Old Fashioned Sponge Cake

From 1910:

Take five eggs and half a pound of loaf sugar, sifted; break the eggs over the sugar and beat well together
with a silver fork for half an hour; previously take the weight of two and one-half eggs in their shells in flour. After you have beaten the eggs and sugar the required time, grate in the yellow rind of one lemon, or use the juice with the rind, as preferred, then stir in the flour a little at a time, beating well until perfectly blended; pour at once on tin sheets, lined with buttered paper, and bake at once in a moderate oven.