What actually took place in the private laboratory of a mid-seventeenth-century alchemist? How did he direct his quest after the secrets of Nature? What instruments and theoretical principles did he employ? Using, as their guide, the previously misunderstood interactions between Robert Boyle, widely known as “the father of chemistry,” and George Starkey, an alchemist and the most prominent American scientific writer before Benjamin Franklin as their guide, the book reveals the hitherto hidden laboratory operations of a famous alchemist and argue that many of the principles and practices characteristic of modern chemistry derive from alchemy. By analyzing Starkey's extraordinary laboratory notebooks, the book shows how this American “chymist” translated the wildly figurative writings of traditional alchemy into quantitative, carefully reasoned laboratory practice—and then encoded his own work in allegorical, secretive treatises under the name of Eirenaeus Philalethes. The intriguing “mystic” Joan Baptista Van Helmont—a favorite of Starkey, Boyle, and even of Lavoisier—emerges from this study as a surprisingly central figure in seventeenth-century “chymistry.” A common emphasis on quantification, material production, and analysis/synthesis, the book argues, illustrates a continuity of goals and practices from late medieval alchemy down to and beyond the Chemical Revolution.