sal ammoniac

[Middle English sal armoniak, from Latin sāl ammōniacus, salt of Amen : sāl, salt; see sal + ammōniacus, of Amen; see ammonia.]

Environment

Volcanic fumarole deposits.

Usually in frosty or rounded octahedral, cubic, or dodecahedral crystals, or combinations of these faces. Also in fragile white crystalline crusts.

White to yellow. Luster glassy; hardness 1-1Ɖ; specific gravity 1.5; fracture conchoidal; cleavage 1 poor. Brittle; transparent; water-soluble.

Ammonium chloride (33.7% NH ₄ , 66.3% Cl).

Volatilizes and sublimes on charcoal, and creeps up on walls of closed tube. Soluble in water, tastes bitter. Curdy white precipitate forms (proving chlorine) when silver nitrate crystal is dropped in distilled water solution of sal ammoniac.

Its manner of occurrence is typical; a test for chlorine and the volatility, together with the absence of sodium or potassium flame coloration (though unnecessary), are usually sufficient.

Sal ammoniac is of very limited occurrence, since it is a mineral that characteristically is present only between showers at gas vents around active volcanoes or at fissures on fresh lava flows. Ammonium chloride vapor is bluish, and the orifice steam smells like a laundry. The mineral forms without a liquid stage as a sublimate around the vent from which the gas is actually escaping, usually at relatively high temperatures, possibly 400°-500°F (250°-300°C). Vesuvius is one of the oldest and most productive localities, but fine crystals up to 蕀 in. (1 cm) across formed during the eurption of Parícutin in Mexico in the mid-1940s. Crusts of free-standing crystals were particularly characteristic of the early stages of a cycle of activity, when gas was abundant.

Sal ammoniac is made artificially as a vapor by blowing ammonia fumes across hydrochloric acid, and this method is often used to make a dull white coating on objects to be photographed.

The noun has one meaning:

Meaning #1: a white salt used in dry cells
  Synonym: ammonium chloride