The alkali component of a raising agent. Can act as a gentle raising agent on its own in recipes (e.g. gingerbread). Also added to recipes where an acid component is already present to achieve a rise, e.g. yogurt, buttermilk etc.
It can be used to make a simple Baking Powder by using one part Bicarbonate of Soda to 2 parts Cream of Tartar.
Also very useful around the home as a natural cleaner.