Ammonia, either directly or indirectly, is also a building block for the synthesis of many chemicals.
Ammonia occurs in nature and has been detected in the interstellar medium. In many countries, it is classified as anextremely hazardous substance.[15]
Ammonia is produced biologically in a process callednitrogen fixation, but even more is generated industrially by theHaber process. The process helped revolutionize agriculture by providing cheap fertilizers. The global industrial production of ammonia in 2021 was 235 million tonnes.[16][17] Industrial ammonia is transported by road intankers, by rail intank wagons, by sea ingas carriers, or incylinders.[18]
Ammonia boils at −33.34 °C (−28.012 °F) at a pressure of oneatmosphere, but the liquid can often be handled in the laboratory without external cooling. Household ammonia orammonium hydroxide is a solution of ammonia in water.
Pliny, in Book XXXI of hisNatural History, refers to a salt namedhammoniacum, so called because of the proximity of its source to the Temple ofJupiter Amun (Greek ἌμμωνAmmon) in the Roman province ofCyrenaica.[19] However, the description Pliny gives of the salt does not conform to the properties ofammonium chloride. According toHerbert Hoover's commentary in his English translation ofGeorgius Agricola'sDe re metallica, it is likely to have been common sea salt.[20] In any case, that salt ultimately gave ammonia andammonium compounds their name.
Ammonia is found throughout theSolar System onMars,Jupiter,Saturn,Uranus,Neptune, andPluto, among other places: on smaller, icybodies such as Pluto, ammonia can act as a geologically important antifreeze, as a mixture of water and ammonia can have a melting point as low as −100 °C (−148 °F; 173 K) if the ammonia concentration is high enough and thus allow such bodies to retain internal oceans and active geology at a far lower temperature than would be possible with water alone.[22][23] Substances containing ammonia, or those that are similar to it, are calledammoniacal.[24]
Ammonia is a colourlessgas with a characteristicallypungent smell. It islighter than air, its density being 0.589 times that ofair. It is easily liquefied due to the stronghydrogen bonding between molecules. Gaseous ammonia turns to a colourlessliquid, whichboils at −33.1 °C (−27.58 °F), andfreezes to colourless crystals[21] at −77.7 °C (−107.86 °F). Little data is available at very high temperatures and pressures, but theliquid-vapor critical point occurs at 405 K and 11.35 MPa.[25]
Ammonia readilydissolves in water. In an aqueous solution, it can be expelled by boiling. Theaqueous solution of ammonia isbasic, and may be described as aqueous ammonia orammonium hydroxide.[30] The maximum concentration of ammonia in water (asaturated solution) has aspecific gravity of 0.880 and is often known as '.880 ammonia'.[31]
Thermal and physical properties of saturated liquid ammonia[32][33]
Temperature (°C)
Density (kg/m3)
Specific heat (kJ/(kg·K))
Kinematic viscosity (m2/s)
Thermal conductivity (W/(m·K))
Thermal diffusivity (m2/s)
Prandtl Number
Bulk modulus (K−1)
−50
703.69
4.463
4.35×10−7
0.547
1.74×10−7
2.6
−40
691.68
4.467
4.06×10−7
0.547
1.78×10−7
2.28
−30
679.34
4.476
3.87×10−7
0.549
1.80×10−7
2.15
−20
666.69
4.509
3.81×10−7
0.547
1.82×10−7
2.09
−10
653.55
4.564
3.78×10−7
0.543
1.83×10−7
2.07
0
640.1
4.635
3.73×10−7
0.540
1.82×10−7
2.05
10
626.16
4.714
3.68×10−7
0.531
1.80×10−7
2.04
20
611.75
4.798
3.59×10−7
0.521
1.78×10−7
2.02
2.45×10−3
30
596.37
4.89
3.49×10−7
0.507
1.74×10−7
2.01
40
580.99
4.999
3.40×10−7
0.493
1.70×10−7
2
50
564.33
5.116
3.30×10−7
0.476
1.65×10−7
1.99
Thermal and physical properties of ammonia (NH3) at atmospheric pressure[32][33]
Temperature (K)
Temperature (°C)
Density (kg/m3)
Specific heat (kJ/(kg·K))
Dynamic viscosity (kg/(m·s))
Kinematic viscosity (m2/s)
Thermal conductivity (W/(m·K))
Thermal diffusivity (m2/s)
Prandtl Number
273
−0.15
0.7929
2.177
9.35×10−6
1.18×10−5
0.0220
1.31×10−5
0.90
323
49.85
0.6487
2.177
1.10×10−5
1.70×10−5
0.0270
1.92×10−5
0.88
373
99.85
0.559
2.236
1.29×10−5
1.30×10−5
0.0327
2.62×10−5
0.87
423
149.85
0.4934
2.315
1.47×10−5
2.97×10−5
0.0391
3.43×10−5
0.87
473
199.85
0.4405
2.395
1.65×10−5
3.74×10−5
0.0467
4.42×10−5
0.84
480
206.85
0.4273
2.43
1.67×10−5
3.90×10−5
0.0492
4.74×10−5
0.822
500
226.85
0.4101
2.467
1.73×10−5
4.22×10−5
0.0525
5.19×10−5
0.813
520
246.85
0.3942
2.504
1.80×10−5
4.57×10−5
0.0545
5.52×10−5
0.827
540
266.85
0.3795
2.54
1.87×10−5
4.91×10−5
0.0575
5.97×10−5
0.824
560
286.85
0.3708
2.577
1.93×10−5
5.20×10−5
0.0606
6.34×10−5
0.827
580
306.85
0.3533
2.613
2.00×10−5
5.65×10−5
0.0638
6.91×10−5
0.817
Liquid ammonia is a widely studied nonaqueous ionising solvent. Its most conspicuous property is its ability to dissolve alkali metals to form highly coloured, electrically conductive solutions containingsolvated electrons. Apart from these remarkable solutions, much of the chemistry in liquid ammonia can be classified by analogy with related reactions inaqueous solutions. Comparison of the physical properties ofNH3 with those of water showsNH3 has the lower melting point, boiling point, density,viscosity,dielectric constant andelectrical conductivity. These differences are attributed at least in part to the weaker hydrogen bonding inNH3. The ionic self-dissociation constant of liquidNH3 at −50 °C is about 10−33.
Liquid ammonia will dissolve all of thealkali metals and otherelectropositive metals such asCa,[35]Sr,Ba,Eu andYb (alsoMg using an electrolytic process[33]). At low concentrations (<0.06 mol/L), deep blue solutions are formed: these contain metal cations andsolvated electrons, free electrons that are surrounded by a cage of ammonia molecules.
These solutions are strong reducing agents. At higher concentrations, the solutions are metallic in appearance and in electrical conductivity. At low temperatures, the two types of solution can coexist asimmiscible phases.
The range of thermodynamic stability of liquid ammonia solutions is very narrow, as the potential for oxidation to dinitrogen,E° (N2 + 6 [NH4]+ + 6 e− ⇌ 8 NH3), is only +0.04 V. In practice, both oxidation to dinitrogen and reduction to dihydrogen are slow. This is particularly true of reducing solutions: the solutions of the alkali metals mentioned above are stable for several days, slowly decomposing to themetal amide and dihydrogen. Most studies involving liquid ammonia solutions are done in reducing conditions; although oxidation of liquid ammonia is usually slow, there is still a risk of explosion, particularly iftransition metal ions are present as possible catalysts.
