OT.filter - kjv nitre:

kjv@Proverbs:25:20 @ As he that taketh away a garment in cold weather, and as vinegar upon nitre, so is he that singeth songs to an heavy heart.

kjv@Jeremiah:2:22 @ For though thou wash thee with nitre, and take thee much soap, yet thine iniquity is marked before me, saith the Lord GOD.