS|title=The discovery of modern anaesthesia-contributions of Davy, Clarke, Long, Wells and Morton|work=Indian J Anaesth 2007;51:472-8|year=2007}}</ref> The method did not come into general use until 1863, when [[Gardner Quincy Colton]] successfully started to use it in all his "Colton Dental Association" clinics, that he just had established in [[New Haven]] and [[New York City]].<ref name="Drug discovery"/> Over the following three years, Colton and his associates successfully administered nitrous oxide to more than 25,000 patients.<ref name="use in dentistry"/> With its efficacy and safety now demonstrated by large numbers, the usage of nitrous oxide rapidly became the preferred anesthetic method in dentistry. Because the gas is mild enough to keep a patient in a conscious and conversational state, and yet in most cases strong enough to suppress the pain caused by dental work, it remains the preferred [[gas anesthetic]] in today's dentistry.

In hospitals, nitrous oxide was however found not to be a strong enough [[anesthetic]] for the use in large operations. Being a stronger and more potent anesthetic, [[sulfuric ether]] was instead demonstrated and accepted for use in October 1846, along with [[chloroform]] in 1847.<ref name="Drug discovery"/> When [[Joseph Thomas Clover]] invented the "gas-ether inhaler" in 1876, it however became a common practice at hospitals to initiate all anesthetic treatments with a mild flow of nitrous oxide, and then gradually increase the [[anaesthesia]] with the stronger ether/chloroform. Clover's gas-ether inhaler was designed to supply the patient with nitrous oxide and ether at the same time, with the exact mixture being controlled by the operator of the device. It remained in use by many hospitals until the 1930s.<ref name="use in dentistry"/> Although hospitals today are using a more advanced [[anaesthetic machine]], these machines still use the same principle launched with Clover's gas-ether inhaler: To initiate the anesthesia with nitrous oxide, before the administration of a more powerful anesthetic.

==Production==
[[File:Nitrous oxide production.png|thumb|right|200px|Nitrous oxide production]]
Nitrous oxide is most commonly prepared by careful heating of [[ammonium nitrate]], which decomposes into nitrous oxide and water vapor.<ref>{{cite book|last = Holleman|first = A. F.|coauthors = Wiberg, E.|title = Inorganic Chemistry|publisher = Academic Press|location = San Diego|year = 2001|isbn = 0-12-352651-5}}</ref> The addition of various [[phosphate]]s favors formation of a purer gas at slightly lower temperatures. One of the earliest commercial producers was [[George Poe]] in [[Trenton, New Jersey]].<ref name=wp>{{cite news|title=George Poe is Dead |url=http://pqasb.pqarchiver.com/washingtonpost_historical/access/243050292.html?dids=243050292:243050292&FMT=ABS&FMTS=ABS:FT&date=FEB+03%2C+1914&author=&pub=The+Washington+Post&desc=GEORGE+POE+IS+DEAD&pqatl=google |quote=Cousin of Famous Poet and Noted as a Scientist. Inventor of the Respirator. Also First to Liquefy Nitrous Oxide. Cadet at [[Virginia Military Institute]] at Time of [[Battle of Newmarket]]. Mentioned for the Nobel Prize for Scientific Attainment in Chemistry. Prof. George Poe, a cousin of the poet Edgar Allan Poe, a noted scientist and inventor, who had been mentioned for the Nobel prize for scientific attainment, a former resident of Washington, died in Norfolk, Virginia, yesterday of general paralysis. Prof. Poe was in his sixty-eighth year. |publisher=[[Washington Post]] |date=February 3, 1914 |accessdate=2007-12-29}}</ref>

:NH<sub>4</sub>NO<sub>3</sub> (s) → 2 H<sub>2</sub>O (g) + N<sub>2</sub>O (g)

This reaction occurs between 170 and 240 °C, temperatures where ammonium nitrate is a moderately sensitive [[explosive]] and a very powerful [[oxidizer]]. Above 240&nbsp;°C the [[exothermic reaction]] may accelerate to the point of [[detonation]], so the mixture must be cooled to avoid such a disaster. Superheated steam is used to reach reaction temperature in some [[turnkey]] production plants.<ref>{{cite web
|url = http://www.sanghioverseas.com/nitrous_oxide_gas_plants/nitrous_oxide_gas_plants.htm
|publisher = Sanghi Organization
|title = Nitrous oxide plant}}</ref>

Downstream, the hot, corrosive mixture of gases must be cooled to condense the steam, and filtered to remove higher oxides of nitrogen. Ammonium nitrate smoke, as an extremely persistent [[colloid]], will also have to be removed. The cleanup is often done in a train of 3 gas washes; namely base, acid and base again. Any significant amounts of nitric oxide (NO) may not necessarily be absorbed directly by the base (sodium hydroxide) washes.

The nitric oxide impurity is sometimes [[chelate]]d out with [[ferrous sulfate]], reduced with iron metal, or oxidised and absorbed in base as a higher oxide. The first base wash may (or may not) react out much of the ammonium nitrate smoke. However, this reaction generates ammonia gas, which may have to be absorbed in the acid wash.

===Other routes===
The direct oxidation of [[ammonia]] may someday rival the ammonium nitrate [[pyrolysis]] synthesis of nitrous oxide mentioned above. This capital-intensive process, which originates in Japan, uses a [[manganese dioxide]]-[[bismuth oxide]] catalyst:<ref>Synthesis of Nitrous Oxide by Oxidation of Ammonia T Suwa, A Matsushima, Y Suziki, Y Namina, Kohyo Kagaku Zasshi, 1961; Showa Denka Ltd.</ref>
:2 NH<sub>3</sub> + 2 O<sub>2</sub> → N<sub>2</sub>O + 3 H<sub>2</sub>O

Higher oxides of nitrogen are formed as impurities. In comparison, [[catalysis|uncatalyzed]] ammonia oxidation (i.e. combustion or explosion) goes primarily to N<sub>2</sub> and H<sub>2</sub>O.

Nitrous oxide can be made by heating a solution of [[sulfamic acid]] and [[nitric acid]]. Many gases are made this way in Bulgaria.{{Citation needed|date=February 2008}}<ref>Brozadzhiew & Rettos, 1975.</ref>

:HNO<sub>3</sub> + NH<sub>2</sub>SO<sub>3</sub>H → N<sub>2</sub>O + H<sub>2</sub>SO<sub>4</sub> + H<sub>2</sub>O

There is no explosive hazard in this reaction if the mixing rate is controlled. However, as usual, toxic higher oxides of nitrogen are formed.

