In "Dr. Heidegger's Experiment," what does the black folio suggest about the nature of his experiment?

I actually find this part of the story one of the more
amusing sections. It comes towards the beginning, after Dr. Heidegger has announced his
intention of performing an experiment with the help of his guests. They, obviously
knowing the doctor of old, expect something mundane and
boring:

When
the doctor's four guests heard him talk of his proposed experiment, they anticipated
nothing more wonderful than the murder of a mouse in an air pump, or the examination of
a cobweb by the microscope, or some similar nonsense, with which he was constantly in
the habit of pestering his
intimates.

However, instead
of any of these possibilities, Dr. Heidegger brings his folio, bound in black leather,
to the table. Note how "common report" affirmed this folio to be a "book of magic,"
which seems to foreshadow the supernatural and miraculous nature of the experiment that
we, just like Dr. Heidegger's guests, are about to witness.