This is a sword bayonet manufactured from the period of 1848 into the 1880s.
These are attached by sliding the bayonet mortise slot over a bar on the rifle, and latched in place by a puch-button latching mechanism on the hilt of the bayonet near the cross-guard. These are virtually identical to the Brunsick Pattern 1837 (aka 1st Pattern Brunswick) and can be differentiated by the location and style of the latching button. The 1837 has a domed nail-head style button located closer to the end of the mortise slot; whereas, the 1848 has a more cylindrical-shaped button that is closer to the cross-guard.
Hilt is of cast brass; latch is of internal spring-steel type with integral steel push-button.
These were designed to fit the Brunswick Rifle and variants manufactured from about 1837 into the 1880s.
Overall length is ~26-1/2"; blade length is ~21-3/4" with a single medial fuller, both sides.
Scabbards were black leather with brass furniture (throat and drag).
These bayonets were used by North and South during the American Civil War.

Please Note: These are currently being reproduced and offered by various distributors. Beware of these being offered as originals by secondary sources.