Nitrous oxide is produced in large volumes as a by-product in the synthesis of [[adipic acid]]; one of the two reactants used in nylon manufacture.<ref>{{cite journal
|title = Abatement of N<sub>2</sub>O emissions produced in the adipic acid industry
|author = Reimer R. A.; Slaten C. S.; Seapan M.; Lower M. W.; Tomlinson P. E.;
|journal = Environmental progress
|year = 1994
|volume = 13
|issue = 2
|pages = 134–137
|doi = 10.1002/ep.670130217}}</ref><ref>.{{cite journal
|title = Abatement of N<sub>2</sub>O emissions produced in the adipic acid industry
|author = A. Shimizu, , K. Tanaka and M. Fujimori
|journal = Chemosphere – Global Change Science
|year = 2000
|volume = 2
|issue = 3-4
|pages = 425–434
|doi = 10.1016/S1465-9972(00)00024-6}}</ref> This might become a major commercial source, but will require the removal of higher oxides of nitrogen and organic impurities. Currently much of the gas is decomposed before release for environmental protection. Greener processes may prevail that substitute [[hydrogen peroxide]] for nitric acid oxidation; hence no generation of oxide of nitrogen by-products.

[[Hydroxylammonium chloride]] can react with [[sodium nitrite]] to produce N<sub>2</sub>O as well:
: NH<sub>3</sub>OH<sup>+</sup>Cl<sup>−</sup> + NaNO<sub>2</sub> → N<sub>2</sub>O + NaCl + 2 H<sub>2</sub>O
If the nitrite is added to the hydroxylamine solution, the only remaining byproduct is salt water. However, if the hydroxylamine solution is added to the nitrite solution (nitrite is in excess), then toxic higher oxides of nitrogen are also formed.
Also, HNO<sub>3</sub> can be reduced to N<sub>2</sub>O by SnCl<sub>2</sub> and HCl mixture:
:2 HNO<sub>3</sub> + 8 HCl + 4 SnCl<sub>2</sub> → 5 H<sub>2</sub>O + 4 SnCl<sub>4</sub> + N<sub>2</sub>O

==Applications==
===Rocket motors===
Nitrous oxide can be used as an [[oxidizing agent|oxidizer]] in a [[rocket]] motor. This has the advantages over other oxidizers in that it is non-toxic and, due to its stability at room temperature, easy to store and relatively safe to carry on a flight. As a secondary benefit it can be readily decomposed to form breathing air. Its high density and low storage pressure enable it to be highly competitive with stored high-pressure gas systems.

In a 1914 patent, American rocket pioneer [[Robert Goddard]] suggested nitrous oxide and gasoline as possible propellants for a liquid-fueled rocket. Nitrous oxide has been the oxidizer of choice in several [[hybrid rocket]] designs (using solid fuel with a liquid or gaseous oxidizer). The combination of nitrous oxide with [[hydroxyl-terminated polybutadiene]] fuel has been used by [[SpaceShipOne]] and others. It is also notably used in [[amateur rocketry|amateur]] and [[high power rocket]]ry with various [[plastic]]s as the fuel.

Nitrous oxide can also be used in a [[monopropellant rocket]]. In the presence of a heated [[catalyst]], N<sub>2</sub>O will decompose exothermically into nitrogen and oxygen, at a temperature of approximately 1300 °C. Because of the large heat release, the catalytic action rapidly becomes secondary as thermal autodecomposition becomes dominant. In a vacuum thruster, this can provide a monopropellant [[specific impulse]] (''I''<sub>sp</sub>) of as much as 180 s. While noticeably less than the ''I''<sub>sp</sub> available from [[hydrazine]] thrusters (monopropellant or [[Bipropellant rocket|bipropellant]] with [[Dinitrogen tetroxide|nitrogen tetroxide]]), the decreased toxicity makes nitrous oxide an option worth investigating.

Specific impulse (''I''<sub>sp</sub>) can be improved by blending a hydrocarbon fuel with the nitrous oxide inside the same storage tank, becoming a nitrous oxide fuel blend (NOFB) monopropellant. This storage mixture does not incur the danger of spontaneous ignition, since N<sub>2</sub>O is chemically stable. When the nitrous oxide decomposes by a heated catalyst, high temperature oxygen is released and rapidly ignites the hydrocarbon fuel-blend. NOFB monopropellants are capable of I{{su|b=sp}} greater than 300 seconds, while avoiding the toxicity associated with hypergolic propulsion systems.<ref>{{cite| url=http://www.faqs.org/patents/app/20090133788|title=Nitrous Oxide Fuel Blend Monopropellants|publisher=Patentdocs| accessdate=2009-11-11}}</ref><ref>{{cite| url=http://www.firestar-engineering.com/|title=FireStar Engineering, LLC| publisher=FireStar Engineering| accessdate=2009-12-11}}</ref> The low freezing point of NOFB eases thermal management compared to hydrazine and dinitrogen tetroxide—a valuable property for space storable propellants.

===Internal combustion engine===
{{Main|Nitrous}}

In vehicle [[racing]], nitrous oxide (often referred to as just "[[nitrous]]") allows the engine to burn more fuel and air, resulting in a more powerful combustion. The gas itself is not flammable, but it delivers more [[oxygen]] than atmospheric air by breaking down at elevated temperatures.

Nitrous oxide is stored as a compressed liquid; the [[heat of vaporization|evaporation]] and expansion of liquid nitrous oxide in the [[intake manifold]] causes a large drop in intake charge temperature, resulting in a denser charge, further allowing more air/fuel mixture to enter the cylinder. Nitrous oxide is sometimes injected into (or prior to) the intake manifold, whereas other systems directly inject right before the cylinder (direct port injection) to increase power.

The technique was used during [[World War II]] by ''[[Luftwaffe]]'' aircraft with the [[GM-1]] system to boost the power output of [[aircraft engine]]s. Originally meant to provide the ''Luftwaffe'' standard aircraft with superior high-altitude performance, technological considerations limited its use to extremely high altitudes. Accordingly, it was only used by specialized planes like high-altitude [[reconnaissance aircraft]], [[schnellbomber|high-speed bombers]], and high-altitude [[interceptor aircraft]].

One of the major problems of using nitrous oxide in a reciprocating engine is that it can produce enough power to damage or destroy the engine. Very large power increases are possible, and if the mechanical structure of the engine is not properly reinforced, the engine may be severely damaged or destroyed during this kind of operation. It is very important with nitrous oxide augmentation of [[internal combustion engine]]s to maintain proper [[operating temperature]]s and fuel levels to prevent "preignition", or "detonation" (sometimes referred to as "knocking" or "pinging"). Most problems that are associated with nitrous do not come from mechanical failure due to the power increases. Since nitrous allows a much denser charge into the cylinder it dramatically increases cylinder pressures. The increased pressure and temperature can cause problems such as melting the piston or valves. It may also crack or warp the piston or head and cause preignition due to uneven heating.

