Molten Silicon
From Captain of Industry Wiki
Molten Glass is an intermediate molten product with the sole purpose of being cast into Silicon (Poly) in a Silicon Reactor. It is produced by either smelting Quartz, Coal, and Graphite in a Arc Furnace, or by smelting the previous ingredients plus Water in an Arc Furnace II.
The creation of Molten Silicon generates a substantial amount of Slag. Casting it into Silicon (Poly) also requires the addition of Hydrogen.