Lightly crush berries with a potato masher. Let sit for about 5 minutes, then pour off juice and reserve. Add enough water to berry juice to equal 1 cup of liquid. Combine gelatin, salt and 1/2 cup sugar in a saucepan. Add berry juice and lemon juice. Bring to a boil over medium heat, stirring constantly. Remove pan from heat and place in a large bowl of ice water. Cool until mixture is the consistency of unbeaten egg whites.
In a separate bowl, beat egg whites with cream of tartar until soft peaks form. Add 1/4 cup sugar, 1 tablespoon at a time, beating well after each addition; beat until stiff peaks form.
Fold gelatin mixture into egg whites. Fold in whipped cream and raspberries. Pour into pastry shell and chill until firm.
Serves 6 to 8