William Ramsay

How to use this course

Between 1894 and 1898 William Ramsay took part in the discovery of five new elements, all gases, all chemically inert, and all invisible to the chemistry of the time. No other chemist has found a whole group of the periodic table. This course follows the experimental reasoning behind each discovery, and the physical chemistry of vapours and liquids that prepared him for it. It ends with his work on radioactivity, where he was right about helium and wrong about transmutation.

The discovery of argon was a joint work with Lord Rayleigh, and Lesson 07 should be read together with Lesson 10 of the Rayleigh course, which gives the physicist’s side. Each technical lesson opens with a paragraph for the general reader, then gives precise statements, derivations and exercises with folded solutions.

Timeline

Glasgow, 1852–1870

William Ramsay was born in Glasgow on 2 October 1852, the only child of William Ramsay, a civil engineer, and Catherine Robertson. Science ran in the family. His uncle Andrew Ramsay was a leading geologist and later director of the Geological Survey of Great Britain. Glasgow was then one of the great industrial cities of the world, built on shipbuilding, chemicals and engineering, and the boy grew up around them.

He was educated at Glasgow Academy and entered the University of Glasgow in 1866, aged fourteen, as was common then. He followed the general arts course, with classics, mathematics and literature, and heard William Thomson, later Lord Kelvin, lecture on natural philosophy. His interest in chemistry grew outside the lecture hall. He trained in the analytical laboratory of Robert Tatlock, a Glasgow consulting chemist, and spent some months in Thomson’s physical laboratory. Languages and travel were lifelong pleasures.

Tübingen and the return to Glasgow, 1870–1880

In 1870, like many British chemists of his generation, Ramsay went to Germany for research training. After a short stay with Robert Bunsen in Heidelberg he moved to Tübingen, to the organic chemist Rudolph Fittig. In 1872 he took his doctorate there with a thesis on orthotoluic acid and its derivatives.

He returned to Glasgow in 1872 as assistant in chemistry at Anderson’s College, and in 1874 became assistant at the University of Glasgow. His work in these years was organic. With James Dobbie he studied the decomposition products of quinine and other alkaloids, and he prepared pyridine from acetylene and hydrogen cyanide, an early synthesis of a heterocyclic ring.

Gradually he moved toward physical chemistry: the properties of liquids and vapours, molecular volumes, and the behaviour of substances near their boiling points. This shift decided the rest of his career. The skills he learned, handling small volumes of gas, measuring densities and vapour pressures precisely, and working at high and low temperatures, were exactly those the noble gases would demand.

Bristol and London, 1880–1894

In 1880 Ramsay was appointed professor of chemistry at University College, Bristol, a young institution, and in 1881 he also became its principal. The same year he married Margaret Buchanan. They had a daughter, Elska, and a son, William George. At Bristol he began his long collaboration with Sidney Young on vapour pressures and thermal dissociation (Lesson 04).

In 1887 he succeeded Alexander Williamson in the chair of chemistry at University College London (UCL), which he held until 1913. He was elected a Fellow of the Royal Society on 7 June 1888. At UCL he extended his physical chemistry. With John Shields he used surface tension to measure the molecular complexity of liquids (Lesson 05). He studied the oxides of nitrogen, and in 1892 he gave one of the first plausible accounts of Brownian motion as the result of molecular impacts on suspended particles (Lesson 06). With Emily Aston he carried out analyses and atomic weight determinations.

By 1894 Ramsay was a respected physical chemist with a reputation for skilful experiments on gases. On 19 April that year he attended a lecture at the Royal Society in which Rayleigh described a puzzle: nitrogen taken from the air was denser than nitrogen made from chemicals. The two men agreed to investigate. What followed is the subject of Part II.

Vapour pressure and the Ramsay–Young rule

For the general reader. Every liquid has a vapour pressure that rises steeply with temperature, and it boils when that pressure equals the pressure of its surroundings. Ramsay and Sidney Young measured these curves for many liquids and found that related liquids behave alike: if you know the curve for one, you can predict the other’s from a single boiling point.

Clausius–Clapeyron

Along the coexistence curve of liquid and vapour, the chemical potentials are equal. Differentiating gives the Clapeyron equation \(dp/dT=\Delta H_{\mathrm{vap}}/(T\,\Delta V)\). Neglecting the liquid volume and treating the vapour as ideal, \(\Delta V\approx RT/p\), so

if \(\Delta H_{\mathrm{vap}}\) is roughly constant.

