This Trombone is currently the earliest in the collection. However, the bell and slide are from different instruments. At some point, a slide from a much later instrument has replaced the original. Serial number of the bell is 3xxx.
Serial number of the slide is 21xxx.
The bell is particularly small, although perhaps not quite in Sackbut territory. The photo shown is with a modern Getzen trombone for size comparison.
Record indicate this instrument was manufactured in 1886, with the slide from an instrument made in the 1920s.