Ammonium chloride, an inorganic compound with the formula NH4Cl, is a white crystalline salt, highly soluble in water. Solutions of ammonium chloride are mildly acidic. Sal ammoniac is a name of the natural, mineralogical form of ammonium chloride. The mineral is commonly formed on burning coal dumps, due to condensation of coal-derived gases. It is also found around some types of volcanic vent. It is used as a flavouring agent in some types of liquorice. It is the product from the reaction of hydrochloric acid and ammonia.
- CO2 + 2 NH3 + 2 NaCl + H2O → 2 NH4Cl + Na2CO3
In addition to being the principal method for the manufacture of ammonium chloride, this method 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.
- NH4Cl → NH3 + HCl
Ammonium chloride reacts with a strong base, e.g. 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
The main application of ammonium chloride is as a nitrogen source in fertilizers, e.g. chloroammonium phosphate. The main crops 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Ammonium chloride was used in pyrotechnics in the 18th century but was superseded by safer and less hygroscopic chemicals.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 used to provide white smoke but its ready double decomposition reaction with potassium chlorate producing the highly unstable ammonium chlorate made its use very suspect.
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 this purpose, it is sold in blocks at hardware stores for use in cleaning the tip of a soldering iron and can also be included in solder as flux.
Ammonium chloride is used as an expectorant in cough medicine. Its expectorant action is caused by irritative action on the bronchial mucosa. This 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.
In several countries, ammonium chloride, known as sal ammoniac, is used as food additive under the E number E510, commonly as a yeast nutrient in breadmaking. 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, in baking to give cookies a very crisp texture, and in the flavouring Salmiakki Koskenkorva for vodkas. In India and Pakistan, it is called nausager and is used to improve the crispiness of snacks such as samosas and jalebi.
In the laboratory 
In paleontology, ammonium chloride vapor is precipitated on fossils, where the substance forms a brilliant white, easily removed and fairly harmless and inert layer of tiny crystals. This 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.
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 lighter than seawater. This differs from the method of flotation used by most fish, which involves a gas-filled swim bladder. The solution tastes somewhat like salmiakki and makes giant squid unattractive for general human consumption.
Other applications 
Ammonium chloride is used in a ~5% aqueous solution to work on oil wells with clay swelling problems. It is also used as electrolyte in zinc–carbon batteries. 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 to luster cotton.
- Solid state data from Ammonium chloride in Linstrom, P.J.; Mallard, W.G. (eds.) NIST Chemistry WebBook, NIST Standard Reference Database Number 69. National Institute of Standards and Technology, Gaithersburg MD. http://webbook.nist.gov (retrieved 22 October 2008)
- Online Sigma Catalogue , accessdate: 16 June 2011.
- Egon Wiberg, Arnold Frederick Holleman (2001) Inorganic Chemistry, Elsevier ISBN 0-12-352651-5, p. 614
- Rowley, Steven P. (2011). General Chemistry I Laboratory Manual (Second ed.). Kendall Hunt. ISBN 978-0-7575-8942-3.
- Dr. K. G. Bothara (7 October 2008). Inorganic Pharmaceutical Chemistry. Pragati Books Pvt. Ltd. pp. 13–. ISBN 978-81-85790-05-3. Retrieved 12 October 2011.
- Karl-Heinz Zapp "Ammonium Compounds" in Ullmann's Encylopedia of Industrial Chemistry 2012, Wiley-VCH, Weinheim. doi:10.1002/14356007.a02_243
- Chemistry of Pyrotechnics. John a Conkling and Christopher J Mocella 2nd edition
- Chemistry of Powder and Explosives. Tenney L Davis
- Encyclopaedic Dictionary of Pyrotechnics. Kosanke Kosanke Sturman and Winokur
- Calculators: surface tensions, and densities, molarities and molalities of aqueous ammonium chloride