Mix the corn starch and sugar and salt, stir into the boiling water, and cook directly over the fire until the mixture thickens. Continue to cook, stirring constantly for 10 minutes, or place in a double boiler and cook 1/2 hour. Beat the egg whites until they are stiff.
When the corn starch is cooked, remove from the fire and mix thoroughly with the fruit juices. Pour over the beaten egg whites and stir slightly until the eggs and corn starch are mixed. Pour into sherbet glasses or molds wet with cold water and set aside until ready to serve.
Moisten the corn starch with a little cold water and stir in 1/2 cupful of the boiling water. Cook for 10 or 15 minutes.
Cream the butter, add the sugar and egg yolks, beat the mixture with a fork, and add the remaining 1/4 cupful of boiling water. Stir this into the corn starch and cook until the eggs thicken slightly.
Remove from the fire and add the orange and lemon juices. Serve cold over the orange fluff.