Wash the rice thoroughly, and boil it in a quart of boiling water. When very soft, drain the Rice of all water by pressing through a colander, and add it to the milk. Beat the yolks of the eggs and sugar together till very light, and add the butter. Then add the juice and the grated rind of a lemon, and mix thoroughly with the Rice and milk. Place the whole mixture into a baking dish, and bake for half an hour in a quick oven. Beat the whites to a stiff froth, and add gradually six tablespoonfuls of powdered white sugar, beating them well all the time. Continue beating till the whites are stiff enough to stand alone. Pour this over the top of the Rice, and set it back in the oven a few minutes to brown. It may be served either hot or cold.