Ammonium chloride NH4Cl is an inorganic compound with the formula NH4Cl. It is a white crystalline salt that is highly soluble in water. Solutions of ammonium chloride are mildly acidic. Sal ammoniac is a name of natural, mineralogical form of ammonium chloride. The mineral is especially common on burning coal dumps (formed by condensation of coal-derived gases), but also on some volcanoes. It is the product from the reaction of hydrochloric acid and ammonia.

Sources
It is a by-product of the Solvay process used to produce sodium carbonate.[3]

Ammonium chloride is prepared commercially by combining ammonia (NH3) with either hydrogen chloride or hydrochloric acid:[3]

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.[4]

Reactions
Ammonium chloride sublimes easily through decomposition into ammonia and hydrogen chloride gas.[3]

NH4Cl → NH3 + HCl
Ammonium chloride reacts with 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