Wash cucumbers and cut off the ends. Slice crosswise into 1/8-inch slices. Toss in a large bowl with the salt and onion slices;
Cover with about 4 to 6 cups of ice cubes. Cover and let stand for 4 hours or refrigerate overnight.
Prepare the boiling water bath. Add water to a large caner with rack and heat to about 180°. The water should be high enough to be at least 1 inch above the filled jars. I usually fill it about halfway and I keep a kettle or saucepan of water boiling on another burner to add to the canner as needed. Wash jars thoroughly and heat water in a small saucepan; put the lids in the saucepan and bring almost to the boil; lower heat to very low to keep the lids hot.
Drain the cucumber mixture. In a large pot (nonreactive) over medium heat, combine the remaining ingredients and bring to a boil.
Add the drained cucumber mixture and bring to a boil. With a slotted spoon, loosely pack the vegetables in prepared jars.
Ladle the liquid into jars, dividing evenly among the jars.
With a clean damp cloth (I keep a little bowl or cup of the boiled water handy for this step), wipe away any drips around the rims of the jars then cover with 2-piece jar lids. A lid lifter comes in handy to get the flat lids out of the water, or you could use tongs. Adjust the screw on rings firmly but do not over-tighten. Place filled in the prepared boiling water bath, adding more hot water as needed to bring the water up to about 1 inch above the jars. Bring the water to a boil. Cover and continue boiling for 10 minutes. Lift the jars out of the water and place on a rack to cool.