Bitumen is a tar-like petroleum based substance. It was added in version 1.4.0 as a logical dependency for crafting Bituminous Coal. AS OF 1.5.0, BITUMEN HAS BEEN REMOVED. BITUMINOUS COAL CAN NOW BE OBTAINED USING Bituminous Coal Ore. The item is currently not usable as a fuel. It's only purpose WAS to be used to craft Bituminous Coal.
Before 1.5.0, you could bitumen by smelting flint in a furnace as shown. This would give you 0.5 experience per flint smelted.