Molecular structure of ammonia and its three-dimensional shape. It has a net dipole moment of 1.484 D.Dot and cross structure of ammonia
The ammonia molecule has atrigonal pyramidal shape, as predicted by thevalence shell electron pair repulsion theory (VSEPR theory) with an experimentally determined bond angle of 106.7°.[36] The central nitrogen atom has five outer electrons with an additional electron from each hydrogen atom. This gives a total of eight electrons, or four electron pairs that are arrangedtetrahedrally. Three of theseelectron pairs are used as bond pairs, which leaves onelone pair of electrons. The lone pair repels more strongly than bond pairs; therefore, the bond angle is not 109.5°, as expected for a regular tetrahedral arrangement, but 106.7°.[36] This shape gives the molecule adipole moment and makes itpolar. The molecule's polarity, and especially its ability to formhydrogen bonds, makes ammonia highly miscible with water. The lone pair makes ammonia abase, a proton acceptor. Ammonia is moderately basic; a 1.0 Maqueous solution has apH of 11.6, and if a strong acid is added to such a solution until the solution is neutral (pH = 7), 99.4% of the ammonia molecules areprotonated. Temperature andsalinity also affect the proportion ofammonium[NH4]+. The latter has the shape of a regulartetrahedron and isisoelectronic withmethane.
As a demonstration experiment under air with ambient moisture, opened bottles of concentrated ammonia andhydrochloric acid solutions produce a cloud ofammonium chloride, which seems to appear 'out of nothing' as the saltaerosol forms where the twodiffusing clouds of reagents meet between the two bottles.
NH3 + HCl → [NH4]Cl
The salts produced by the action of ammonia on acids are known as theammonium salts and all contain theammonium ion ([NH4]+).[38]
Ammonia often functions as aweak base, so it has somebuffering ability. Shifts in pH will cause more or fewerammonium cations (NH+4) andamide anions (NH−2) to be present insolution. At standard pressure and temperature,
HeatedCr2O3 catalyzes the combustion of a flask of ammonia.
Ammonia does not burn readily or sustaincombustion, except under narrow fuel-to-air mixtures of 15–28% ammonia by volume in air.[40] When mixed withoxygen, it burns with a pale yellowish-green flame. Ignition occurs whenchlorine is passed into ammonia, forming nitrogen andhydrogen chloride; if chlorine is present in excess, then the highly explosivenitrogen trichloride (NCl3) is also formed.
The combustion of ammonia in air is very difficult in the absence of acatalyst (such asplatinum gauze or warmchromium(III) oxide), due to the relatively lowheat of combustion, a lower laminar burning velocity, highauto-ignition temperature, highheat of vapourization, and a narrowflammability range. However, recent studies have shown that efficient and stable combustion of ammonia can be achieved using swirl combustors, thereby rekindling research interest in ammonia as a fuel for thermal power production.[41] The flammable range of ammonia in dry air is 15.15–27.35% and in 100% relative humidity air is 15.95–26.55%.[42][clarification needed] For studying thekinetics of ammonia combustion, knowledge of a detailed reliable reaction mechanism is required, but this has been challenging to obtain.[43]
Ammonia is a direct or indirect precursor to mostmanufactured nitrogen-containing compounds. It is the precursor to nitric acid, which is the source for most N-substituted aromatic compounds.
Amides can be prepared by the reaction of ammonia withcarboxylic acid and their derivatives. For example, ammonia reacts withformic acid (HCOOH) to yieldformamide (HCONH2) when heated.Acyl chlorides are the most reactive, but the ammonia must be present in at least a twofold excess to neutralise thehydrogen chloride formed.Esters andanhydrides also react with ammonia to form amides. Ammonium salts of carboxylic acids can bedehydrated to amides by heating to 150–200 °C as long as no thermally sensitive groups are present.
Pentavalent ammonia is known as λ5-amine,nitrogen pentahydride decomposes spontaneously into trivalent ammonia (λ3-amine) and hydrogen gas at normal conditions. This substance was once investigated as a possible solidrocket fuel in 1966.[45]
Ammonia is also used to make the following compounds:
Ammonia is aligand formingmetal ammine complexes. For historical reasons, ammonia is namedammine in the nomenclature ofcoordination compounds. One notable ammine complex iscisplatin (Pt(NH3)2Cl2, a widely used anticancer drug. Ammine complexes ofchromium(III) formed the basis ofAlfred Werner's revolutionary theory on the structure of coordination compounds. Werner noted only twoisomers (fac- andmer-) of the complex[CrCl3(NH3)3] could be formed, and concluded the ligands must be arranged around the metal ion at thevertices of anoctahedron.
Ammonia forms 1:1adducts with a variety ofLewis acids such asI2,phenol, andAl(CH3)3. Ammonia is ahard base (HSAB theory) and itsE & C parameters are EB = 2.31 and CB = 2.04. Its relative donor strength toward a series of acids, versus other Lewis bases, can be illustrated byC-B plots.
Ammonia and ammonium salts can be readily detected, in very minute traces, by the addition ofNessler's solution, which gives a distinct yellow colouration in the presence of the slightest trace of ammonia or ammonium salts. The amount of ammonia in ammonium salts can be estimated quantitatively by distillation of the salts withsodium (NaOH) orpotassium hydroxide (KOH), the ammonia evolved being absorbed in a known volume of standardsulfuric acid and the excess of acid then determinedvolumetrically; or the ammonia may be absorbed inhydrochloric acid and the ammonium chloride so formed precipitated asammonium hexachloroplatinate,[NH4]2[PtCl6].[46]
Sulfur sticks are burnt to detect small leaks in industrial ammonia refrigeration systems. Larger quantities can be detected by warming the salts with a caustic alkali or withquicklime, when the characteristic smell of ammonia will be at once apparent.[46] Ammonia is an irritant and irritation increases with concentration; thepermissible exposure limit is 25 ppm, and lethal above 500 ppm by volume.[47] Higher concentrations are hardly detected by conventional detectors, the type of detector is chosen according to the sensitivity required (e.g. semiconductor, catalytic, electrochemical). Holographic sensors have been proposed for detecting concentrations up to 12.5% in volume.[48]
In a laboratorial setting, gaseous ammonia can be detected by using concentrated hydrochloric acid or gaseous hydrogen chloride. A dense white fume (which isammonium chloride vapor) arises from the reaction between ammonia and HCl(g).[49]
Ammoniacal nitrogen (NH3–N) is a measure commonly used for testing the quantity ofammonium ions, derived naturally from ammonia, and returned to ammonia via organic processes, in water or waste liquids. It is a measure used mainly for quantifying values inwaste treatment andwater purification systems, as well as a measure of the health of natural and man-made water reserves. It is measured in units of mg/L (milligram perlitre).
Jabir ibn Hayyan wrote about ammonia in the 9th centuryThis high-pressure ammonia reactor was built in 1921 byBASF inLudwigshafen and was re-erected on the premises of theUniversity of Karlsruhe in Germany.
