What kind of wizardry do you have going on that there's an army in the setting batshit crazy enough to a.) have enough FOOF on-hand to use as a weapon and b.) huck it at people?
Chemical warfare in a steampunk world
I did say "like" FOOF, but I'd actually forgotten just how cold (-180C) you have to keep it.
Fun fact, an absolute madman did once react FOOF and ClF3
Steampunk is an advanced technology in a victorian setting - It's not only steam, it can be electricity, petrol, etc etc
You can also translate the all "chemical warfare" into the colonies, since it's a victorian setting.
I can easily see the evil british experiments on the poor indian subject for military reason.
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If it has electricity, it is not steampunk. If it has internal combustion engines, it is not steampunk either.
Learn about teslapunk and dieselpunk, you dumbass. You probably think that Dishonored is steampunk, don't you?