PastryJoe, while writing about the history of Irish Sourdough Bread, traced the history of chemical leavening agents, potash –> pearl ash –> saleratus (as opposed to the more ancient technique of only yeast as leavening agent). Visit his first entry and then click his upper right links to finish at saleratus. Great reflections on history!
Then you can pick up the timeline of chemical leavening agents at History of Baking Powder by Whats Cooking America. Additionally, Rumford Baking Powder was first available in stores in 1859.
Baking powder has been made with different ingredients at different times: now baking powder is made with sodium bicarbonate and monocalcium phosphate, or, sodium bicarbonate and sodium aluminum sulfate, or just calcium acid phosphate. Corn starch is often an ingredient added to postpone activity if the baking powder is in contact with moisture, allowing the baking powder to be active later when it is heated in the oven.
Note from wikipedia: “…In times past, when chemically manufactured baking soda was not available, ash water was used instead, especially in confectionery. Wood ash is also weakly alkaline. To prepare ash water, one used a fistful of ash from the fireplace in a big pot of water. Ash from solid woods, such as the olive tree, is preferred, whereas resinous woods, like pine, cannot be used. The ash water is given a boil, then left overnight to settle. The water is then filtered through a cloth and is ready to use. Many traditional recipes call for ash water instead of baking soda, because of some unique qualities: for example, ash water dripped on hot vegetable oils congeals into a gel-like mixture…”
Asides:
- The word potassium is derived from the word potash.
- When cooks switched from potash, or pearl ash, to saleratus, they could use fewer eggs.
or you may prefer to read Peter Macinnis’s earlier book 