Automotive-grade liquid nitrous oxide differs slightly from medical-grade nitrous oxide. A small amount of sulfur dioxide is added to prevent substance abuse.<ref name="Automotive gas">{{cite web |url=http://www.holley.com/TechService/FAQ.asp?category=NOS|author=Holley|title=Holley performance products, FAQ for Nitrous Oxide Systems}}</ref>

===Aerosol propellant===
[[Image:Nitrous oxide - 10 x 8g.jpg|thumb|200px|An 8&nbsp;g canister of nitrous oxide intended for use as a [[whipped cream]] aerating agent]]
The gas is approved for use as a [[food additive]] (also known as E942), specifically as an [[Aerosol spray#Aerosol propellants|aerosol spray propellant]]. Its most common uses in this context are in aerosol [[whipped cream]] canisters, [[cooking spray]]s, and as an inert gas used to displace oxygen, to inhibit bacterial growth, when filling packages of [[potato chips]] and other similar snack foods.

The gas is extremely soluble in fatty compounds. In aerosol whipped cream, it is dissolved in the fatty cream until it leaves the can, when it becomes gaseous and thus creates foam. Used in this way, it produces whipped cream four times the volume of the liquid, whereas whipping air into cream only produces twice the volume. If air were used as a propellant, oxygen would accelerate [[rancidification]] of the butterfat; nitrous oxide inhibits such degradation. Carbon dioxide cannot be used for whipped cream because it is acidic in water, which would curdle the cream and give it a seltzer-like 'sparkling' sensation.

However, the whipped cream produced with nitrous oxide is unstable and will return to a more or less liquid state within half an hour to one hour. Thus, the method is not suitable for decorating food that will not be immediately served.

Similarly, [[cooking spray]], which is made from various types of oils combined with [[lecithin]] (an [[emulsifier]]), may use nitrous oxide as a [[propellant]]; other propellants used in cooking spray include food-grade [[alcohol]] and [[propane]].

Users of nitrous oxide often obtain it from whipped cream dispensers that use nitrous oxide as a propellant (see above section), for recreational use as a euphoria-inducing [[inhalant]] drug. It is not harmful in small doses, but risks due to lack of oxygen do exist (see ''[[Nitrous oxide#Recreational use|Recreational use]] below).

===In medicine===

[[Image:N2O Medical Tanks.jpg|thumb|100px|right|Medical grade N<sub>2</sub>O tanks used in [[dentistry]].]]

Nitrous oxide has been used for [[anesthesia]] in [[dentistry]] since December 1844, where [[Horace Wells]] made the first 12-15 dental operations with the gas in [[Hartford]]. Its debut as a generally accepted method however only came in 1863, when [[Gardner Quincy Colton]] introduced it more broadly at all the Colton Dental Association clinics, that he founded in [[New Haven]] and [[New York city]].<ref name="Drug discovery">{{cite book|url=http://books.google.com/?id=mYQxRY9umjcC&printsec=frontcover&dq=Drug+Discovery+history&cd=1|author=Sneader W|title=Drug Discovery –A History|work=(Part 1: Legacy of the past, chapter 8: systematic medicine, p.74-87)|year=2005|accessdate=2010-04-21|publisher=John Wiley and Sons|isbn=9780471899808}}</ref> The first devices used in dentistry to administer the gas, known as Nitrous Oxide inhalers, were designed in a very simple way with the gas stored and breathed through a breathing bag made of rubber cloth, without a [[scavenger system]] and [[flowmeter]], and with no addition of oxygen/air.<ref name="use in dentistry">{{cite web |url=http://journals.lww.com/anesthesiology/citation/1941/07000/Technical_Development_of_Gas_Anesthesia.4.aspx |author=Miller AH|title=Technical Development of Gas Anesthesia|work=Anesthesiology journal (July 1941, vol.2, is.4, p.398-409)|year=1941}}</ref> Today these simple and somewhat unreliable inhalers, of course have been replaced by the more modern [[relative analgesia machine]], which is an automated machine designed to deliver a precisely dosed and breath-actuated flow of nitrous oxide mixed with oxygen, for the patient to inhale safely. The machine used in dentistry is designed as a more simplified version of the larger [[anaesthetic machine]] used by hospitals, as it doesn't feature the additional [[anaesthetic vaporiser]] and [[medical ventilator]]. The purpose of the machine allows for a more simple design, as it only delivers a mixture of nitrous oxide and oxygen for the patient to inhale, in order to depress the feeling of pain -while keeping the patient in a conscious state.

The relative analgesia machine typically feature a constant-supply [[flowmeter]], which allow the proportion of nitrous oxide and the combined gas flow rate to be individually adjusted. The gas is administered by dentists through a [[Diving_regulator#Demand_valve|demand-valve]] inhaler over the nose, which will only release gas when the patient inhales through the nose. Because nitrous oxide is minimally metabolized in humans (with a rate of 0.004%), it retains its potency when exhaled into the room by the patient, and can pose an intoxicating and prolonged exposure hazard to the clinic staff if the room is poorly ventilated. Where nitrous oxide is administered, a continuous-flow fresh-air [[Ventilation (architecture)|ventilation system]] or nitrous [[scavenger system]] is used to prevent a waste-gas buildup.

Hospitals are administering nitrous oxide as one of the [[anesthetic]] drugs delivered by [[anaesthetic machine]]s. Nitrous oxide is a weak [[general anesthetic]], and so is generally not used alone in [[general anesthesia]]. In general anesthesia it is used as a carrier gas in a 2:1 ratio with oxygen for more powerful general anesthetic drugs such as [[sevoflurane]] or [[desflurane]]. It has a MAC ([[minimum alveolar concentration]]) of 105% and a blood:gas partition coefficient of 0.46.

When nitrous oxide is inhaled as the only anesthetic drug, it is normally administered as a mixture with 30% gas and 70% oxygen.<ref name=Dentalfear>{{cite web|url=http://www.dentalfearcentral.org/laughing_gas.html|author=Dental Fear Central|title=Inhalation sedation (aka Laughing Gas)|year=2004|accessdate=2010-04-18}}</ref> The medical grade gas tanks, with the tradename [[Entonox|Entonox and Nitronox]] contain a mixture with 50%, but this will normally be diluted to a lower percentage upon the operational dilevery to the patient. Inhalation of nitrous oxide is frequently used to relieve pain associated with [[childbirth]], [[Physical trauma|trauma]], [[dentistry|oral surgery]], and [[heart attack]]s.

In Britain, Entonox and Nitronox are commonly used by ambulance crews (including unregistered practitioners) as a rapid and highly effective analgesic gas.

