In a large bowl, combine the sugar, egg white, and lemon juice. With a wooden spoon, mix the ingredients together until the icing is thickened and smooth, about 2 minutes. The icing will keep up to 2 days in an airtight container in the refrigerator; before using, beat it with a fork. Stir in very small amounts of water if it seems too thick. This recipes yields enough icing for 2 to 4 dozen cookies.