Baking Soda (Sodium Bicarbonate) is a chemical compound, in the form of a white crystalline powder. It is primarily used as a leavening agent in baking. .
Baking Soda is mainly prepared by a process involving water, brine and ammonia in a tank. The mixture resulting is then treated with carbon dioxide. The resulting substance will stay, quit firm, on the bottom of the tank. To get the powder, it needs to be filtered, washed with water, and the pulverized. In late XVIII century, Nicolas LeBlanc invented a formula to produce sodium carbonate, or soda ash. Later, Ernest Solvay found a process much less damaging for environment, to transform limestone and salt brine in actual bicarbonate. This process spread all around Europe quite quickly.
In cooking, nowadays, Baking Soda does not substitute baking powder any more, but it can help it in its rising function, for example to make cookies or other desserts. Baking Soda is also used to clean vegetable: it contributes to remove dirt and small bugs and parasites. If added to cooking water, it may help to soften legumes, or to mantain vegetable colors bright. You can even use it to clean chopping boards and plastic containers, or even your microwave oven.
Fun fact: in ancient times, old Egyptians used a mixture of Sodium Bicarbonate to produce soap, and even in embalming.