Mix gelatin with 1/4 cup of the sugar and salt.Beat egg yolks with water and orange juice concentrate.Add to gelatin mixture.Stir over low heat until gelatin is completely dissolved, 5 to 8 minutes.Remove from heat. Add orange peel, eggnog and rum extract.Chill, stirring occasionally, until mixture mounds slightly when dropped from a spoon.Beat egg whites with cream of tartar until frothy;gradually add remaining sugar and beat until soft peaks form.Fold in gelatin mixture. Whip 1 1/2 cups of the cream until soft peaks form;fold into gelatin mixture.Pour into 1 qt. Souffle dish with collar.To make collar, tear off 4" piece of foil 4" longer than the circumference of the dish.Fold it in thirds lengthwise.Place around top of dish and tape it together so that it fits snugly. Chill until set, at least 6 hours.Remove collar.Whip remaining 1/2 cup cream until stiff;garnish with whipped cream and orange slice.