Dissolve gelatin in hot water.
Add cold water, lemon juice, salt and mayonnaise. Blend with rotary beater.
Pour into freezer tray.
Chill until firm, one inch from the edges, but still soft in the center.
Dump mixture into a bowl and whip until fluffy.
Fold in apples, celery and walnuts.
Pour into 1 quart mold.
Chill in refrigerator until firm, about 30-60 minutes.
Serve on top of salad greens and garnish with sliced apples and walnuts.