Rinse split peas well in colander.
Place ham bone and split peas in a large kettle.
Cut onion into 1/8ths. Add to kettle.
Add powdered mustard.
Add enough water to cover bone.
Bring to boil. Will probably foam.
Stir often or it will burn on the bottom.
Add water if level falls.
Ham will come off the bone.
After a couple of hours remove the bone.
Continue stirring often.