Scotland's Only Element: Thomas Charles Hope and Strontium

The Strontian Mine

The story begins not in a laboratory but in the West Highlands. Strontian sits on the north shore of Loch Sunart in Sunart, Argyllshire — since 1975 part of Highland. Its Gaelic name, Sròn an t-Sìthein, means "the point of the fairy hill." In 1722 the landowner Sir Alexander Murray began mining lead — galena — in the hills above the village, the beginning of some 250 years of mining and the reason the village exists at all. In a nice historical footnote, lead from Strontian was cast into bullets during the Napoleonic Wars, and captured French soldiers were reportedly put to work in the mines.

Among the lead ore, miners turned up an unusual pale-green to brown mineral. It reached Edinburgh around 1787 and was at first assumed to be a form of the barium mineral witherite, which it superficially resembled. But it behaved differently in acids and in its precipitation reactions. The scientific question crystallised: was this simply an odd barium or calcium mineral, or did it contain an entirely new "earth"?

In 1790 the Irish physician-chemist Adair Crawford, working with William Cruickshank — both connected with the Royal Military Academy at Woolwich, though the specimens came through Edinburgh — published experiments in Medical Communications concluding that the Strontian mineral differed from barium minerals and that "it is probable indeed, that the scotch mineral is a new species of earth which has not hitherto been sufficiently examined." That careful, cautious statement gives Crawford and Cruickshank priority for first recognising the new earth. The German mineralogist Friedrich Gabriel Sulzer, with Johann Friedrich Blumenbach, analysed the mineral and gave it the name strontianit — strontianite — in 1791.

Hope's Experiments at Glasgow

This is where Thomas Charles Hope enters decisively. Hope began working on the Strontian mineral in 1791, in his laboratory at Glasgow — a detail sometimes muddled in secondary sources, which tend to place all of Hope's work in Edinburgh because that is where his chair and his fame lie. He carried out a systematic comparison of the new "strontian earth" against baryta, the barium earth, and lime, the calcium earth, running the same chemical tests on each and showing repeatedly that the strontian earth behaved as neither. He prepared pure strontium oxide and hydroxide and described the preparation of some thirteen other strontium compounds — a far fuller chemical characterisation than had gone before.

Two of Hope's contributions stand out. First, the flame test. Hope observed that strontian compounds coloured a flame a brilliant red — crimson — completely unlike the pale green of barium and distinct from the brick-red of calcium. The Royal Society of Chemistry's own periodic-table entry credits him directly: "In 1791, another Edinburgh man, Thomas Charles Hope, made a fuller investigation of it and proved it was a new element. He also noted that it caused the flame of a candle to burn red." A caution for accuracy: some popular accounts imply Crawford noted the flame colour in 1790, but a clear 1790 flame observation by Crawford or Cruickshank is not well attested in primary sources, whereas Hope's association with the red flame is firmly documented.

Second, his publication and conclusion. Hope read his paper, An Account of a Mineral from Strontian, and of a Peculiar Species of Earth which it contains, to the Royal Society of Edinburgh on 4 November 1793. It was summarised in the Society's Transactions in 1794 but not published in full until 1798, in volume 4, pages 3–39. Hope's conclusion was unambiguous: the mineral contained a "hitherto unknown kind of earth," a distinct new alkaline earth different from both lime and baryta. In a surviving letter to Black of 18 October 1793 he even asked whether he might "exhibit specimens of the Strontian mineral and of its more remarkable combinations" to the Society. Two glass flasks labelled "Strontia" and "Baryta," traditionally held to be Hope's own preparations, are still preserved in the Department of Chemistry at Edinburgh.

The honest historical verdict, set out by the historian of chemistry J. R. Partington in "The Early History of Strontium" (Annals of Science, 1947 and 1951), is that the discovery of the individual nature of strontianite belongs to Crawford and Cruickshank, while Hope — along with Martin Klaproth in Germany and Richard Kirwan in Ireland, all working independently in 1793–94 — contributed to characterising the new earth and its compounds. Hope's work was the most systematic, and that is the reason his name is so closely tied to strontium.

Strontian to Strontium

Hope named the new earth strontites, and he was refreshingly candid about his reasoning. He proposed the name "from the place it was found; a mode of derivation in my opinion, fully as proper as any quality it may possess, which is the present fashion." In other words: never mind naming an element for a chemical property — name it for the little Highland village that produced it.

