Final answer:
The irony in the song Blanche sings likely lies in the contrast between the content of the song and her actual circumstances, which is a common literary device to highlight a character's inner turmoil or façade.
Step-by-step explanation:
The irony of the song Blanche sings in the bathtub revolves around its juxtaposition to her current situation and the thematic elements of the play she's a part of. Often, the content of what Blanche sings or says contrasts with the reality she faces, which is a literary device used by playwrights to create a deeper meaning or to emphasize the character's state of mind.
Without the specific lyrics or further context of Blanche's song, providing examples of irony from its content would be conjecture. However, it's a common trope in literature for characters like Blanche to express emotions or perceptions in song that contradict their circumstances, symbolizing their internal conflict or a façade they're trying to uphold.