If you flick back through your Tricky Words cuttings to the dawn of time, you might find one edition dealing with "lixiviation", which means making a solution (roztok)
in water of ash from burned wood (the English word for this solution is "lye", and the Slovak is "lúh"). Specially burning wood in a pot to make ash produces potash, which is in fact potassium
carbonate, but potash can mean potassium generally, which is one of the so-called alkali metals (together with sodium and calcium).
The word "alkali" comes from Arabic and means "something roasted" - they burned seaweed (morské riasy) in a pot and got sodium carbonate - but somehow in Europe the
name "kali" became associated with potassium, and sodium is known as "natrium", which also originated in Arabic and Greek. Potassium nitrate, otherwise known as "nitre" or "saltpeter", is one of
the constituents of gunpowder.