A small coil of magnesium ribbon is placed in a crucible. The crucible cover have a mass of 21.35 grams. Measuring the mass, including the magnesium, gives 21.63 grams. The crucible, cover and contents are heated and then cooled and treated with water. A second heating and measuring of the final product (magnesium combined with oxygen) gives a mass of 21.82 grams. Determine the empirical formula of this oxide of magnesium.