Combine sugar, corn syrup and vinegar in heavy saucepan. Cook over medium heat, stirring until sugar dissolves. Continue cooking, without stirring, to 300 degrees on candy thermometer or until a little dropped in cold water becomes very brittle. Remove candy from heat. Quickly stir in soda; mix well. Pour into lightly buttered 9 x 9 x 2-inch pan. Do not spread as candy will spread itself. Cool. Break into pieces. Melt chocolate; dip pieces into chocolate and place on waxed paper. Allow chocolate to cool and harden. Yield: About one pound.