Dissolve gelatin in 4 T. cold water. Add 1 cup boiling water. Add crushed pineapple and lemon juice, salt and sugar. Mix well and chill. When partially congealed, beat one package dream whip and fold in. Break up cake in small pieces and put in bowl lined in saran wrap. Put in layers of cake pieces and mixture until is all used up with cake on top. Chill overnight then turn out on plate. Remove saran wrap and frost with other package of Dream whip which has been prepared by package directions.