===Recreational use===
Nitrous oxide can cause [[Analgesic|analgesia]], [[depersonalization]], [[derealization]], [[dizziness]], [[Euphoria (emotion)|euphoria]], and some sound distortion.<ref>AJ Giannini. Volatiles. In NS Miller (Ed.). [http://books.google.com/books?doi=VgetLfJBQv0C&pg=PA396 Comprehensive Handbook of Drug and Alcohol Addiction]. NY, Marcel Dekker, 1991 ISBN 082478474X</ref> Research has also found that it increases [[suggestibility]] and [[imagination]].<ref>Whalley MG, Brooks GB. (2009). Enhancement of suggestibility and imaginative ability with nitrous oxide. Psychopharmacology (Berl). 203(4):745-52. 10.1007/s00213-008-1424-0 PMID 19057896</ref> Inhalation of nitrous oxide for recreational use, with the purpose to cause euphoria and slight hallucinations, began as a phenomenon for the British upper class in 1799, known as "laughing gas parties". Until at least 1863, a low availability of equipment to produce the gas, combined with a low usage of the gas for medical purposes, meant it was a relatively rare phenomenon that mainly took place among students at medical universities. When equipment became more widely available for dentistry and hospitals, most countries also restricted the legal access to buy pure nitrous oxide [[gas cylinder]]s to those sectors. As only medical staff and dentists today are legally allowed to buy the pure gas, the recreational use is also believed to be somewhat limited. The consumers union report from 1972, however found that the use of the gas for recreational purpose still take place in present time, based upon reports of its use in [[Maryland]] 1971, [[Vancouver]] 1972, and a survey made by Dr.Edward J.Lynn of its nonmedical use in [[Michigan]] 1970.<ref name="Illicit drugs"/>

*'''Citation of the results from the Michigan survey in 1970:''' ''"It was not uncommon [in the interviews] to hear from individuals who had been to parties where a professional (doctor, nurse, scientist, inhalation therapist, researcher) had provided nitrous oxide. There also were those who work in restaurants who used the N<sub>2</sub>O stored in tanks for the preparation of whip cream. Reports were received from individuals who used the gas contained in aerosol cans both of food and non-food products. At a recent rock festival nitrous oxide was widely sold for 25 cents a balloon. Contact was made with a "mystical-religious" group that used the gas to accelerate arriving at their transcendental-meditative state of choice. Although a few, more sophisticated users employed nitrous oxide-oxygen mixes with elaborate equipment, most users employed balloons or plastic bags. They either held a breath of N<sub>2</sub>O or rebreathed the gas. There were no adverse effects reported in the more than one hundred individuals surveyed."'' <ref name="Illicit drugs"/>

Inhaling nitrous oxide from tanks used in automotive systems is unsafe, because the toxic gas [[sulfur dioxide]] is mixed in around 100 ppm, specifically to discourage recreational use.<ref name="Automotive gas"/>

==Neuropharmacology==

The pharmacological [[mechanism of action]] of N<sub>2</sub>O in medicine is not fully known. However, it has been shown to directly modulate a broad range of [[ligand-gated ion channel]]s, and this likely plays a major role in many of its effects. It moderately blocks [[NMDA receptor|NMDA]] and [[CHRNB2|β<sub>2</sub>-subunit]]-containing [[nicotinic acetylcholine receptor|nACh channel]]s, weakly inhibits [[AMPA receptor|AMPA]], [[kainate receptor|kainate]], [[GABAC receptor|GABA<sub>C</sub>]], and [[5-HT3 receptor|5-HT<sub>3</sub> receptor]]s, and slightly potentiates [[GABAA receptor|GABA<sub>A</sub>]] and [[glycine receptor]]s.<ref name="pmid11020766">{{cite journal|author = Yamakura T, Harris RA|title = Effects of gaseous anesthetics nitrous oxide and xenon on ligand-gated ion channels. Comparison with isoflurane and ethanol|journal = Anesthesiology|volume = 93|issue = 4|pages = 1095–101|year = 2000|pmid = 11020766|url = http://meta.wkhealth.com/pt/pt-core/template-journal/lwwgateway/media/landingpage.htm?issn=0003-3022&volume=93&issue=4&spage=1095|doi = 10.1097/00000542-200010000-00034}}</ref><ref name="pmid9822732">{{cite journal|author = Mennerick S, Jevtovic-Todorovic V, Todorovic SM, Shen W, Olney JW, Zorumski CF|title = Effect of nitrous oxide on excitatory and inhibitory synaptic transmission in hippocampal cultures|journal = The Journal of Neuroscience : the Official Journal of the Society for Neuroscience|volume = 18|issue = 23|pages = 9716–26|year = 1998|pmid = 9822732}}</ref> It has also been shown to activate [[tandem pore domain potassium channel|two-pore-domain K<sup>+</sup> channel]]s.<ref name="pmid14742687">{{cite journal|author = Gruss M, Bushell TJ, Bright DP, Lieb WR, Mathie A, Franks NP|title = Two-pore-domain K+ channels are a novel target for the anesthetic gases xenon, nitrous oxide, and cyclopropane|journal = Molecular Pharmacology|volume = 65|issue = 2|pages = 443–52|year = 2004|pmid = 14742687|doi = 10.1124/mol.65.2.443}}</ref> While N<sub>2</sub>O affects quite a few ion channels, its [[anesthetic]], [[hallucinogenic]], and [[euphoriant]] effects are likely caused predominantly or fully via inhibition of NMDAR-mediated currents.<ref name="pmid11020766"/><ref name="pmid17352529">{{cite journal|author = Emmanouil DE, Quock RM|title = Advances in understanding the actions of nitrous oxide|journal = Anesthesia Progress|volume = 54|issue = 1|pages = 9–18|year = 2007|pmid = 17352529|pmc = 1821130|doi = 10.2344/0003-3006(2007)54[9:AIUTAO]2.0.CO;2|url = http://www.anesthesiaprogress.org/doi/abs/10.2344/0003-3006(2007)54[9:AIUTAO]2.0.CO;2}}</ref> In addition to its effects on ion channels, N<sub>2</sub>O may act to imitate [[nitric oxide]] (NO) in the central nervous system as well, and this may relate to its [[analgesic]] and [[anxiolytic]] properties.<ref name="pmid17352529"/>

===Anxiolytic effect===
In behavioral tests of [[anxiety]], a low dose of N<sub>2</sub>O is an effective anxiolytic, and this anti-anxiety effect is associated with enhanced activity of GABA<sub>A</sub> receptors as it is partially reversed by [[GABAA receptor|benzodiazepine receptor]] [[receptor antagonist|antagonist]]s. Mirroring this, animals which have developed tolerance to the anxiolytic effects of [[benzodiazepine]]s are partially tolerant to N<sub>2</sub>O.<ref name="emmanouil">{{cite journal|title = Nitrous oxide anxiolytic effect in mice in the elevated plus maze: mediation by benzodiazepine receptors|author = Emmanouil, D.E., Johnson, C.H. & Quock, R.M.|journal = Psychopharmacology|volume = 115|issue = 1-2|pages = 167–72|year = 1994|url = |doi = 10.1007/BF02244768|pmid = 7862891}}</ref> Indeed, in humans given 30% N<sub>2</sub>O, benzodiazepine receptor antagonists reduced the subjective reports of feeling "high", but did not alter psycho-motor performance, in human clinical studies.<ref name="zacny">{{cite journal|title = Flumazenil may attenuate some subjective effects of nitrous oxide in humans: a preliminary report|author = Zacny, J.P., Yajnik, S., Coalson, D., Lichtor, J.L., Apfelbaum, J.L., Rupani, G., Young, C., Thapar, P. & Klafta, J.|journal = Pharmacology Biochemistry and Behavior|volume = 51|issue = 4|pages = 815–9|year = 1995|doi = 10.1016/0091-3057(95)00039-Y|pmid = 7675863}}</ref>

