A quick introduction to Oxides of Nitrogen
Nitrogen and Oxygen can combine in many different ways, they are often confused by non-scientists who might simply refer to all of them as nitrous. There are the following possible molecules combining Nitrogen and Oxygen:
|NO||Nitric Oxide||Naturally occuring free radical. Produced in combustion (eg. In cars) and by the action of electricity on air (either naturally in lightening or man-made when a sparkplug discharges). An important component in the fixing of nitrogen, which is essential to al plant life.|
|NO2||Nitrogen Dioxide||Toxic Brown Gas. Toxic by inhalation. Product of combustion, major cause of pollution before catalytic converters were fitted to engine exhausts. In low concentration then when inhaled it can caused asthmatic effects. Also produced during lightening storms, which is why it is possible to “smell” lightening and also why asthma attacks are more frequent during thunder storms. Nitrogen dioxide is involved in the production of ozone at lower levels than the Ozone layer, this can result in health effects and photochemical smog when it is formed at low-levels. (not to be confused with the useful stratospheric Ozone)|
|N2O||Nitrous Oxide||Can be referred to as “laughing gas” due to its affect when used as an anaesthetic. Global warming contributor. Reduces low-level ozone concentrations. Inert at low temperatures (hence safe for use in cream chargers and food use) but an oxidising agent at high temperatures (hence use as NOZ in motors.|
|N4O||Nitrosylazide||Not very stable, only exists transiently as an in-between step in other reactions.|
|N2O3||Dinitrogen Trioxide||Solid at -20 degrees.|
|N2O4||Dintrogen Tetroxide||Exists in dynamic equlibrium with its partner in crime Nitrogen Dioxide. NB:: SEE ROCKET FUELS!!|
|N2O5||Dinotrogen Pentoxide||Unstable, highly explosive oxidising agent|
Most of these compounds are gases and can occur naturally, their properties can be very different. This article is specifically looking at Nitrous Oxide (N2O) but will mention the other oxides of nitrogen is passing as they are relevant. Of all these possible nitrogen/oxygen combinations only NO, N2O and NO2 would exist naturally at room temperature, all of the others are either to reactive/unstable or only exist as intermediaries in reactions. These compounds contain oxygen so as you might well expect, they are the products of combustion,they are also happy to release their oxygen which makes them useful oxidising agents – hence the term “nitro” to refer to powerful engines and combustion.
A brief history of Nitrous Oxide
The gas was discovered by Joseph Priestly and christened Diminished Nitrous Air in 1772. Priestly was not looking for nitrous oxide, but was simply trying to make and isolate as many gases as possible. At the time then most thought that there was only one gas “air” and Priestly was very much going against current thinking when he set about isolating and collecting different gases. The collection apparatus he used would be familiar to any school student, and involved collecting gases “over water” by displacement. As well as Nitrous Oxide, Priestly also identified Oxygen. He didn't discover Carbon Dioxide but he did notice that it could b dissolved to make soda water. As you might expect from a scientist that is involved in both Oxygen and Carbon Dioxide, Joseph Priestly also provided the foundations for the discovery of photosynthesis. His experiment with gas were no laughing matter for the mice involved... basically he firstly removed the oxygen from air and observed that a mouse would then suffocate, he the used a plant (mint) to photosynthesise and replace the oxygen thus keeping a mouse alive in an 18th Century Biosphere!
Once he'd discovered nitrous oxide, Joseph Priestly didn't really do much more work with – he was too busy supporting revolutions and emigrating to America. The next part of the nitrous story involves Humphry Davy who took up the baton in1798. He was tasked with finding the potential medical uses of the many recently discovered and isolated gases. Later in his life Davy was to save hundreds of lives by his invention the Davy Lamp – which relied upon hos knowledge of the properties of methane. His work clearly pointed out that inhaling Nitrous Oxide could have an anaesthetic affect he stated “nitrous oxide appears capable of destroying physical pain, it may probably be used with advantage during surgical operations in which no great effusion of blood takes place”. You would have thought that would be enough of a pointer for “laughing gas” to become used as an anaesthetic it would in fact be almost 50 years before its potential was realised.
