Place cucumber slices in a large bowl; sprinkle with salt and toss gently.
Cover with ice cubes and let stand 2 to 3 hours or until cucumbers are thoroughly crisped.
Drain and stir in onions.
Combine remaining ingredients in a large, heavy-bottomed saucepan.
Bring to a boil and allow to boil for 10 minutes.
Stir in cucumber and onion slices and allow to return to boiling.
Pack at once in hot, sterilized jars, and seal.
Process in boiling water bath for 30 minutes.
Remove and cool before storing.