===Analgesic effect===
The analgesic effects of N<sub>2</sub>O are linked to the interaction between the [[Opioid#Endogenous_opioids|endogenous opioid]] system and the descending [[Norepinephrine|noradrenergic]] system. When animals are given [[morphine]] chronically they develop tolerance to its pain-killing effects, and this also renders the animals tolerant to the analgesic effects of N<sub>2</sub>O.<ref>{{cite journal|title = Tolerance to nitrous oxide analgesia in rats and mice|author = Berkowitz, B.A., Finck, A.D., Hynes, M.D. & Ngai, S.H.|journal = Anesthesiology|volume = 51|issue = 51|pages = 309–12|year = 1979|url = |doi = 10.1097/00000542-197910000-00006}}</ref> Administration of [[antibodies]] which bind and block the activity of some endogenous opioids (not [[beta-endorphin|β-endorphin]]) also block the antinociceptive effects of N<sub>2</sub>O.<ref name="branda">{{cite journal|title = Role of brain dynorphin in nitrous oxide antinociception in mice|author = Branda, E.M., Ramza, J.T., Cahill, F.J., Tseng, L.F. & Quock, R.M.|journal = Pharmacology Biochemistry and Behavior|volume = 65|pages = 217–21|year = 2000|doi = 10.1016/S0091-3057(99)00202-6}}</ref> Drugs which inhibit the breakdown of endogenous opioids also potentiate the antinociceptive effects of N<sub>2</sub>O.<ref name="branda"/> Several experiments have shown that opioid receptor antagonists applied directly to the brain block the antinociceptive effects of N<sub>2</sub>O, but these drugs have no effect when injected into the [[spinal cord]].

Conversely, [[alpha-2 adrenergic receptor|α<sub>2</sub>-adrenoceptor]] antagonists block the antinociceptive effects of N<sub>2</sub>O when given directly to the spinal cord, but not when applied directly to the brain.<ref name="guo">{{cite journal|title = Nitrous oxide produces antinociceptive response via alpha2B and/or alpha2C adrenoceptor subtypes in mice|author = Guo, T.Z., Davies, M.F., Kingery, W.S., Patterson, A.J., Limbird, L.E. & Maze, M.|journal = Anesthesiology|volume = 90|issue =2|pages = 470–6|year = 1999|pmid = 9952154|url = http://www.anesthesiology.org/pt/re/anes/abstract.00000542-199902000-00022.htm|doi = 10.1097/00000542-199902000-00022}}</ref> Indeed, [[alpha-2B adrenergic receptor|α<sub>2B</sub>-adrenoceptor]] knockout mice or animals depleted in [[norepinephrine]] are nearly completely resistant to the antinociceptive effects of N<sub>2</sub>O.<ref>{{cite journal|title = Antinociceptive action of nitrous oxide is mediated by stimulation of noradrenergic neurons in the brainstem and activation of [alpha]<sub>2B</sub> adrenoceptors|author = Sawamura, S., Kingery, W.S., Davies, M.F., Agashe, G.S., Clark, J.D., Koblika, B.K., Hashimoto, T. & Maze, M.|journal = J. Neurosci.|volume = 20|issue = 24|pages = 9242–51|year = 2000|pmid = 11125002}}</ref> It seems N<sub>2</sub>O-induced release of endogenous opioids causes disinhibition of [[brain stem]] noradrenergic neurons, which release [[norepinephrine]] into the spinal cord and inhibit pain signaling.<ref name="pmid10781114">{{cite journal|author = Maze M, Fujinaga M|title = Recent advances in understanding the actions and toxicity of nitrous oxide|journal = Anaesthesia|volume = 55|issue = 4|pages = 311–4|year = 2000|pmid = 10781114|doi = 10.1046/j.1365-2044.2000.01463.x}}</ref> Exactly how N<sub>2</sub>O causes the release of endogenous opioid peptides is still uncertain.

===Euphoric effect===
In rats, N<sub>2</sub>O stimulates the [[mesolimbic pathway|mesolimbic reward pathway]] via inducing [[dopamine]] release and activating [[dopaminergic]] [[neuron]]s in the [[ventral tegmental area]] and [[nucleus accumbens]], presumably through [[NMDA receptor antagonist|antagonization of NMDA receptors]] localized in the system.<ref name="pmid17122223">{{cite journal|author = Sakamoto S, Nakao S, Masuzawa M, ''et al.''|title = The differential effects of nitrous oxide and xenon on extracellular dopamine levels in the rat nucleus accumbens: a microdialysis study|journal = Anesthesia and Analgesia|volume = 103|issue = 6|pages = 1459–63|year = 2006|pmid = 17122223|doi = 10.1213/01.ane.0000247792.03959.f1}}</ref><ref name="pmid18571333">{{cite journal|author = Benturquia N, Le Marec T, Scherrmann JM, Noble F|title = Effects of nitrous oxide on dopamine release in the rat nucleus accumbens and expectation of reward|journal = Neuroscience|volume = 155|issue = 2|pages = 341–4|year = 2008|pmid = 18571333|doi = 10.1016/j.neuroscience.2008.05.015}}</ref><ref name="pmid8726543">{{cite journal|author = Lichtigfeld FJ, Gillman MA|title = Role of dopamine mesolimbic system in opioid action of psychotropic analgesic nitrous oxide in alcohol and drug withdrawal|journal = Clinical Neuropharmacology|volume = 19|issue = 3|pages = 246–51|year = 1996|pmid = 8726543|doi = 10.1097/00002826-199619030-00006}}</ref><ref name="pmid18499630">{{cite journal|author = Koyanagi S, Himukashi S, Mukaida K, Shichino T, Fukuda K|title = Dopamine D2-like receptor in the nucleus accumbens is involved in the antinociceptive effect of nitrous oxide|journal = Anesthesia and Analgesia|volume = 106|issue = 6|pages = 1904–9|year = 2008|pmid = 18499630|doi = 10.1213/ane.0b013e318172b15b}}</ref> This action has been implicated in its euphoric effects, and notably, appears to augment its analgesic properties as well.<ref name="pmid17122223"/><ref name="pmid18571333"/><ref name="pmid8726543"/><ref name="pmid18499630"/>

