hydrofluoric acid, rubidium and caesium. Most production at this time still involved platinum, which was used in more and more applications due to its chemical and physical properties. As it is also highly resistant to acids and heat, platinum was also used to make instruments such as scientific tools, crucibles and vessels used in chemistry and physics. As early as the 19th century, platinum had already been used in locking pins to hold false teeth in place. Platinum was also used to make filaments in light bulbs and non-corrosive electrical contacts in telephones. As the company continued to expand, it needed new premises – so in 1896, the W.C. Heraeus Platinum Smelting Factory was established just outside Hanau, employing 40 people. Two years later, Wilhelm and Heinrich Heraeus, the two sons of the company founder, took over as managers. They were responsible for pushing ahead with research and development, and bringing on board a former school friend, the physicist and chemist Richard Küch. Küch, who became a director in 1909, had many contacts in the world of science and continued to carry out fundamental research, resulting in further growth in the company. Among his achievements were the development of a process to melt rock crystal at around 2000 °C to produce quartz glass. The quartz glass produced by the company was almost entirely free of defects and was of outstanding purity. It is still used in medicine today and is a highly sought-after material in manufacturing on account of its translucence and resistance to heat and acids. With the advent of ceramic colours, more and more platinum was needed for production processes and Heraeus started supplying products to the electrochemical and plastics industries. By the beginning of the 20th century, a major platinum processing boom was underway, caused by demand in the chemicals industry for large volumes of platinum thermocouples and platinum-rhodium catalysts needed to produce nitric acid. One of the most significant technical innovations in metal processing is credited to Heraeus: the melting of metals under vacuum. Heraeus Vacuumschmelze and Doctor Wilhelm Rohn applied for a patent on this process on 12 January 1918 and were granted a German patent DE 345161. Heraeus was subsequently granted British patent GB 138648, Swiss patent CH 89145, and several French patents on the process. For a short time, Heraeus set up an independent division dedicated to this technology, ‘Heraeus Vacuum Smelting’, which