Why it works. Trouton’s rule says that \(\Delta H_{\mathrm{vap}}/T_b\) at the normal boiling point is about the same for many liquids, near \(88\ \text{J mol}^{-1}\text{K}^{-1}\). Write \(\Delta H_{\mathrm{vap}}=\kappa\,T_b\) with the same \(\kappa\) for A and B. The integrated Clausius–Clapeyron equation from \(T_b\) at 1 atm to pressure \(p\) gives \(\ln p=-\frac{\kappa}{R}\big(\frac{T_b}{T}-1\big)\) (with \(p\) in atm). So \(p\) depends only on \(T/T_b\), and equal pressures occur at equal \(T/T_b\): \(T_A/T_B=T_{b,A}/T_{b,B}\). Ramsay and Young reported tests of the rule for some thirty pairs of liquids.

Surface tension and molecular association

For the general reader. How do you weigh a molecule in a liquid? In a gas you can use its density, but in a liquid molecules may cling together in pairs or larger clusters. Ramsay and John Shields found a way to detect such clustering from the way surface tension falls as the liquid is heated. Water, alcohols and acids turned out to be associated; most other liquids were not.

Molar surface energy

Let \(\gamma\) be the surface tension and \(V_m=M/\rho\) the molar volume. A face of a cube holding one mole has area proportional to \(V_m^{2/3}\), so \(\gamma V_m^{2/3}\) is a molar surface energy. In 1886 Loránd Eötvös found that this quantity falls linearly with temperature and vanishes at the critical point.

The 6 K shift reflects the observation that the straight line meets zero a few degrees below the critical point, where the linear law breaks down. Ramsay and Shields measured 55 liquids. When a liquid gave a smaller apparent constant, they supposed that its molecules form clusters of average size \(x\). Then the true molar volume is \(xV_m\), and requiring the normal constant gives

Water, alcohols and carboxylic acids gave \(x>1\). The modern explanation is hydrogen bonding, which links molecules into transient networks rather than stable clusters, so \(x\) is a useful index of association more than a literal cluster size.

Molecules in motion: Brownian movement

For the general reader. Under a microscope, pollen grains and fine particles in water jitter without stopping. Robert Brown described the motion in 1827, but its cause was disputed for decades. In 1892 Ramsay argued that it is produced by the uneven bombardment of each particle by the molecules of the liquid. Einstein turned this idea into a quantitative theory in 1905, and Jean Perrin’s measurements with it convinced the last sceptics that atoms are real.

Kinetic theory

For an ideal gas, each translational degree of freedom carries mean energy \(\tfrac12k_BT\), so \(\tfrac12m\langle v^2\rangle=\tfrac32k_BT\) and the root-mean-square speed is \(v_{\mathrm{rms}}=\sqrt{3RT/M}\). The same equipartition applies to a suspended particle of any size: a grain of mass \(m\) has \(\tfrac12m\langle v_x^2\rangle=\tfrac12k_BT\), whatever its size. Large particles move slowly, but they never stop.

Ramsay’s argument of 1892 was qualitative. A particle a micrometre across is struck by an enormous number of molecules each second; at any instant the impacts on one side do not quite balance those on the other, and the particle is pushed at random. Smaller particles show larger motions, and the motion does not decay, as it would if it came from convection or vibration of the apparatus.

Derivation sketch. In a dilute suspension under gravity, the equilibrium concentration falls with height as \(n(z)\propto e^{-m'gz/k_BT}\), with \(m'\) the buoyancy-corrected mass. The downward drift velocity is \(m'g/(6\pi\eta a)\) by Stokes’ law, and the upward diffusive flux is \(-D\,dn/dz=D\,n\,m'g/k_BT\). Setting the two fluxes equal gives \(D=k_BT/(6\pi\eta a)\). For a random walk, the solution of the diffusion equation starting at a point has variance \(2Dt\) in each direction. Measuring \(\langle x^2\rangle\), \(t\), \(\eta\), \(a\) and \(T\) then gives \(k_B\), and hence \(N_A=R/k_B\).

Argon, 1894–1895

For the general reader. Nitrogen made from the air was about half a percent heavier than nitrogen made from chemicals. Rayleigh had measured the difference and could not explain it. Ramsay took up the problem in the spring of 1894. Within four months the two men had found a new gas in the air, about one percent of it, that would combine with nothing. They named it argon, from the Greek for idle.

