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CATEGORIES (articles) > Fuel System > Technical > Nitrous oxide (NOS) explained

Nitrous oxide (NOS) explained


Name Dinitrogen oxide
Chemical formula N2O
Appearance Colorless gas


Formula weight 44.0 u
Melting point 182.29 K (−90.86 °C)
Boiling point 184.67 K (−88.48 °C)
Critical temperature 309.6 K (36.4 °C)
Critical pressure 7.245 MPa
Density 1.2 g/cm3 (liquid)
Solubility 0.112 g in 100g water


ΔfH0gas 82.05 kJ/mol
ΔfH0liquid ? kJ/mol
ΔfH0solid ? kJ/mol
S0gas, 100 kPa 219.96 J/(mol·K)
S0liquid, 100 kPa ? J/(mol·K)
S0solid ? J/(mol·K)


Inhalation See main text. May cause asphyxiation without warning.
Skin Hazardous when cryogenic or compressed.
Eyes Hazardous when cryogenic or compressed.
More info Hazardous Chemical Database
SI units were used where possible. Unless otherwise stated, standard conditions were used.

Disclaimer and references

This article is about nitrous oxide, or laughing gas. For other meanings of laughing gas, see the disambiguation page.

Nitrous oxide, also known as dinitrogen oxide or dinitrogen monoxide, is a chemical compound with chemical formula N2O. Under room conditions, it is a colourless non-flammable gas, with a pleasant, slightly-sweet odor. It is used in surgery and dentistry for its anaesthetic and analgesic effects, where it is commonly known as laughing gas due to the euphoric effects of inhaling it. It is also used as an oxidizer in internal combustion engines. In this use it is known as nitrous, or NOS after a well-known brand which has become a genericized trademark. Nitrous oxide is present in the atmosphere where it acts as a powerful greenhouse gas.


The structure of the nitrous oxide molecule is a linear chain of a nitrogen atom bound to a second nitrogen, which in turn is bound to an oxygen atom. It can be considered a resonance hybrid of N≡N+−O and N=N+=O.

Nitrous oxide, N2O, should not be confused with the other nitrogen oxides such as nitric oxide NO and nitrogen dioxide NO2.

Nitrous oxide is isoelectronic with carbon dioxide.

It can be prepared by heating ammonium nitrate in the laboratory and can be used to produce nitrites by mixing it with boiling alkali metals, and to oxidize organic compounds at high temperatures.

The CAS number of nitrous oxide is 10024-97-2 and its UN number is 1070.


The gas was discovered by Joseph Priestley in 1772, who called it phlogisticated nitrous air (see phlogiston). Humphry Davy in the 1790s tested the gas on himself and some of his friends, including the poets Samuel Taylor Coleridge and Robert Southey. They soon realised that nitrous oxide considerably dulled the sensation of pain, even if the inhaler were still semi-conscious. And so it came into use as an anaesthetic, particularly by dentists, who do not typically have access to the services of an anesthesiologist and who may benefit from a patient who can respond to verbal commands.


Nitrous oxide is most commonly made by fusing and "boiling" ammonium nitrate to form steam, nitrous oxide, nitrogen, ammonium nitrate 'fog' and small amounts of very toxic higher oxides of nitrogen; (NO2, NO, etc):

NH4NO3 → N2O + 2H2O, ΔH = −36.8 kJ:

The addition of various phosphates favors formation of a purer gas. This reaction occurs at around 240°C, a temperature where ammonium nitrate is a moderately sensitive explosive and a very powerful oxidizer (perhaps on the order of fuming nitric acid). At temperatures much above 240°C the exothermic reaction may run away, perhaps up to the point of detonation. The mixture must be cooled to avoid such a disaster. In practice, the reaction involves a series of tedious adjustments to control the temperature to within a narrow range, which it will not naturally tend to stay in. Professionals have destroyed whole neighborhoods by losing control of such commercial processes. Examples include the Ohio Chemical debacle in Montreal, 1966 and the Air Products & Chemicals, Inc. disaster in Delaware City, Delaware, 1977.

The direct oxidation of ammonia may someday rival the ammonium nitrate pyrolysis synthesis of nitrous oxide mentioned above. This is a capital-intensive process originating in Japan that uses a manganese dioxide-bismuth oxide catalyst. (Suwa et al. 1961; Showa Denka Ltd.)

2NH3 + 2O2 → N2O + 3H2O:

Higher oxides of nitrogen are formed as impurities. Note that uncatalyzed ammonia oxidation (i.e. combustion or explosion) goes primarily to N2 and H2O. The Ostwald process oxidizes ammonia to nitric oxide (NO), using platinum; this is the beginning of the modern synthesis of nitric acid from ammonia (see above).

