Drawing on research into the use of experts in early 19th-century criminal trials, the image of mad alchemists in popular culture representations of science, and the distinction between empirical and contingent “interpretive repertoires” in the discourse of scientific controversies, this article explores the controversy over arsenic-detection technologies prior to the Marsh test. In addition to noting the predictable criticism of incompetent expertise in the service of law, this article highlights implied accusations of hubris and amorality on the part of over-confident experts, both in the early 19th-century and in today's crisis of forensic science.