Swiss chemist and physicist (1846–1929)
Born in Geneva, Pictet was professor of physics at the university there from 1879 and at the University of Berlin from 1886. He later moved to Paris.
Pictet was first interested in the production of artificial ice and then turned his attention to the study of extremely low temperatures and the liquefaction of gases. On 22 December 1877 he was involved in one of those strange simultaneous discoveries that sometimes occur in science. He announced on that day, by telegram to the French Academy, that he had liquefied oxygen. Just two days later the French physicist Louis Cailletet made a similar announcement.
Both Pictet and Cailletet had recognized that both cooling and compression were necessary to liquefy oxygen but they had achieved this using different techniques. Pictet had used his cascade method, in which he evaporated liquid sulfur dioxide to liquefy carbon dioxide, which in turn was allowed to evaporate and to cool oxygen to below its critical temperature. The oxygen could then be liquefied by pressure. The advantage over Cailletet's method was that it produced the liquid gas in greater quantity and was easier to apply to other gases.
