Histories of nineteenth-century chemistry have focused on what organic chemists made using which reactions. But an equally important issue for the chemists themselves was how to identify what they had made. By its smell? By its taste? By its chemical reactions? By its physical properties? By its ability to kill frogs? And whilst chemists in different labs knew a dead frog when they saw one, they certainly didn’t always agree about melting and boiling points. At the mid-century, for example, boiling points reported for coniine, the active constituent of hemlock, ranged over more than sixty degrees – which surprised nobody. And as we follow this history things get even worse: the product of the first claimed synthesis of coniine turned out not to be coniine at all, even though it killed frogs in exactly the right way!

So how did nineteenth-century organic chemists identify the products of their reactions? When and how did melting and boiling points become decisive arbitrators of chemical identity? And what does all this tell us about chemistry in the nineteenth-century that we didn’t already know? A fresh history of synthetic organic chemistry?