Mix the flour, baking-powder, and salt thoroughly together. Mix the yolks with the milk; then the melted butter, the flour, and lastly the beaten whites. Have the waffle-iron very clean; let it be thoroughly heated on both sides. Rub it over with a piece of salt pork, or with a piece of butter tied in a clean rag. Close the iron, and turn it so the grease will cover every part. Put enough batter into each section of the iron to fill it two-thirds full. Shut the iron, and cook the waffles a minute or longer on each side. Serve the waffles hot, using with them syrup or powdered sugar mixed with ground cinnamon.