The modern form strontium, with the "-ium" ending that marks a metal and matches sodium, potassium, calcium and barium, was settled when Humphry Davy isolated the metal in 1808. So the naming, too, is a shared achievement: Hope gave us the root, by way of the village and the mineral strontianite, and Davy fixed the modern metallic form.

This makes strontium the only chemical element named after a place in Scotland — indeed the only one named after a place anywhere in Britain. Geographic element names are a rare and charming club: the Swedish village of Ytterby alone gave its name to four (yttrium, terbium, erbium and ytterbium), and elements such as polonium and germanium honour countries. But Strontian, a tiny West Highland village, stands alone for Scotland — and National Museums Scotland notes it is the smallest settlement in the world, by population, to have an element named after it.

Davy and the Pure Metal

Identifying a new "earth" is not the same as holding the pure element in your hand. In the 1790s chemists worked with metal oxides — "earths" — and had no way to reduce these stubborn alkaline earths to their metals. That final step fell to Sir Humphry Davy, and it is only fair to be generous about his achievement.

Davy had concluded that electrolysis — passing an electric current through compounds — was the most powerful way to tear substances apart into their elements. In 1807 he electrolysed molten potash and soda and isolated potassium and sodium. Then, building on work by the Swedish chemists Berzelius and Pontin, who had obtained calcium and barium amalgams using a mercury cathode, Davy extended the method. On 30 June 1808 he reported to the Royal Society that he had isolated four new metals, which he named barium, calcium, strontium and magnium — soon changed to magnesium. Strontium was thus one of a remarkable cluster of elements Davy first isolated in 1807–08.

The division of credit is clean and worth stating plainly: Crawford and Cruickshank suspected a new earth; Hope characterised it and named it; Davy isolated the pure metal. All three steps were essential to establishing strontium as a genuine element in the modern sense. There is a lovely Scottish coda: it was Hope who, in 1799, first recommended the young Davy to the Royal Institution in London — Hope later said that recommending Davy was "the greatest service which it has been in my power to render to Chemistry."

The Density of Water

Hope's second great contribution has nothing to do with strontium and everything to do with everyday life. After returning to Edinburgh he investigated the puzzling thermal behaviour of water, and in 1805 published Experiments on the Contraction of Water by Heat in the Transactions of the Royal Society of Edinburgh, volume 5. Through careful experiment he established that water does not become steadily denser as it cools to freezing; instead it reaches its maximum density a few degrees above freezing. He measured between 39.5° and 40 °F, remarkably close to the modern value of 39.2 °F, roughly 4 °C.

The demonstration is still known as Hope's experiment, using Hope's apparatus: a tall cylinder of water is surrounded at its middle by a trough of freezing ice, with thermometers above and below. As the water cools towards 4 °C it becomes denser and sinks, so the lower thermometer settles at about 4 °C while the water above continues to cool towards 0 °C and freezes at the top.

This "anomalous expansion" of water is one of the most consequential quirks in nature. Because the densest water sits at 4 °C and ice is less dense still, lakes and lochs freeze from the top down rather than the bottom up. A layer of surface ice insulates the water beneath, so fish and other aquatic life survive even a hard Scottish winter — and, as Hope's contemporaries put it, it also explains why icebergs float.

Strontium Today

Hope's crimson flame turned out to be commercially priceless.

Fireworks and flares. Strontium salts — chiefly strontium nitrate and strontium carbonate — produce the brilliant red in fireworks and emergency flares. When the salt is heated, strontium ions emit light in the red part of the spectrum; the effect is the direct, everyday descendant of the flame Hope characterised. Figures from the US Geological Survey record that "about a third of all strontium nitrate in the United States is used for pyrotechnics", and more recent USGS Mineral Commodity Summaries put pyrotechnics and signals at 29% of US end use, alongside ceramic ferrite magnets at 29% and drilling fluids at 23%. Every red firework in a Guy Fawkes, Fourth of July or Hogmanay display owes its colour to strontium's flame.

