Prov 25:20

“Vinegar upon niter, etc. Niter took its name from the province of Nitria, where it is especially accustomed to be produced; nor does it differ much from the appearance of ammoniac salt. For just as salt is made on the seashore by the heat of the sun, hardening the sea waters into rock, which the greater force of the winds or the heat of the sea itself hurls further onto the shore, so in Nitria, where the prolonged rains of summer soak the land, there is so much heat of the star, which coagulates the very rain waters through the breadth of the sands into a stone very similar to salt or ice in appearance, but having neither any cold rigor nor salty taste. Yet according to the nature of salt, it is accustomed to harden in the heat and to flow and liquefy in cloudy weather. The inhabitants take and keep this, and where it is needed, they use it for washing. Hence the prophet says to sinning Judah, "Though you wash yourself with lye, and use much soap, yet your iniquity is marked before me," says the Lord God (Jer. II). It fizzes in water like living glass, and it itself dissolves, but it makes the water suitable for washing. Solomon, seeing its nature and to whom it is aptly figured, says, "Like vinegar upon lye, so is he who sings songs to a heavy heart." For if vinegar is put into lye, it immediately bubbles up, and a perverse mind, when rebuked through chastisement, or persuaded to good by the sweetness of preaching, becomes worse through correction; and from that correction, incited to the iniquity of murmuring, it should have been restrained from iniquity.”