Sift the soda with the flour three times; cream the butter and add the flour to it; whip the eggs to a stiff froth and add the sugar, then beat them gradually into the butter and flour, and add the lemon-juice. When it is thoroughly mixed and smooth put it into a biscuit or flat tin, so it will make a layer one and a half inches thick when done. Bake it in a moderate oven; while it is still warm spread it with royal icing. Before the icing fully hardens, mark two lines down the length of the cake, dividing it into three sections, then across in even lines, giving slices one inch broad and about two and a half inches long; to do this hold over it a straight edge and mark it with the back of a knife. Put into a pastry bag some of the frosting, made a little stiffer with sugar, and place two dots of icing on each slice. This cake may be made with baking-powder, using one teaspoonful and mixing it in the usual way. It will then be a lighter cake and should be baked in a loaf; the first gives a firm, fine-grained cake.