Piano sonatas (Beethoven)
Ludwig van Beethoven wrote his 32 piano sonatas between 1795 and 1822. Although originally not intended to be a meaningful whole, as a set they compose one of the most important collections of works in the history of music. Hans von Bülow called them "The New Testament" of the piano literature (Johann Sebastian Bach's "The Well-Tempered Clavier" being "The Old Testament").
Piano Sextet (Mendelssohn)
Felix Mendelssohn's Sextet in D major, Op. 110, MWV Q 16, for piano, violin, two violas, cello, and double bass was composed in April-May 1824, when Mendelssohn was only 15, the same time he was working on a comic opera "Die Hochzeit des Camacho". Its composition took place between the Viola Sonata and the Piano Quartet No. 3. It also preceded the famous Octet, Op. 20 by about a year. 1824 is also the probable year of the composition of the Clarinet Sonata. Like the latter, the Sextet was not published during the composer's lifetime. Its first edition was issued in 1868 as a part of a complete collection of Mendelssohn's works. Hence the misleading high opus number.