Gunpowder from China
Like the idea of zero, gunpowder developed gradually over time. In 142 AD, during the Han Dynasty, a man named Wei Boyang was the first to write anything about gunpowder. He wrote about a mixture of three powders that would "fly and dance" violently. We aren't sure that he meant gunpowder, but that's the only explosive that uses three ingredients that we know of. He may have been a Taoist trying to find a potion to let you live forever.
By 300 AD, a Chin dynasty scientist named Ge Hong had certainly written down the ingredients of gunpowder and described the explosion. Scientists made gunpowder by mixing sulfur, charcoal, and saltpeter, or potassium nitrate. You get sulphur by mining it out of the ground, where it exists naturally as a yellowish rock. You can make potassium nitrate, or saltpeter, by taking animal manure and letting it sit around for a while and decay. Then potassium nitrate crystals formed in the manure, and you could drain them off by washing water through the manure pile. You mix the three powders together, using about fifteen parts of saltpeter to three parts of charcoal and two parts of sulphur. The reason gunpowder explodes is that it burns very fast, and when it burns it releases gases that are bigger in volume than the original powder (just the way steam is bigger than water is).
But it was under the rule of the T'ang Dynasty, about 700 AD, that people really began to use gunpowder. T'ang Dynasty emperors used gunpowder to put on great fireworks displays. By 904 AD, Chinese inventors saw that you could also use gunpowder for a powerful weapon. First the army used gunpowder in the form of rockets. They put small stone cannonballs inside bamboo tubes and shot the cannonballs out by lighting gunpowder at one end. This is the same idea that makes guns and cannons work today.
The Chinese emperors tried to keep their discovery secret, but by the 1100s AD their secret had gotten out, and people in the Islamic Empire and then the Roman Empire began to understand how to use gunpowder for weapons. After that, it wasn't long before people in Europe also learned how to use gunpowder. We aren't sure exactly how they found out, but it might have something to do with the Third Crusade. By 1216 AD, a monk named Roger Bacon in England described gunpowder as a weapon. He thought of it as something that came from foreign places. Unfortunately for the people of West Africa, they hadn't heard about gunpowder yet when European people attacked them in the 1400s AD, which is one reason why the Europeans were able to defeat them.
Science in Ancient China, by George Beshore (1998). For kids.
The Ambitious Horse: Ancient Chinese Mathematics Problems, by Lawrence Swienciki (2001).
Ancient China: 2,000 Years of Mystery and Adventure to Unlock and Discover (Treasure Chest), by Chao-Hui Jenny Liu (1996). Lots of activities for kids, including a Chinese calligraphy set.
A History of Chinese Mathematics, by Jean-Claude Martzloff (1997). For adults. Explains the differences between Chinese and Euclidean (Greek) mathematics.
Zero: The Biography of a Dangerous Idea, by Charles Seife and Matt Zimet (2000).
The Nine Chapters (a Chinese math textbook)
More Chinese science