Cut the cabbages2 lengthwise into quarters, then across into thick ribbons. Put the cabbage in a big bowl and use your hands to toss it with the salt⅓ cup. Pour in cold water to cover the cabbage. It will float, so invert a plate on top, or a zipper-lock plastic bag of water, or whatever is handy, to keep it submerged. Cover the bowl with a towel and leave it out overnight.