Daniel Rivosts age Mp o Bridgeport Conn for his question:

What is cream of tartar?

Tartar is a bitter tasting material produced in certain plants and fruits. It is present in the grapes gathered to make wine. Crusts of it form on the wine vats. Chemically it is also called acid potassium tartrate. Cream of tarter is a purified form of this substance.

It is purified in a liquid, During the process the pure crystals float in a crust to the surface, It floats like cream on unhomogonized milk ‑ which is how the substance got its name, The finished product is a dry white powders somewhat gritty and acid to the taste.

As an acid cream of tartar reacts with certain alkaline chemicals, This is how is comes to be used in baking powder and biscuit making. Baking powder is often a mixture of cream of tartar and bicarbonate of soda. When moist# the two chemicals react to give off the bubbles of carbon dioxide, which make the cake light and fluffy.