The anomaly

In September 1892 Rayleigh wrote to Nature asking chemists to explain why nitrogen from air, freed of oxygen, water and carbon dioxide, was denser than nitrogen prepared from ammonia. On 19 April 1894 Ramsay heard Rayleigh describe the problem at the Royal Society, and the two agreed to work on it, Rayleigh at Terling and Ramsay at UCL.

Two routes to the residue

Ramsay passed atmospheric nitrogen repeatedly over red-hot magnesium, which absorbs nitrogen as the nitride:

As the nitrogen was removed, the density of the remaining gas rose steadily, until a small volume was left that the magnesium would not absorb. Rayleigh meanwhile repeated Henry Cavendish’s experiment of 1785, passing electric sparks through air with added oxygen over alkali until no more nitrogen was absorbed. Cavendish had noticed a small bubble, about one part in 120 of the original nitrogen, that refused to react. Both men were left with a residue whose spectrum, examined with William Crookes’s help, showed lines belonging to no known element.

On 13 August 1894 Rayleigh and Ramsay announced the new gas at the British Association meeting in Oxford. Their full paper, Argon, a new constituent of the atmosphere, appeared in the Philosophical Transactions in 1895.

The density of argon was about 20 times that of hydrogen gas, so its molar mass was about 40. Since the molecule is a single atom, the atomic weight is about 40. This created a problem. An inert element of weight 40 would fall between chlorine (35.5) and potassium (39.1) only if it were lighter than potassium, which it was not. Ramsay and Rayleigh were cautious about its place in the table. Mendeleev himself was at first reluctant to accept argon as a new element. The solution came with helium (Lesson 08), which showed that argon was one member of a whole family.

Terrestrial helium

For the general reader. In 1868 astronomers saw a yellow line in the spectrum of the Sun that matched no element on Earth, and it was named helium after the Greek word for the Sun. In March 1895, looking for more argon in a uranium mineral, Ramsay found the same line in a gas from a test tube in London. Helium was real, it was terrestrial, and it was a second inert gas.

From the Sun to cleveite

During the total eclipse of 18 August 1868, Jules Janssen observed a bright yellow line in the solar chromosphere. Norman Lockyer called it D₃, as it lay near the sodium D₁ and D₂ lines, and attributed it to a new element. The American chemist William Hillebrand had obtained an unreactive gas from uranium minerals by heating them with acid, and taken it for nitrogen.

In early 1895 Ramsay repeated the experiment with cleveite, a uranium mineral, hoping that it contained argon. On 26 March 1895 he examined the gas in a discharge tube and saw a bright yellow line close to, but not coinciding with, sodium’s. Crookes and Lockyer identified it as the solar D₃ line at 587.6 nm. Per Teodor Cleve and Abraham Langlet in Uppsala independently isolated helium from cleveite the same year and measured its atomic weight.

Two inert monatomic gases, of weights 4 and 40, suggested a new column of the periodic table, separated by a period. In his 1897 address to the chemistry section of the British Association, Ramsay predicted an undiscovered member with atomic weight about 20. He also suspected heavier members beyond argon. Lesson 09 shows how they were found.

Ramsay could not yet explain why helium occurs in uranium minerals. The explanation came in 1903 (Lesson 10): it is produced by the radioactive decay of uranium and its daughters, as alpha particles that capture electrons.

Liquid air: neon, krypton, xenon

For the general reader. If the new column held more elements, where were they? Ramsay and his assistant Morris Travers searched minerals, meteorites and spring waters without success. Then a new machine made liquid air available in quantity. By boiling it off slowly and examining each fraction, they found three new gases in a few weeks of 1898: krypton (“hidden”), neon (“new”) and xenon (“stranger”).

The apparatus

William Hampson’s liquefier, based on the Joule–Thomson effect with a counter-current heat exchanger, gave Ramsay and Travers about a litre of liquid air. They allowed it to evaporate and kept the last, least volatile fraction. After removing oxygen and nitrogen, its spectrum showed bright new lines in the yellow and green. They named the gas krypton and announced it to the Royal Society in early June 1898. Working on the most volatile part of their argon, they found a gas with a brilliant red-orange glow, which they named neon and announced later in June. Repeated fractionation of krypton left a still heavier gas, xenon, announced in September 1898. To free neon from helium, Travers later built a hydrogen liquefier.

