And he looked out toward Sedom and Amorah and toward all the land of the plain, and he saw, and behold, the smoke of the land went up like the smoke of a furnace.
English: “Like the smoke of a furnace.” This teaches that a furnace does not give off smoke until the fire has taken hold of the greater part of it.
On the daf / in context: The comparison is used to establish a practical rule about when a furnace (or kiln) is considered fully ignited for ritual purposes.
Type of Learning
Derash on the verse (Bavli sugya) — not a formal named middah of the 13. A narrative simile yields a technical criterion.
What Is Learned
A furnace produces visible smoke only after the fire has spread through most of it; the verse supplies the image for that threshold.