Denatured
alcohol is
ethanol (ethyl alcohol, whatcha find in
booze, my friend) which has been rendered
unfit for
drinking by the addition of bad-tasting and
poisonous chemicals. Waste of perfectly good
liquor, if you ask me. I guess it's supposed to keep those
lab technicians honest (and sober).
Unlike with denatured proteins or DNA, denatured alcohol hasn't been subjected to a process that causes molecular change -- it just has nasty stuff mixed into it.
There is no one additive used in producing denatured alcohol; different suppliers use different recipes. Some use methanol or isopropanol, some use gasoline.
Another name for denatured alcohol, used mostly in the UK and Australia, is methylated spirits, so called because it has methanol mixed in.
Denatured alcohol is the fuel of choice for alcohol lamps.