A Hidden Element in the Air
In the late 19th century, the periodic table was far from complete, and the atmosphere itself still held chemical secrets. The discovery of krypton in 1898 was the result of one of the most productive streaks in the history of chemistry — a period in which Scottish chemist Sir William Ramsay and his colleague Morris Travers isolated multiple new elements from air itself.
The Road to Discovery: Argon First
The story of krypton begins a few years earlier. In 1894, Ramsay and physicist Lord Rayleigh discovered argon — the first noble gas ever isolated. Their method was simple in principle: they removed all known components from air (nitrogen, oxygen, carbon dioxide, water vapor) and were left with a small residue of unreactive gas. Argon accounted for about 1% of the atmosphere and had completely evaded detection because of its chemical inertness.
The discovery of argon raised an immediate question: were there other similar gases hiding in air? The periodic table, as Mendeleev had structured it, had no obvious home for argon, which suggested there might be an entire undiscovered group of elements.
The Method: Fractional Distillation of Liquid Air
By 1898, advances in cryogenic technology allowed scientists to liquify air and then carefully separate its components based on their different boiling points — a technique called fractional distillation. Ramsay and Travers used this approach to systematically search for new elements.
Their process involved:
- Cooling large quantities of air until it liquified
- Slowly allowing the liquid air to evaporate in a controlled manner
- Collecting fractions at different temperature ranges
- Analyzing each fraction spectroscopically to identify unknown elements by their unique spectral "fingerprints"
In the spring and summer of 1898, this approach yielded extraordinary results. In rapid succession, Ramsay and Travers announced the discovery of three new elements: krypton, neon, and xenon.
Krypton Is Isolated: May 1898
Krypton was the first of the three to be identified, in May 1898. When Ramsay and Travers evaporated a sample of liquid argon and examined the small residue that remained, spectroscopic analysis revealed bright new lines that matched no known element. The new gas had been hiding within what they had assumed was pure argon.
They named the new element "krypton" from the Greek word kryptos, meaning "hidden" — a fitting tribute to how thoroughly this gas had concealed itself.
Placing Krypton on the Periodic Table
Krypton's discovery helped cement the existence of what we now call Group 18 — the noble gases. Ramsay had already suspected that argon was part of a family, and the discovery of helium, neon, krypton, and xenon within a few years confirmed that this was an entirely new group of elements. In 1900, Ramsay published a coherent account of the noble gas group, and the periodic table was updated to include them.
For his work on the noble gases — which he summarized as discovering an entirely new column of the periodic table — William Ramsay was awarded the Nobel Prize in Chemistry in 1904.
Krypton's Legacy in Measurement
The scientific significance of krypton grew decades later when, in 1960, the international standard for the meter was redefined using krypton-86's spectral emission. This redefinition replaced the physical platinum-iridium bar kept in Paris and was a landmark moment in metrology — demonstrating that a pure element's properties could serve as a universal, reproducible standard of measurement.
A Discovery That Reshaped Chemistry
The discovery of krypton was more than just finding a new element. It revealed that the periodic table had an entire hidden group, forced chemists to reconsider their understanding of chemical bonding and reactivity, and ultimately led to one of the most important Nobel Prizes in the history of the discipline.