Fluorescein: Phthalic Anhydride and Resorcinol Melted with Zinc Chloride (Baeyer, Cohen 1920)

Baeyer's fluorescein: phthalic anhydride and resorcinol melted together with zinc chloride until the melt sets hard, then boiled out with dilute hydrochloric acid. 10 g of anhydride gives about 20 g of fluorescein, whose solutions glow yellow-green. Not given: how much water and alcohol the washing takes. Source: J. B. Cohen, Practical Organic Chemistry (1920), Preparation 82, after Baeyer (1876). Picture: Bricksnite, Wikimedia Commons, CC BY 3.0.