John (in Sheffield)

The COD defines Carboy and Demi-John so closely together, that the difference doesn't matter...;^)

Large glass vessels - usually enclosed in wickerwork.

Hosomever...

I think of a Carboy as containing a noxious laboratory chemical, while a Demi-John is filled with .... Whisky... Alas I only have a Bottle of the latter to hand...;(

Slainte - Sam