1. Sprinkle salt over cucumbers and onion in a large kettle, let stand for one hour and then drain off the liquid.
2. Add remaining ingredients except the alum powder, stir together and bring to a boil to scald the pickles.
3. Sprinkle alum powder over mixture, stir to combine, then ladle pickles into hot jars and seal.
4. Process in water bath for 5 minutes for pints, 10 minutes for quarts. (Start counting time after water returns to a boil.)
5. Makes about 5 pints.
6. Note: You should be able to find alum powder in the spices section of your grocery store or with the canning supplies during the summer.