Complex sentence: Another advance was the manufacture of kiln charcoal by distilling wood in heated iron retorts instead of burning it in earthern pits; controlling the temperature influenced the power and consistency of the finished gunpowder.
Split into simpler sentences: Another advance was the manufacture of kiln charcoal by distilling wood in heated iron retorts instead of burning it in earthern pits. Controlling the temperature influenced the power and consistency of the finished gunpowder.