Cold water is indeed the best way to preserve cut potatoes for more than a day. If you want to prep them for use later in the same day, however, you can blanch them for a few minutes, then chill them.
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|From the notebook of J.L. from Avon Lake, Ohio. Dated 1915.|
Select potatoes of uniform size. Wash, pare, and drop [at] once in cold water to prevent discoloration. Cook in boiling salted water until soft. For seven potatoes allow one tablespoon salt.
Add boiling water, enough to cover. Drain from the water and keep uncovered in a warm place until serving time.