While in Leipzig he became acquainted with Heinrich von Herzogenberg, and it was through him that he met Brahms. He also studied piano with Franz Lachner, the conductor and composer that was good friends with Franz Schubert. Röntgen became a professional pianist at 18, and eventually moved to Amsterdam where he worked to create the Amsterdam Conservatory as well as the Concertgebouw Orchestra. He was in demand as an accompanist for singers and instrumentalists and toured with two of his sons playing piano trios.
Cello Sonata No. 2 In A Minor, Opus 41 is in 4 movements:
I. Allegro non troppo ed affettuoso - The sonata begins with an A minor theme that appears throughout the sonata.
II. Vivace, ma non troppo presto - Written in 6/8 time, this is a scherzo in all but name. It trips its way through music of lightness and humor, especially the slurred pizzicato notes in the cello. The first and third themes from the first movement make a brief appearance in altered form before the movement quickly ends.
III. Adagio - The piano plays a chorale in full chords before the cello enters with an altered repeat of the first theme of the first movement. This theme and parts of it dominate the music of this movement as the chorale and theme intertwine and develop.
IV. Allegro agitato - The rhythm and movement of the first theme resembles the finale of Beethoven's Piano Sonata In D minor, opus 31, No. 2 'Tempest'. The other themes of the movement take their turn with this one as Röntgen varies each one. The form is similar to the first movement, as the themes are worked out in a type of development/recapitulation hybrid.