Interestingly, Davy failed to promote the use of inhaling nitrous oxide as an anaesthetic but he was a big fan of its recreational use. Within a few years of him publishing his report then the British upper classes were having Nitrous Oxide Parties – it was perhaps the poet Samuel Coleridge that coined the term “laughing gas”. The gas was expensive at the time and its negative health effects weren't know see our report of misuse for more details. It should also be noted that at the time then other dangerous narcotics were more accepted in society (eg. Opium) so perhaps we shouldn't pay too much heed to their proclivities for narcotic parties! If we take Samuel Coleridge Taylor as an example he became an addict and suffered from chronic anxiety and depression.
Early medical use of Nitrous oxide, was demonstrated in the 1840s but it was not to become common until 1870. Although it was demonstrated to be effective it was resisted by patients “you'll take all of my teeth out if I'm asleep” and doctors “I like to hear them scream!”. As with all new treatments nitrous oxide gas was expensive at first, which possibly made it more popular with surgeons that could profit from the sale of nitrous oxide.
Uses of Nitrous Oxide
The uses of nitrous oxide can basically be broken down into three categories – (I) culinary and (ii) fuel oxidiser (iii)medical
Nitrous Oxide in the Kitchen: the properties that makes nitrous oxide useful as a cooking tool are that it is inert at low temperatures, will not react with other ingredients or impart any taste on food and it is only partially soluble in fats, and insoluble in aqueous solutions. If you compare this with CO2 you can see the merits of N2O. CO2 makes things taste – think of seltzer water, it has a distinct acidic flavour imparted by the gas, Nitrous does not have this affect. Carbon dioxide is slow to come out of solution – I takes hours for a bottle of coca cola to loose its fizz after the top has been removed. Compare this with nitrous whipped cream which has no lasting dissolved gas or fizz. The most common way of using the gas is to use cream chargers and a whipped cream dispenser. This site has lots of recipe ideas and explanations for how to use Nitrous Oxide for cooking, so I won't dwell on them here. But will point out that the fact Nitrous oxide from a cream charger will dissolve in fats but not water, mean you can whip with it and also simply use it as a means to get pressure inside the whipped cream dispenser.
Nitrous oxide as a fuel oxidiser: this relies upon the fact that nitrous oxide will release its Oxygen when heated to allow it to react with the fuel. See more at the end of this page.
Medical use of nitrous oxide: from a slow start in the early 19th century whereby the upper class were more keen on holding laughing gas parties than using it for medicine, it was the main anaesthetic for 100 years until the 1960s and is still commonly used in dental surgeries, hospitals and anywhere where an easily administered quick acting anaesthetic is needed. Some of its main advantages -even when more modern anaesthetics have been developed are that it is cheap and the effects of nitrous oxide gas are relatively short lived. It is sold in tanks that contain both nitrous oxide and oxygen which means it is impossible to inadvertently suffocate a patient by giving them pure Nitrous Oxide – this makes it safe to be administered even by untrained personnel, in ambulances or even by the patient themselves.
Where does Nitrous Oxide come from?
Nitrous oxide occurs naturally and can also be manufactured. There are various routes to the manufacture of nitrous oxide gas, but most involve the heat of a Nitrate Salt. Extreme caution needs to be used because not only are some oxides of nitrogen oxidisers but also some of the starting reagents can be explosive. Nitrous oxide is an entirely naturally occurring gas and is part of the nitrogen cycle that is essential to life on earth. It is worth noting that although atmospheric nitrous oxide gas is a natural phenomenon man's use and abuse of soils in modern farming techniques release greater levels of the gas than would occur naturally – see the later chapter on Nitrous Oxide the green house gas.
The method used by Joseph Priestly was to reduce Nitric oxide with warm iron filings. Which is why he referred to is as diminished nitrous air. The nitrous air was made by by reaction of copper with Nitric acid:
8 HNO3 + 3 Cu → 3 Cu(NO3)2 + 4 H2O + 2 NO
then followed by:
2NO + H2O + Fe ---> N2O + Fe(OH)2
It is in fact possible to make the Nitrous Oxide in a single stage by heating Ammonium Nitrate:
NH4NO3 (s) ---> 2 H2O (g) + N2O (g)
Ammonium nitrate is a common fertilizer and also an explosive, which is why making Nitrous Oxide is a simple but potentially dangerous procedure. Heating to 170 degrees will liberate the nitrous oxide gas, whereas heating to higher temperature, inducing an electric charge or extreme pressure can cause a violent explosion – furthermore the Nitrous Oxide gas liberated in the explosion will oxidise and accelerate any resulting fires. Indeed overheating by as little as 30 degrees could initiate a runaway exothermic reaction resulting in an explosion!
