The Collaborative International Dictionary
Seidlitz \Seid"litz\, a. Of or pertaining to Seidlitz, a village in Bohemia. [Written also Sedlitz.]
Seidlitz powders, effervescing salts, consisting of two separate powders, one of which contains forty grains of sodium bicarbonate mixed with two drachms of Rochell? salt (tartrate of potassium and sodium) and the other contains thirty-five grains of tartaric acid. The powders are mixed in water, and drunk while effervescing, as a mild cathartic; -- so called from the resemblance to the natural water of Seidlitz. Called also Rochelle powders.
Seidlitz water, a natural water from Seidlitz, containing magnesium, sodium, calcium, and potassium sulphates, with calcium carbonate and a little magnesium chloride. It is used as an aperient.
Wikipedia
Seidlitz powders is the generic name under which a commonly known laxative and digestion regulator was marketed and sold by numerous manufacturers under names such as "Rexall Seidlitz Powders".
The three ingredients of Seidlitz powders ( tartaric acid, potassium sodium tartrate and sodium bicarbonate) were manufactured by chemical factories from the mid-19th century onwards. The name 'Seidlitz powders' ultimately derives from the village of Sedlec in the Czech Republic. See also § Etymology below.
The municipality of Sedlec (somewhat confusingly) is also the source of 'Sedlitz bitter water' (see also § Sedlitz water below), a naturally-occurring spa mineral water which has an entirely different chemical composition and side-effects from Seidlitz powders: there is apparently no connection between the two products except the name.
The powders were often packaged in a small envelope containing two coloured paper wraps, one white and one blue. The white packets contained tartaric acid, and the blue packets contained a mixture of 75% w/w Rochelle salt ( potassium sodium tartrate) and 25% baking soda ( sodium bicarbonate). The powdery contents of both packets were stirred or dissolved separately in water and then mixed, giving off carbon dioxide with a characteristic fizzing sound. The drink was described as "a cooling, agreeable draught".
After ingestion, the powder combines with gastric juices to develop cathartic intestinal gases which can be somewhat helpful in evacuating the users's bowels. However their use can also lead to unpleasant side effects, and can even be fatal[http://www.webpwh
Usage examples of "seidlitz powders".
Thompson was trying to achieve yet another tonic for Governor Seward, whose morning malaises no longer yielded to the usual mixture of elm bark and bicarbonate while Seidlitz powders had long since been abandoned.
I beat her on the head, and he came running with Seidlitz powders.
Presently the waiter brought me a very small paper packet, such as might have contained a couple of Seidlitz powders.