The viola was gradually given more important work to do, until in the late 19th century and 20th century the instrument was looked upon as a solo instrument as well. This was due not in small part to some musicians that raised the level of viola playing to virtuoso status, thus giving composers more incentive to write works that could exploit the viola's unique tonal qualities.
Julius Röntgen's greatest period of composing activity came after he retired from public life in 1924, a time that was ripe with experimentation and the avant garde in classical music. While Röntgen was familiar with the trends in music of his time, he remained somewhat conservative in his musical language and use of form. For that reason, his music was mostly forgotten shortly after his death in 1932, but with the passage of time his music has come to be appreciated. As his friend Donald Tovey said of him in memoriam:
Röntgen's compositions, published and unpublished, cover the whole range of music in every art form; they all show consummate mastery in every aspect of technique. Even in the most facile there is beauty and wit. Each series of works culminates in something that has the uniqueness of a living masterpiece.Röntgen wrote three sonatas for viola and piano, one in C minor in 1924 and two in 1925; one in A-flat major and one in A minor. The Viola Sonata In C minor of 1924 is in 4 movements:
I. Allegro assai - The viola begins the movement with a motive that recurs in other parts of the work. The first section of the movement acts as an exposition for themes and fragments of others. The development section flows from the exposition and leads to the recapitulation where themes are expanded and the movement ends suddenly.
II. Andante mesto - lento, quasi fantasia - Perhaps the most interesting of the 4 movements begins with the viola once again playing solo, this time a rhythmic motive that is somewhat related to the opening motive of the first movement, that soon accompanies the piano's theme high in its register. The instruments change places with both playing low in their registers as the viola takes the thematic material with the piano accompanying. The opening material is repeated, this time with a few loud interruptions by the piano. A contrasting lyrical theme is played by the viola, which is briefly interrupted by the motive of the opening of the first movement. The contrasting theme alternates with the opening material of the first movement until the music quietly ends.
III. Allegro molto - A hyperactive movement that is a scherzo. The trio is reminiscent of Debussy in its tonal palette and gentle rhythm. The scherzo is repeated, along with a final reference to the trio section, and the movement fades away.
IV. Un poco sostenuto - allegro molto - The movement begins slowly with a section that sounds strangely modern, evidence that Röntgen was not always the musical reactionary he was accused of being. The piano plays the theme to the viola's arpeggios until the movement shifts gears and the music becomes faster paced and the theme gets a grand treatment from both instruments. The movement ends with a brief reference to the opening motive of the first movement.