Refrigerator Cucumber Slices
["4 lbs. cucumbers (about 6 large), cut into 1/4-inch slices", "3 med. onions, cut into 1/8-inch slices", "3 C. sugar", "3 C. vinegar", "4 tsp. canning salt", "1 1/2 tsp. mustard seed", "1/2 tsp. alum"]
["In a large container combine cucumbers and onions.", "In a large bowl combine remaining ingredients, stirring until sugar is dissolved.", "Pour over cucumbers, mix well."]
["cucumbers", "onions", "sugar", "vinegar", "canning salt", "alum"]