Risky business There would be no guns without gunpowder, the volatile mixture of saltpetre (potassium nitrate), charcoal and sulphur that came to Europe in the 14th century. Chinese chemists were experimenting with early forms of gunpowder by the 9th century or even earlier. Mixing gunpowder was a tricky procedure largely carried out by hand under the constant threat of accidental explosions. Gunpowder production was as dirty as it was dangerous. To make saltpetre, workers mixed rotting vegetable waste and animal (or human!) excreta together in large beds and waited for nitrates to form as a white powder, which was later refined. OK abacus Ancient Egyptians are thought to have used an abacus-like device around 500 BC. But the Chinese version is widely seen as the world's first calculating machine, without which we would never have been able to develop the concept of the computer. A classic, Chinese abacus has two decks of beads running on 13 parallel wires. Two upper beads represent five apiece. Five lower beads represent one each. Moving a bead towards the beam separating the two decks makes it "active". References to the abacus first appeared in Chinese documents dating from the 2nd century AD. The device became widespread during the Song Dynasty (960-1279). Despite the prevalence of modern computers and calculators, abacuses are still in use in many parts of Asia. Reach for the sky When Sir Frank Whittle was developing his revolutionary jet engines during the 1940s, he needed robust but lightweight airframes to attach them to. Aluminium was the answer. Modern aviation could not have developed without this versatile, light and durable metal. The raw form of aluminium, bauxite, was first discovered in 1807 by Sir Humphry Davy (who also invented the famous miner's safety lamp) but it took years for scientists to develop it into a usable metal. By the late 19th century, aluminium was being used to make airship frames. By the 1920s, the first all-aluminium aircraft were flying. Totally wired At the time of Alexander Graham Bell and Thomas Watson's first successful telephone transmission in 1875, the only wires strong enough to be strung over long distances were made of iron. Iron wires had been used for telegraph systems but they were unsuitable for long-distance telephone links. But, in 1877, an American, Thomas Doolittle, developed a method of manufacturing copper wires strong enough to be strung between telegraph poles. Copper's superior conductivity preserved the integrity of the telephone signal to an extent that iron could not. The age of mass communications was born. Ray of light Television would never have developed without the cathode ray tube (CRT). It was invented by a German, Karl Ferdinand Braun, in 1897. A CRT is a glass vacuum tube with a narrow neck that flares into a flat "screen" at one end. The inside surface of the screen is covered with a phosphorescent layer. Electrons are fired at high voltage along the tube, illuminating when they hit the phosphorescent layer. Refined versions of this basic tube were at the heart of millions of TVs, radars and computer monitors manufactured in the 20th century. Find out more National Army Museum The International Aluminium Institute BBC's biography of Sir Frank Whittle The Copper Development Association (U.S. site) BBC's biography of John Logie Baird