Which musical instrument is used in the opening of George Gershwin's 'Rhapsody in Blue'?

'Rhapsody in Blue' is a piece of music composed by George Gershwin (1898-1937) for solo piano and jazz band in 1924. The 'American Heritage' magazine says the famous opening clarinet 'glissando' has become as instantly recognizable to concert audiences as Beethoven's 'Symphony No. 5'. It premiered in a concert in the Aeolian Hall, New York City on 12th February 1924 under the title 'An Experiment in Modern Music".

Gershwin originally named the composition 'American Rhapsody' but changed it to 'Rhapsody in Blue' at the suggestion of his brother, Ira Gershwin. Ira had recently visited an exhibition of James McNeill Whistler paintings, which had titles such as 'Nocturne in Black and Gold' and 'Arrangement in Grey and Black'.

According to the critic Orrin Howard, Gershwin's rhapsody "made an indelible mark on the history of American music, on the fraternity of serious composers and performers—many of whom were present at the premiere—and on Gershwin himself, for its enthusiastic reception encouraged him to other and more serious projects." Other critics have written about the "Beginning with that incomparable, flamboyant clarinet solo".