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Nitrogen makes up most of every breath you take, yet it was first described in a student thesis: Daniel Rutherford's doctoral dissertation at Edinburgh in 1772. This post covers how he did it, how to read his results in modern terms, and a calculation using his own fractions.
Do not confuse him with Ernest Rutherford of the gold foil experiment, who was born more than a century later.
Who was Daniel Rutherford?
The chemist William Ramsay wrote a careful account of him in *The Gases of the Atmosphere* (1896). Rutherford was born in Edinburgh on 3 November 1749, the son of Dr John Rutherford, one of the founders of the city's medical school. He studied arts and then medicine at Edinburgh, and received his MD in 1772. After three years of travel he returned in 1775 to practise medicine, became professor of botany in 1786, and was president of the Royal College of Physicians of Edinburgh from 1796 to 1798. He died in 1819.
He was a pupil of Joseph Black, who had shown that "fixed air" (carbon dioxide) is a distinct gas. Ramsay says Black had noticed that a residue of air remained after burning and absorbing the fixed air, and suggested that Rutherford study it.
What did Rutherford's 1772 thesis show?
His thesis, *Dissertatio inauguralis de aere fixo dicto, aut mephitico*, was published in Edinburgh in 1772. Ramsay summarises the experiments:
A mouse left in a closed volume of air until it died reduced the volume by one-tenth.
Shaking the remaining air with alkali removed a further one-eleventh, the fixed air.
What was left still put out a candle flame, though tinder smouldered in it briefly.
Burning a candle, charcoal or phosphorus in air and then absorbing the fixed air left the same kind of residue.
So, after the fixed air was gone, the remaining gas still could not support life or burning. Rutherford explained it with the phlogiston theory of his day: the air had become saturated with phlogiston from the burning body. In Ramsay's translation he admitted, "I had intended to add something regarding the composition of mephitic air ... but I have not been able to find out anything with certainty."
Ramsay notes the thesis came a year or two before the published work of Priestley and Scheele, and concludes that Rutherford "may be well credited with the discovery of nitrogen." Our post on Joseph Priestley and oxygen tells the next part of the story.
Worked example: reading Rutherford's numbers
Start with 100 volumes of air and apply his fractions.
After the mouse: 100 − 100/10 = 90 volumes.
Fixed air removed by alkali: 90 ÷ 11 = 8.2 volumes, leaving 90 − 8.2 = 81.8 volumes.
What should be left if all oxygen were gone? Dry air is 78.084% nitrogen, 20.946% oxygen and 0.934% argon by volume, according to NOAA's JetStream guide to the atmosphere. Nitrogen plus argon is 79.0 volumes.
Estimate: 81.8 − 79.0 = 2.8 volumes of something else, most likely unused oxygen, about 13% of the original 20.9.
This is rough, since the mouse experiment is not a precise measurement, but it fits his observation that tinder still glowed briefly: the residue was not quite oxygen-free.
The hidden gas: argon is 0.934 ÷ 79.0 = 1.2% of Rutherford's "nitrogen."
That last 1.2% mattered. The Nobel Prize page for William Ramsay explains that by comparing the weight of nitrogen from air with nitrogen made chemically, Ramsay and Lord Rayleigh showed in 1894 that air contained a new element, argon. Ramsay won the 1904 Nobel Prize in Chemistry; our post on William Ramsay and the noble gases has the full story.
Common mistakes about nitrogen's discovery
Mixing up the Rutherfords. Daniel (nitrogen, 1772) and Ernest (the nucleus, 1911) are different people.
Assuming he knew it was an element. He thought it was air altered by phlogiston.
Thinking his residue was pure nitrogen. It contained argon and probably some oxygen.
Mixing the old names. Fixed air, mephitic air and dephlogisticated air are three different gases.
Nitrogen is in Group 15, part of the p-block covered in Unit 10 of the JEE (Main) 2026 syllabus; check the syllabus for your exam year.
If you mix up which gas did what in these early experiments, the Fermi Concept Library covers every concept in physics, chemistry, biology, mathematics and computing, so you can check each one.
What can a student take from Rutherford?
Rutherford did one clear experiment well, reported exactly what he saw, and said plainly where he could not reach a conclusion. That honesty let later chemists build on his result even after his theory was abandoned.
Practice routine for this week:
Redo the worked example assuming the mouse removed one-eighth of the air instead of one-tenth.
Calculate the mass of 1 litre of nitrogen and of argon at STP and explain why argon made "air nitrogen" denser.
Write the modern name for each of fixed air, mephitic air and dephlogisticated air.
Start with step 3; it takes two minutes and clears up most confusion in this chapter of history.
