Ammonium chloride NH4Cl (also Sal ammoniac, salmiac, nushadir salt, sal armagnac, sal armoniac, salt armoniack) is, in its pure form, a clear white water-soluble crystalline salt of ammonia. The aqueous ammonium chloride solution is 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.

Ammonium chloride dissolved in water becomes an acid. Ammonium chloride is used to produce low temperatures in cooling baths. For example, the zero point of Fahrenheit temperature scale is determined by placing the thermometer in a mixture of ice, water, and ammonium chloride. Ammonium chloride solutions with ammonia are used as buffer solutions.

In biological applications ammonium chloride acts as a nitrogen source and is used in fertilizers, as a feed supplement for cattle and as an ingredient in nutritive media for yeast microbiological organisms.

In Pyrotechnics, Ammonium chloride is an ingredient in fireworks and safety and contact explosives.

Ammonium chloride is used in the textile and leather industry in dyeing, tanning textile printing and to luster cotton.

In metal work, 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. 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.

In medicine application, 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. It 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. Ammonium chloride is also used as a diuretic in forced acid diuresis.

In several countries Ammonium Chloride is known as sal ammoniac and used as food additive. It 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.