The next time you’re in a casino in Sin City, try taking a deep breath! Just not too deep, or you might get a head rush from all that oxygen! At least that’s the Las Vegas urban legend: That casinos pump pure oxygen onto the casino floors just to keep players awake and gambling. And many people have believed this for years, but is it true?  Well, Vegas casinos do have sophisticated ventilation systems, and they have invested heavily in what’s called scent branding. So, they are pumping in floral and citrus aromas to keep things smelling nice, but releasing…