I can't quite remember, is it the Tom Collins that is made with gin and the John Collins with vodka, or vice versa?
A recipe for a John Collins is featured in the Steward and Barkeeper's Manual of 1869: Teaspoonful of powdered sugar The juice of half a lemon A wine glass of Old Tom Gin A bottle of plain soda Shake up, or stir up with ice. Add a slice of lemon peel to finish.[3] I'm surprised you don't have a copy
The Steward and Barkeeper's manual does sound like something every self respecting dipso should have.Where would one get such a thing?