Nitre

The substance older versions called "nitre" appears in UPDV as "lye" — a strong alkaline cleanser. Two short passages preserve it: a proverb that pictures it reacting with vinegar, and a Jeremiah oracle that uses it as a figure for trying to scrub away guilt.

Vinegar on Lye

The proverb places the chemical reaction next to a social misjudgment. "[As] vinegar on lye, and [as] smoke for the eyes, So is he who sings songs to a heavy heart" (Pr 25:20). Acid poured on lye fizzes and ruins both — the wrong remedy at the wrong moment.

Washing That Cannot Cleanse

Jeremiah turns the same substance against the worshipper trying to outwash sin: "For though you wash yourself with lye, and take yourself much soap, yet your iniquity is marked before me, says the Sovereign Yahweh" (Jer 2:22). The strongest cleanser available — combined with all the soap one cares to use — does not touch the stain Yahweh sees.