In 1909, Fritz Haber discovered how to synthesize ammonia from atmospheric nitrogen and hydrogen using high heat and pressure. Carl Bosch, a metallurgist at BASF, was asked to scale the process up. Robert Le Rossignol, a British chemist, was Haber's assitant, and he built the first prototype of the machine that produced the first drops of ammonia. The invention of synthetic fertiliser allowed food production to grow, and the human population went from 1 billion to 8 billion. Nitrogen atoms form triple bonds with each other, and are hard to break apart. Lightning is the only natural force that can do so. This is equivalent to temperatures up to 1000 degrees celcius. But ammonia burns off at that temperature. So pressure equivalent to 20 megapascal (1 megapascal is 10 bar), which is about 100 times the pressure in a bike tire, must be used to achieve the same result under lower temperatures. The chemists had to use layers of softer and harder steel in order to contain the pressure.