Lyon Playfair, Baron St Andrews, Scottish chemist and politician, c 1870.

UNITED KINGDOM - SEPTEMBER 09: Carte de visite photograph by Robert W Thrupp of Lyon Playfair, FRS, MP, first Baron St. Andrews (1818-1898). Playfair studied medicine at Glasgow and Edinburgh and chemistry at University College London, completing his doctorate under Liebig (1803-1873) at Giessen, Germany. He rose from being a chemist in the Geological Survey in 1846, to becoming Secretary for Science and Art in 1855 and President of the Chemical Society in 1857. He discovered the nitroprussides class of salts, and took part in organising the Great Exhibition of 1851. He was Professor of Chemistry at Edinburgh University from 1858 to 1896, and ended his career as Chairman and Deputy Speaker of the House of Commons. He was created Baron Playfair of St Andrews in 1892. (Photo by SSPL/Getty Images)