Derivation. \(L\,dx+x\,dL=\frac x\alpha dL\), so \(\frac{dx}{x}=\big(\frac1\alpha-1\big)\frac{dL}{L}\). For heavy components such as krypton and xenon, with \(\alpha\gg1\), the exponent is close to \(-1\): almost all of the krypton stays in the liquid, and its concentration rises in proportion to the reduction in volume. This is how a trace of one part in a million could be seen in a residue.

A new group

With atomic weights of about 4, 20, 40, 82 and 128, the five gases fitted a single column. Ramsay proposed in 1900 that they form a new group between the halogens and the alkali metals, and Mendeleev accepted this, placing them as group 0 in 1902. The anomaly of argon’s weight relative to potassium remained until Moseley showed in 1913 that the true order is by nuclear charge (argon 18, potassium 19).

Radioactivity: helium from radium, and radon

For the general reader. Radium gives off a radioactive gas, the “emanation”. In 1903 Ramsay and Frederick Soddy sealed some of it in a tube and watched its spectrum change over days into the spectrum of helium. One element had turned into another before their eyes. Ramsay went on to weigh the emanation itself, a fraction of a cubic millimetre of gas, and placed it as the heaviest noble gas, now called radon.

Helium from emanation (1903)

Soddy had just come from Montreal, where with Ernest Rutherford he had argued that radioactivity is the spontaneous transformation of one element into another. At UCL, Ramsay and Soddy collected the emanation from about 60 mg of radium bromide, purified it, and sealed it in a small spectrum tube. At first the spectrum showed no helium lines. Over the following days the D₃ line and the other helium lines appeared and strengthened. This was the first direct evidence that a radioactive decay produces a known element. In 1908–09 Rutherford and Thomas Royds showed that the helium comes from the alpha particles themselves.

Derivation. The daughter obeys \(dN_2/dt=\lambda_1N_1-\lambda_2N_2\). With \(N_1\) effectively constant and \(N_2(0)=0\), the solution is \(N_2(t)=\frac{\lambda_1N_1}{\lambda_2}\big(1-e^{-\lambda_2t}\big)\), which approaches the stated value after a few daughter half-lives.

Radon

The emanation is now known as radon-222 (half-life 3.82 days), the daughter of radium-226 (half-life 1600 years). The quantity in equilibrium with a gram of radium is tiny. In 1910 Ramsay and Robert Whytlaw-Gray measured its density with a sensitive microbalance on a sample of a fraction of a cubic millimetre, found an atomic weight of about 223, close to the modern 222, and confirmed that it belonged at the foot of the noble gas column. They called it niton, from the Latin for shining; the name radon was adopted later.

Transmutation claims

Ramsay also believed that the energy of the emanation could transform other elements. Between 1905 and 1908 he reported, with Alexander Cameron, that copper solutions exposed to emanation produced lithium, and earlier that water exposed to emanation gave excess hydrogen. Marie Curie and others could not reproduce the lithium result. The traces most likely came from contamination by glass and reagents. Induced transmutation was first demonstrated by Rutherford in 1919, using alpha particles on nitrogen.

The UCL laboratory and the Nobel Prize

Ramsay’s laboratory at UCL attracted chemists from across the world. Morris Travers, his principal collaborator on the noble gases, became director of the Indian Institute of Science in 1906; Ramsay had advised on its founding and suggested Bangalore as its site. Edward Baly and Robert Whytlaw-Gray worked with him on spectra and gas densities. Otto Hahn came to UCL in 1904 to learn radiochemistry and in 1905 discovered radiothorium there, the start of a career that would lead to nuclear fission. Jaroslav Heyrovský, later the inventor of polarography and a Nobel laureate, began his research under him.

He was knighted (KCB) in 1902. In 1904 he received the Nobel Prize in Chemistry for his discovery of the inert gaseous elements in air and his determination of their place in the periodic system. In the same year Rayleigh received the Physics prize for his investigations of the densities of the most important gases and his discovery of argon, so the two partners in that discovery were honoured together. Ramsay also received the Davy Medal (1895), the Longstaff Prize (1897), the Hofmann Medal of the German Chemical Society (1903) and the Matteucci Medal (1907), and was elected to academies in many countries.

