In a heavy saucepan, combine the sugar, corn syrup and vinegar. Cook over medium heat, stirring constantly, until sugar dissolves. Cook without stirring until the temperature reaches 300° (hard-crack stage) on a candy thermometer. Do not overcook.
Remove from the heat and quickly stir in baking soda. Pour into a buttered 13-in. x 9-in. pan. Do not spread candy; mixture will not fill pan.
When cool, break into bite-size pieces. Dip into melted chocolate; place on waxed paper until the chocolate is firm. Store candy tightly covered. Yield: 1-1/2 pounds.