It is essential to remove the toxic NO (nitric oxide) during the manufacture of nitrous oxide gas this is done by washing the gas with sodium hydroxide solution. If you are purchasing nitrous oxide in the form of cream chargers then you will be obviously getting 100% pure nitrous oxide which is safe for making whipped cream, the same would apply to the cylinders of nitrous oxide that are supplied to dentists, hospitals and medical professionals. The same cannot be said for automotive nitrous oxide which is not just impure but also has sulphur additives added to it in order to make it toxic to make sure that it is not safe for human consumption.
Making your own Nitrous Oxide in a lab
It is indeed to make nitrous oxide in a simple school standard laboratory, although before you find out how it is worth noting three things!
- It is possible to create an explosion if a runaway exothermic reaction takes place.
- The nitrous oxide gas product is not going to be pure and is likely to contain highly toxic bi-products.
Instructions were published in the fantastically enthusiastic hobbyist magazine Popular Science in 1949 under the imaginative title The Gas That Makes You Laugh. These are perhaps the most detailed instructions, perhaps because in 1949 the people had more patience and wanted to do things correctly? Anyway, there is a much shorter version How To Make Laughing Gas if you don't have the patience to do it correctly! The second method claims to make “pure nitrous oxide” but then later on notes that it will contain “small quantities of oxides of nitrogen”. So there is a bit of a contradiction at that point – and remember that some of those oxides are very toxic and will literally blister your lungs of inhaled.
Nitrous oxide is an important, and naturally occurring gas. It's concentrations in the atmosphere is held constant by biological and chemical cycles – predominately as part of the nitrogen cycle, a process by which Nitrogen is moved between gaseous structures and soluble salts (nitrates) which as essential to plants (and animals). Nitrates are the only way that nitrogen, an essential component of amino acids can find their way into our cells. So without nitrous oxide, there would be no life on earth!
Nitrogen is present in a wide range of areas, home aquariums being a prime example. You can learn how the nitrogen cycle in the aquarium works.
The nitrogen cycle basically has two components:
- Nitrification – this is when nitrogen is “fixed”. Atmospheric nitrogen gas is converted by bacteria in the soil into various nitrates, which are water soluble and are available for plants to convert into growth, and from their into animals that eat then whereby the nitrogen becomes part of proteins in cells.
- De-nitrification – this process takes fixed nitrogen from the nitrates and converts it (via amongst other intermediaries Nitrous Oxide) back into atmospheric nitrous oxide gas.
Within our atmosphere these two processes would be in balance and the amount of fixed gaseous nitrogen would be fixed to be used by plants or re-released as gases by bacteria in a harmonious balanced cycle.
However.... if too much nitrates is available then the part of the cycle that releases the gas de-nitrification overwhelms the other half of the process. This is something that is occurring at the moment because of two main reasons:
- The use of synthetic fertilizers means that far more nitrates are being added to the soil than the plants could possibly hope to take up. This excess of nitrates causes a feeding frenzy of the de-nitrification bacteria – which results in an overload of nitrous oxide.
- The waste from animals whether deposited directly onto soils by free-roaming animals or processed and then used as from fertilizers – becomes food for the bacteria that create nitrous oxide, so once again the denitrifying side of the cycle becomes to powerful for it's yin-yan partner.
Nitrous Oxide the green house gas
Nitrous oxide is a substantial contributory factor to the greenhouse gas dilemma along with carbon dioxide and methane. The nitrous oxide cream chargers that we sell are every bit as responsible as the other sources - which is why we'd like to educate our customers of the role that cream chargers can play in global warming. Everyone is (or should be!) aware of carbon dioxide as a greenhouse gas that has an influence on global warming. Less people are aware that Nitrous Oxide is also a greenhouse as, indeed it is considerably more potent a greenhouse gas than carbon dioxide for four reasons:
- It has a more powerful effect for each molecule that exists in the atmosphere
- Nitrous Oxide lasts 10 times as long in the atmosphere as Carbon Dioxide, because the processes that remove it are more limited.
