The ironic struggle against time
There is a primal instinct in human nature to hang onto the orderly past, instead of progressing into the future. This is symbolized by the radical era of time before the French Revolution, because that conflict originates when the powers that be retain archaic modes of government at the expense of a growing urban populace. In other words, the powerful people want things to stay the way they are, but the times change without their permission.
Dramatic irony and the Great Fire
There is a kind of dramatic irony in Daniel's experience of London's Great Fire, because it puts him in close contact with the cast of a changing Europe. The dramatic irony reminds the reader early in the novel that although this epic change of eras is well studied, well explored in literature (who hasn't heard of Dickens? Who hasn't heard of Marx?) but to Daniel, it's still just happening for the first time.
The irony of slavery
The discussion about slavery comes mostly from Eliza's character, as she encounters other characters in the novel. Her position in society as a powerless, disenfranchised person is a symbol of something to which all humans are enslaved: The forward march of time. Who cares, though, right? After all, the future is a happy time of awesome technological progress, right? Well, yes, but as Eliza well knows, any slavery is deathly slavery. Time surely propels every human toward their own death.
The political irony
There are scenes in the third act of the novel's plot when the irony of politics is demonstrated by the characters. When Daniel hob-knobs with the politically powerful, it proves that politicians are people, and that those people can be as forward-thinking as they want, or instead, they can be traditionalists and conservatives, but that implies that the government is man-made and fallible—as fallible as a person.
The irony of role reversal
In its treatment of opposites, as the title implies alchemically (Mercury is Quicksilver, and the metal's meaning in alchemy is that it stands for perplexing states of paradoxical duality, since the metal is both solid and liquid at the same time). This leads to an ironic role reversal where Daniel is trapped in the Tower of London, imprisoned for treason. The imprisonment makes him like a damsel in distress, because he's trapped in a tower. Just like the archetypal maiden in distress, he too needs the help of heroic empathizer to be freed. Although he is a man, he has just wandered through a feminine story arc. This is a sign of role reversal and paradoxical duality.
