In Europe, alchemists were obsessed with generating gold, but in China, they preferred to work on youth elixirs. A string of Chinese alchemists claimed to have created a rejuvenating potion; Joseph Needham, the historian, scientist, and Sinologist, was so struck by the frequency with which Chinese emperors were poisoned by these drugs that he tabulated a list of victims. In around 300 A.D., a Chinese alchemist called Ge Hong collated various recipes. Three centuries later, a more detailed treatise specified the inclusion of obscure, exotic substances such as mercurial salts and compounds of sulfur. There are more than a thousand different names for these potions, most of which carried the same basic mineral ingredients.