Soak four ounces of gum arabic in a cupful of water until it is dissolved. Strain it to take out any black specks that may be in the gum. Put the dissolved gum arabic into a saucepan with a half pound of powdered sugar. Place the saucepan in a second pan containing boiling water. Stir until the mixture becomes thick and white. When it begins to thicken, test it by dropping a little into cold water. When it will form a firm ball remove it from the fire, and stir into it the whites of three eggs whipped to a stiff froth. This will give it a spongy texture. Lastly, flavor it with two teaspoonfuls of orange-flower water. Turn the paste into a pan covered thick with corn-starch. The layer of paste should be one inch thick. Too large a pan must not be used, or it will spread and make a thin layer. After the paste has stood twelve hours, turn it onto a slab and cut it into inch squares, dust them well with corn-starch or with confectioner's sugar, and pack in boxes. As the paste is more or less cooked, it will be more or less stiff. Marshmallows become harder the longer they are kept, but are best when as soft as they can be handled.