Nitrous oxide can be made by heating a solution of sulfamic acids and nitric acids. A lot of gas was made this way in Bulgaria (Brozadzhiew & Rettos, 1975).

HNO3 + NH2SO3H → N2O + H2SO4 + H2O:

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

Colorless solutions of hydroxylamine hydrochloride and sodium nitrite may also be used to produce N2O.

(NH3OH+Cl-) + NaNO2 → N2O + NaCl + H2O:
If the nitrite is added to the hydroxylamine solution, the gas produced is pure enough for inhalation, and 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 form are produced.


Inhalant effects — laughing gas

8g canister of nitrous oxide

Nitrous oxide (N2O) is a dissociative that can cause analgesia, euphoria, dizziness, flanging of sound, and, in some cases, slight hallucinations and mild aphrodisiac effect. It can also result in mild nausea or lingering dizziness if too much is inhaled in too short a time. Other commonly reported side effects include stomach irritation and headache.

During the 19th century, William James and many contemporaries found that inhalation of nitrous oxide resulted in a powerful spiritual and mystical experience for the user. James claimed to experience the fusing of dichotomies into a unity and a revelation of ultimate truth during the inhalation of nitrous oxide. Memory of this experience, however, quickly faded and any attempt to communicate was difficult at best.

The drug currently (as of 2005) enjoys moderate popularity in some countries as an inhalant. It was often sold at Grateful Dead and Phish concerts. One slang term for the drug is Hippie Crack; this term implies commentary on the typical user of the substances as well as purported similarities between its psychological addiction potential or the short-lived duration of its effects and similar properties of "crack" cocaine.

The recreational use of nitrous oxide is restricted in many districts of the United States. In California, for instance, inhalation of nitrous oxide "for the purpose of causing euphoria, or for the purpose of changing in any manner one’s mental processes," is a criminal offense under its criminal code (Cal. Pen. Code, Sec. 381b).

Since nitrous oxide can cause dizziness, dissociation, and temporary loss of motor control, it is unsafe to inhale while standing up. Inhalation directly from a tank poses serious health risks, as it can cause the lungs to collapse from high levels of pressure, forcing air into the chest cavity, and can cause frostbite since the gas is very cold when released. For those reasons, most recreational users will discharge the gas into a balloon or whipped-cream dispenser before inhaling.

While the pure gas itself is not toxic, death can result if it is inhaled in such a way that not enough oxygen is breathed in. Long-term use in large quantities has been associated with dangerous symptoms similar to vitamin B12 deficiency: anemia due to reduced hemopoiesis, neuropathy, tinnitus, and numbness in extremities. In chronic use it is also teratogenic, and foetotoxic. It can be habit-forming, mainly because of its short-lived effect (generally from 1 - 5 minutes in recreational doses) and ease of access.

Inhaling industrial-grade nitrous oxide is also dangerous, as it contains many impurities and is not intended for use on humans. Food grade nitrous oxide is also not meant to be inhaled; the bulbs commonly have industrial lubricants from their manufacturing process on and in them. When the bulb is punctuated, these solvents can aerosol, introducing unknown particles into the gas. These lubricants commonly leave an oily residue on the bulb "cracker" or inside the whipped cream dispenser.

Finally, nitrous oxide should not be confused with nitric oxide, an extremely poisonous gas.


Medical grade nitrous oxide tanks used in dentistry

Nitrous oxide is a weak general anesthetic, and is generally not used alone in anaesthesia. However, it has a very low short-term toxicity and is an excellent analgesic, so a 50/50 mixture of nitrous oxide and oxygen ("gas and air", supplied under the trade name Entonox) is commonly used during childbirth, for dental procedures, and in emergency medicine.

In general anesthesia it is often used in an 2:1 ratio with oxygen in addition to more powerful general anaesthetic agents such as sevoflurane or desflurane. Its lower solubility in blood means it has a very rapid onset and offset.

It has a MAC of 105% and a blood:gas partition coefficient of 0.46. Less than 0.004% is metabolised in humans.

Nitrous oxide is liquid at approximately 760 psi at room temperature, and is usually stored and shipped as a self-pressurized liquid.


