Jerry Thomas' Tom Collins Gin (1876)
(Use large bar-glass.)
Take 5 or 6 dashes of gum syrup.
Juice of a small lemon.
1 large wine-glass of gin.
2 or 3 lumps of ice;
Shake up well and strain into a large bar-glass. Fill up the glass with plain soda water and drink while it is lively.
http://en.wikipedia.org/wiki/Gum_syrup#Gomme_syrup
http://en.wikipedia.org/wiki/Birch_syrup The sap is reduced in the same way as maple sap, using reverse osmosis machines and evaporators in commercial production. While maple sap may be boiled down without the use of reverse osmosis, birch syrup is difficult to produce this way: the sap is more temperature sensitive than is maple sap because fructose burns at a lower temperature than sucrose, the primary sugar in maple sap. This means that boiling birch sap to produce syrup can much more easily result in a scorched taste.