- Nitrous Oxide is less acknowledged as a greenhouse gas so less is being done to control its emission
- The causes of to much nitrous oxide gas in the atmosphere will be harder to confront than those that are releasing too much carbon dioxide. Even when we have found alternatives to fossil fuels – will we have alternatives to animals and agriculture?
The main reasons that are causing an excess of nitrous oxide in the atmosphere are:
- Artificial fertilizer – leading to too much nitrates, in the soil and in runoff
- Too much animal manure – 95% of the nitrogen consumed by an animal becomes manure, however that is dealt with it will produce Nitrous Oxide gas.
- Human waste – the bacteria used in sewage plants are in fact the very de-nitrifying bacteria that cause the release of too much N2O
- Burning biomass, unlike fossil fuels – plants contain a lot of nitrogen, most of which can become nitrous oxide when burned.
Nitrous Oxide and the ozone layer
Nitrous Oxide when in natural, expected quantities is one of the few ways that ozone is removed from our atmosphere and keeps levels in check. (It works via a free-radical nitrogen peroxide pathway). However, as levels of nitrous oxide increase (as outlined in the previous two sections) then it's ability to destroy ozone faster that it can be created will lead to a thinning of the ozone layer. As an interesting aside, NO2 (Nitrogen Dioxide) from vehicle exhausts is responsible for the production of ozone at lower levels where it is a pollutant.
NOx and Nitrous Oxide as a fuel oxidant (NOS)
Whilst the nitrous is the same – even if you were to purchase wholesale cream chargers you'd be out of pocket if this was your source of Nitrous so a more appropriate source would be somewhere like .
There is much confusion with all of the various oxides of nitrogen as to why it is called NOS after all this suggests (to me at least!) that is should contain more Oxygen than nitrogen, similar to the generic formula Nox, or maybe it is NO2 with the two reversed? No, it is in fact because the most popular brand of nitrous injectors is “Nitrous Oxide Systems” who market themselved using the acronym NOS. So don't be confused it is called NOS but it is N2O!
To put it in the simplest, most easily understood terms: fuel needs oxygen to burn, making more oxygen available can make a fuel burn better/faster, nitrous oxide contains Nitrogen and Oxygen so is an easily compressed liquid way of carrying around oxygen. So why not just use tanks of oxgen? After all we can go woohoo bcause Nitrous Oxide contains 12% more oygen than air (33% vs 21%) so why not go the whole hog and just use elemental O2 at 100%? Well the answer to that is that you can't easily liquify Oxygen without getting very, very cold, whereas NO2 will liquefy at room temperature. So, if you were to try and carry around oxygen you'd need a large balloon rather than a small pressure cylinder. There is also the rather useful fact that liquefied gases will release from a cylinder at a relatively constant rate, unlike pressurized gas which reduces in pressure as it is used. A more detailed explanation can be found
The first instance of Nitrous Oxide being used in motors was when those nasty Nazis wanted their aircraft to go higher and faster, but specifically higher. The problem was that the higher you go, the less oxygen is available, in each litre of air there are fewer atoms of Oxygen to react with your fuel and release its energy. You may notice this yourself if you drive a car over a high mountain road. The principles that the Germans discovered cover the basics of use as Nitrous Oxide as a fuel oxidant in cars today.
- At a temperature of about 300 Celsius then NO2 will thermally decompose into Nitrogen and Oxygen, the liberated Oxygen is free to take part in combustion.
- This is an exothermic process, so even more heat is released.
- In order to take advantage of the extra oxygen, more fuel needs to be simultaneously released.
The theory is simple enough (read a more complex version) the hard part is controlling it. You could simply just pipe some nitrous into your engine and simultaneously release more fuel, but even if you were to get the ratios correct, the timing is pivotal too; if the fuel gets into the cylinder first a rich mixture would result in lost power, if the nitrous gets there first you'd get a lean mixture and overheating and a damaged cylinder. So, that is why you would use a purpose made nitrpus oxide system. In hi-tech sportsters and drag-racers then the whole system is computer controlled. However you add that nitrous to your engine, there is a price to pay – all of that extra power means more wear and faster failure of components – more nitrous equals more problems!
