In a medium bowl, combine flour, 1 cup sugar and salt. In another bowl, whisk egg yolks, milk, and butter. Gradually add to the dry ingredients, stirring until smooth. Toss the rhubarb with the remaining 1 tablespoon of sugar, gently stir into batter. In a mixing bowl, beat egg whites until stiff. Fold into batter. In skillet, heat oil to 375. Drop batter by tablespoonfuls into oil. Fry a few at a time, turning until golden brown. Drain on paper towels.