The ancient Greek historianHerodotus mentioned that there wereoutcrops of salt in an area of Libya that was inhabited by a people called the 'Ammonians' (now theSiwa oasis in northwestern Egypt, where salt lakes still exist).[50][51] The Greek geographerStrabo also mentioned the salt from this region. However, the ancient authorsDioscorides,Apicius,Arrian,Synesius, andAëtius of Amida described this salt as forming clear crystals that could be used for cooking and that were essentiallyrock salt.[52]Hammoniacus sal appears in the writings ofPliny,[53] although it is not known whether the term is equivalent to the more modern sal ammoniac (ammonium chloride).[21][54][55]
The fermentation ofurine by bacteria produces asolution of ammonia; hence fermented urine was used inClassical Antiquity to wash cloth and clothing, to remove hair from hides in preparation for tanning, to serve as amordant in dying cloth, and to remove rust from iron.[56] It was also used byancient dentists to wash teeth.[57][58][59]
In the form of sal ammoniac (نشادر,nushadir), ammonia was important to theMuslim alchemists. It was mentioned in theBook of Stones, likely written in the 9th century and attributed toJābir ibn Hayyān.[60] It was also important to the Europeanalchemists of the 13th century, being mentioned byAlbertus Magnus.[21] It was also used bydyers in theMiddle Ages in the form of fermentedurine to alter the colour of vegetable dyes. In the 15th century,Basilius Valentinus showed that ammonia could be obtained by the action of alkalis on sal ammoniac.[61] At a later period, when sal ammoniac was obtained by distilling the hooves and horns of oxen and neutralizing the resulting carbonate withhydrochloric acid, the name 'spirit of hartshorn' was applied to ammonia.[21][62]
The production of ammonia from nitrogen in the air (and hydrogen) was invented byFritz Haber and Robert LeRossignol. The patent was sent in 1909 (USPTO Nr 1,202,995) and awarded in 1916. Later,Carl Bosch developed the industrial method for ammonia production (Haber–Bosch process). It was first used on an industrial scale inGermany duringWorld War I,[70] following the allied blockade that cut off the supply ofnitrates fromChile. The ammonia was used to produce explosives to sustain war efforts.[71] The Nobel Prize in Chemistry 1918 was awarded to Fritz Haber "for the synthesis of ammonia from its elements".
In the US as of 2019[update], approximately 88% of ammonia was used asfertilisers either as its salts, solutions oranhydrously.[72] When applied to soil, it helps provide increased yields ofcrops such asmaize andwheat.[73] 30% of agricultural nitrogen applied in the US is in the form of anhydrous ammonia, and worldwide, 110 million tonnes are applied each year.[74]Solutions of ammonia ranging from 16% to 25% are used in thefermentation industry as a source of nitrogen for microorganisms and to adjust pH during fermentation.[75]
Because of ammonia's vapourization properties, it is a usefulrefrigerant.[70] It was commonly used before the popularisation ofchlorofluorocarbons (Freons). Anhydrous ammonia is widely used in industrial refrigeration applications and hockey rinks because of its highenergy efficiency and low cost. It suffers from the disadvantage of toxicity, and requiring corrosion resistant components, which restricts its domestic and small-scale use. Along with its use in modernvapour-compression refrigeration it is used in a mixture along with hydrogen and water inabsorption refrigerators. TheKalina cycle, which is of growing importance to geothermal power plants, depends on the wide boiling range of the ammonia–water mixture.
Ammonia coolant is also used in the radiators aboard theInternational Space Station in loops that are used to regulate the internal temperature and enable temperature-dependent experiments.[76][77] The ammonia is under sufficient pressure to remain liquid throughout the process. Single-phase ammonia cooling systems also serve the power electronics in each pair of solar arrays.
The potential importance of ammonia as a refrigerant has increased with the discovery that vented CFCs and HFCs are potent and stable greenhouse gases.[78]
As early as in 1895, it was known that ammonia was 'stronglyantiseptic ... it requires 1.4 grams per litre to preservebeef tea (broth).'[79] In one study, anhydrous ammonia destroyed 99.999% ofzoonotic bacteria in three types ofanimal feed, but notsilage.[80][81] Anhydrous ammonia is currently used commercially to reduce or eliminatemicrobial contamination ofbeef.[82][83]Lean finely textured beef (popularly known as 'pink slime') in the beef industry is made from fattybeef trimmings (c. 50–70% fat) by removing the fat using heat andcentrifugation, then treating it with ammonia to killE. coli. The process was deemed effective and safe by theUS Department of Agriculture based on a study that found that the treatment reducesE. coli to undetectable levels.[84] There have been safety concerns about the process as well as consumer complaints about the taste and smell of ammonia-treated beef.[85]
Ammonia has been used as fuel, and is a proposed alternative to fossil fuels and hydrogen. Being liquid at ambient temperature under its own vapour pressure and having high volumetric and gravimetric energy density, ammonia is considered a suitable carrier for hydrogen,[86] and may be cheaper than direct transport of liquid hydrogen.[87]
Compared to hydrogen, ammonia is easier to store. Compared tohydrogen as a fuel, ammonia is much more energy efficient, and could be produced, stored and delivered at a much lower cost than hydrogen, which must be kept compressed or as a cryogenic liquid.[88][89] The rawenergy density of liquid ammonia is 11.5 MJ/L,[88] which is about a third that ofdiesel.
Ammonia can be converted back to hydrogen to be used to power hydrogen fuel cells, or it may be used directly within high-temperaturesolid oxide direct ammonia fuel cells to provide efficient power sources that do not emitgreenhouse gases.[90][91] Ammonia to hydrogen conversion can be achieved through thesodium amide process[92] or the catalytic decomposition of ammonia using solid catalysts.[93]
Ammonia engines or ammonia motors, using ammonia as aworking fluid, have been proposed and occasionally used.[94] The principle is similar to that used in afireless locomotive, but with ammonia as the working fluid, instead of steam or compressed air. Ammonia engines were used experimentally in the 19th century byGoldsworthy Gurney in the UK and theSt. Charles Streetcar Line inNew Orleans in the 1870s and 1880s,[95] and duringWorld War II ammonia was used to power buses inBelgium.[96]
Ammonia production currently creates 1.8% of global CO2 emissions. 'Green ammonia' is ammonia produced by usinggreen hydrogen (hydrogen produced by electrolysis with electricity fromrenewable energy), whereas 'blue ammonia' is ammonia produced usingblue hydrogen (hydrogen produced by steam methane reforming (= SMR) where the carbon dioxide has been captured and stored (cfr. carbon capture and storage = CCS).[105]
Rocket engines have also been fueled by ammonia. TheReaction Motors XLR99 rocket engine that powered theX-15 hypersonic research aircraft used liquid ammonia. Although not as powerful as other fuels, it left nosoot in the reusable rocket engine, and its density approximately matches the density of the oxidiser,liquid oxygen, which simplified the aircraft's design.
In 2020,Saudi Arabia shipped 40metric tons of liquid 'blue ammonia' to Japan for use as a fuel.[106] It was produced as a by-product by petrochemical industries, and can be burned without giving offgreenhouse gases. Its energy density by volume is nearly double that of liquid hydrogen. If the process of creating it can be scaled up via purely renewable resources, producing green ammonia, it could make a major difference inavoiding climate change.[107] The companyACWA Power and the city ofNeom have announced the construction of a green hydrogen and ammonia plant in 2020.[108]
Green ammonia is considered as a potential fuel for future container ships. In 2020, the companiesDSME andMAN Energy Solutions announced the construction of an ammonia-based ship, DSME plans to commercialize it by 2025.[109] The use of ammonia as a potential alternative fuel foraircraftjet engines is also being explored.[110]
Japan intends to implement a plan to develop ammonia co-firing technology that can increase the use of ammonia in power generation, as part of efforts to assist domestic and other Asian utilities to accelerate their transition tocarbon neutrality.[111]In October 2021, the first International Conference on Fuel Ammonia (ICFA2021) was held.[112][113]
In June 2022,IHI Corporation succeeded in reducing greenhouse gases by over 99% during combustion of liquid ammonia in a 2,000-kilowatt-class gas turbine achieving truly CO2-free power generation.[114]In July 2022,Quad nations of Japan, the U.S., Australia and India agreed to promote technological development for clean-burning hydrogen and ammonia as fuels at the security grouping's first energy meeting.[115] As of 2022[update], however, significant amounts ofNOx are produced.[116]Nitrous oxide may also be a problem as it is a "greenhouse gas that is known to possess up to 300 times the Global Warming Potential (GWP) of carbon dioxide".[117]
TheIEA forecasts that ammonia will meet approximately 45% of shipping fuel demands by 2050.[118]
At high temperature and in the presence of a suitablecatalyst ammonia decomposes into its constituent elements.[119] Decomposition of ammonia is a slightly endothermic process requiring 23 kJ/mol (5.5 kcal/mol) of ammonia, and yieldshydrogen andnitrogen gas.