In the UK then it is perfectly legal to use nitrous oxide in cars, as long as they still conform to emission testing, however although using nitrous oxide might not mean you're breaking the law – it almost certainly means that you have invalidated your insurance. Trying to find an insurer might not be too easy – read the discussion. The conclusion they reach is that if you disconnect when on the road then it isn't a modification, but the compressed nitrous oxide gas may require labelling on your vehicle in order to make it legal.
Nitrous Oxide in Rocket Motors
The same reasons for using nitrous systems to add extra oomph to burning fuels in car engines also apply to the science of using Nitrous Oxide in Rockets Motors. This is particularly important in space where there is no oxygen present unless you bring it yourself!
Th basic concept of a hybrid motor is that the fuel and the oxidiser are in different phases (eg.one solid and one liquid). The reasons for this are simplicity – which is why if you have the scale and budget of NASA then you don't need to use this technology. The oxidiser could be N2O, LOX (liquid oxygen) or H2O2 (Hydrogen Peroxide) the advantage of nitrous is that is not cryogenic so is less prone to causing valve/tank failures. It needs to be heated to decompose which can happen either in the same chamber as the fuel or in a separate chamber from which it is fed over the burning fuel. The rate of thrust can be controlled by throttling back the rate of the N2O – because without the oxidant than the fuel grain will smoulder rather than burn explosively. This is the technology that was used on the SpaceshipOne and on the follow-up Virgin Galactic. The rocket motor in SpaceshipOne uses granulated rubber as the fuel and as is explained , the Nitrous Oxide is the choice because it simplifies the motor and reduces costs. To understand the basic idea of how a rocket motor works then blow up a balloon and let it go.... the balloon will fly around the room because it is propelling gas backwards, that is the basis of rocket propulsion; to shoot mass in the opposite direction to that which you wish to travel in. Just like with the deflating balloon,the faster you can throw gas behind you, the faster you go forwards.
If you want to try this out at home, there is a rocket motor kit that makes use of a 16gm cream charger. It is simple in it's design.
- The cream charger is pierced to release and vaporize the liquid Nitrous Oxide.
- The gaseous N2O is stored in the same chamber as the fuel (plastic)
- An igniter simultaneously releases the pressure and ignites the fuel.
- The rocket motor burns for approx one second until the Nitrous or the fuel is spent.
Of course it doesn't just apply in rockets that fly into the air, the same principal of using a hybrid motor can be used in rocket cars, as demonstrated in “Laffing Gas” a rocket car powered by the hybrid rocket combination of Vegetable Oil and Nitrous Rocket – a very eco combination! Read more . The Laffing Gas demonstrates the principal of the hybrid motor quite well, with it's liquid fuel (vegetable oil) gaseous oxidant (N2O) and ignition system (a firework!). The thrust is controlled by controlling the flow rate of the nitrous oxide gas. The system is a whole lot bigger than anything you're likely to construct yourself with 35kg of liquid nitrous oxide burned each outing – that is the equivalent to 4,000 cream chargers!
Laughing Gas isn't Funny
With all the discussion of Nitrous Oxide and it's history and uses – it needs to remembered that although it might be referred as laughing gas as – it is dangerous when inhaled, there are long-term and short term dangers of use which are outlined in some detail – but the most significant danger is of immediate death by asphyxiation. Nitrous oxide is always administered by medical professional in combination with either air or oxygen – pure Nitrous Oxide is fatal if inhaled on its own.
- The first commercial space flight used Nitrous Oxide as a propellant
- Nitrous Oxide many times more potent as a greenhouse gas than Carbon Dioxide.
- Nitrous Oxide is made by bacteria in the soil.
- After it's discovered it was used as a recreational drug for many years before it was ever used as an anaesthetic. In the 17th Century then high society invented the “Laughing Gas Party”
- It was discovered by Joseph Priestly who also said “Society Has the Teenagers it deserves”!
- Nitrous Oxide is sometimes referred to as “sweet air”
- It was first used as NOS in car motors by Nascar racers until it was banned for giving drivers an unfair advantage.
- Manmade factor are massively increasing the amount of Nitrous Oxide in the environment.
- Nitorus oxide can destroy ozone.