Ammonium chloride

Ammonium chloride is an inorganic chemical compound with the chemical formula NH4Cl, also written as [NH4]Cl. It is an ammonium salt of hydrogen chloride. It consists of ammonium cations [NH4]+ and chloride anions Cl−. It is a white crystalline salt that is highly soluble in water. Solutions of ammonium chloride are mildly acidic. In its naturally occurring mineralogic form, it is known as salammoniac. The mineral is commonly formed on burning coal dumps from condensation of coal-derived gases. It is also found around some types of volcanic vents. It is mainly used as fertilizer and a flavouring agent in some types of liquorice. It is a product of the reaction of hydrochloric acid and ammonia.

Production
It is a product of the Solvay process used to produce sodium carbonate:
 * CO2 + 2 NH3 + 2 NaCl + H2O → 2 NH4Cl + Na2CO3

Not only is that method the principal one for the manufacture of ammonium chloride, but also it is used to minimize ammonia release in some industrial operations.

Ammonium chloride is prepared commercially by combining ammonia (NH3) with either hydrogen chloride (gas) or hydrochloric acid (water solution):
 * NH3 + HCl → NH4Cl

Ammonium chloride occurs naturally in volcanic regions, forming on volcanic rocks near fume-releasing vents (fumaroles). The crystals deposit directly from the gaseous state and tend to be short-lived, as they dissolve easily in water.

Reactions
Ammonium chloride appears to sublime upon heating but actually reversibly decomposes into ammonia and hydrogen chloride gas:
 * NH4Cl NH3 + HCl

Ammonium chloride reacts with a strong base, like sodium hydroxide, to release ammonia gas:
 * NH4Cl + NaOH → NH3 + NaCl + H2O

Similarly, ammonium chloride also reacts with alkali-metal carbonates at elevated temperatures, giving ammonia and alkali-metal chloride:
 * 2 NH4Cl + Na2CO3 → 2 NaCl + CO2 + H2O + 2 NH3

A solution of 5% by mass of ammonium chloride in water has a pH in the range 4.6 to 6.0.

Some reactions of ammonium chloride with other chemicals are endothermic, such as its reaction with barium hydroxide and its dissolving in water.

Applications
The dominant application of ammonium chloride is as a nitrogen source in fertilizers (corresponding to 90% of the world production of ammonium chloride) such as chloroammonium phosphate. The main crops fertilized this way are rice and wheat in Asia.

Ammonium chloride was used in pyrotechnics in the 18th century but was superseded by safer and less hygroscopic chemicals. Its purpose was to provide a chlorine donor to enhance the green and blue colours from copper ions in the flame.

It had a secondary use to provide white smoke, but its ready double decomposition reaction with potassium chlorate producing the highly unstable ammonium chlorate made its use very dangerous.

Metalwork
Ammonium chloride is used as a flux in preparing metals to be tin coated, galvanized or soldered. It works as a flux by cleaning the surface of workpieces by reacting with the metal oxides at the surface to form a volatile metal chloride. For that purpose, it is sold in blocks at hardware stores for use in cleaning the tip of a soldering iron, and it can also be included in solder as flux.

Medicine
Ammonium chloride is used as an expectorant in cough medicine. Its expectorant action is caused by irritative action on the bronchial mucosa, which causes the production of excess respiratory tract fluid, which presumably is easier to cough up. Ammonium salts are an irritant to the gastric mucosa and may induce nausea and vomiting.

Ammonium chloride is used as a systemic acidifying agent in treatment of severe metabolic alkalosis, in oral acid loading test to diagnose distal renal tubular acidosis, to maintain the urine at an acid pH in the treatment of some urinary-tract disorders.

Food
Ammonium chloride, under the name sal ammoniac or salmiak is used as food additive under the E number E510, working as a yeast nutrient in breadmaking and as an acidifier. It is a feed supplement for cattle and an ingredient in nutritive media for yeasts and many microorganisms.

Ammonium chloride is used to spice up dark sweets called salty liquorice (popular in the Nordic countries, Benelux and northern Germany), in baking to give cookies a very crisp texture, and in the liquor Salmiakki Koskenkorva for flavouring. In Turkey, Iran, Tajikistan, India, Pakistan and Arab countries it is called "noshader" and is used to improve the crispness of snacks such as samosas and jalebi.

In the laboratory
Ammonium chloride has been used historically to produce low temperatures in cooling baths.

