Solar furnace. Historical artwork of a solar furnace designed by the French chemist Antoine Lavoisier (1743-1794) for use in his experiments. The furnace focused the heat of the Sun using lenses (upper left). The furnace was needed as Lavoisier was concerned about contamination from the combustion products of the fuels usually used to produce heat in experiments. In one experiment, Lavoisier burned a diamond in air in a glass jar. By analysing the combustion products he showed that diamond was comprised solely of carbon. In a separate experiment, Lavoisier showed that air was composed of oxygen and nitrogen. He was guillotined during the French Revolution.