Ammonia is used to scrubSO2 from the burning of fossil fuels, and the resulting product is converted toammonium sulfate for use as fertiliser. Ammonia neutralises the nitrogen oxide (NOx) pollutants emitted by diesel engines. This technology, called SCR (selective catalytic reduction), relies on avanadia-based catalyst.[120]
Ammonia may be used to mitigate gaseous spills ofphosgene.[121]
Anti-meth sign on tank of anhydrous ammonia,Otley, Iowa. Anhydrous ammonia is a common farm fertiliser that is also a critical ingredient in making methamphetamine. In 2005, Iowa used grant money to provide thousands of locks to prevent criminals from gaining access to the tanks.[122]
Ammonia, as the vapour released bysmelling salts, has found significant use as a respiratory stimulant. Ammonia is commonly used in the illegal manufacture ofmethamphetamine through aBirch reduction.[123] The Birch method of making methamphetamine is dangerous because the alkali metal and liquid ammonia are both extremely reactive, and the temperature of liquid ammonia makes it susceptible to explosive boiling when reactants are added.[124]
Liquid ammonia is used for treatment of cotton materials, giving properties likemercerisation, using alkalis. In particular, it is used for prewashing of wool.[125]
At standard temperature and pressure, ammonia is less dense than atmosphere and has approximately 45–48% of the lifting power of hydrogen orhelium. Ammonia has sometimes been used to fill balloons as alifting gas. Because of its relatively high boiling point (compared to helium and hydrogen), ammonia could potentially be refrigerated and liquefied aboard anairship to reduce lift and add ballast (and returned to a gas to add lift and reduce ballast).[126]
Ammonia has been used to darken quartersawn white oak in Arts & Crafts and Mission-style furniture. Ammonia fumes react with the naturaltannins in thewood and cause it to change colour.[127]
The USOccupational Safety and Health Administration (OSHA) has set a 15-minute exposure limit for gaseous ammonia of 35 ppm by volume in the environmental air and an 8-hour exposure limit of 25 ppm by volume.[129] TheNational Institute for Occupational Safety and Health (NIOSH) recently reduced the IDLH (Immediately Dangerous to Health or Life, the level to which a healthy worker can be exposed for 30 minutes without suffering irreversible health effects) from 500 ppm to 300 ppm based on recent more conservative interpretations of original research in 1943. The 1 hour IDLH limit is still 500 ppm. Other organisations have varying exposure levels. US Navy Standards [U.S. Bureau of Ships 1962] maximum allowable concentrations (MACs): for continuous exposure (60 days) is 25 ppm; for exposure of 1 hour is 400 ppm.[130]
Ammonia vapour has a sharp, irritating, pungent odor that acts as a warning of potentially dangerous exposure. The average odor threshold is 5 ppm, well below any danger or damage. Exposure to very high concentrations of gaseous ammonia can result in lung damage and death.[129] Ammonia is regulated in the US as a non-flammable gas, but it meets the definition of a material that is toxic by inhalation and requires a hazardous safety permit when transported in quantities greater than 3,500 US gallons (13,000 L; 2,900 imp gal).[131]
The toxicity of ammonia solutions does not usually cause problems for humans and other mammals, as a specific mechanism exists to prevent its build-up in the bloodstream. Ammonia is converted tocarbamoyl phosphate by the enzymecarbamoyl phosphate synthetase, and then enters theurea cycle to be either incorporated intoamino acids or excreted in the urine.[132]Fish andamphibians lack this mechanism, as they can usually eliminate ammonia from their bodies by direct excretion. Ammonia even at dilute concentrations is highly toxic to aquatic animals, and for this reason it isclassified as"dangerous for the environment". Atmospheric ammonia plays a key role in the formation offine particulate matter.[133]
Ammonia is present in coking wastewater streams, as a liquid by-product of the production ofcoke fromcoal.[135] In some cases, the ammonia is discharged to themarine environment where it acts as a pollutant. TheWhyalla Steelworks inSouth Australia is one example of a coke-producing facility that discharges ammonia into marine waters.[136]
Ammonia toxicity is believed to be a cause of otherwise unexplained losses infish hatcheries. Excess ammonia may accumulate and cause alteration of metabolism or increases in the body pH of the exposed organism. Tolerance varies among fish species.[137] At lower concentrations, around 0.05 mg/L, un-ionised ammonia is harmful to fish species and can result in poor growth and feed conversion rates, reduced fecundity and fertility and increase stress and susceptibility to bacterial infections and diseases.[138] Exposed to excess ammonia, fish may suffer loss of equilibrium, hyper-excitability, increased respiratory activity and oxygen uptake and increased heart rate.[137] At concentrations exceeding 2.0 mg/L, ammonia causes gill and tissue damage, extreme lethargy, convulsions, coma, and death.[137][139] Experiments have shown that the lethal concentration for a variety of fish species ranges from 0.2 to 2.0 mg/L.[139]
During winter, when reduced feeds are administered to aquaculture stock, ammonia levels can be higher. Lower ambient temperatures reduce the rate of algal photosynthesis so less ammonia is removed by any algae present. Within an aquaculture environment, especially at large scale, there is no fast-acting remedy to elevated ammonia levels. Prevention rather than correction is recommended to reduce harm to farmed fish[139] and in open water systems, the surrounding environment.
Similar topropane,anhydrous ammonia boils below room temperature when at atmospheric pressure. A storage vessel capable of 250 psi (1.7 MPa) is suitable to contain the liquid.[140] Ammonia is used in numerous different industrial applications requiring carbon or stainless steel storage vessels. Ammonia with at least 0.2% by weight water content is not corrosive to carbon steel.NH3carbon steel construction storage tanks with 0.2% by weight or more of water could last more than 50 years in service.[141] Experts warn that ammonium compounds not be allowed to come in contact withbases (unless in an intended and contained reaction), as dangerous quantities of ammonia gas could be released.
The hazards of ammonia solutions depend on the concentration: 'dilute' ammonia solutions are usually 5–10% by weight (< 5.62 mol/L); 'concentrated' solutions are usually prepared at >25% by weight. A 25% (by weight) solution has a density of 0.907 g/cm3, and a solution that has a lower density will be more concentrated. TheEuropean Union classification of ammonia solutions is given in the table.
The ammonia vapour from concentrated ammonia solutions is severely irritating to the eyes and therespiratory tract, and experts warn that these solutions only be handled in afume hood. Saturated ('0.880'–see§ Properties) solutions can develop a significant pressure inside a closed bottle in warm weather, and experts also warn that the bottle be opened with care. This is not usually a problem for 25% ('0.900') solutions.
Experts warn that ammonia solutions not be mixed withhalogens, as toxic and/or explosive products are formed. Experts also warn that prolonged contact of ammonia solutions withsilver,mercury oriodide salts can also lead to explosive products: such mixtures are often formed inqualitative inorganic analysis, and that it needs to be lightly acidified but not concentrated (<6% w/v) before disposal once the test is completed.
