It is impossible to say with certainty when and where the art of alchemy originated. There is no evidence that it has the antiquity which certain of its adepts claimed for it. Oleus Borrichius referred it to the time of Tubal-cain. The earliest writers on alchemy were probably Byzantine ecclesiastics, some of whom professed to ascribe the art to Egypt, and eventually to the mythological deity Hermes, whose association with chemistry in such terms as “the hermetic art,” “hermetically sealed,” etc., is thus explained. This much is established—that at some period prior to the tenth century there arose a special class of operative chemists, for the most part more learned in the knowledge of chemical phenomena in general, and more skilled in chemical manipulation, than the craftsmen and artisans engaged in the manufacture of technical products. They devoted themselves to searching for methods whereby the common and baser metals might be converted into silver and gold. The first known definition of chemistry relates to the aim and operations of this special class. It occurs in the lexicon of Suidas, a Greek writer of the eleventh century, who defines chemistry, χημíα as the preparation of silver and gold. Attempts at the artificial preparation of the noble metals probably originated with the Arabians, who followed the Egyptians and the Greeks in the cultivation of chemical pursuits. Neither Hesiod nor Homer makes mention of the art of producing gold from any other metal, or speaks of the universal medicine. Nor are they referred to by Aristotle or by his pupil Theophrastus. Pliny nowhere speaks of the philosopher’s stone, although he tells the story of Caligula, who, tempted by his avarice, sought to make gold from orpiment (_auripigmentum_) by distillation. “The result was that he did indeed obtain both, and of the finest kind; but in so small quantity, and with so much labour and apparatus, that, the profit not countervailing the expense, he desisted.” According to Boerhaave, the first author who mentions _al-chemia_ is Julius Firmicus Maternus, who lived under Constantine the Great, and who, in his _Mathesis_, c. 15, speaking of the influences of the heavenly bodies, affirms “that, if the moon be in the house of Saturn when a child is born, he shall be skilled in alchemy.”