Faraday achieved his early renown as a chemist. His reputation as an analytical chemist led to his being called as an expert witness in legal trials and to the building up of a clientele whose fees helped to support the Royal Institution. In 1820 he produced the first known compounds of carbon and chlorine, C2Cl6 and C2Cl4. These compounds were produced by substituting chlorine for hydrogen in “olefiant gas” (ethylene), the first substitution reactions induced. (Such reactions later would serve to challenge the dominant theory of chemical combination proposed by Jöns Jacob Berzelius.) In 1825, as a result of research on illuminating gases, Faraday isolated and described benzene. In the 1820s he also conducted investigations of steel alloys, helping to lay the foundations for scientific metallurgy and metallography. While completing an assignment from the Royal Society of London to improve the quality of optical glass for telescopes, he produced a glass of very high refractive index that was to lead him in 1845 to the discovery of diamagnetism. In 1821 he married Sarah Barnard, settled permanently at the Royal Institution, and began the series of researches on electricity and magnetism that were to revolutionize physics.