How much bleach should be used to whiten handkerchiefs and how long should I soak them?

A great bleach soaking solution for white bleachable laundry is ¼ cup Clorox^® Regular-Bleach per gallon of water (or if you are using new Concentrated Clorox^® Regular-Bleach, use 3 tablespoons bleach per gallon of water). Fully submerge the items (in your case, handkerchiefs) in the bleach solution for up to 5 minutes, and then rinse. You can then follow up with a hot water machine wash using detergent and Clorox Regular-Bleach. Also, you didn't specify the fiber content of your handkerchiefs--I'm assuming they are cotton or poly/cotton and that you can bleach them, but I also wanted to clarify that you should avoid bleaching wool, silk, mohair, leather, and spandex. I would hate to find out you were asking about silk handkerchiefs, which per the above list you can't bleach!