Ok, I found this on foodreference.com
CREAM OF TARTAR
Tartaric acid is a brownish-red acid powder (potassium bitartrate) that is precipitated onto the walls of casks used to age wine. When refined into a white acid powder, cream of tartar, it is used in baking.
Cream of tartar is an acid powder. Combined with baking SODA it makes baking POWDER.
Cream of tartar is also used to give a creamier texture to sugary things like candy and frosting and to stabilize and increase the volume of beaten egg whites.
Cream of tartar can be used to clean brass and copper cookware.