The chemical equation for synthesis of ammoniaAmmonia. from its elements is simple, but the method of synthesis is not. It requires a high pressure, an active catalyst, and a high temperature. Even then the yield is low. The potential for an industrial process was first demonstrated in 1909 by physical chemist Fritz Haber[aut]Haber, Fritz. He achieved around 5–8% yield per cycle in a closed-loop, steel apparatus. The process was scaled up by Carl Bosch[aut]Bosch, Carl of the BASFCatalystsBASF company, based at LudwigshafenBadische Anilin & Soda-Fabrik (BASF)Ludwigshafen, Germany. There were many challenges, including the need for an inexpensive catalyst, the manufacture of powerful reciprocating compressorsCompressorsreciprocating, the design of a converter that did not explode from attack by hydrogen, the assembly of control instruments, and the production of pure hydrogen and nitrogen. Manufacture commenced at OppauBadische Anilin & Soda-Fabrik (BASF)Oppau, north of LudwigshafenBadische Anilin & Soda-Fabrik (BASF)Ludwigshafen, in September 1913, with the intention of supplyingBadische Anilin & Soda-Fabrik (BASF)ammonium sulfate ammonium sulfateAmmonium sulfate fertilizer to farmers. World War IWorld War I intervened, and what became known as the Haber–Bosch processCatalystsHaber Bosch process was diverted to the manufacture of munitions. In 1917, a second factory was opened at Merseburg (Leuna)Leuna, but wartime problems prevented it from reaching its intended capacity. Allied chemists and engineers were amazed at the industrial achievement in fixing atmospheric nitrogen. However, they were unable to replicate the process.