Use of nitrous oxide for prolonged periods results in inhibition of the enzyme methionine synthase which is involved in protein synthesis, causing changes in bone marrow after as short a time as 3-4 hours. The enzyme is very important, as methionine, an amino acid, it helps produce is the starting amino acid for all proteins synthesised. This is a direct result of irreversibly oxidising the Cobalt II up to the III state in the Vitamin B12, a cofactor in the methionine synthase. Furthermore the enzyme cannot displace the oxidised B12, so the only regeneration possible is de-novo synthesis of new enzyme, in the presence of fresh, intact B12. Prolonged exposure to nitrous oxide may cause agranulocytosis, as well as leading to increased plasma concentrations of Homocysteine which has been implicated as a risk factor for peri-operative myocardial ischemia.

Aerosol propellant

The gas is licensed for use as a food additive, specifically as an aerosol spray propellant. Its most common uses in this context are in aerosol whipped cream canisters and as an inert gas used to displace staleness-inducing oxygen 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, under increased pressure the oxygen would accelerate the butterfat turning rancid, while nitrous oxide inhibits such degradation.

Rocket motors

Nitrous oxide can be used as an oxidizer in a rocket engine. This has the advantages over other oxidizers that it is non-toxic and, due to its stability at room temperature, easy to store and relatively safe to carry on a flight.

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 and high power rocketry with various plastics as the fuel. An episode of MythBusters featured a hybrid rocket built using a paraffin/powdered carbon mixture (and later salami) as its solid fuel and nitrous oxide as its oxidizer.

Internal combustion engine

Main article: Nitrous

In car racing, nitrous oxide (often just "nitrous" in this context) is sometimes injected into the intake manifold (or just prior to the intake manifold) to increase power: even though the gas itself is not flammable, it delivers more oxygen than atmospheric air by breaking down at elevated temperatures, thus allowing the engine to burn more fuel and air. Additionally, since nitrous oxide is stored as a liquid, the evaporation of liquid nitrous oxide in the intake manifold causes a large drop in intake charge temperature. This results in a smaller, denser charge, and can reduce detonation, as well as increase power available to the engine.

The same technique was used during by World War II Luftwaffe aircraft with the GM 1 system to boost the power output of aircraft engines. 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, high-speed bombers and high-altitude interceptors.

One of the major problems of using nitrous oxide in a reciprocating engine is that it can produce enough power to destroy the engine. Power increases of 100-300% are possible, and unless the mechanical structure of the engine is reinforced, most engines would not survive this kind of operation.

There are several ways of introducing nitrous into a motor. Nitrous kits such as BOSS NOSS, NOS, Nitrous Express, Nitrous Direct brands offer different solutions. You will find Dry kits, Wet kits & Direct port.

It is very important with nitrous oxide augmentation of internal combustion engines to maintain temperatures and fuel levels so as to prevent preignition, or detonation (sometimes referred to as knocking or pinging).


The major safety hazards of nitrous oxide come from the fact that it is a compressed liquified gas, and a dissociative anaesthetic.

While normally inert in storage and fairly safe to handle, nitrous oxide can decompose energetically and potentially detonate if initiated under the wrong circumstances. Liquid nitrous oxide acts a good solvent for many organic compounds; liquid mixtures can form somewhat sensitive explosives. Contamination with fuels has been implicated in a handful of rocketry accidents, where small quantities of nitrous / fuel mixtures detonated, triggering the explosive decomposition of residual nitrous oxide in plumbing.

Nitrous oxide in the atmosphere

Greenhouse gas trends.

Unlike the other Nitrogen oxides, nitrous oxide is a greenhouse gas; per unit of weight, nitrous oxide has 296 times the effect of carbon dioxide (CO2) for producing global warming ([1] 248.htm) . Nitrous oxide is thus part of efforts to curb greenhouse gas emissions, such as the Kyoto Protocol. Behind carbon dioxide and methane, which has 23 times the greenhouse warming potential of carbon dioxide (over 100 years), nitrous oxide is the third most important gas that contributes to global warming. (The other nitrogen oxides contribute to global warming indirectly, by contributing to tropospheric ozone production during smog formation).

Nitrous oxide also attacks ozone in the stratosphere, aggravating the excess amount of UV striking the earth's surface in recent decades (various freons and related halogenated organics also consume ozone in the stratosphere). In the pre-industrial atmosphere nitrous oxide was (and remains) the main natural regulator of stratospheric ozone.

Nitrous oxide is naturally emitted by bacteria in soils and oceans. Agriculture is the main source of human-produced nitrous oxide: cultivating soil, the use of nitrogen fertilizers, and animal waste handling can all stimulate naturally-occuring bacteria to produce more nitrous oxide. Industrial sources make up only about 20% of all anthropogenic sources, and include the production of nylon and nitric acid and the burning of fossil fuel in internal combustion engines.

