Often portable, Ge 15:17. They were used for melting the precious metals, Pr 17:3. The furnace into which Daniel's three friends were cast was large, and remained open after they were cast in, Da 3. The fearful punishment spoken of in Jer 29:22 is still used in the East. The word furnace is used to illustrate a state of oppression, De 4:20, and of affliction, Isa 48:10.