Section grapefruit over bowl and save juice. Drain sections and set fruit and 4 cups of juice aside.
In saucepan combine other 2 cups of juice with water and gelatin. Let stand 1 minute. Cook and stir over low heat until gelatin is dissolved. Remove from head and add sugar and salt. Add lemon juice and reserved grapefruit and juice.
Pour into two 13 x 9 inch pans (8 inch square). Cover and refrigerate until set. Cut into squares and serve on lettuce lined plates.
30 Servings. (6 servings)