\Al"ka*li\ (?; 277), n.; pl. {Alkalis} or {Alkalies}. [F.
alcali, ultimately fr. Ar. alqal[=i] ashes of the plant
saltwort, fr. qalay to roast in a pan, fry.]
1. Soda ash; caustic soda, caustic potash, etc.
2. (Chem.) One of a class of caustic bases, such as soda,
   potash, ammonia, and lithia, whose distinguishing
   peculiarities are solubility in alcohol and water, uniting
   with oils and fats to form soap, neutralizing and forming
   salts with acids, turning to brown several vegetable
   yellows, and changing reddened litmus to blue.
{Fixed alkalies}, potash and soda.
{Vegetable alkalies}. Same as {Alkaloids}.
{Volatile alkali}, ammonia, so called in distinction from the
   fixed alkalies.

\Al"ka*li\, n.
Soluble mineral matter, other than common salt, contained in
soils of natural waters. [Western U. S.]