Sal ammoniac is a rare mineral composed of
ammonium chlorideAmmonium 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...
, NH
4Cl. It forms colorless to white to yellow-brown crystals in the isometric-hexoctahedral class. It has very poor cleavage and a brittle to
conchoidal fractureConchoidal fracture describes the way that brittle materials break when they do not follow any natural planes of separation. Materials that break in this way include flint and other fine-grained minerals, as well as most amorphous solids, such as obsidian and other types of glass.Conchoidal...
. It is quite soft, with a Mohs hardness of 1.5 to 2, and has a low
specific gravitySpecific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...
of 1.5. It is water-soluble. Sal ammoniac is also the
archaicIn language, an archaism is the use of a form of speech or writing that is no longer current. This can either be done deliberately or as part of a specific jargon or formula...
name for the chemical compound
ammonium chlorideAmmonium 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 Romans called the ammonium chloride deposits they collected from near the Temple of Jupiter
AmunAmun, reconstructed Egyptian Yamānu , was a god in Egyptian mythology who in the form of Amun-Ra became the focus of the most complex system of theology in Ancient Egypt...
(
GreekGreek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
Ἄμμων
Ammon) in
ancient LibyaThe Latin name Libya referred to the region west of the Nile Valley, generally corresponding to modern Northwest Africa. Climate changes affected the locations of the settlements....
'sal ammoniacus' (salt of Amun) because of proximity to the nearby temple. Salts of ammonia have been known from very early times; thus the term
Hammoniacus sal appears in the writings of
PlinyGaius Plinius Secundus , better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire, and personal friend of the emperor Vespasian...
, although it is not known whether the term is identical with the more modern
sal-ammoniac. In any case, this salt ultimately gave
ammoniaAmmonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
and
ammoniumThe ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
compounds their name.
It typically forms as encrustations formed by sublimation around volcanic vents. It is found around volcanic
fumaroleA fumarole is an opening in a planet's crust, often in the neighborhood of volcanoes, which emits steam and gases such as carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrogen sulfide. The steam is created when superheated water turns to steam as its pressure drops when it emerges from...
s,
guanoGuano is the excrement of seabirds, cave dwelling bats, and seals. Guano manure is an effective fertilizer due to its high levels of phosphorus and nitrogen and also its lack of odor. It was an important source of nitrates for gunpowder...
deposits and burning
coalCoal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
seams. Associated minerals include sodium
alumAlum is both a specific chemical compound and a class of chemical compounds. The specific compound is the hydrated potassium aluminium sulfate with the formula KAl2.12H2O. The wider class of compounds known as alums have the related empirical formula, AB2.12H2O.-Chemical properties:Alums are...
, native
sulfurSulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
and other fumarole minerals. Notable occurrences include
TajikistanTajikistan , officially the Republic of Tajikistan , is a mountainous landlocked country in Central Asia. Afghanistan borders it to the south, Uzbekistan to the west, Kyrgyzstan to the north, and China to the east....
; Mt. Vesuvius,
ItalyItaly , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
; and
ParícutinParícutin is a cinder cone volcano in the Mexican state of Michoacán, close to a lava-covered village of the same name. It appears on many versions of the Seven Natural Wonders of the World...
, Michoacan,
MexicoThe United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
.
Uses
It is commonly used as a flux in the soldering of stained-glass windows. In both 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. Anything other than 24-karat gold has silver and copper added. Usually the addition of silica, zinc, and deoxidants in very small amounts relative to the pennyweight (dwt.) of gold are processed into gold from as low as 8-karat to as high as 23.5-karat gold. This is added to prevent porosity or cracking while milling the ingot further into wire, sheet, or tubing. Without those additives an otherwise poor-quality ingot will result in open crucible melting with a hand torch or blowpipe and flame, as was done before electric melting furnaces were invented for use in the precious metals industry.
Sal ammoniac has also been used in the past in bakery products to give cookies a very crisp texture, although that application is rapidly dying due to the general disuse of it as an ingredient. However, in some areas of Europe, particularly
ScandinaviaScandinavia is a cultural, historical and ethno-linguistic region in northern Europe that includes the three kingdoms of Denmark, Norway and Sweden, characterized by their common ethno-cultural heritage and language. Modern Norway and Sweden proper are situated on the Scandinavian Peninsula,...
, it is still widely used in the production of salty licorice candy known as Salmiak or Salmiakki.