Photos of this era are all "wet plate", a lengthy process in which the plate is coated with a chemical called a colloid, then placed in a light-proof holder for use in the camera. After exposure it must be developed before drying. Lots of info online. Sounds like a fascinating craft for someone with time and an interest in exacting hobbies. After around 1880 "dry plate" came in (thanks partly to George Eastman) and you could buy your plates ready- made and develop at your leisure.

You can likely find more information than you ever thought possible at http://www.apug.org
That's the Analog Photography Users Group and there are a lot of people doing "old school" photography.

Streetcars. Thanks for the info. Your knowledge is so helpful in understanding the contents of these amazing photos.

Does anyone know anything about developing glass plate negatives?

Those two sets of rails we see in the street...would some Shorpy history expert be able to say what ran on them? And it appears the rails themselves have an unusual design compared to a common railroad track. An no apparent rail ties underneath would indicate whatever rolled on those tracks couldn't have been too heavy.

[Those are streetcar tracks. - Dave]

to think my great-great grandpa could be in that crowd. I would love to find a picture of him during that time.

This is the victory parade of the Union Army. Three days of parading and festivities marked the end of the Civil War. I've seen a picture of the official reviewing stand with President Johnson, General Grant, and other notables. The stand was decorated with the names of battles.