Krypton was discovered in May 1898, in the residues resulting from of the evaporation of great amounts of liquid air used to prepare argon. In fact, this element was discovered by chance, when Ramsay and Travers decided to do a fractional distillation of liquid air when trying to isolate the neon, unknown at that time. They centered their attention in the heaviest fraction and, purifying it of possible nitrogen sludge and oxygen that could still exist, observed its spectrum. They were extremely surprised with a bright yellow line, that did not belong to the helium or to the sodium, revealing the presence of an unknown gas. This new gas was denominated krypton, from the Greek word "hidden" due to the circumstances of discovery.