Röntgen was a friend of Grieg, Brahms, and many other composers and musicians of the late 19th and early 20th centuries. In 1919 he became a Dutch citizen, and in 1924 he retired from public life and devoted the last 10 years of his life to composing. He wrote in all of the genres of traditional classical music except opera, and wrote his first compositions when he was 9 years old. Röntgen's compositional output was considerable; over 600 compositions of all types. Röntgen had a multi-faceted career of teacher, piano soloist, chamber music performer, conductor and composer.
He is most well known for his works for chamber ensembles. He wrote his opus 50 piano trio in 1904 and dedicated it to his friend the Dutch composer Carl Nielsen. The trio won a prize in a competition held in Paris, and Nielsen wrote about it in a letter to the composer:
The new trio is the most characteristic of the works of yours I learned when you were in Denmark. It is carried along by an extremely individual and compelling musical current, which despite its modern content seems to have its roots in the vicinity of Schubert.The trio is in 3 movements:
I. Allegro non troppo e serioso - The trio begins with a short introduction, followed by the first theme played by violin and then cello. The second theme is more lyrical as well as being longer. A third theme begins rather abruptly and plays until fragments of previous themes are heard at the end of the exposition. There is no repeat of the exposition as the short development section takes up material from the introduction. The recapitulation is followed by a coda that brings back the introductory material again as well as shortened versions of the themes.
II. Andante - The middle movement begins with the violin and cello playing a duet of a folksong-like melody as the piano plays a simple accompaniment:
III. Allegro non troppo - The finale begins with an agitated section before it blooms into more drama with a theme that swells until the music becomes more subdued with a second theme. These two themes repeat in Röntgen's version of sonata form until the music goes into a coda that wraps up a well crafted piano trio.