From nathak; a melting -- is melted.
see HEBREW nathak
H2046. hittuk
הִתּוּךְ noun [masculine] a melting (Hophal-formative, dissimilated from הֻתּוּךְ, according to BaNB § 102 d); — construct כּוּר בְּתוֺךְ כֶּסֶף כְּהִתּוּךָ Ezekiel 22:22 like a melting of silver in a smelting-pot.