Potash

Wood ash from a campfire, a major source of potash.

Potassium carbonate, or potash, is a carbonate salt notable for its presence in wood ash and ease of extraction therefrom. Potash has several uses and is extremely simple to produce in large quantities even with the most basic of technology, this makes it a critical primitive chemical feedstock. It may be used to produce lye by a reaction with slaked lime (calcium hydroxide). It is a necessary compound for the production of saltpeter from organic material and may also be used in baking as a leavening agent.

Prerequisites

• Fire
• Wood
• Pottery

Production

Potash is extremely simple to make, in fact it doesn't require the use of any chemical reaction, only a simple extraction. All that is needed are a piece of cloth (or any other material that can act as a filter, such as straw or grass), two containers (one wider than the other), and a lot of water.

1. Cut a hole in the bottom of the wider container and stuff the filter material down in the bottom to act as a filter.
2. Place the wider container over top of the other container, so that any liquid from the top drains into the bottom.
3. Fill the top container with wood ash and begin pouring water through the wood ash. Continue this until the water changed from dark yellow to clear (or, light yellow if energy is being conserved).
4. Boil down the liquid. This should be done in a non-metallic container (glazed pottery, glass, etc.) as potash is mildly caustic.

What is left will be relatively pure potash which can be used for any of the above mentioned processes. If higher purity is needed, potash may be recrystallized from methanol or ethanol, but this is a very inconvenient process.

Hardwood ash tends to consist of about 10% potash, therefore, if one fully leaches their wood ash, they are likely to get 1 g of potash for every 10 g of wood ash. However, this is rather energy inefficient as it necessitates boiling off exponentially more water per amount of potash. This, combined with the fact that anyone rebuilding society is likely to have a massive surplus of wood ash from heating, cooking, metallurgy, etc. means that it is generally advisable to only seep out about half of that amount.

Uses

Potash is an important starting point for a lot of useful chemicals, most notably lye and saltpeter.

Additionally it will react with acids to produce carbon dioxide, so it can be used as a leavening agent much the same as baking soda, with about a 2:1 conversion of potash to baking soda.