Laboratory use of anhydrous ammonia (gas or liquid)
Anhydrous ammonia is classified as toxic (T) and dangerous for the environment (N). The gas is flammable (autoignition temperature: 651 °C) and can form explosive mixtures with air (16–25%). Thepermissible exposure limit (PEL) in the United States is 50 ppm (35 mg/m3), while theIDLH concentration is estimated at 300 ppm. Repeated exposure to ammonia lowers the sensitivity to the smell of the gas: normally the odour is detectable at concentrations of less than 50 ppm, but desensitised individuals may not detect it even at concentrations of 100 ppm. Anhydrous ammonia corrodescopper- andzinc-containingalloys, which makesbrass fittings not appropriate for handling the gas. Liquid ammonia can also attackrubber and certain plastics.
Graphs are unavailable due to technical issues. Updates on reimplementing the Graph extension, which will be known as the Chart extension, can be found onPhabricator and onMediaWiki.org.
Global ammonia production 1950–2020 (expressed as fixed nitrogen in U.S. tons)[142]
Ammonia has one of the highest rates of production of any inorganic chemical. Production is sometimes expressed in terms of 'fixed nitrogen'. Global production was estimated as being 160 million tonnes in 2020 (147 tons of fixed nitrogen).[143] China accounted for 26.5% of that, followed by Russia at 11.0%, the United States at 9.5%, and India at 8.3%.[143]
This reaction is thermodynamically favorable at a high temperature, but the kinetics are prohibitively slow. At high temperatures at which catalysts are active enough that the reaction proceeds to equilibrium, the reaction is reactant-favored rather than product-favored. As a result, high pressures are needed todrive the reaction forward.
The German chemistsFritz Haber andCarl Bosch developed the process in the first decade of the 20th century, and its improved efficiency over existing methods such as theBirkeland-Eyde andFrank-Caro processes was a major advancement in the industrial production of ammonia.[149][150][151] The Haber process can be combined withsteam reforming to produce ammonia with just three chemical inputs: water, natural gas, and atmospheric nitrogen. Both Haber and Bosch were eventually awarded theNobel Prize in Chemistry: Haber in 1918 for ammonia synthesis specifically, and Bosch in 1931 for related contributions tohigh-pressure chemistry.
Theelectrochemical synthesis of ammonia involves the reductive formation oflithium nitride, which can beprotonated to ammonia, given aproton source. The first use of this chemistry was reported in 1930, where lithium solutions in ethanol were used to produce ammonia at pressures of up to 1000 bar, with ethanol acting as the proton source.[152] Beyond simply mediating proton transfer to the nitrogen reduction reaction, ethanol has been found to play a multifaceted role, influencing electrolyte transformations and contributing to the formation of the solid electrolyte interphase, which enhances overall reaction efficiency[153][154]
In 1994, Tsuneto et al. used lithium electrodeposition intetrahydrofuran to synthesize ammonia at more moderate pressures with reasonableFaradaic efficiency.[155] Subsequent studies have further explored the ethanol–tetrahydrofuran system for electrochemical ammonia synthesis.[154][156]
In 2020, a solvent-agnosticgas diffusion electrode was shown to improve nitrogen transport to the reactive lithium.NH3 production rates of up to30 ± 5 nmol/(s⋅cm2) and Faradaic efficiencies of up to 47.5 ± 4% at ambient temperature and 1 bar pressure were achieved.[157]
In 2021, it was demonstrated that ethanol could be replaced with a tetraalkylphosphonium salt.[158] The study observedNH3 production rates of53 ± 1 nmol/(s⋅cm2) at 69 ± 1% Faradaic efficiency experiments under 0.5 bar hydrogen and 19.5 bar nitrogenpartial pressure at ambient temperature.[158] Technology based on this electrochemistry is being developed for commercial fertiliser and fuel production.[159][160]
In 2022, ammonia was produced via the lithium mediated process in a continuous-flow electrolyzer also demonstrating the hydrogen gas as proton source. The study synthesized ammonia at 61 ± 1% Faradaic efficiency at a current density of −6 mA/cm2 at 1 bar and room temperature.[161]
Main symptoms of hyperammonemia (ammonia reaching toxic concentrations).[162]
Ammonia is essential for life.[163] For example, it is required for the formation ofamino acids andnucleic acids, fundamental building blocks of life. Ammonia is however quite toxic. Nature thus uses carriers for ammonia. Within a cell,glutamate serves this role. In the bloodstream,glutamine is a source of ammonia.[164]
Ammonia is both ametabolic waste and a metabolic input throughout thebiosphere. It is an important source of nitrogen for living systems. Although atmospheric nitrogen abounds (more than 75%), few living creatures are capable of using atmospheric nitrogen in itsdiatomic form,N2 gas. Therefore,nitrogen fixation is required for the synthesis of amino acids, which are the building blocks ofprotein. Some plants rely on ammonia and other nitrogenous wastes incorporated into the soil by decaying matter. Others, such as nitrogen-fixinglegumes, benefit fromsymbiotic relationships withrhizobia bacteria that create ammonia from atmospheric nitrogen.[166]
In humans, inhaling ammonia in high concentrations can be fatal. Exposure to ammonia can causeheadaches,edema, impaired memory,seizures andcoma as it isneurotoxic in nature.[167]
In certain organisms, ammonia is produced from atmospheric nitrogen byenzymes callednitrogenases. The overall process is callednitrogen fixation. Intense effort has been directed toward understanding the mechanism of biological nitrogen fixation. The scientific interest in this problem is motivated by the unusual structure of theactive site of the enzyme, which consists of anFe7MoS9 ensemble.[168]
Ammonia is also a metabolic product ofamino aciddeamination catalyzed by enzymes such asglutamate dehydrogenase 1. Ammonia excretion is common in aquatic animals. In humans, it is quickly converted tourea (byliver), which is much less toxic, particularly lessbasic. This urea is a major component of the dry weight ofurine. Most reptiles, birds, insects, and snails excreteuric acid solely as nitrogenous waste.
Ammonia plays a role in both normal and abnormal animalphysiology. It isbiosynthesised through normal amino acid metabolism and is toxic in high concentrations. Theliver converts ammonia tourea through a series of reactions known as theurea cycle. Liver dysfunction, such as that seen incirrhosis, may lead to elevated amounts of ammonia in the blood (hyperammonemia). Likewise, defects in the enzymes responsible for the urea cycle, such asornithine transcarbamylase, lead tohyperammonemia. Hyperammonemia contributes to the confusion andcoma ofhepatic encephalopathy, as well as the neurological disease common in people with urea cycle defects andorganic acidurias.[169]
Ammonia is important for normal animal acid/base balance. After formation of ammonium fromglutamine,α-ketoglutarate may be degraded to produce twobicarbonate ions, which are then available as buffers for dietary acids. Ammonium is excreted in the urine, resulting in net acid loss. Ammonia may itself diffuse across therenal tubules, combine with a hydrogen ion, and thus allow for further acidexcretion.[170]
Ammonium ions are atoxic waste product ofmetabolism inanimals. In fish and aquatic invertebrates, it is excreted directly into the water. In mammals, sharks, and amphibians, it is converted in theurea cycle tourea, which is less toxic and can be stored more efficiently. In birds, reptiles, and terrestrial snails, metabolic ammonium is converted intouric acid, which is solid and can therefore be excreted with minimal water loss.[171]
Ammonia occurs in theatmospheres of the outer giant planets such asJupiter (0.026% ammonia),Saturn (0.012% ammonia), and in the atmospheres andices ofUranus andNeptune.