Human activity is thought to account for somewhat less than 2 teragrams (this is multiplied by about 300 when calculated as a ratio to carbon dioxide) of nitrogen oxides per year, nature for over 15 teragrams ([2] sources.html) . The global anthropogenic nitrous oxide flux is about 1 petagram of carbon dioxide carbon-equivalents per year; this compares to 2 petagrams of methane carbon dioxide carbon-equivalents per year, and to an atmospheric loading rate of about 3.3 petagrams of carbon dioxide carbon-equivalents per year.


Under United States federal law, possession of nitrous oxide is legal and is not subject to DEA purview. 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 human consumption (the recreational drug use market). Given the necessity of proving intent of either buyer or seller in this case, though, such prosecution are rare.

Many states have laws regulating the possession, sale, and distribution of nitrous oxide; ([3] N20_state_laws.htm) but these are normally limited to either banning distribution to minors, or to setting an upper limit for the amount of nitrous oxide that may be sold without special license, rather than banning possession or distribution completely. In most jurisdictions, like at the federal level, sale or distribution for the purpose of human consumption is illegal.

In all jurisdictions, however, such distribution, possession, and use are legal even though intended for human consumption, when done under the supervision and diretion of licensed medical professional such as a physician or dentist.

Nitrous oxide injection systems for automobiles are usually legal, although some localities require certified system components. There have been reported instances of police officers arresting drivers of vehicles equipped with N2O injection systems on the grounds that he or she intends to inhale it, although such auto-grade N2O is often mixed with about 100 ppm sulfur dioxide, which makes inhalation a noxious or even fatal affair.

Sanctioning bodies in motor sport have banned the material in some classes; in 1976, NASCAR disqualified many drivers for nitrous oxide; in June 1998, the NHRA suspended Pro Stock driver Jerry Eckman and car owner Bill Orndorff for a year, stripped the team of all points, and imposed a fine for violations. The team closed down shortly after the suspension.


Nitrous oxide shares many pharmacological similarities with other inhaled anesthetics, but there are a number of differences.

Nitrous oxide is relatively non-polar, has a low molecular weight, and high lipid solubility. As a result it can quickly diffuse into phospholipid cell membranes.

Like many classical anesthetics, the exact mechanisms of action is still open to some conjecture. It inhibits the NMDA receptor at partial pressures similar to those used in general anaesthesia (Jevtovic-Todorovic et al., 1998; Mennerick et al., 1998; Yamakura & Harris, 2000). The evidence on the effect of N2O on GABA-A currents is mixed, but tends to show a lower potency potentiation (Dzoljic & Van Duijn, 1998; Mennerick et al., 1998; Yamakura & Harris, 2000). N2O, like other volatile anesthetics, activates twin-pore potassium channels, albeit weakly. These channels are largely responsible for keeping neurons at the resting (unexcited) potential (Gruss et al., 2004). Unlike many anesthetics, however, N2O does not seem to affect calcium channels (Mennerick et al., 1998).

Unlike most general anesthetics, N2O appears to affect the GABA receptor. In many behavioral tests of anxiety, a low dose of N2O is a successful anxiolytic. This anti-anxiety effect is partially reversed by benzodiazepine receptor antagonists. Mirroring this, animals which have developed tolerance to the anxiolytic effects of benzodiazepines are partially tolerant to nitrous oxide (Czech & Green, 1992; Emmanouil et al., 1994; Quock et al., 1992). Indeed, in humans given 30% N2O, benzodiazepine receptor antagonists reduced the subjective reports of feeling “high”, but did not alter psycho-motor performance (Zacny et al., 1995).

The effects of N2O seem linked to the interaction between the endogenous opioid system and the descending noradrenergic system. When animals are given morphine chronically they develop tolerance to its antinociceptive (pain killing) effects; this also renders the animals tolerant to the antinociceptive effects of N2O (Berkowitz et al., 1979). Administration of antibodies which bind and block the activity of some endogenous opioids (not beta-endorphin), also block the antinociceptive effects of N2O (Branda et al., 2000; Cahill et al., 2000). Drugs which inhibit the breakdown of endogenous opioids also potentiate the antinociceptive effects of N2O (Branda et al., 2000). Several experiments have shown that opioid receptor antagonists applied directly to the brain block the antinociceptive effects of N2O, but these drugs have no effect when injected into the spinal cord. Conversely, alpha-adrenoreceptor antagonists block the antinociceptive effects of N2O when given directly to the spinal cord, but not when applied directly to the brain (Fang et al., 1997; Guo et al., 1999; Guo et al., 1996). Indeed, alpha2B-adrenoreceptor knockout mice or animals depleted in noradrenaline are nearly completely resistant to the antinociceptive effects of N2O (Sawamura et al., 2000; Zhang et al., 1999). It seems N2O-induced release of endogenous opioids causes disinhibition of brain stem noradrenergic neurons, which release norepinephrine into the spinal cord and inhibit pain signaling (Maze, M. and M. Fujinaga, 2000). Exactly how N2O causes the release of opioids is still uncertain.

