Lemon Fizz (Juice of lemon teaspoonful)

A two-ingredient fountain drink whose only real technique is speed: the whole point is to serve it while the carbonation is still violent.

• Serve immediately"Stir and serve quickly" is the recipe. Stirring knocks a good deal of gas out of the seltzer, so the glass should reach the drinker within seconds; a fizz left standing is just cloudy lemonade.
• The glassA 12-ounce fountain glass filled half full gives roughly 6 ounces of liquid in all, so a little under that in seltzer over the juice of half a lemon — a sharp, barely sweetened drink by modern standards. Filling the glass to the top would roughly halve the tartness if that suits you better, though the recipe does not call for it.
• Powdered sugarIn fountain usage this means fine granulated or what is now sold as caster or superfine sugar, not the cornstarch-laced confectioners' sugar of today. Presumably it was preferred because it dissolves in cold liquid with less stirring.
• Dissolve firstCombine the juice and sugar in the empty glass and stir until the sugar is gone, then add the seltzer. Sugar added after the water needs far more agitation and costs you the fizz.
• SeltzerFountain seltzer was drawn from apparatus charged under pressure, and was likely livelier than much bottled sparkling water. Use the freshest, most aggressively carbonated water available, and keep it cold — cold water holds more gas.
• YieldOne drink. Scaling up defeats the purpose; mix each glass to order.