Ammonium chloride solutions with ammonia are used as buffer solutions including ACK (Ammonium-Chloride-Potassium) lysis buffer.

In paleontology, ammonium chloride vapor is deposited on fossils, where the substance forms a brilliant white, easily removed and fairly harmless and inert layer of tiny crystals that covers up any coloration the fossil may have, and if lighted at an angle highly enhances contrast in photographic documentation of three-dimensional specimens. The same technique is applied in archaeology to eliminate reflection on glass and similar specimens for photography.

In organic synthesis saturated NH4Cl solution is typically used to quench reaction mixtures.

It has a lambda transition at 242.8 K and zero pressure.

Flotation
Giant squid and some other large squid species maintain neutral buoyancy in seawater through an ammonium chloride solution which is found throughout their bodies and is less dense than seawater. This differs from the method of flotation used by most fish, which involves a gas-filled swim bladder.

Batteries
Around the turn of the 20th century, ammonium chloride was used in aqueous solution as the electrolyte in Leclanché cells that found a commercial use as the "local battery" in subscribers' telephone installations. Those cells later evolved into zinc–carbon batteries still using ammonium chloride as electrolyte.

Concrete treatments
Ammonium chloride is known to be an aggressive cleaning agent.

A penetrating and intense reddish brown color is stained into concrete surfaces with a mixture of ammonium chloride and ferric chloride. Pre-treatment with acid is unnecessary.

Other applications
Ammonium chloride is used in a ~5% aqueous solution to work on oil wells with clay swelling problems. Other uses include in hair shampoo, in the glue that bonds plywood, and in cleaning products. In hair shampoo, it is used as a thickening agent in ammonium-based surfactant systems such as ammonium lauryl sulfate. Ammonium chloride is used in the textile and leather industry, in dyeing, tanning, textile printing and cotton clustering. In woodworking, a solution of ammonium chloride and water, when applied to unfinished wood, will burn when subjected to a heat gun resulting in a branding iron mark without use of a branding iron. The solution can be painted onto the wood or applied with a common rubber stamp.

Ammonium chloride can also be used in the process of making albumen silver prints.

