This is from an old Mennonite cookbook (Oklahoma) and this is the way popcorn balls used to be made.

GRAMA'S POPCORN BALLS

1 cups sugar
1/2 Tablespoon vinegar (1 1/2 teaspoons)
4 quarts (16 cups) popped corn, well salted
1 cup corn syrup
1 Tablespoon butter

Cook sugar, syrup and vinegar until it forms a soft ball when tested in cold water. T

This is called the soft ball stage because after you put about 1 teaspoon of the cooked mixture; when you pinch it together between your fingers and it holds together, but is soft (like well-chewed gum).

Remove from fire. Add butter and stir well.

ADD:
1/4 teaspoon baking soda, dissolved in 1/2 tablespoon hot water.

Pour onto popped corn, mixing well.

Butter your hands (lightly) and form popcorn mixture in balls.