Have the water in which you wash flannel as hot as you can bear your hands in, and rub the soap in the water, or it will shrink the flannel. The water it is rinsed in should also be hot.
When flannels have become yellow and fulled up, I have often smoked them with brimstone, and they will be as white as new, and the fulled places will open. The best plan is to have a box or chest, with strings put across to hang the flannels on, and a drawer to pull out where you can set in a pan with coals and brimstone. Have the flannels nicely washed, and put them in wet, close it up till you think it wants more brimstone, when you can pull out the drawer and renew it.
After they are bleached, they should hang up in the air to let the smell of the brimstone escape. If you have but a few things to do, you can put strings across the top of an old barrel, (with both the heads out,) cover it with a thick cloth, and lift it up to put in a pan of brimstone and coals. Always wash scarlet flannel with hard soap.