1,2,4-Trihydroxyanthraquinone, a natural red/yellow dye found in the madder plant
Together with Carl Theodore Liebermann, he synthesized the orange-red dye alizarin in 1868; alizarin had been isolated and identified from madder root some forty years earlier in 1826 by the French chemist Pierre Robiquet, simultaneously with purpurin, a violet dye.