Beat egg whites with cream of tartar in a large bowl until soft mounds begin to form, using high speed of electric mixer or rotary beater or flat wire whip.
Beat in 1/2 cup of sugar, 2 Tbs at a time; then beat until very stiff peaks form; do not underbeat.
Sift flour with remaining 1 cup sugar, baking powder and salt into a small bowl.
Add egg yolks, water and lemon extract; beat with a spoon just until blended (about 75 strokes).
Carefully fold into egg white mixture, using about 30 fold-over strokes; do not stir or beat.
Pour into an ungreased 10-inch tube pan; gently cut through batter to remove large air bubbles.
Bake at 375°F for about 35 minutes, until cake springs back when pressed lightly.
Invert and cool thoroughly in pan.
Remove from pan; sprinkle with sifted confectioners' sugar or top with a glaze, if desired.