However, it is remarkable that in mice, N<sub>2</sub>O blocks [[amphetamine]]-induced and dopamine release in the nucleus accumbens and [[behavioral sensitization]], abolishes the [[conditioned place preference]] (CPP) of [[cocaine]] and [[morphine]], and does not produce reinforcing (or aversive) effects of its own.<ref name="pmid16427030">{{cite journal|author = David HN, Ansseau M, Lemaire M, Abraini JH|title = Nitrous oxide and xenon prevent amphetamine-induced carrier-mediated dopamine release in a memantine-like fashion and protect against behavioral sensitization|journal = Biological Psychiatry|volume = 60|issue = 1|pages = 49–57|year = 2006|pmid = 16427030|doi = 10.1016/j.biopsych.2005.10.007}}</ref><ref name="pmid17905521">{{cite journal|author = Benturquia N, Le Guen S, Canestrelli C, ''et al.''|title = Specific blockade of morphine- and cocaine-induced reinforcing effects in conditioned place preference by nitrous oxide in mice|journal = Neuroscience|volume = 149|issue = 3|pages = 477–86|year = 2007|pmid = 17905521|doi = 10.1016/j.neuroscience.2007.08.003}}</ref> Studies on CPP of N<sub>2</sub>O in rats is mixed, consisting of reinforcement, aversion, and no change.<ref name="pmid12543228">{{cite journal|author = Ramsay DS, Watson CH, Leroux BG, Prall CW, Kaiyala KJ|title = Conditioned place aversion and self-administration of nitrous oxide in rats|journal = Pharmacology, Biochemistry, and Behavior|volume = 74|issue = 3|pages = 623–33|year = 2003|pmid = 12543228|doi = 10.1016/S0091-3057(02)01048-1}}</ref> In contrast, it is a positive reinforcer in squirrel monkeys,<ref name="pmid408480">{{cite journal|author = Wood RW, Grubman J, Weiss B|title = Nitrous oxide self-administration by the squirrel monkey|journal = The Journal of Pharmacology and Experimental Therapeutics|volume = 202|issue = 3|pages = 491–9|year = 1977|pmid = 408480}}</ref> and is well known as a [[drug abuse|drug of abuse]] in humans.<ref name="pmid9915336">{{cite journal|author = Zacny JP, Galinkin JL|title = Psychotropic drugs used in anesthesia practice: abuse liability and epidemiology of abuse|journal = Anesthesiology|volume = 90|issue = 1|pages = 269–88|year = 1999|pmid = 9915336|url = http://meta.wkhealth.com/pt/pt-core/template-journal/lwwgateway/media/landingpage.htm?issn=0003-3022&volume=90&issue=1&spage=269}}</ref> These discrepancies in response to N<sub>2</sub>O may reflect specie variations or methodological differences.<ref name="pmid17905521"/> Though, it is noteworthy that in human clinical studies, N<sub>2</sub>O was found to produce mixed responses similarly to rats, reflecting high subjective individual variability.<ref name="pmid8462415">{{cite journal|author = Dohrn CS, Lichtor JL, Coalson DW, Uitvlugt A, de Wit H, Zacny JP|title = Reinforcing effects of extended inhalation of nitrous oxide in humans|journal = Drug and Alcohol Dependence|volume = 31|issue = 3|pages = 265–80|year = 1993|pmid = 8462415|doi = 10.1016/0376-8716(93)90009-F}}</ref><ref name="pmid11470344">{{cite journal|author = Walker DJ, Zacny JP|title = Within- and between-subject variability in the reinforcing and subjective effects of nitrous oxide in healthy volunteers|journal = Drug and Alcohol Dependence|volume = 64|issue = 1|pages = 85–96|year = 2001|pmid = 11470344|doi = 10.1016/S0376-8716(00)00234-9}}</ref>

===Neurotoxicity===
Similarly to other [[NMDA antagonist]]s like [[ketamine]], N<sub>2</sub>O has been demonstrated to produce [[neurotoxicity]] in the form of [[Olney's lesions]] (damage to the [[posterior cingulate]] and [[retrosplenial region|retrosplenial cortices]] of the [[brain]]) in rodents upon prolonged (e.g., several hour) exposure.<ref name="pmid14622904">{{cite journal|author = Jevtovic-Todorovic V, Beals J, Benshoff N, Olney JW|title = Prolonged exposure to inhalational anesthetic nitrous oxide kills neurons in adult rat brain|journal = Neuroscience|volume = 122|issue = 3|pages = 609–16|year = 2003|pmid = 14622904|doi = 10.1016/j.neuroscience.2003.07.012}}</ref><ref name="pmid12854473">{{cite journal|author = Nakao S, Nagata A, Masuzawa M, ''et al.''|title = [NMDA receptor antagonist neurotoxicity and psychotomimetic activity]|language = Japanese|journal = Masui. the Japanese Journal of Anesthesiology|volume = 52|issue = 6|pages = 594–602|year = 2003|pmid = 12854473}}</ref><ref name="pmid10928976">{{cite journal|unused_data = DUPLICATE DATA: doi = 10.1038/sj.bjp.0703479|author = Jevtovic-Todorovic V, Benshoff N, Olney JW|title = Ketamine potentiates cerebrocortical damage induced by the common anaesthetic agent nitrous oxide in adult rats|journal = British Journal of Pharmacology|volume = 130|issue = 7|pages = 1692–8|year = 2000|pmid = 10928976|pmc = 1572233|doi = 10.1038/sj.bjp.0703479}}</ref><ref name="pmid15718054">{{cite journal|author = Jevtovic-Todorovic V, Carter LB|title = The anesthetics nitrous oxide and ketamine are more neurotoxic to old than to young rat brain|journal = Neurobiology of Aging|volume = 26|issue = 6|pages = 947–56|year = 2005|pmid = 15718054|doi = 10.1016/j.neurobiolaging.2004.07.009}}</ref> However, it also simultaneously exerts widespread [[neuroprotective]] effects via inhibiting [[glutamate]]-induced [[excitotoxicity]], and it has been argued that on account of its very short duration under normal circumstances, N<sub>2</sub>O may not share the neurotoxicity of other NMDA antagonists.<ref name="pmid16179534">{{cite journal|author = Abraini JH, David HN, Lemaire M|title = Potentially neuroprotective and therapeutic properties of nitrous oxide and xenon|journal = Annals of the New York Academy of Sciences|volume = 1053|pages = 289–300|year = 2005|pmid = 16179534|doi = 10.1196/annals.1344.025}}</ref> Indeed, in rodents, short-term exposure results in only mild injury that is rapidly reversible, and permanent neuronal death only occurs after constant and sustained exposure.<ref name="pmid14622904"/>

==Safety==
The major safety hazards of nitrous oxide come from the fact that it is a compressed liquefied gas, an asphyxiation risk, and a [[dissociative]] [[anaesthetic]]. Exposure to nitrous oxide causes short-term decreases in mental performance, audiovisual ability, and manual dexterity.<ref>Criteria for a recommended standard: occupational exposure to waste anesthetic gases and vapors. Cincinnati, OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health, DHEW (NIOSH) Publication No. 77B140.</ref> Long term exposure can cause vitamin B{{ssub|12}} deficiency, numbness, reproductive side effects, and other problems (see ''[[Nitrous oxide#Recreational use|Recreational use]]'' and ''[[Nitrous oxide#Biological|Biological]]'' factors in this article).

