We prize them for their rough-plastic, abstergent force; to get people out of the quadruped state; to get them washed, clothed, and set up on end; to slough their animal husks and habits; compel them to be clean; overawe their spite and meanness, teach them to stifle the base, and choose the generous expression, and make them know how much happier the generous behaviors are.
-- Ralph Waldo Emerson, The Conduct of Life
Those of them which are of an abstergent nature, and purge the whole surface of the tongue, if they do it in excess, and so encroach as to consume some part of the flesh itself, like potash and soda, are all termed bitter.
-- Plato, Timaeus
Abstergent comes from the Latin word abstergēre which meant "to wipe off".