As he that taketh away a garment in cold weather, and as vinegar upon nitre, so is he that singeth songs to a heavy heart.
– Proverbs 25:20
The first image depicts irritation as well as an actual worsening of a person’s situation. The second image is somewhat obscure in terms of the precise meaning. The word for nitre refers to sodium carbonate, which is neutralized by vinegar and doing so is counterproductive. Most likely it depicts ruining and making useless something otherwise useful. The point of the images is explained in the last phrase. The singing of songs here indicates an insensitive jollity. The effect is opposite of a word fitly spoken (Proverbs 12:25; 25:10-11).