Ten of the twelve études published as Frédéric Chopin's Opus 25 were actually composed at the same time as the Twelve Études, Op.10; only the first and last pieces of the Opus 25 collection (published in 1837) were put together at a later date. Opinion on the relative merit of the two sets has varied throughout the last two centuries (some, such as the Hungarian pianist and composer Stephen Heller, a contemporary of Chopin's, see the Opus 25 Etudes as clearly superior to the Opus 10 group, while Robert Schumann is known to have preferred the earlier publication), both collections occupy vital positions within the pianist's repertoire, and, when viewed collectively, we can find examples of almost every facet of pianistic technique and expression. Like the Opus 10 etudes, those of Opus 25 are very much intended for serious concert performance, and not solely for the virtuosic display of technique.
The Étude in B minor, Op.25, No.10, is a tiring exercise in legato octaves. The extreme agitation--one might almost say ordered chaos--of the piece is interrupted by a sublime (and to the performer, most welcome and physically relaxing) B major melody.