In a food processor or a mini chopper, blend sugar until it becomes fine but not powdered.
In a bowl, sift together cake flour, salt and 1/2 of the fine sugar.
Combine egg whites, warm water, vanilla, and cream of tartar in the stand mixer bowl. Whisk together in a low speed for 30 seconds. Change the speed to medium high and sprinkle 1/2 of the sugar while mixing continuously until medium peaks.
Take the bowl out of the stand mixer. Slowly sprinkle the cake flour mixture and fold in gently with a spatula until cake flour mixture is gone.
Spoon the mixtures into an ungreased tube pan. Smooth the top so it is even.
Place the tube pan in a cold oven. Turn the oven on to 325 degrees F and bake for 1 hour.
Invert cake and cool it in the pan. Once it is completely cool, remove the removable bottom and scrapes the sides and bottom of the pan.