History
The earliest mention of ammonium chloride was in 554 in China. At that time, ammonium chloride came from two sources: (1) the vents of underground coal fires in Central Asia, specifically, in the Tian Shan mountains (which extend from Xinjiang province of northwestern China through Kyrgyzstan) as well as in the Alay (or Alai) mountains of southwestern Kyrgyzstan, and (2) the fumaroles of the volcano Mount Taftan in southeastern Iran. Ammonium chloride was later harvested from other volcanoes: The Arabs harvested it from Mount Etna in Sicily during the 10th century. Europeans later harvested it from the Solfatara crater and Mount Vesuvius near Naples, Italy. Ammonium chloride was also found on the island of Réunion in the western Indian Ocean. Ammonium chloride was subsequently found at Mount Hekla in Iceland, Mount Chinyero on Tenerife in the Canary Islands, and the Valley of Ten Thousand Smokes in Alaska.
 * The Arab geographer Al-Muqaddasi (c. 945/946 - 991) mentioned that ammonium chloride was obtained from Mt. Etna. See:  Lippmann, Edmund Oskar von, Entstehung und Ausbreitung der Alchemie … (Origin and Spread of Alchemy … ), vol. 1, (Berlin, Germany:  Springer, 1919), p. 404.  From p. 404:   " … er erwähnt, daß der dortige Salmiak nicht von gleicher Güte ist wie der Siciliens, dessen Lager jetzt aber schon erschöpft seien, … " ( … he mentions that the salmiak [i.e., ammonium chloride] there [i.e., in Fergana ] is not of equal value to that of Sicily’s, whose deposits are now, however, exhausted, … )
 * The Arab geographer ibn Hawqal (d. ca. 978) also mentioned that ammonium chloride was obtained from fumaroles on the slopes of Mt. Etna.
 * Sutton et al., p. 595.
 * Breislak, Scipion, Essais mineralogiques sur la solfatare de Pouzzole (Naples, Italy: Janvier Giaccio, 1792), p. 140.  From p. 140:  "Deux endroits de la Solfatare, celui où est construite la fontaine de vapeurs, et un autre à peu de distance produisent le muriate d'ammoniaque." (Two places on Solfatare — that where the fumerole has formed and another a little distance away — produce muriate of ammonia [i.e., ammonium chloride].)
 * (Lémery, Nicolas) (1705) "Diverses observations chimiques. I." (Various chemical observations.  I.), Histoire de l'Académie royale des sciences: année MDCCV, avec les memoires …, p. 66. From p. 66:   "Monsieur Lémery a eu entre les mains un Sel tiré du Mont Vesuve, & que l'on appelle Sel Armoniac naturel."  (Mr. Lémery got hold of a salt [which was] extracted from Mount Vesuvius, and which is called natural Armenian salt [i.e., ammonium chloride].)
 * Bischof, p. 212.
 * Sutton et al., p. 599.
 * Marcellin, Jean Baptiste Geneviève, Baron Bory de Saint-Vincent, Dictionnaire classique d'histoire naturelle, vol. 1 (Paris, France: Rey et Gravier, 1822).  p. 270:   "On trouve ce Minéral dans presque tous les volcans. … Elle se trouve également en Tartarie, dans le pays des Kalmuks; en Perse, au Thibet, dans l'île de Bourbon, en Bucharie, … " (One finds this mineral [i.e., ammonium chloride] in nearly every volcano … It is found also in Tartary [i.e.,  a region extending from Central Asia eastwards to the Pacific Ocean], in the country of the Kalmyks, in Persia, in Tibet, on Bourbon Island [i.e., Réunion], in Bucharia [i.e., a region of Central Asia extending from Turfan through Uzbekistan and Tajikistan ] … )
 * Bunsen, Robert (1847) "Ueber den innern Zusammenhang der pseudovulkanischen Erscheinungen Islands" (On the intrinsic relationship of pseudo-volcanic phenomena of Iceland), Annalen der Chemie and Pharmacie, 62 : 1–59, see pp. 8–9.  From pp. 8–9:   "Im Juli 1846, also nur wenige Monate nach dem Ausbruch des Vulkans, wo ich in diesen Gegenden verweilte, zeigte sich der untere Theil dieses Stromes mit dampfenden Fumarolen übersäet, in denen sich eine solche Menge reiner, zum Theil sehr schön krystallisirter Salmiak sublimirte, dass man dort, trotz der unaufhörlichen Regengüsse, dieses wertvolle Salz zu Hunderten von Pfunden hätte sammeln können."  (In July 1846, thus only months after the eruption of the volcano [i.e., Mt. Hekla], where I stayed in this region, the lower part of this [lava] flow appeared studded with steaming fumaroles, in which such a quantity of pure and sometimes very beautifully crystallized ammonium chloride had sublimated that one could have collected there — despite ceaseless downpours — hundreds of pounds of this valuable salt.)
 * Del Campo, Ángel (1912) "Los sublimados blancos del volcán Chinyero (Canarias)" (The white sublimates of the volcano Chinyero in the Canary Islands), Anales de la Sociedad Española de Física y Química, 10 : 431–449.
 * Sutton et al., p. 599. (Indeed, the word for ammonium chloride in several Asian languages derives from the Iranian phrase anosh adur (immortal fire), a reference to the underground fires. )  Ammonium chloride was then transported along the Silk Road eastwards to China and westwards to the Muslim lands and Europe.
 * Sutton et al., p. 599. (Indeed, the word for ammonium chloride in several Asian languages derives from the Iranian phrase anosh adur (immortal fire), a reference to the underground fires. )  Ammonium chloride was then transported along the Silk Road eastwards to China and westwards to the Muslim lands and Europe.

