Strangely that a rather awkward thing to find. Mostly a 15 or 20 min google search would give the answer.... However not really on this occasion!
This is the best i could find:
The
Eb Alto Clarinet, at 43 inches long, is said to be the modern form of the bassett horn. They first appeared around 1770. You find alto clarinets in wind or symphonic bands, but rarely in classical symphony orchestras, especially in light of Adolphe Sax’s technical improvements to the bass clarinet. Although Berlioz said about the alto clarinet, “it is a very beautiful instrument which ought to take its place in all well established orchestras”, he never wrote music for it. Many outstanding composers of the band repertoire, such as Grainger, Dello Joio, Copland, etc., have written significant parts for the alto clarinet.
