Preheat the oven to 375 degrees F. Be sure that your 10 inch tube pan is clean and dry. Any amount of oil or residue could deflate the egg whites. Sift together the flour, and 3/4 cup of the sugar, set aside.
In a large bowl, whip the egg whites along with the vanilla, cream of tartar and salt, to medium stiff peaks. Gradually add the remaining sugar while continuing to whip to stiff peaks. When the egg white mixture has reached its maximum volume, fold in the sifted ingredients gradually, one third at a time. Do not overmix. Put the batter into the tube pan.
Bake for 40 to 45 minutes in the preheated oven, until the cake springs back when touched. Balance the tube pan upside down on the top of a bottle, to prevent decompression while cooling. When cool, run a knife around the edge of the pan and invert onto a plate.