You are most welcome Char, I think the cream of tartar has something to do with stabilizing the egg whites. Sarah Phillips (In the kitchen with Sarah) could probably answer that question. Here is the divinity recipe.
DIVINITY
2 cups sugar
1/2 cup corn syrup (The recipe did not specify, but I would assume you would use the white corn syrup)
2 egg whites
1 cup chopped nuts
1/2 cup water
1/8 tsp. salt
1/2 tsp. vanilla
1/8 tsp. cream of tartar
Combine sugar, syrup,water, salt and cream of tartar. Cover and boil 5 minutes. Uncover. Wipe sides of pan with damp cloth. Boil without stirring to firm ball stage(245-248*) Remove from heat. Pour slowly, over stiffly beaten egg whites, beating constantly. Continue beating until mixture holds its shape when dropped from a spoon. Add vanilla and nuts. Drop by teaspoonsful onto waxed paper or pour into a well buttered pan. When cold cut into squares.