Salammoniac

Salammoniac,[1] 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.

Sal ammoniac
Sal ammoniac crystals from a mine in Eisden, Maasmechelen, Limburg, Belgium (field of vision: 1.5 cm)
General
CategoryHalide mineral
Formula
(repeating unit)		NH4Cl
Strunz classification3.AA.25
Crystal systemIsometric
Crystal classHexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space groupPm3m
Unit cella = 3.859 Å; Z = 1
Identification
Formula mass53.49 g/mol
ColorColorless, white, pale gray; may be pale yellow to brown, if impure.
Crystal habitCrystals skeletal or dendritic; massive, encrustations
TwinningOn {111}
CleavageImperfect on {111}
FractureConchoidal
TenacitySectile
Mohs scale hardness1–2
LusterVitreous
StreakWhite
DiaphaneityTransparent
Specific gravity1.535
Optical propertiesIsotropic
Refractive indexn = 1.639
BirefringenceWeak after deformation
Ultraviolet fluorescenceNo
Absorption spectraNo
SolubilityIn water
References[1][2][3]
Sal ammoniac crystal from Ravat Village, Tajikistan. One of many unusual sal ammoniac crystal specimens found in the area of Ravat Village, near Yaghnob River, where the crystals have grown in a feather-like or three-dimensional arborescent. Size: miniature, 3.3 x 1.4 x 1.4 cm

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).[4] 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.[5] 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.[6]

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. 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.

Sal ammoniac has also been used in the past in bakery products to give cookies or biscuits their crisp texture, but the application of food grade baking ammonia (ammonium carbonate) is generally being substituted with the creation of modern baking powder or baking soda (sodium bicarbonate). Sal ammoniac is known, inter alia, by its use in salmiac liquorice, for instance salty liquorice or salmiak pastilles. In addition, the mineral or better its synthetic counterpart also serves for the production of cooling baths as well as in the dyeing and leather tanning (see also use of ammonium chloride).[7]

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

It was also brought into pharmacopeias by Islamic physicians for medicinal purposes.[8]

References
  1. "Salammoniac". mindat.org and the Hudson Institute of Mineralogy.
  2. "Redirect for Sal-ammoniac". webmineral.com.
  3. "Handbook of Mineralogy" (PDF).
  4. "Pliny the Elder, The Natural History, Book XXXI, Chapter 39. (7.) - The various kinds of salt; the methods of preparing it, and the remedies derived from it".
  5. Hoover, Herbert (1950). Georgius Agricola De Re Metallica - Translated from the first Latin edition of 1556. New York: Dover Publications. p. 560. ISBN 978-0486600062.
  6. "Geberis philosophi perspicacissimi, summa perfectionis magisterii in sua natur ex bibliothecae Vaticanae exemplari".
  7. "In Salmiak Territory - Opinion - The Harvard Crimson". www.thecrimson.com.
  8. Pormann, Peter E.; Savage-Smith, Emilie (2007). Medieval Islamic Medicine. Washington D.C.: Georgetown University Press. p. 120. ISBN 978-1-58901-161-8.
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