Preheat oven to 350 degrees. Grease one 10 inch tube pan
Sift the flour, baking soda, and salt together. Set mixture aside.
Separate the eggs. In a large bowl beat the egg whites until soft peaks form. Gradually add 1/2 cup of the sugar, beating until stiff glossy peaks form. Set aside.
Cream butter, 1 1/2 cups sugar, egg yolks, lemon zest, and lemon juice together until fluffy. Add flour mixture alternately with yogurt to the egg mixture. Gently fold in the egg whites and pour the batter into the prepared pan.
Bake at 350 for 50-60 minutes. Let cake cool in pan for 10 minutes, then turn out onto a rack to finish cooling.