One interesting and admittedly potentially horrifying application could be as chemical dispense vehicle.
"DDT ("dichlorodiphenyltrichloroethane") is a colorless, crystalline, tasteless and almost odorless organochloride known for its insecticidal properties. DDT has been formulated in almost every conceivable form, including solutions in xylene or petroleum distillates, emulsifiable concentrates, water-wettable powders, granules, aerosols, smoke candles and charges for vaporizers and lotions. First synthesized in 1874, DDT's insecticidal action was discovered by the Swiss chemist Paul Hermann Müller in 1939."
(wikipedia)
Let's say DDT's proprieties are discovered around 1880, and people begin to dream big, and by that I mean disease free colony big. Now something like that could also lead down some dark path. Once the European Empires realize that they have chemical spraying flying fortresses at their disposal some OTL “pacification” attempts of natives might become even uglier. Still, either way, the scenario might serve as food for thoughts.