N2O seems to induce its effects through antagonism on NMDA receptors, GABA-A receptor potentiation and potassium channel activation, as well as having a benzodiazepine-like effect and stimulating endogenous opioid receptors.

Laughing gas in movies and fiction

  • Laughing Gas (movie)
  • Laughing Gas (novel)
  • Laughing Gas is one of the main weapons used by the Batman villain, The Joker, only he uses a concoction which is portrayed as being green and lethal.
  • In order to experience a "high", the dentist character (Steve Martin) in the musical film version of Little Shop of Horrors dies from the inhalation of laughing gas.
  • In the television program, Hey Arnold!, Helga Pataki calls Arnold while on laughing gas and confesses her love for him. When she realizes what she did, she sneaks into his house and tries to get the answering machine tape in which the confession is recorded.
  • Two of the main characters in the American re-make of the film Taxi get trapped in a room filled with laughing gas.
  • The main character of Zodiac, Sangamon Taylor, uses it as a drug, and even came up with Sangamon's Principle to explain why it should be used over other drugs.
  • In Black Sheep, the two main protagonists borrow a police car and its nitrous oxide boosters leak after hitting a pothole, intoxicating the duo.
  • In the Munsters episode where Herman sneaks into the hospital to visit Eddie after hours, Herman is given laughing gas by the staff. Lily thinks that he was out drinking.
  • In the Problem Child 3: Junior in Love the dentist used laughing gas to hibernate Junior.
  • In the movies Fast and the Furious and 2 Fast 2 Furious, nitrous oxide is largely used in most of cars.
  • In the film Mission: Impossible II, emergency oxygen masks are deployed on a commercial airliner, but instead of providing oxygen they dispense nitrous oxide, rendering the passengers and pilot unconscious.
  • In The Pink Panther Strikes Again, Inspector Clouseau, disguised as a dentist, administers laughing gas to Dreyfus (and to himself) and proceeds to remove the wrong tooth.
  • In the film Final Destination 2, Tim Carpenter is nearly killed when he is accidentally administered a constant stream of pure nitrous oxide at a dentist's office. In the dentist's absence, a toy from a mobile above the chair falls into Tim's mouth forcing him either to breathe the pure nitrous oxide or choke.
  • An episode of The Fresh Prince of Bel Air shows Will and Carlton in a dentist's office with William Shatner and the valve on a nitrous oxide tank comes loose. The three become extremely intoxicated and later show the hangover symptoms.
  • In the animated series GI Joe, laughing gas was commonly used to torture prisoners of Cobra, most often by the Dreadnoks. The torture was actually unrealistic to actual laughing gas, in that the Cobra laughing gas made its victims laugh so hard they soon were in pain and, in at least one episode, the gas appeared to tickle its victims when coming into contact with skin.
  • Nitrous oxide use is portrayed in the movie Kids.
  • Nitrous oxide is used by characters in the movie Bio-Dome.
  • Nitrous oxide is used by several characters in the movie Tank Girl.
  • Use of Nitrous Oxide is implied, but not shown, in the movie Old School.
  • In the 1998 movie Lethal Weapon 4, Mel Gibson, Danny Glover, Chris Rock and Kim Chan fight in a dentist's office which slowly fills with laughing gas from a leaking canister, causing the combatants to discontinue the fighting due to uncontrollable laughing.
  • 'Laughing Gas' is the name of a poem by Beat poet Allen Ginsberg.
  • Laughing Gas is also used in A Night At The Roxbury.

Laughing gas as a sexual fetish

In recent years, a number of adult sites and groups have appeared on the internet, which caterto various medical fetishes. There have been a number of Yahoo and MSN groups that cater to laughing gas as a sexual fetish exclusively or attatch it to the larger fetishes of dental, medical or sleeping gas fetishes. The oldest and longest running website devoted to the fetish of laughing gas exclusively, is The Laughing Gas Zone, which started out as a Yahoo adult group in 1997 and later became a website devoted to "fantasy" laughing gas mixed with the fetish of tickling. The site disclainmer states that it does not condone the actual use of laughing gas and further states that it promotes healthy fantasy based scenarios, rather than the real thing.

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