Ammonia was first detected in interstellar space in 1968, based onmicrowave emissions from the direction of thegalactic core.[173] This was the firstpolyatomic molecule to be so detected. The sensitivity of the molecule to a broad range of excitations and the ease with which it can be observed in a number of regions has made ammonia one of the most important molecules for studies ofmolecular clouds.[174] The relative intensity of the ammonia lines can be used to measure the temperature of the emitting medium.
The following isotopic species of ammonia have been detected:NH3,15NH3,NH2D,NHD2, andND3. The detection of triplydeuterated ammonia was considered a surprise as deuterium is relatively scarce. It is thought that the low-temperature conditions allow this molecule to survive and accumulate.[175]
Since its interstellar discovery,NH3 has proved to be an invaluable spectroscopic tool in the study of the interstellar medium. With a large number of transitions sensitive to a wide range of excitation conditions,NH3 has been widely astronomically detected–its detection has been reported in hundreds of journal articles. Listed below is a sample of journal articles that highlights the range of detectors that have been used to identify ammonia.
The study of interstellar ammonia has been important to a number of areas of research in the last few decades. Some of these are delineated below and primarily involve using ammonia as an interstellar thermometer.
The interstellar abundance for ammonia has been measured for a variety of environments. The [NH3]/[H2] ratio has been estimated to range from 10−7 in small dark clouds[176] up to 10−5 in the dense core of theOrion molecular cloud complex.[177] Although a total of 18 total production routes have been proposed,[178] the principal formation mechanism for interstellarNH3 is the reaction:
[NH4]+ + e− → NH3 + H
The rate constant,k, of this reaction depends on the temperature of the environment, with a value of at 10 K.[179] The rate constant was calculated from the formula. For the primary formation reaction,a = 1.05×10−6 andB = −0.47. Assuming anNH+4 abundance ofand an electron abundance of 10−7 typical of molecular clouds, the formation will proceed at a rate of1.6×10−9 cm−3s−1 in a molecular cloud of total density105 cm−3.[180]
All other proposed formation reactions have rate constants of between two and 13 orders of magnitude smaller, making their contribution to the abundance of ammonia relatively insignificant.[181] As an example of the minor contribution other formation reactions play, the reaction:
H2 + NH2 → NH3 + H
has a rate constant of 2.2×10−15. AssumingH2 densities of 105 and [NH2]/[H2] ratio of 10−7, this reaction proceeds at a rate of 2.2×10−12, more than three orders of magnitude slower than the primary reaction above.
Some of the other possible formation reactions are:
There are 113 total proposed reactions leading to the destruction ofNH3. Of these, 39 were tabulated in extensive tables of the chemistry among C, N and O compounds.[182] A review of interstellar ammonia cites the following reactions as the principal dissociation mechanisms:[174]
NH3 + [H3]+ → [NH4]+ + H2
1
NH3 + HCO+ → [NH4]+ + CO
2
with rate constants of 4.39×10−9[183] and 2.2×10−9,[184] respectively. The above equations (1,2) run at a rate of 8.8×10−9 and 4.4×10−13, respectively. These calculations assumed the given rate constants and abundances of [NH3]/[H2] = 10−5, [[H3]+]/[H2] = 2×10−5, [HCO+]/[H2] = 2×10−9, and total densities ofn = 105, typical of cold, dense, molecular clouds.[185] Clearly, between these two primary reactions, equation (1) is the dominant destruction reaction, with a rate ≈10,000 times faster than equation (2). This is due to the relatively high abundance of[H3]+.
Radio observations ofNH3 from theEffelsberg 100-m Radio Telescope reveal that the ammonia line is separated into two components–a background ridge and an unresolved core. The background corresponds well with the locations previously detected CO.[186] The 25 mChilbolton telescope inEngland detected radio signatures of ammonia inH II regions, HNH2Omasers, H–H objects, and other objects associated with star formation. A comparison of emission line widths indicates that turbulent or systematic velocities do not increase in the central cores of molecular clouds.[187]
Microwave radiation from ammonia was observed in several galactic objects including W3(OH),Orion A,W43,W51, and five sources in the galactic centre. The high detection rate indicates that this is a common molecule in the interstellar medium and that high-density regions are common in the galaxy.[188]
VLA observations ofNH3 in seven regions with high-velocity gaseous outflows revealed condensations of less than 0.1 pc in L1551, S140, andCepheus A. Three individual condensations were detected in Cepheus A, one of them with a highly elongated shape. They may play an important role in creating the bipolar outflow in the region.[189]
Extragalactic ammonia was imaged using the VLA inIC 342. The hot gas has temperatures above 70 K, which was inferred from ammonia line ratios and appears to be closely associated with the innermost portions of the nuclear bar seen in CO.[190]NH3 was also monitored by VLA toward a sample of four galactic ultracompact HII regions: G9.62+0.19, G10.47+0.03, G29.96-0.02, and G31.41+0.31. Based upon temperature and density diagnostics, it is concluded that in general such clumps are probably the sites of massive star formation in an early evolutionary phase prior to the development of an ultracompact HII region.[191]
Absorption at 2.97 micrometres due to solid ammonia was recorded from interstellar grains in theBecklin–Neugebauer Object and probably in NGC 2264-IR as well. This detection helped explain the physical shape of previously poorly understood and related ice absorption lines.[192]
A spectrum of the disk of Jupiter was obtained from theKuiper Airborne Observatory, covering the 100 to 300 cm−1 spectral range. Analysis of the spectrum provides information on global mean properties of ammonia gas and an ammonia ice haze.[193]
A total of 149 dark cloud positions were surveyed for evidence of 'dense cores' by using the (J,K) = (1,1) rotating inversion line of NH3. In general, the cores are not spherically shaped, with aspect ratios ranging from 1.1 to 4.4. It is also found that cores with stars have broader lines than cores without stars.[194]
Ammonia has been detected in theDraco Nebula and in one or possibly two molecular clouds, which are associated with the high-latitude galacticinfrared cirrus. The finding is significant because they may represent the birthplaces for the Population I metallicity B-type stars in the galactic halo that could have been borne in the galactic disk.[195]
By balancing and stimulated emission with spontaneous emission, it is possible to construct a relation betweenexcitation temperature and density. Moreover, since the transitional levels of ammonia can be approximated by a 2-level system at low temperatures, this calculation is fairly simple. This premise can be applied to dark clouds, regions suspected of having extremely low temperatures and possible sites for future star formation. Detections of ammonia in dark clouds show very narrow lines – indicative not only of low temperatures, but also of a low level of inner-cloud turbulence. Line ratio calculations provide a measurement of cloud temperature that is independent of previous CO observations. The ammonia observations were consistent with CO measurements of rotation temperatures of ≈10 K. With this, densities can be determined, and have been calculated to range between 104 and 105 cm−3 in dark clouds. Mapping ofNH3 gives typical clouds sizes of 0.1 pc and masses near 1 solar mass. These cold, dense cores are the sites of future star formation.
Ultra-compact HII regions are among the best tracers of high-mass star formation. The dense material surrounding UCHII regions is likely primarily molecular. Since a complete study of massive star formation necessarily involves the cloud from which the star formed, ammonia is an invaluable tool in understanding this surrounding molecular material. Since this molecular material can be spatially resolved, it is possible to constrain the heating/ionising sources, temperatures, masses, and sizes of the regions. Doppler-shifted velocity components allow for the separation of distinct regions of molecular gas that can trace outflows and hot cores originating from forming stars.
