Seidlitz powder
Concise Oxford English Dictionary © 2008 Oxford University Press:
Seidlitz powder /ˈsɛdlɪts/
▶noun a laxative preparation containing tartaric acid, sodium potassium tartrate, and sodium bicarbonate which effervesces when mixed with water.
– origin C18: named with ref. to the mineral water of Seidlitz, a village in Bohemia.
'Seidlitz powder' also found in these Oxford entries:

