1. Drain juice from pineapple; heat juice and reserve pineapple.
2. In a large bowl, soak gelatin in water until soft.
3. Stir in lemon or lime juice, hot pineapple juice, salt and vanilla.
4. Refrigerate mixture until consistency is that of unbeaten egg whites.
5. Remove bowl from refrigerator and using an electric or rotary beater, beat until mixture is fluffy.
6. Add drained crushed pineapple; fold to mix.
7. In another bowl, beat egg white with an electric mixer until soft peaks are formed.
8. Add sugar and gradually beat to blend.
9. Add beaten egg mixture to gelatin mixture; fold to mix.
10. Rinse a 1-quart mold with cold water and pour the egg-gelatin mixture into it.
11. Refrigerate until chill and firm.
12. On a serving plate, unmold and garnish with fresh mint leaves, if desired.