How to find acids with flowers: Robert Boyle’s ‘syrrup of violets’ and the chemistry of color indicators

Abstract The modernization of chemistry began with simple experiments on premodern compounds, gathered together in documents like Robert Boyle’s Experimental History of Colours (1664). Among these were a series of experiments with the syrup of violets, an everyday botanical extract which exhibits surprising color-changing qualities in acidic and alkaline solutions. This skill-share reconstructs several historical recipes for violet syrup, and discusses both the historical and modern explanations of the color changes that result.