Ammonia has been detected in external galaxies,[196][197] and by simultaneously measuring several lines, it is possible to directly measure the gas temperature in these galaxies. Line ratios imply that gas temperatures are warm (≈50 K), originating from dense clouds with sizes of tens of parsecs. This picture is consistent with the picture within ourMilky Way galaxy – hot dense molecular cores form around newly forming stars embedded in larger clouds of molecular material on the scale of several hundred parsecs (giant molecular clouds; GMCs).
^"Ammonia". The American Chemical Society. 8 February 2021. Retrieved20 March 2024.
^Perrin, D. D. (1982).Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution (2nd ed.). Oxford: Pergamon Press.
^Iwasaki, Hiroji; Takahashi, Mitsuo (1968). "Studies on the transport properties of fluids at high pressure".The Review of Physical Chemistry of Japan.38 (1).
^abZumdahl, Steven S. (2009).Chemical Principles (6th ed.). Houghton Mifflin. p. A22.ISBN978-0-618-94690-7.
^Hoover, Herbert (1950).Georgius Agricola De Re Metallica – Translated from the first Latin edition of 1556. New York: Dover Publications. p. 560.ISBN978-0486600062.
^Hewat, A. W.; Riekel, C. (1979). "The crystal structure of deuteroammonia between 2 and 180 K by neutron powder profile refinement".Acta Crystallographica Section A.35 (4): 569.Bibcode:1979AcCrA..35..569H.doi:10.1107/S0567739479001340.
^Ammonia in Linstrom, Peter J.; Mallard, William G. (eds.);NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg (MD)
^abcNeufeld, R.; Michel, R.; Herbst-Irmer, R.; Schöne, R.; Stalke, D. (2016). "Introducing a Hydrogen-Bond Donor into a Weakly Nucleophilic Brønsted Base: Alkali Metal Hexamethyldisilazides (MHMDS, M = Li, Na, K, Rb and Cs) with Ammonia".Chem. Eur. J.22 (35):12340–12346.doi:10.1002/chem.201600833.PMID27457218.
^abcCombellas, C; Kanoufi, F; Thiébault, A (2001). "Solutions of solvated electrons in liquid ammonia".Journal of Electroanalytical Chemistry.499:144–151.doi:10.1016/S0022-0728(00)00504-0.
^Cleeton, C. E.; Williams, N. H. (1934). "Electromagnetic Waves of 1.1 cm (0 in). Wave-Length and the Absorption Spectrum of Ammonia".Physical Review.45 (4): 234.Bibcode:1934PhRv...45..234C.doi:10.1103/PhysRev.45.234.
^Khan, A.S.; Kelley, R.D.; Chapman, K.S.; Fenton, D.L. (1995).Flammability limits of ammonia–air mixtures. U.S.: U.S. DOE Office of Scientific and Technical Information.OSTI215703.
^(OSHA) Source: Sax, N. Irving (1984)Dangerous Properties of Industrial Materials. 6th Ed. Van Nostrand Reinhold.ISBN0-442-28304-0.
^Hurtado, J. L. Martinez; Lowe, C. R. (2014). "Ammonia-Sensitive Photonic Structures Fabricated in Nafion Membranes by Laser Ablation".ACS Applied Materials & Interfaces.6 (11):8903–8908.doi:10.1021/am5016588.ISSN1944-8244.PMID24803236.
^Holleman, A. F.; Wiberg, Egon; Wiberg, Nils; Eagleson, Mary; Brewer, William; Aylett, Bernhard J., eds. (2001).Holleman-Wiberg inorganic chemistry. San Diego, Calif. London: Academic.ISBN978-0-12-352651-9.
^Herodotus with George Rawlinson, trans.,The History of Herodotus (New York, New York: Tandy-Thomas Co., 1909), vol.2, Book 4, § 181,pp. 304–305.
^The land of the Ammonians is mentioned elsewhere in Herodotus'History and inPausanias'Description of Greece:
Herodotus with George Rawlinson, trans.,The History of Herodotus (New York, New York: Tandy-Thomas Co., 1909), vol. 1, Book 2, § 42,p. 245, vol. 2, Book 3, § 25,p. 73, and vol. 2, Book 3, § 26,p. 74.
Pausanias with W.H.S. Jones, trans.,Description of Greece (London, England: William Heinemann Ltd., 1979), vol. 2, Book 3, Ch. 18, § 3, pp. 109 and111 and vol. 4, Book 9, Ch. 16, § 1,p. 239.
^Kopp, Hermann,Geschichte der Chemie [History of Chemistry] (Braunschweig, (Germany): Friedrich Vieweg und Sohn, 1845), Part 3,p. 237. [in German]
^Chisholm 1911 cites PlinyNat. Hist. xxxi. 39. See: Pliny the Elder with John Bostock and H. T. Riley, ed.s,The Natural History (London, England: H. G. Bohn, 1857), vol. 5, Book 31, § 39,p. 502.
^Pliny also mentioned that when some samples of what was purported to benatron (Latin:nitrum, impure sodium carbonate) were treated with lime (calcium carbonate) and water, thenatron would emit a pungent smell, which some authors have interpreted as signifying that thenatron either was ammonium chloride or was contaminated with it. See:
Pliny with W.H.S. Jones, trans.,Natural History (London, England: William Heinemann Ltd., 1963), vol. 8, Book 31, § 46, pp. 448–449.From pp. 448–449:"Adulteratur in Aegypto calce, deprehenditur gusto. Sincerum enim statim resolvitur, adulteratum calce pungit et asperum[oraspersum] reddit odorem vehementer." (In Egypt it [i.e., natron] is adulterated with lime, which is detected by taste; for pure natron melts at once, but adulterated natron stings because of the lime, and emits a strong, bitter odour [or: when sprinkled [(aspersum) with water] emits a vehement odour])
Kidd, John,Outlines of Mineralogy (Oxford, England: N. Bliss, 1809), vol. 2,p. 6.
Moore, Nathaniel Fish,Ancient Mineralogy: Or, An Inquiry Respecting Mineral Substances Mentioned by the Ancients: ... (New York, New York: G. & C. Carvill & Co., 1834),pp. 96–97.
Forbes, R.J.,Studies in Ancient Technology, vol. 5, 2nd ed. (Leiden, Netherlands: E.J. Brill, 1966), pp.19,48, and65.
Moeller, Walter O.,The Wool Trade of Ancient Pompeii (Leiden, Netherlands: E.J. Brill, 1976),p. 20.
Faber, G.A. (pseudonym of: Goldschmidt, Günther) (May 1938) "Dyeing and tanning in classical antiquity,"Ciba Review,9 : 277–312. Available at:Elizabethan Costume
Smith, William,A Dictionary of Greek and Roman Antiquities (London, England: John Murray, 1875), article: "Fullo" (i.e., fullers or launderers),pp. 551–553.
Bond, Sarah E.,Trade and Taboo: Disreputable Professions in the Roman Mediterranean (Ann Arbor, Michigan: University of Michigan Press, 2016),p. 112.
Binz, Arthur (1936) "Altes und Neues über die technische Verwendung des Harnes" (Ancient and modern [information] about the technological use of urine),Zeitschrift für Angewandte Chemie,49 (23) : 355–360. [in German]
Witty, Michael (December 2016) "Ancient Roman urine chemistry,"Acta Archaeologica,87 (1) : 179–191. Witty speculates that the Romans obtained ammonia in concentrated form by adding wood ash (impurepotassium carbonate) to urine that had been fermented for several hours.Struvite (magnesium ammonium phosphate) is thereby precipitated, and the yield of struvite can be increased by then treating the solution withbittern, a magnesium-rich solution that is a byproduct of making salt from sea water. Roasting struvite releases ammonia vapours.
