碳酸钠
In the medieval and early post-medieval centuries, various glasswort plants were collected at tidal marshes and other saline places in the Mediterranean region. The collected plants were burned. The resulting ashes were mixed with water. Sodium carbonate is soluble in water. Non-soluble components of the ashes sank to the bottom of the water container. The water with the sodium carbonate dissolved in it was then transferred to another container, and then the water was evaporated off, leaving behind the sodium carbonate. Another major component of the ashes that is soluble in water is potassium carbonate, a.k.a. potash. The resulting product consisted mainly of a mixture of sodium carbonate and potassium carbonate. This product was called "soda ash" (it was also called "alkali"). It contained 20% to 30% sodium carbonate. For glassmaking, it was superior to a potash product obtained by the same procedure from the ashes of non-salty plants. If plant ashes were not washed as just described, they were still usable in glassmaking but the results were not as good.