Around 800 A.D. the Arabs of Egypt discovered ammonium chloride in the soot that resulted from burning camel dung, and this source became an alternative to those in Central Asia. The Persian geographer Al-Istakhri (d. 957 A.D.) stated that ammonium chloride was obtained from the soot of camel dung that was burned to heat the public baths in Alexandria. See: (Lippmann, 1919), p. 403. From p. 403:  Istakhri " … bestätigt das persische Vorkommen … des Nûschâdirs, 'den die Ägypter aus dem Rauche ihrer Bäder haben' [aus dem Rauche des zum Heizen gebräuchlichen getrockneten Kamelmistes], … " (Istakhri confirms the occurrence in Persia … of ammonium chloride (nûshâdir), "which the Egyptians have [obtained] from the smoke of their baths" [i.e., from the smoke of the dried camel dung that's used for heating] … )  See also: Sutton et al., p. 595. The production of ammonium chloride from the soot of burned animal dung was reported early in the 18th century by a number of European observers:
 * Sicard, Claude (S.J.), Nouveaux Mémoires de la Compagnie de Jesus dans le Levant [New memoirs of the Jesuits in the Levant], vol. 2 (Paris, France: Nicolas le Clerc, 1717), pp. 96–98.  From pp. 96–98: " … nous arrivâmes sur le midy à Desmayer … " ( … we arrived at midday at Desmayer, a town [in the Nile delta] which is inhabited only by Muslims.  It is in this place that the most esteemed sal armoniac [i.e., ammonium chloride] in all Egypt is made.  This salt is made in ovens, whose top is vented lengthwise and in several places.  One places in these vents twenty or thirty round glass bottles, about a foot and a half in diameter, with a neck of half a foot [across].  The bottles are sealed well: filled with soot and a little sea salt, and animal urine.  Then one constructs a layer of loam and brick [on top of the oven], which covers everything except the tops of the bottles' necks, which [remain open] to the air.  Then a fire is lit in the oven, and it is maintained continually for three days and three nights.  The phlegm [i.e., liquid components] of the material contained in the bottles is driven off, and the acid salts and alkalies meet and cling to each other near the neck, [where they] form a white, round mass.  The operation being completed, all of the bottles are broken, and these masses are removed, which are called "sal armoniac".  It is to be noted that the soot of which I spoke, is produced by the smoke of pats, which is called gellée in Arabic.   They [i.e., the pats] are formed from animal manure.  Any other smoke is unlikely to condense into sal armoniac.)
 * Geoffroy, Étienne (1720) "Observations sur la nature et la composition du sel ammoniac"  (Observations on the nature and composition of ammonium chloride), Histoire de l'Académie Royale des Sciences: année MDCCXX, avec les memoires …, pp. 189–191.
 * Lemere (1719) "Adressé à l'Académie sur le sel ammoniac, etc." (Address to the [French Royal] Academy [of Sciences] on ammonium chloride, etc.), Histoire de l'Académie Royale des Sciences: année MDCCXX, avec les memoires …, pp. 191–194.
 * (Lemere) (1716) "Observations sur la nature et la composition du sel ammoniac," Histoire de l'Académie Royale des Sciences: année MDCCXX, avec les memoires …, pp. 195–207.  On p. 202, Lemere states that ammonium chloride can be made by combining ammonium carbonate and hydrochloric acid:  "L'on prend de l'esprit ou du sel volatil d'urine; on jette dessus de l'esprit de sel marin, jusqu'à ce qu'il ne se fasse plus de fermentation; on fait évaporer au sable la liqueur, qui, étant séche, fournit un sel salé qui a les mêmes effets que le sel ammoniac."  (One takes the spirit or volatile salt of urine [i.e., ammonium carbonate]; one tosses on it spirit of sea salt [i.e., hydrochloric acid], until it no longer makes fermentation [i.e., effervesces]; one evaporates, on a sand [bath], the solution, which, [upon] being dry, furnishes a salty solid which has the same effects as ammonium chloride.)
 * Duhamel du Monceau, Henri-Louis (1735) "Sur le sel ammoniac," Histoire de l'Académie Royale des Sciences: année MDCCXXXV, avec les memoires …, pp. 106–116; 414–434; 483–504.
 * Beckmann, Johann, Beyträge zur Geschichte der Erfindungen [Contributions to the history of inventions] (Leipzig, Germany: Paul Gotthelf Kummer, 1805), vol. 5, 4. Salmiak, pp. 254–285. English translations:  (1) Beckmann, Johann with William Johnston, trans., A History of Inventions and Discoveries, 2nd ed.  (London, England:  Walker, 1814), vol. 4, pp. 360–384.  ; and (2) Beckmann, Johann with William Johnston, trans., A History of Inventions, Discoveries, and Origins, 4th ed. (London, England:  Henry G. Bohn, 1846), vol. 2, pp. 396–407.
 * Beckmann, Johann, Beyträge zur Geschichte der Erfindungen [Contributions to the history of inventions] (Leipzig, Germany: Paul Gotthelf Kummer, 1805), vol. 5, 4. Salmiak, pp. 254–285. English translations:  (1) Beckmann, Johann with William Johnston, trans., A History of Inventions and Discoveries, 2nd ed.  (London, England:  Walker, 1814), vol. 4, pp. 360–384.  ; and (2) Beckmann, Johann with William Johnston, trans., A History of Inventions, Discoveries, and Origins, 4th ed. (London, England:  Henry G. Bohn, 1846), vol. 2, pp. 396–407.