History of Chemistry

Discovering Nitrogen: Rutherford’s Jar Experiment

Rutherford Suggests the Existence of Nitrogen 

200 years ago, a scientist discovered an invisible, odorless, and colorless gas. Chemists at the time propagated the theory of phlogiston. According to the theory, all flammable substances contained a “phlogiston”–a material released upon combustion. Phlogistons were also invisible, odorless, and colorless. These similarities contributed to nitrogen’s existence being overlooked. But Daniel Rutherford (1749-1819), a Scottish chemist, physician, and botanist, explored the overgeneralized theory. He investigated more acutely what really composed these “phlogistons.” 

Experimentally Isolating Nitrogen 

Rutherford postulated the existence of a gas that does not catalyze combustion reactions. This inability set it apart from the other components of our atmosphere, such as oxygen and carbon dioxide. He explored this hypothesis by conducting an experiment in 1772 that facilitated the isolation of this gas. His test included discrete steps that eliminated oxygen and carbon dioxide from a gaseous sample. 

Rutherford’s Experimental Steps:

  1. Placing a living mouse inside a closed glass jar until it expired. 
  2. Burning a candle in the same jar until its flame died. 
  3. Burning solid phosphorus in the jar until it, too, stopped burning. At this point, he had removed all of the oxygen from the gaseous sample; the mouse, candle, and phosphorus had consumed this oxygen and, in turn, produced carbon dioxide. 
  4. Passing the remaining air from the jar through a solution that absorbed this carbon dioxide via chemical reactions, thus removing it from the gaseous sample. 

Unpacking Rutherford’s Conclusion

His Experimental Successes

Upon removing all oxygen and carbon dioxide from his initial sample of gas, Rutherford was left with what he dubbed “noxious” air. He employed this term to convey the fact that the mouse, and by association, living organisms, could not live in it. Nor could substances combust in it. But while he had successfully isolated nitrogen gas, his subsequent inferences regarding its identity as “phlogisticated air” proved incorrect. 

His Experimental Shortcomings

Rutherford deduced, based off of the theory of phlogiston, that his noxious gas must have played a compositional role as a phlogiston substance. He bolstered this assumption by noting that the substance was “left over” from the combustion reactions. Thus, while it had not necessarily catalyzed the burning of the candle or phosphorus, its presence at the end of the experiment reflected the expected behavior of a phlogiston.

In the late 1770s, French chemist Antoine Lavoisier, a great scientist, disproved the theory of phlogiston by introducing his findings regarding oxygen combustion. Essentially, Lavoisier pointed out that pro-phlogiston chemists could not account for weight changes that occurred during combustion reactions, given that fire itself could not be weighed. As decades passed, phlogiston became regarded more as a principle as opposed to a physical substance; eventually, its overcomplication and overly assumptive nature contributed to its demise. But while the theory thus cannot be applied to Rutherford’s findings, accounting for Lavoisier’s ideas supports the elimination of oxygen that occurred during the combustion reactions, which led to the ultimate, successful isolation of the “noxious gas.”

Visualization of nitrogen orbitals, distinguished by color.

Nitrogen as an Element

Around 1800, scientists coined the word “nitrogen.” This term stems from the French words “nitre” and “gène,” which combine to convey nitrogen’s status as a key constituent of nitric acid (learn how nitric acid helped discover molybdenum). Today, we know that nitrogen is the most abundant element in Earth’s atmosphere. It is present in all living matter. 

This element has proven crucial to life on our planet. Nitrogen compounds exist in everything from fertilizers to explosives. They constitute nearly all organic materials and food items. So while we have Rutherford to thank for distilling nitrogen and demonstrating its non-flammable nature, its identity, value, and traits are far more intricate than this single property.

Further Reading

Discovering the Nucleus: Rutherford’s Gold Foil Experiment
Phase Diagrams
Producing Oxygen (On AmazingRust)

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