Here is an old Gulf No Nox ad from the back cover of a 1927 Primer of The Vehicle Code of Pennsylvania.
Huh. That is one of the weirdest things I've ever heard of...think it's alcohol based?
I don't fancy taking a swig, myself. Any brave souls care to try?
"... no more harmful ... than ordinary gasoline..." !
I think they were advertising that there was no lead in their gas. One way of marketing non-ethyl gas!
BTW, today we pay extra for "unleaded" gasoline. Excuuuuuse me! Lead has to ADDED to gasoline, it isn't there naturally.