Potash is the name for several different potassium compounds, including potassium hydroxide, potassium oxide, and potassium carbonate. Potash was originally made by boiling the ashes of trees in large pots, hence the name pot-ash. It was widely made and used in the colonial United States in the 1700s and 1800s and was considered the country’s first industrial chemical. Potassium got its name from potash because researchers in the late 1800s used it to first isolate the element.
Potash was originally made from the ashes of burned trees such as beech, maple, and elm. The dry ashes were placed in large pots along with a large amount of water. The potassium oxide present in the ashes would mix with the water to form potassium hydroxide, a strong base also known as lye. This liquid was often saved and combined with fats to make soap. Most of the other compounds in the ashes, including carbon, potassium carbonate, and other potassium salts, sank to the bottom and formed a black sludge. This residue was transferred to another pot and boiled until all moisture was gone. This black solid was called potash or black salt. It contained high concentrations of potassium and was commonly used by early settlers for fertilizing their fields. It was an extremely important trade item and was sold throughout the colonial United States as well as to England. The very first patent in the United States was issued to Samuel Hopkins on July 31, 1790 for his improvements on making potash.
Besides being used as fertilizer, potash was also further purified to make a compound called “pearl ash” or “saleratus.” The potash was heated in high temperature ovens that burned off most of the carbon and other impurities, leaving a gray block that consisted mostly of potassium carbonate. Once the blocks cooled the color changed to a pearly white color, hence the name pearl ash. It was widely used in households as early as the 1790s as a leavening agent for various baked goods. Before this time cooks had to use yeast, spirits, or beaten egg whites to lighten their dough. Pearl ash quickly replaced these agents because it helped the dough rise faster than yeast and higher than spirits or egg whites. It was often mixed with acidic solutions such as molasses or sour milk that reacted with the basic potassium carbonate to form carbon dioxide that made dough rise.
The widespread use of pearl ash led to the development of baking soda (sodium bicarbonate) in the 1840s. Baking soda provided a better, faster rise and households quickly replaced their potash with baking soda. Its popularity spread it throughout the world and today it is still a staple in kitchens. For those interested in recipes using potash or pearl ash it can be still be found on some online catalogs and in German markets. Crude recipes to make your own potash from ashes can also be found on the internet for extreme traditionalists.