Last years and legacy, 1904–1916

After the Nobel Prize, Ramsay spent much of his time on radioactivity (Lesson 10) and on public roles. He was President of the British Association in 1911. His reputation suffered from the transmutation claims, and also from his endorsement in 1905 of a company that claimed it could extract gold from sea water, which produced none. He retired from UCL in 1913 and moved to Hazlemere in Buckinghamshire, where he set up a small private laboratory.

He developed cancer of the nose and died at High Wycombe on 23 July 1916, aged 63. He was buried at Hazlemere parish church. A memorial to him is in Westminster Abbey, and in 1923 UCL named its department of chemical engineering after him, funded by the Ramsay Memorial Fund.

Legacy

• The periodic table: a complete new group, and the strongest test the table ever passed; group 18 holds the five gases he found, plus radon, which he characterized, and the synthetic oganesson.
• Method: precise measurement of tiny gas volumes, spectroscopy as a tool of discovery, and cryogenic separation.
• Applications: argon for inert atmospheres and welding, neon in discharge lamps, helium in cryogenics and balloons, xenon in lamps and anaesthesia.
• Radioactivity: the first direct observation of an element produced by decay.
• Chemical bonding: the inertness of the noble gases became the starting point of the octet theories of Gilbert Lewis and Irving Langmuir. Compounds of xenon, made in 1962, showed that the inertness is not absolute.

Connections

People linked to William Ramsay across this collection. A name without a link has no page here yet. See William Ramsay in the network of all 337 lives →

Teachers and advisors

• Rudolph Fittig 1871-1872

Students

• Otto Hahn 1904-1905
• Edward Charles Cyril Baly
• Jaroslav Heyrovský

Influenced by

• Henry Cavendish
• Robert Bunsen 1870
• William Thomson, Lord Kelvin 1866-1869

Influenced

• Otto Hahn 1904-1905

Colleagues and collaborators

• Dmitri Mendeleev
• Ernest Rutherford
• Frederick Soddy 1903-1904
• Heike Kamerlingh Onnes
• John William Strutt, Lord Rayleigh 1894-1895
• William Crookes
• Alexander Williamson
• James Johnston Dobbie 1878-1879
• John Shields 1893
• Morris Travers 1894-1903
• Robert Whytlaw-Gray 1908-1913
• Sidney Young 1884-1889

Family

• Andrew Ramsay

Also mentioned in this life

• Amedeo Avogadro
• Rudolf Clausius
• Humphry Davy
• Albert Einstein
• James Prescott Joule
• Marie Curie
• Henry Moseley
• Jean Perrin
• George Gabriel Stokes

Fields

• chemistry 21 lives
• physical chemistry 9 lives
• radiochemistry 6 lives

On CoursesHub

• Physical Chemistry

Sources and further reading

Biography

1. Sir William Ramsay, Biographical, NobelPrize.org.
2. William Ramsay, Wikipedia.
3. William Ramsay, Royal Society, Science in the Making.
4. Sir William Ramsay, Complete Dictionary of Scientific Biography (via Encyclopedia.com).
5. W. A. Tilden, Sir William Ramsay: Memorials of His Life and Work, Macmillan, 1918.
6. M. W. Travers, A Life of Sir William Ramsay, Arnold, 1956.
7. J. Wisniak, William Ramsay, Educación Química 19 (2008).

Chemistry and physics

1. Lord Rayleigh and W. Ramsay, Argon, a new constituent of the atmosphere, Phil. Trans. R. Soc. A 186 (1895).
2. W. Ramsay, The rare gases of the atmosphere, Nobel Lecture, 1904.
3. L. Rayleigh, The density of gases in the air and the discovery of argon, Nobel Lecture, 1904.
4. W. Ramsay and M. W. Travers, On a new constituent of atmospheric air, Proc. R. Soc. Lond. 63 (1898) 405.
5. W. Ramsay and F. Soddy, Experiments in radioactivity and the production of helium from radium, Proc. R. Soc. Lond. 72 (1903).
6. W. Ramsay and J. Shields, The molecular complexity of liquids, J. Chem. Soc. 63 (1893).
7. W. Ramsay, The Gases of the Atmosphere: The History of Their Discovery, Macmillan, 1896.
8. Eötvös rule, Wikipedia.
9. Helium: history, Wikipedia.
10. Radon: history, Wikipedia.