John Collins or Tom Collins? The same drink or not? It's hard to tell. The New York Bartender's Guide makes a clear distinction. John incorporates blended whiskey, Tom gin. The official IBA recipe for John, though, calls for gin. Both drink names date to the 1860s and have been popular enough to inspire their own glassware: the Collins glass.
I mixed the whiskey version. It tasted a lot like last week's sour, though less sour. The whiskey-to-lemon juice ratio is the same, 2:1. No doubt, the addition of sparkling water dilutes the sourness a bit.