Ninety-five percent ethanol is commonly referred to as rectified spirit, reagent alcohol, or an azeotropic ethanol-water mixture. During standard fractional distillation processes, ethanol and water form a constant-boiling azeotropic mixture when ethanol concentration reaches approximately 95.6% by volume (or about 191 proof). Because of this thermodynamic limit, standard distillation cannot yield 100% pure alcohol without introducing specialized drying agents or secondary molecular sieve dehydration techniques.