DYES AND INTOXICANTS. “They had taken the waste product of used-up coal, something so cheap and plentiful you could buy a year’s supply for mere pennies, and transformed it into one of the by-products of indigo, a plant so desired and profitable that it was sometimes referred to as “blue gold.” What was even more remarkable, was that aniline had all the characteristics of an organic base, or alkaloid, those compounds like nicotine and caffeine that acted so wondrously on the body.”
https://www.tandfonline.com/doi/full/10.1080/00026980.2020.1867786