Dissolve 1 cup salt in water(enough to cover the gallon of sliced cucumbers). Soak for 2 days in this water. After 2 days, discard the water & rinse the cucumbers. Dissolve the alum in water. Soak the cucumbers in this mixture for 2 days. After 2 days, discard the alum water & rinse the cucumbers in cold water. For next 2 days, soak the cucumbers in plain water. Heat vinegar & 1/2 gallon of sugar with pickling spices(Mother always tied the spices up in a clean piece of fabric). Add cucumbers & boil 30 minutes. Pack cucumbers in clean canning jars & seal with lids.