The analyses of a text #6

The narrator recalls his adolescence.

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The mere vehemence of her words can convey, I am sensible, but a weak impression of the passion by which she was possessed, and which made itself articulate in her whole figure, though her voice, instead of being raised, was lower than usual. No description I could give of her would do justice to my recollection of her, or to her entire deliverance of herself to her anger. I have seen passion in many forms, but I have never seen it in such a form as that.
[David Copperfield by Charles Dickens]
1. I'd like to know if the noun phrase in blue is the object of "convey."
2. I'd like to know if "I am sensible" is a parenthesis.
3. I'd like to know if "but" means "only."
4. And I'd like to know if "of" means "about."
Thank you in advance for your help.