Bert wrote:
I would like to plug a 220V welder into my dryer outlet, since that is
the only 220V outlet I have. But the house I'm renting is old enough
that the dryer outlet is a hot-hot-neutral outlet with no separate
ground.

I strongly suggest that you clear any renovations with your
landlord. He's gonna want proof that you have a safe work
area and adequate insurance to protect his investment. Then
he's going to want you to hire a competent electrician to do
the work.

Failure to do this might get you evicted.

Stuart