In a large mixing bowl, combine gelatin and two cups of boiling water; stir until dissolved. Stir in 4 cups of cold water. Cover and chill at least 4 hours. Gelatin will be partially set.
To serve, stir gelatin with a large spoon, fork, or wire whisk until gelatin is broken into small pieces. Place 1/4 cup of the lemonade in a large, clear glass or plastic tumbler. Add 1/2 cup of the gelatin to the lemonade, then add 1/4 cup of the carbonated beverage.
Stir slightly and you're ready to slurp some slime. Makes 12 servings.