Soak raisins in water for 3 hours. Sift flour with baking soda, salt and sugar. Cut the lids off of four tin cans (14-ounce vegetable size). Wash cans, dry and grease liberally (I use solid vegetable shortening such as Crisco). Combine raisins and water with the shortening, dry ingredients and optional nuts. Pour into greased cans, filling them about ⅔ of the way. Bake in a 350 degree (F) oven about one hour. Use a cake tester to check doneness. Cool on rack, then remove from tins.