In a very large bowl, beat the egg whites with the lemon juice and salt at high speed until soft peaks form. Beat in the remaining 1 cup of confectioners' sugar, 1/4 cup at a time, and continue beating until firm peaks form. Sift the dry ingredients over the egg whites and fold them in completely. Divide the batter between the 2 prepared pans and smooth the tops. Bake for about 25 minutes, or until golden and the tops spring back when lightly tapped. Invert the cake pans onto a wire rack and let the angel food cakes cool completely.