Strontium-90. The radioactive isotope strontium-90 is a fission product of nuclear weapons and reactors, and became one of the defining fears of the Cold War. Because strontium behaves chemically like calcium, fallout travelled from bomb tests through grass, into cattle, into milk, and finally into the growing bones and teeth of children. The St Louis "Baby Tooth Survey," led by Dr Louise Reiss and running from 1958 to 1970, collected roughly 320,000 teeth; it found that children born in St Louis in 1963 had about fifty times as much strontium-90 in their teeth as children born in 1950. The findings helped persuade President Kennedy to sign the 1963 Partial Nuclear Test Ban Treaty, which ended atmospheric testing.

Medicine. Strontium ranelate — two stable strontium atoms bound to ranelic acid — was used to treat osteoporosis, but was withdrawn and then heavily restricted by the European Medicines Agency after reports of increased cardiovascular risk; it is now reserved for severe cases in patients without heart or circulatory disease. This is historical and restricted use, not current first-line practice. The radioactive isotope strontium-89, marketed as Metastron, is given intravenously to relieve the bone pain of metastatic cancers such as prostate cancer.

Cathode ray tubes. For decades, strontium carbonate was added to the faceplate glass of colour television and monitor CRTs to absorb the X-rays generated by the electron beam; the US ATSDR/USGS Toxicological Profile for Strontium records that "major manufacturers of television picture tube glass incorporate about 8% by weight of strontium oxide (SrO) into the glass faceplate material." According to the USGS, at its peak as much as 75% of strontium consumed in the United States went into faceplate glass for colour CRTs — a market that collapsed when the last US CRT glass plant closed in 2006 and flat panels took over.

Toothpaste. Strontium chloride and strontium acetate are active ingredients in some toothpastes for sensitive teeth, such as Sensodyne, where they help block pain signals from exposed dentine.

Hope the Lecturer

If Hope's research output was modest — essentially strontium and the density of water — his influence as a teacher was immense. He considered teaching, not research, his vocation, and he raised the lecture-demonstration to an art. He was the first in Britain to use large-scale demonstrations so extensively, a practice that continued in Edinburgh first-year chemistry courses into the 1950s. Contemporaries admired that he "simplified and legitimately popularized chemistry without vulgarizing it. There were no needless blazings of phosphorus, or showy exhibitions of blue lights."

His reputation was extraordinary. Attendance at his classes rose from 293 in 1799 to a peak of 559 in 1823. Robert Christison, who attended in 1814, recalled that although Hope's manner was "somewhat pompous," this was "more than counterbalanced by uncommon clearness of exposition, and unexampled splendour and success in experimental demonstration" — and that with a class of 500 requiring experiments on a huge scale, "there was not a single failure to attain exactly what he announced." In spring 1826 Hope even gave a fashionable public course open to "Ladies and Gentlemen"; the fees allowed him to endow a chemistry prize at Edinburgh with £800 in 1828.

His most famous student needs no introduction. Charles Darwin studied medicine at Edinburgh from 1825 to 1827, and in his autobiography wrote that the lectures "were intolerably dull, with the exception of those on chemistry by Hope" — a striking endorsement from a man who found most of his Edinburgh education tedious.

Hope's legacy at Edinburgh is tangible. His 1828 endowment funds the Hope Prize Scholarships, still awarded to outstanding chemistry students. A memorial fountain, gifted by his nephew, stands in the quadrangle of Old College. And a point of accuracy worth flagging: the Hope Park area of Edinburgh, and the Meadows, historically "Hope Park", are not named after Thomas Charles Hope or his botanist father John Hope. They commemorate Sir Thomas Hope of Rankeillor, the 8th Baronet (c. 1681–1771), who drained the old Borough Loch and laid out the park from 1722 — a different Hope entirely.

Timeline

1. 1722

   Sir Alexander Murray begins mining lead above Strontian, Argyll

   The village and its mines exist because of this; the mineral comes out of the galena workings

2. 1766

   Thomas Charles Hope born in Edinburgh, 21 July

   Third son of John Hope, Regius Professor of Botany

3. 1779

   Enters the University of Edinburgh aged thirteen

   Arts, then medicine; MD in 1787 with a thesis on plant movement

4. c.1787

   The unusual Strontian mineral reaches Edinburgh

   Initially mistaken for the barium mineral witherite

5. 1787

   Hope appointed Lecturer in Chemistry at the University of Glasgow

   Eight formative years; the first British university teacher to abandon phlogiston for Lavoisier's chemistry

