An examination of the literature of alchemy serves to show how its principles and tenets developed. The philosopher’s stone is first heard of in the twelfth century. Prior to that period the greater number of the Greek and Arabian writers contented themselves with affirming the fact of transmutation, without indicating how it might be accomplished. The universal medicine and the elixir of life were the products of a later age; no mention of them is known before the thirteenth century. Alchemy flourished vigorously during the Middle Ages, and lingered on even until the early part of the nineteenth century. Its history is simply a long chapter in the history of human credulity. For the most part it is a record of self-deception, imposture, and fraud. It produced an abundant literature, mainly the work of ecclesiastics, between the seventh and fourteenth centuries; but as regards the artificial preparation of the noble metals or the discovery of the universal medicine or the elixir of life it was barren of result. Although no clear line of demarcation is possible, it may be convenient, in dealing with the personal history of alchemy, to divide it into the two periods before and after Paracelsus, since under his inspiration and example alchemy underwent a great development as regards its professed objects. These eventually became so extravagant that, wide as are the limits of human credulity, its pretensions gradually brought it into disrepute, and it fell by the weight of its own absurdities. One of the most reputable of the early Western alchemists was =Albert Groot=, or =Albertus Magnus=, born at Lauingen in 1193. He was a Dominican monk, who became Bishop of Regensburg, but, resigning his bishopric, retired to a convent at Cologne, where he devoted himself to science until his death in 1282. He is credited with having written a number of chemical tracts, for the most part in clear and intelligible language, which is more than can be said of the greater portion of alchemistical literature. He gives an account of the origin and main properties of the chemical substances known in his time, and describes the apparatus and processes used by chemists, such as the water-bath, alembics, aludels, and cupels. He speaks of cream of tartar, alum and caustic alkali, red lead, liver of sulphur and arsenic, green vitriol and iron pyrites.