It is a Colt "Old Line" Open Top Pocket Revolver. They were made in .22 and will fire both .22 Short and .22 Long (not Long Rifle). There were some 114,000 made from 1871 to 1877 in two versions; that is the first version.
The brass frames were nickel plated, some silver plated, the barrels blued. That gun looks like the finish has been stripped or worn down to the brass. The pictures are not good enough to provide any real evaluation, but as close as I can tell, the value might run to $700 or so, retail. One in like-new condition could bring over $3000, but the pictures don't indicate any such condition.