Nitre
2 verses in 2 books of the King James Bible.
By Book
Every Occurrence
Proverbs 25:20As he that taketh away a garment in cold weather, and as vinegar upon nitre, so is he that singeth songs to an heavy heart.
Jeremiah 2:22For though thou wash thee with nitre, and take thee much sope, yet thine iniquity is marked before me, saith the Lord GOD.