^Spiritus salis urinæ (spirit of the salt of urine, i.e., ammonium carbonate) had apparently been produced before Valentinus, although he presented a new, simpler method for preparing it in his book: Valentinus, Basilius,Vier Tractätlein Fr. Basilii Valentini ... [Four essays of Brother Basil Valentine ... ] (Frankfurt am Main, (Germany): Luca Jennis, 1625),"Supplementum oder Zugabe" (Supplement or appendix), pp. 80–81:"Der Weg zum Universal, damit die drei Stein zusammen kommen." (The path to the Universal, so that the three stones come together.).From p. 81:"Der Spiritus salis Urinæ nimbt langes wesen zubereiten / dieser proceß aber ist waß leichter unnd näher auß dem Salz von Armenia, ... Nun nimb sauberen schönen Armenischen Salz armoniac ohn alles sublimiren / thue ihn in ein Kolben / giesse ein Oleum Tartari drauff / daß es wie ein Muß oder Brey werde / vermachs baldt / dafür thu auch ein grosen vorlag / so lege sich als baldt der Spiritus Salis Urinæ im Helm an Crystallisch ... " (Spirit of the salt of urine [i.e., ammonium carbonate] requires a long method [i.e., procedure] to prepare; this [i.e., Valentine's] process [starting] from the salt from Armenia [i.e., ammonium chloride], however, is somewhat easier and shorter ... Now take clean nice Armenian salt, without sublimating all [of it]; put it in a [distillation] flask; pour oil of tartar [i.e., potassium carbonate that has dissolved only in the water that it has absorbed from the air] on it, [so] that it [i.e., the mixture] becomes like a mush or paste; assemble it [i.e., the distilling apparatus (alembic)] quickly; for that [purpose] connect a large receiving flask; then soon spirit of the salt of urine deposits as crystals in the "helmet" [i.e., the outlet for the vapours, which is atop the distillation flask] ...) See also: Kopp, Hermann,Geschichte der Chemie [History of Chemistry] (Braunschweig, (Germany): Friedrich Vieweg und Sohn, 1845), Part 3,p. 243. [in German]
Schofield, Robert E.,The Enlightened Joseph Priestley: A Study of His Life and Work from 1773 to 1804 (University Park, Pennsylvania: Pennsylvania State University Press, 2004),pp. 93–94.
By 1775, Priestley had observed that electricity could decompose ammonia ("alkaline air"), yielding a flammable gas (hydrogen). See: Priestley, Joseph,Experiments and Observations on Different Kinds of Air, vol. 2 (London, England: J. Johnson, 1775),pp. 239–240.
^Berthollet (1785)"Analyse de l'alkali volatil" (Analysis of volatile alkali),Mémoires de l'Académie Royale des Sciences, 316–326.
^Tajkarimi, Mehrdad; Riemann, H. P.; Hajmeer, M. N.; Gomez, E. L.; Razavilar, V.; Cliver, D. O.; et al. (2008). "Ammonia disinfection of animal feeds – Laboratory study".International Journal of Food Microbiology.122 (1–2):23–28.doi:10.1016/j.ijfoodmicro.2007.11.040.PMID18155794.
^Giddey, S.; Badwal, S. P. S.; Munnings, C.; Dolan, M. (10 October 2017). "Ammonia as a Renewable Energy Transportation Media".ACS Sustainable Chemistry & Engineering.5 (11):10231–10239.doi:10.1021/acssuschemeng.7b02219.
^Włochowicz, A.; Stelmasiak, E. (1983). "Change in thermal properties of wool after treatment with liquid ammonia".Journal of Thermal Analysis and Calorimetry.26 (1): 17.doi:10.1007/BF01914084.S2CID96930751.
^Habers process chemistry. India: Arihant publications. 2018. p. 264.ISBN978-93-131-6303-9.
^Appl, M. (1982). "The Haber–Bosch Process and the Development of Chemical Engineering".A Century of Chemical Engineering. New York: Plenum Press. pp. 29–54.ISBN978-0-306-40895-3.
^Smil, Vaclav (2004).Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production (1st ed.). Cambridge, MA: MIT.ISBN978-0-262-69313-4.
^Hager, Thomas (2008).The Alchemy of Air: A Jewish genius, a doomed tycoon, and the scientific discovery that fed the world but fueled the rise of Hitler (1st ed.). New York, New York: Harmony Books.ISBN978-0-307-35178-4.
^Sittig, Marshall (1979).Fertilizer Industry: Processes, Pollution Control, and Energy Conservation. Park Ridge, New Jersey: Noyes Data Corp.ISBN978-0-8155-0734-5.
^Identifying the direct effects of ammonia on the brain – PubMed
^Igarashi, Robert Y.; Laryukhin, Mikhail; Dos Santos, Patricia C.; Lee, Hong-In; Dean, Dennis R.; Seefeldt, Lance C.; Hoffman, Brian M. (May 2005). "Trapping H- Bound to the Nitrogenase FeMo-Cofactor Active Site during H2 Evolution: Characterization by ENDOR Spectroscopy".Journal of the American Chemical Society.127 (17):6231–6241.Bibcode:2005JAChS.127.6231I.doi:10.1021/ja043596p.PMID15853328.
^Zschocke, Johannes; Hoffman, Georg (2004).Vademecum Metabolism. Schattauer Verlag.ISBN978-3794523856.
^Cheung, A. C.; Rank, D. M.; Townes, C. H.; Thornton, D. D.; Welch, W. J. (1968). "Detection of NH3 molecules in the interstellar medium by their microwave emission".Phys. Rev. Lett.21 (25): 1701.Bibcode:1968PhRvL..21.1701C.doi:10.1103/PhysRevLett.21.1701.
^Lininger, W.; Albritton, D. L.; Fehsenfeld, F. C.; Schmeltekopf, A. L.; Ferguson, E. E. (1975). "Flow–drift tube measurements of kinetic energy dependences of some exothermic proton transfer rate constants".J. Chem. Phys.62 (9): 3549.Bibcode:1975JChPh..62.3549L.doi:10.1063/1.430946.
^Torrelles, J. M.; Ho, P. T. P.; Rodriguez, L. F.; Canto, J. (1985). "VLA observations of ammonia and continuum in regions with high-velocity gaseous outflows".Astrophysical Journal.288: 595.Bibcode:1985ApJ...288..595T.doi:10.1086/162825.S2CID123014355.
^Cesaroni, R.; Churchwell, E.; Hofner, P.; Walmsley, C. M.; Kurtz, S. (1994). "Hot ammonia toward compact HII regions".Astronomy and Astrophysics.288: 903.Bibcode:1994A&A...288..903C.
^Orton, G. S.; Aumann, H. H.; Martonchik, J. V.; Appleby, J. F. (1982). "Airborne spectroscopy of Jupiter in the 100- to 300-cm−1 region: Global properties of ammonia gas and ice haze".Icarus.52 (1): 81.Bibcode:1982Icar...52...81O.doi:10.1016/0019-1035(82)90170-1.
^Mebold, U.; Heithausen, A.; Reif, K. (1987). "Ammonia in the galactic halo and the infrared cirrus".Astronomy and Astrophysics.180: 213.Bibcode:1987A&A...180..213M.
^Martin, R. N.; Ho, P. T. P. (1979). "Detection of extragalactic ammonia".Astronomy and Astrophysics.74 (1): L7.Bibcode:1979A&A....74L...7M.
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