I've seen a similar jar marked as a jam jar. Could have been a number of things though. It's British, and probably dates to around the turn of the 20th century.
I suppose it could be, but that style of jar was much more common in the UK than the States. I'm not sure Mellin's Food was even sold in the UK, and if it was I don't think the bottle would be quite as recognizable there as it was in the States.