The [[National Institute for Occupational Safety and Health]] recommends that workers' exposure to nitrous oxide should be controlled during the administration of anesthetic gas in medical, dental, and veterinary operators.<ref>[http://www.cdc.gov/niosh/noxidalr.html CDC.gov NIOSH Alert: Controlling Exposures to Nitrous Oxide During Anesthetic Administration]. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 94-100</ref>

===Chemical/physical===
At room temperature (20°C) the saturated vapor pressure is 58.5 bar, rising up to 72.45 bar at 36.4°C — the [[critical temperature]]. The pressure curve is thus unusually sensitive to temperature.<ref>[http://encyclopedia.airliquide.com/encyclopedia.asp?LanguageID=11&CountryID=19&Formula=&GasID=55&UNNumber= Air Liquid data on Nitrous oxide]</ref> Liquid nitrous oxide acts as a good solvent for many [[organic compounds]]; liquid mixtures may form shock sensitive explosives.{{Citation needed|date=August 2007}}

As with many strong oxidizers, contamination of parts with fuels have been implicated in rocketry accidents, where small quantities of nitrous/fuel mixtures explode due to 'water hammer' like effects (sometimes called 'dieseling' — heating due to [[adiabatic]] compression of gases can reach decomposition temperatures).<ref>[http://www.ukrocketman.com/rocketry/hybridukhistory.shtml Vaseline triggered explosion of hybrid rocket]</ref> Some common building materials such as stainless steel and aluminium can act as fuels with strong oxidisers such as nitrous oxide, as can contaminants, which can ignite due to adiabatic compression.<ref>[http://www.airproducts.com/nr/rdonlyres/8c46596e-2f7d-4895-b12a-e54cd63e1996/0/safetygram20.pdf Safetygram 20: Nitrous Oxide]</ref>

There have also been accidents where nitrous oxide decomposition in plumbing has led to the explosion of large tanks.<ref>[http://www.hobbyspace.com/AAdmin/archive/SpecialTopics/Misc/eindhoven.pdf Nitrous Oxide Trailer Rupture July 2, 2001] Report at CGA Seminar “Safety and Reliability of Industrial Gases, Equipment and Facilities”, October 15–17, 2001, St. Louis, Missouri by Konrad Munke, LindeGas AG</ref>

===Biological===
Nitrous oxide inactivates the cobalamin form of vitamin B{{ssub|12}} by oxidation. Symptoms of vitamin B{{ssub|12}} deficiency, including [[sensory neuropathy]], [[myelopathy]], and [[encephalopathy]], can occur within days or weeks of exposure to nitrous oxide [[anesthesia]] in people with subclinical vitamin B{{ssub|12}} deficiency.{{Citation needed|date=April 2008}} Symptoms are treated with high doses of vitamin B{{ssub|12}}, but recovery can be slow and incomplete.<ref>AJ Giannini. Drug Abuse. Los Angeles, Health Information Press, 1999 ISBN 1885987110</ref> People with normal vitamin B{{ssub|12}} levels have stores to make the effects of nitrous oxide insignificant, unless exposure is repeated and prolonged (nitrous oxide abuse).{{Citation needed|date=April 2008}} Vitamin B{{sub|12}} levels should be checked in people with risk factors for vitamin B{{ssub|12}} deficiency prior to using nitrous oxide anesthesia.

A study of workers<ref>{{cite journal|doi=10.1056/NEJM199210013271405|pmid=1298226|year=1992|last1=Rowland|first1=AS|last2=Baird|first2=DD|last3=Weinberg|first3=CR|last4=Shore|first4=DL|last5=Shy|first5=CM|last6=Wilcox|first6=AJ|title=Reduced fertility among women employed as dental assistants exposed to high levels of nitrous oxide.|volume=327|issue=14|pages=993–7|journal=The New England journal of medicine}}</ref>
and several experimental animal studies<ref name="ReferenceA">{{cite journal|pmid=7189346|year=1980|last1=Vieira|first1=E|last2=Cleaton-Jones|first2=P|last3=Austin|first3=JC|last4=Moyes|first4=DG|last5=Shaw|first5=R|title=Effects of low concentrations of nitrous oxide on rat fetuses.|volume=59|issue=3|pages=175–7|journal=Anesthesia and analgesia}}</ref><ref name="ReferenceA"/><ref>{{cite journal|pmid=465253|year=1979|last1=Vieira|first1=E|title=Effect of the chronic administration of nitrous oxide 0.5% to gravid rats.|volume=51|issue=4|pages=283–7|journal=British journal of anaesthesia|doi=10.1093/bja/51.4.283}}</ref><ref>{{cite journal|pmid=6821624|year=1983|last1=Vieira|first1=E|last2=Cleaton-Jones|first2=P|last3=Moyes|first3=D|title=Effects of low intermittent concentrations of nitrous oxide on the developing rat fetus.|volume=55|issue=1|pages=67–9|journal=British journal of anaesthesia|doi=10.1093/bja/55.1.67}}</ref> indicate that adverse reproductive effects for pregnant females may also result from chronic exposure to nitrous oxide.

===Environmental===
Nitrous oxide is a [[greenhouse gas]], accounting for around 6% of the heating effect of greenhouse gases in the atmosphere.<ref>[http://news.nationalgeographic.com/news/2009/09/090908-global-warming-greenhouse-gases.html Manure, HD TVs Among Greenhouse Gas Sources to Watch] John Roach National Geographic News September 8, 2009</ref> According to 2006 data from the [[United States Environmental Protection Agency]], industrial sources make up only about 20% of all [[anthropogenic]] sources, and include the production of [[nylon]], and the burning of fossil fuel in internal combustion engines. Human activity is thought to account for 30%; tropical soils and oceanic release account for 70%.<ref>{{cite web
|url = http://www.epa.gov/nitrousoxide/sources.html
|title = Sources and Emissions -- Where Does Nitrous Oxide Come From?
|publisher = U. S. Environmental Protection Agency
|author =
|accessdate = 2008-02-02
|year = 2006
}}</ref> However, a 2008 study by Nobel Laureatte [[Paul Crutzen]] suggests that the amount of nitrous oxide release attributable to agricultural nitrate fertilizers has been seriously underestimated, most of which would presumably come under soil and oceanic release in the Environmental Protection Agency data.<ref>{{cite web|url=http://www.atmos-chem-phys.net/8/389|title=N<sub>2</sub>O release from agro-biofuel production negates global warming reduction by replacing fossil fuels}}</ref> Atmospheric levels have risen by more than 15% since 1750.<ref>{{Cite web|title=Climate Change 2007: The Physical Sciences Basis| url=http://ipcc-wg1.ucar.edu/wg1/wg1-report.html|publisher=[[Intergovernmental Panel on Climate Change|IPCC]]|accessdate=2007-04-30}}</ref> Nitrous oxide also causes [[ozone depletion]]. A new study suggests that N{{ssub|2}}O emission currently is the single most important ozone-depleting substance (ODS) emission and is expected to remain the largest throughout the 21st century.<ref>[http://www.sciencemag.org/cgi/content/abstract/1176985 Sciencemag.org]</ref><ref>[http://www.newscientist.com/article/dn17698-laughing-gas-is-biggest-threat-to-ozone-layer.html Newscientist.com]</ref>

