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.
And it came to pass, that, when the sun went down, and it was dark, behold a smoking furnace, and a burning lamp that passed between those pieces.
But the LORD has taken you, and brought you forth out of the iron furnace, even out of Egypt, to be unto him a people of inheritance, as you are this day.
The refining pot is for silver, and the furnace for gold: but the LORD tries the hearts.
Behold, I have refined you, but not with silver; I have tested you in the furnace of affliction.
And because of them shall be taken up a curse by all the captivity of Judah who are in Babylon, saying, The LORD make you like Zedekiah and like Ahab, whom the king of Babylon roasted in the fire;