Pharmacopoeias. In Europe and US.
European Pharmacopoeia, 6th ed. (Potassium Sodium Tartrate Tetrahydrate). A white or almost white, crystalline powder or colourless transparent crystals. Very soluble in water practically insoluble in alcohol.
The United States Pharmacopeia 31, 2008 (Potassium Sodium Tartrate). Colourless crystals or a white, crystalline powder, with a cooling, saline taste. It effloresces slightly in warm dry air, the crystals often being coated with a white powder. Soluble 1 in 1 of water practically insoluble in alcohol. Store in airtight containers.
Potassium sodium tartrate has been used as an osmotic laxative. It is also used as a food additive.
For the general properties of potassium salts, and of sodium salts.
BPC 1973: Compound Effervescent Powder
UK: Jaaps Health Salt.