Sal ammoniac
Sal ammoniac crystals from a mine in Eisden, Maasmechelen, Limburg, Belgium (field of vision: 1.5 cm)
General
Category	Halide mineral
Formula (repeating unit)	NH4Cl
IMA symbol	Sam[1]
Strunz classification	3.AA.25
Crystal system	Isometric
Crystal class	Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m)
Space group	Pm3m
Unit cell	a = 3.859 Å; Z = 1
Identification
Formula mass	53.49 g/mol
Color	Colorless, white, pale gray; may be pale yellow to brown, if impure.
Crystal habit	Crystals skeletal or dendritic; massive, encrustations
Twinning	On {111}
Cleavage	Imperfect on {111}
Fracture	Conchoidal
Tenacity	Sectile
Mohs scale hardness	1–2
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Specific gravity	1.535
Optical properties	Isotropic
Refractive index	n = 1.639
Birefringence	Weak after deformation
Ultraviolet fluorescence	No
Absorption spectra	No
Solubility	In water
References	[2][3][4]

Salammoniac,^[2] also sal ammoniac or salmiac, is a rare naturally occurring mineral composed of ammonium chloride, NH₄Cl. It forms colorless, white, or yellow-brown crystals in the isometric-hexoctahedral class. It has very poor cleavage and is brittle to conchoidal fracture. It is quite soft, with a Mohs hardness of 1.5 to 2, and it has a low specific gravity of 1.5. It is water-soluble. Sal ammoniac is also the archaic name for the chemical compound ammonium chloride.

History

Pliny, in Book XXXI of his Natural History, refers to a salt produced in the Roman province of Cyrenaica named hammoniacum, so called because of its proximity to the nearby Temple of Jupiter Amun (Greek Ἄμμων Ammon).^[5][6] However, the description Pliny gives of the salt does not conform to the properties of ammonium chloride. According to Herbert Hoover's commentary in his English translation of Georgius Agricola's De re metallica, it is likely to have been common sea salt.^[7] In any case, that salt ultimately gave ammonia and ammonium compounds their name.

The first attested reference to sal ammoniac as ammonium chloride is in the Pseudo-Geber work De inventione veritatis, where a preparation of sal ammoniac is given in the chapter De Salis armoniaci præparatione, salis armoniaci being a common name in the Middle Ages for sal ammoniac.^[8]

It typically forms as encrustations formed by sublimation around volcanic vents and is found around volcanic fumaroles, guano deposits and burning coal seams. Associated minerals include sodium alum, native sulfur and other fumarole minerals. Notable occurrences include Tajikistan; Mount Vesuvius, Italy; and Parícutin, Michoacan, Mexico.

Uses

It is commonly used to clean the soldering iron in the soldering of stained-glass windows.

Metal refining

In jewellery-making and the refining of precious metals, potassium carbonate is added to gold and silver in a borax-coated crucible to purify iron or steel filings that may have contaminated the scrap. It is then air-cooled and remelted with a one-to-one mixture of powdered charcoal and sal ammoniac to yield a sturdy ingot of the respective metal or alloy in the case of sterling silver (7.5% copper) or karated gold.

Food

Sal ammoniac has also been used in the past in bakery products to give cookies or biscuits their crisp texture,^{[citation needed]} but the application of food grade baking ammonia (ammonium carbonate or (NH₄)₂CO₃) is generally being substituted with the creation of modern baking powder or baking soda (sodium bicarbonate).

Sal ammoniac is used in salmiac liquorice, for instance salty liquorice or salmiak pastilles.

Dyeing

In addition, the mineral or, better, its synthetic counterpart, also serves for the production of cooling baths as well as in dyeing and leather tanning.^[9]

Sal ammoniac (ammonium chloride) was the electrolyte in Leclanché cells, a forerunner of the dry battery; a carbon rod and a zinc rod or cylinder formed the electrodes.

Medicine

It was also brought into pharmacopeias by Islamic physicians for medicinal purposes.^[10]