Which preposition to use with soliloquise

in Occurrences 3%

he soliloquised in an undertone as he relieved me of my horse.

about Occurrences 1%

[Footnote 36: The fierce Hugh Capet, soliloquising about the Virgin in the tones of a lady in child-bed, is rather too ludicrous an association of ideas.

over Occurrences 1%

Then "Master" (as the Sporting Times would irreverently speak of him) soliloquises over Master's father's coffin.

Which preposition to use with  soliloquise