==Legality==
In the [[United States]], possession of nitrous oxide is legal under federal law and is not subject to [[Drug Enforcement Administration|DEA]] purview.<ref name="ccle">[http://www.cognitiveliberty.org/dll/N20_state_laws.htm Center for Cognitive Liberty and Ethics: State Laws Concerning Inhalation of Nitrous Oxide]</ref> It is, however, regulated by the [[Food and Drug Administration]] under the Food Drug and Cosmetics Act; prosecution is possible under its "misbranding" clauses, prohibiting the sale or distribution of nitrous oxide for the purpose of [[recreational drug use|human consumption]].

Many states have laws regulating the possession, sale, and distribution of nitrous oxide. Such laws usually ban distribution to minors or limit the amount of nitrous oxide that may be sold without special license.{{Citation needed|date=July 2008}}
*In the state of California, possession for recreational use is prohibited and qualifies as a misdemeanor.<ref>[http://codes.lp.findlaw.com/cacode/PEN/3/1/10/s381b CAL. PEN. CODE § 381b : California Code – Section 381b]</ref>

In some countries, it is illegal to have nitrous oxide systems plumbed into an engine's intake manifold. These laws are ostensibly used to prevent [[street racing]] and to meet [[emission standard]]s. {{Citation needed|date=October 2009}}

Nitrous oxide is entirely legal to possess and inhale in the United Kingdom, although supplying it to others to inhale, especially minors, is more likely to end up with a prosecution under the Medicines Act.{{Citation needed|date=October 2009}}

In [[New Zealand]], the [[New Zealand Ministry of Health|Ministry of Health]] has warned that nitrous oxide is a prescription medicine, and its sale or possession without a prescription is an offense under the Medicines Act.<ref>[http://www.beehive.govt.nz/ViewDocument.aspx?DocumentID=23487 Beehive.govt.nz – Time's up for sham sales of laughing gas]</ref> This statement would seemingly prohibit all non-medicinal uses of the chemical, though it is implied that only recreational use will be legally targeted.

In [[India]], for general anaesthesia purposes, nitrous oxide is available as Nitrous Oxide IP. India's gas cylinder rules (1985) permit the transfer of gas from one cylinder to another for breathing purposes. This law benefits remote hospitals, which would otherwise suffer as a result of India's geographic immensity. Nitrous Oxide IP is transferred from bulk cylinders (17,000 liters capacity gas) to smaller pin-indexed valve cylinders (1,800 liters of gas), which are then connected to the yoke assembly of [[Boyle's machine]]s. Because India's Food & Drug Authority (FDA-India) rules state that transferring a drug from one container to another (refilling) is equivalent to manufacturing, anyone found doing so must possess a drug manufacturing license.

==See also==
*[[Whipped-cream charger]]
*[[Diffusion hypoxia]]

==References==
{{Reflist|2}}

==External links==
*[http://www.osha.gov/SLTC/healthguidelines/nitrousoxide/recognition.html Occupational Safety and Health Guideline for Nitrous Oxide]
*[http://www.vega.org.uk/video/programme/111 Paul Crutzen Interview] Freeview video of Paul Crutzen Nobel Laureate for his work on decomposition of ozone talking to Harry Kroto Nobel Laureate by the Vega Science Trust.
*[http://www.npi.gov.au/database/substance-info/profiles/67.html National Pollutant Inventory – Oxide of nitrogen fact sheet]
*[http://www.cdc.gov/niosh/topics/nitrousoxide/ National Institute for Occupational Safety and Health – Nitrous Oxide]
*[http://www.justsayn2o.com Nitrous Oxide FAQ]
*[http://www.erowid.org/chemicals/nitrous/nitrous.shtml Erowid article on Nitrous Oxide]
*[http://www.sciencenews.org/view/generic/id/46776/title/Nitrous_oxide_fingered_as_monster_ozone_slayer Nitrous oxide fingered as monster ozone slayer], Science News

{{Drug use}}
{{Hallucinogens}}
{{General anesthetics}}
{{Analgesics}}
{{Anxiolytics}}
{{Glutamatergics}}
{{Cholinergics}}
{{Neurotransmitters}}
{{E number infobox 930-949}}

{{DEFAULTSORT:Nitrous Oxide}}
[[Category:Inorganic nitrogen compounds]]
[[Category:Aerosol propellants]]
[[Category:General anesthetics]]
[[Category:Dissociative drugs]]
[[Category:Greenhouse gases]]
[[Category:NMDA receptor antagonists]]
[[Category:Monopropellants]]
[[Category:Rocket oxidizers]]
[[Category:Inhalants]]
[[Category:Occupational safety and health]]
[[Category:Vehicle modification]]
[[Category:World Health Organization essential medicines]]
[[Category:Euphoriants]]

[[ar:أكسيد النيتروس]]
[[bs:Dušik suboksid]]
[[bg:Диазотен оксид]]
[[ca:Òxid nitrós]]
[[cs:Oxid dusný]]
[[da:Lattergas]]
[[de:Distickstoffmonoxid]]
[[et:Dilämmastikoksiid]]
[[es:Óxido de nitrógeno (I)]]
[[eo:Ridgaso]]
[[fa:مونوکسید دی نیتروژن]]
[[fr:Protoxyde d'azote]]
[[gl:Óxido nitroso]]
[[ko:아산화 질소]]
[[hi:नाइट्रस ऑक्साइड]]
[[id:Nitrogen dioksida]]
[[it:Ossido di diazoto]]
[[he:חמצן דו-חנקני]]
[[lt:Diazoto monoksidas]]
[[hu:Dinitrogén-oxid]]
[[arz:غاز مضحك]]
[[nl:Lachgas]]
[[ja:亜酸化窒素]]
[[no:Dinitrogenoksid]]
[[nds:Distickstoffmonoxid]]
[[pl:Podtlenek azotu]]
[[pt:Óxido nitroso]]
[[ro:Protoxid de azot]]
[[ru:Оксид азота(I)]]
[[simple:Nitrous oxide]]
[[sk:Oxid dusný]]
[[sl:Didušikov oksid]]
[[sr:Азотсубоксид]]
[[fi:Ilokaasu]]
[[sv:Lustgas]]
[[th:ไนตรัสออกไซด์]]
[[uk:Оксид азоту]]
[[ur:Nitrous oxide]]
[[zh-yue:笑氣]]
[[zh:一氧化二氮]]
[[Category:2Fix]]