6. 1790

   Crawford and Cruickshank publish in Medical Communications

   'It is probable indeed, that the scotch mineral is a new species of earth' — the first published recognition

7. 1791

   Sulzer and Blumenbach name the mineral strontianit

   The mineral gets its name before the earth inside it is proven

8. 1791

   Hope begins his own experiments, in his Glasgow laboratory

   Systematic comparison of strontian earth against baryta and lime

9. 18 Oct 1793

   Hope writes to Joseph Black about exhibiting his specimens

   A surviving letter asking to show 'the Strontian mineral and of its more remarkable combinations'

10. 4 Nov 1793

    Hope reads his paper to the Royal Society of Edinburgh

    'An Account of a Mineral from Strontian, and of a Peculiar Species of Earth which it contains'

11. 1793–94

    Klaproth in Germany and Kirwan in Ireland work independently on the same earth

    Hope's characterisation was the most systematic, but not the only one

12. 1794

    The paper is summarised in the Society's Transactions

    Full publication is delayed

13. 1795

    Joseph Black chooses Hope as his assistant and successor

    Appointed conjoint Professor of Chemistry at Edinburgh, 4 November 1795

14. 1798

    The strontium paper is published in full

    Transactions of the Royal Society of Edinburgh, vol. 4, pp. 3–39

15. 1799

    Hope recommends the young Humphry Davy to the Royal Institution

    He later called it 'the greatest service which it has been in my power to render to Chemistry'

16. 1805

    Hope publishes Experiments on the Contraction of Water by Heat

    Water's maximum density measured between 39.5° and 40 °F — close to the modern 39.2 °F

17. 30 Jun 1808

    Davy isolates strontium metal by electrolysis

    Reported to the Royal Society alongside barium, calcium and 'magnium'

18. 1823

    Hope's Edinburgh class peaks at 559 students

    Up from 293 in 1799

19. 1825–27

    Charles Darwin studies medicine at Edinburgh

    He later rated Hope's chemistry the only interesting lectures he attended

20. 1828

    Hope endows a chemistry prize with £800

    Funded by his fashionable 1826 public course; the Hope Prize Scholarships still run

21. 1843

    Hope resigns the Edinburgh chair

    After nearly fifty years teaching chemistry

22. 1844

    Hope dies at 31 Moray Place, 13 June

    Buried in Greyfriars Kirkyard

Myths & Facts

Did You Know?

• Strontium is named after Strontian, a tiny village on Loch Sunart in Argyll — the only element named after a Scottish place, and the smallest settlement in the world to have an element named after it.
• Every red firework you have ever seen owes its crimson to the strontium flame Thomas Charles Hope first characterised in the 1790s.
• Hope was born into an Edinburgh academic dynasty: his father John Hope was Professor of Botany, and Thomas succeeded the great Joseph Black in the chemistry chair.
• Charles Darwin attended Edinburgh in 1825–27 and rated Hope's chemistry lectures the only interesting part of his studies.
• Hope also discovered that water is densest at about 4 °C, not 0 °C — the reason lochs freeze from the top and fish survive winter.
• Strontium-90 fallout from 1950s bomb tests entered children's bones through grass, cattle and milk, helping drive the 1963 Partial Nuclear Test Ban Treaty.
• Lead from the Strontian mines was cast into bullets during the Napoleonic Wars, and captured French soldiers were reportedly put to work in the mines.

Honest Caveats

Priority for the crimson flame is not absolutely settled. Authoritative modern sources, including the Royal Society of Chemistry and IUPAC/CIAAW, credit Hope with the diagnostic red flame and this article follows them — but a direct quotation from Hope's original paper was not available in open sources, and a few popular accounts attribute an early flame observation to Crawford.

Dates for first scientific attention to the mineral vary between 1787, when the rock reached Edinburgh, and 1790, when Crawford published. This article treats 1790 as the first published recognition of a new earth and 1791 as the start of Hope's own experiments.

Hope did his key strontium work at Glasgow, not Edinburgh, even though his fame and his chair are associated with Edinburgh — a point sometimes muddled in secondary sources.

Who "named" the element depends on definitions. Hope coined strontites for the earth; Davy is often said to have named the metal strontium in 1808, when he fixed the modern "-ium" form.

Strontium ranelate's status is restricted, not current. Its medical use is presented here as historical and limited rather than as current best practice.