Bicarbonate of soda
Bicarbonate of Soda is classic raising agent that has been used by bakers for many years. Its other names include: baking soda, bread soda and cooking soda. Bicarbonate of Soda can, also, be used as a cleaning agent or to freshen up smells, e.g. in your fridge.
Bicarbonate of soda is used as a leavening agent. It releases carbon dioxide or (for these purposes) creates bubbles with an acid, so cakes or biscuits can rise.
The classic acids used with bicarbonate of soda was cream of tartar in baking powder or buttermilk, cocoa, honey and treacle. More industrial acids are used in combination with bicarbonate for baking powder presently.
Dowell, P., Bailey, A. (1980) The Book of Ingredients, Dorling Kindersley. ISBN 0718119150.