One of the negro superstitions was that when the fire burned with a blue flame, it was the devil seeking to speak to them. A handful of salt would make him go away.
Alabama.

One of the negro superstitions was that when the fire burned with a blue flame, it was the devil seeking to speak to them. A handful of salt would make him go away.
Source: Current Superstitions (1896), entry 1451.
Fanny D. Bergen, editor.
Modern normalized navigation; the historical attribution above remains unchanged.