In 1044 AD Zeng Gongliang and Yang Weide wrote a treatise called "Wujing Zongyao" or "Collection of the Most Important Military Techniques" in which several formulas for producing a powerful explosive powder with a large percentage of nitrates were contained. These experiments and improvements in gunpowder formulas led to more powerful weapons, including bombs (Needham, Joseph (1986e), Science and Civilization in China: Volume 5, Chemistry and Chemical Technology, Part 7: Military Technology; The Gunpowder Epic , Cambridge: University of Cambridge