"...Equal parts of thrice rectified spirit of wine (ethanol) and oil of vitriol are allowed to remain in contact for two months, and then the mixture is distilled from a water or sand bath. The distillate consists of two layers of liquid, of which the upper one is oleum vitrioli dulce verum."

Roscoe and Schorlemmer, Treatise on Chemistry, Vol. III, Pt. I, 1884, pg. 342.

For a detailed account of the life of Valerius Cordus, see Leake, C. D., Valerius Cordus and the Discovery of Ether, Isis. 1925, 7, 14-24. [thanks to F. L. Holmes (Yale) for a copy of this paper.]