Chapter 1: Section 5: Page 43: Lines 188-189 (770-771)

 "Ironworkers' Union," he nodded. "After enough of 'em, a man begins to develop an ear."

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The Iron Workers Union wasn't founded until 1896. So Nate Privett doesn't have as good an ear as he thinks he does. Or maybe it's even better and he can hear future bombings? Being that Chicago was a burgeoning battleground for unions and workers' rights, and because it was the first place to truly begin building iron and steel buildings (due to a new ordnance prohibiting wooden buildings in downtown Chicago after the Great Fire in 1871), a movement among ironworkers had begun and maybe they were calling themselves the "Ironworkers' Union" before the actual Iron Workers Union that was formed in 1896 and exists today.
    The essence of Nate's statement is that workers from different unions and associations, all being used and bled dry by employers, were using bombs in their fight for 8 hour days, health & safety, and living wages. And because they all made their own bombs, and bombings were so frequent, Nate now had an ear for it.
    Mostly it just sounds to me like Nate is playing up the chaos because he's one of those jerks definitely on the side of the employers and big business. I mean, it's not like he's going to make any money off of immigrant workers barely being paid enough to take care of their families.

Chapter 1: Section 5: Page 36: Line 3 (585)

 If there were any plots afoot to commit bomb or other outrages upon the Fair, the Inconvenience was ideal not only for scanning the grounds fence to fence, but also for keeping an eye out against any sea-borne assaults contemplated from the Lake side.

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When the Chums weren't on "ground-leave," they were busy spying from the air on the Fair in attempt to find labor organizers who might cause trouble with the status quo (the status quo being terrible and dangerous labor practices by employers). They didn't know they were trying to find labor organizers. They thought they were stopping potential anarchists from blowing things up for the pure pleasure of anarchy. But "anarchist" was just coded language for "disgruntled employee who has no other options than to cause some kind of uproar." This was an official assignment and like all official assignments given to the majority of people in America, it wasn't truthfully represented to them. This was to make it easier for them to do rather than burdening them with questions of ethics and morality. In America, "shades of gray" is just another way of saying "loss of profits."

Later we'll see that maybe there's another reason to worry about violent threats because an important European figure presents himself at the Fair and his death could cause a lot of trouble! Or will cause a lot of trouble eventually? But as long as it doesn't cause trouble at the Fair, that's the important thing! But never mind that! I'm getting ahead of the plot and that would mean I'd lose points on this assignment if I were back in my Children's Lit course in college!