Soda ash; caustic soda, caustic potash, etc.
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.
Webster's Revised Unabridged Dictionary (1913), edited by Noah Porter. About
waste \alkali waste\ waste material from the manufacture of alkali; specif., soda waste.
Anything that will neutralize an acid, as lime, magnesia, etc.