nitre

also known as: natron

Proverbs 25:20; Revised King James Version marginal note: “soda”

properly “natron,” a substance so called because, rising from the bottom of the Lake Natron in Egypt, it becomes dry and hard in the sun, and is the soda which effervesces when vinegar is poured on it

It is a carbonate of soda, not saltpeter, which the word generally denotes (Jeremiah 2:22; Revised King James Version “lye”).