Chromatic voice leading, sustained dissonance, a wide dynamic range, and rhythmic independence between a slow-moving right-hand line and pulsing left-hand chords.
How to practise it
In bars 2-4 your right hand holds a long B and then a C over the left hand's chords. Play the chords pp so the long right-hand notes still sound above them.
The left hand's eighth-note chords change slowly, often by just one note. Practise bars 2-9 with the left hand alone and listen for the note that moves.
Bars 17-19 are the one loud moment: the right hand climbs and the bass drops to a low B in bar 18, f. Loop them at 40 BPM, then let the sound fall back to p in bar 20.
In bar 24 the music stops on a rest with a fermata: hold the silence a little longer than written. Then play the last chords of bars 25-26 pp, both hands together.
Credit: Typeset by Magnus Lewis-Smith for the Mutopia Project (Mutopia-2016/10/28-468) from the Peters edition of 1879, and placed in the public domain by the typesetter.