Due to the neck shape, I'd say it wasn't a ceramic/wire style capped bottle, most likely a wide cork, the smooth center was probably where the identifying paper label would have been, I agree possibly late 1800's to early 1900's. As to what...bath salts, elixir/tonic, perfume, haven't seen one exactly like this, but some awful close. Definitely a rare find, I'd hang onto this one and don't let it go too easy, I'm sure more bottle collectors will chime in. The fact it had a pat appd for, probably for the contents I would assume more so than the bottle shape, and definitely domestic. My best guess.
Nice find for sure.