Well, if I'm wrong, you should have a desire to argue with me. Otherwise you will be allowing misinformation to stand unchallenged, and that's bad for the hobby.
"I looked at the bottle of denatured alcohol that I keep in the shop. The label does not state which type of alcohol it is, but I took a quick sniff of it then sniffed some Isopropyl 'rubbing alcohol' and they smell similar."
We have a lack of understanding of terminology at work here.
Denatured alcohol is ethyl alcohol that has been rendered undrinkable by the addition of other chemicals. The law requires this so you can't get around liquor laws. All ethanol that a consumer can buy anywhere but from a licensed seller of alcoholic beverages must be denatured; ethanol-based rubbing alcohol is an example.
"The rubbing alcohol is marked 70% on the label. The denatured alcohol label is marked as 190 proof AND 'Completely Denatured Alcohol', which probably means it is as denatured as can be made."
No. That actually means it complies with the laws for denaturing alcohol by adding poisonous or unpalatable additives. It could be, I suppose, made more denatured by adding even more impurities, but there would be no reason to do so from a compliance standpoint.
"I do not know that 200 proof alcohol could be achieved."
I don't know why not. It's simply pure alcohol. That's the starting point for denatured alcohols. You can buy 200 proof ethanol at the liquor store.
"I was curious as to how alcohol proof and percentages are related"
Simple. Proof is percentage times two.
"There are some specific gravity i.e. weight differences and chemical composition differences between isopro[p]yl and ethanol alcohols, but I think even with those differences there would be similarities between proof and percentages."
Proof is percentage times two.
"I think that rubbing alcohol is a lower percentage of alcohol than that which is sold as denatured and that was what I tried to determine. They may indeed both be a type of Isopropyl. I was under the impression that they were somehow different in chemical makeup. My bad!"
Rubbing alcohol is some formulation that is safe to rub on the skin. It may be mostly isopropanol, or mostly ethanol (typically denatured with a bit of isopropanol). It generally has about 30% water as well. It is safe for contact with the skin, as that is its intended purpose.
Some denatured alcohol is rubbing alcohol; some rubbing alcohol is denatured alcohol. All rubbing alcohol, regardless of formulation, is safe for contact with skin, by definition.
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