Carl Wilhelm Scheele

How to use this course

Carl Wilhelm Scheele prepared oxygen before Joseph Priestley, described chlorine, recognised manganese, barium, molybdenum and tungsten as new elements, made hydrogen fluoride, hydrogen sulfide, arsine and hydrogen cyanide, and isolated a long list of organic acids together with glycerol. He also showed that light blackens silver chloride fastest at the violet end of the spectrum and separated radiant heat from heat carried by air. He did all this as a working pharmacist in provincial Sweden, with shop equipment and his own savings, and he interpreted almost all of it in the language of the phlogiston theory.

Each technical lesson opens with a paragraph for the general reader, then states Scheele’s findings precisely, translates them into modern chemistry and ends with exercises whose solutions are folded. Scheele’s names for substances appear alongside modern ones: fire air (O\(_2\)), foul air (mostly N\(_2\)), aerial acid (CO\(_2\)), dephlogisticated muriatic acid (Cl\(_2\)), manganese or black magnesia (MnO\(_2\), pyrolusite), heavy earth (BaO), fluor acid (HF), prussic or Berlin-blue acid (HCN). Gas volumes in exercises are at 0 °C and 1 atm, with molar volume 22.414 L.

Timeline

Stralsund and Gothenburg, 1742–1765

Carl Wilhelm Scheele was born on 9 December 1742 in Stralsund, a Baltic port that then belonged to Sweden as part of Swedish Pomerania. His father, Joachim Christian Scheele, was a merchant who traded in grain and brewed beer; his mother was Margaretha Eleonora Warnekros. Carl was the seventh of eleven children. The family spoke German, and German remained his preferred language all his life, as it was for many Swedish pharmacists of the time.

From 1748 to 1757 he attended a private school in Stralsund. Friends of the family who were apothecaries taught him to read prescriptions and the symbols of chemistry and pharmacy. An elder brother, Johann Martin, had been an apprentice apothecary and died in 1754. In 1757, aged fourteen, Carl was sent to Gothenburg as apprentice to the apothecary Martin Andreas Bauch at the Unicorn pharmacy.

An apprentice’s education

He stayed with Bauch for eight years, first as apprentice and then as assistant, until Bauch sold the business in 1765. A pharmacy laboratory of the period distilled waters and spirits, prepared salts and acids, dissolved metals and evaporated extracts. It was a good place to learn manipulations, and Scheele learned them thoroughly. He read the chemistry books available to him and repeated their experiments in his spare hours. He had no formal schooling in chemistry, Latin or mathematics beyond the elementary, and he never attended a university.

Like his contemporaries, he smelled and tasted the new substances he made. The habit gave him a sharp sense of materials. Over twenty years it also exposed him to arsenic, mercury, lead compounds and hydrogen cyanide.

Malmö and Stockholm, 1765–1770

In 1765 Scheele moved to Malmö as assistant to Peter Magnus Kjellström at the Spotted Eagle pharmacy. There he met Anders Jahan Retzius, who became a friend and correspondent. Retzius encouraged him to keep a laboratory journal, and Scheele’s notebooks from then on are the main record of his discoveries and their dates.

In 1768 he moved to Stockholm as prescription clerk at the Raven pharmacy of Johann Scharenberg. The shop was busy and the laboratory was not his; he could experiment only in his free time. Two results date from these years. He separated tartaric acid from cream of tartar (potassium hydrogen tartrate), and Retzius published the work in 1770 with acknowledgement of Scheele. He also found that sunlight blackens silver chloride, the starting point of Lesson 10.

Stockholm also gave him contacts. He became acquainted with Abraham Bäck, the brothers Peter Jonas and Bengt Bergius, and Carl Friedrich von Schultzenheim, all members of the Royal Swedish Academy of Sciences. Peter Jonas Bergius later nominated him to the Academy.

Uppsala and Bergman, 1770–1775

In the autumn of 1770 Scheele became head of the laboratory of Christian Ludwig Lokk’s pharmacy in Uppsala, with permission to pursue his own experiments. The pharmacy supplied chemicals to Torbern Bergman, professor of chemistry at the university and one of the leading analytical chemists in Europe.

The saltpetre puzzle

Bergman and his assistant Johan Gottlieb Gahn had noticed that saltpetre (potassium nitrate) which had been strongly heated gave off red fumes when treated with vinegar, while fresh saltpetre did not. Scheele explained it: heating converts part of the nitrate into a different salt, which weak acids decompose. In modern terms, \(2\,\mathrm{KNO_3}\to2\,\mathrm{KNO_2}+\mathrm{O_2}\), and acidified nitrite releases nitrogen oxides. The explanation reached Bergman through Gahn and began a lasting friendship. Bergman gave Scheele the use of his laboratory, brought his papers to the Academy and arranged for their publication. A later saying held that Scheele was Bergman’s greatest discovery.

The explanation already contains a discovery: the gas released when nitre is heated is oxygen. In the Uppsala years, roughly 1771–72, Scheele prepared “fire air” in several independent ways (Lesson 04). In 1774, prompted by Bergman to examine the black mineral called magnesia nigra (pyrolusite), he wrote the memoir that announced chlorine, recognised the calx of a new metal, manganese, and found the new earth baryta (Lessons 05 and 06). Gahn reduced the oxide to manganese metal the same year.

On 30 September 1774 Scheele wrote to Antoine Lavoisier, thanking him for his Opuscules and describing how to obtain fire air by heating silver carbonate with a burning lens, with lime under the bell jar to absorb the fixed air. Lavoisier received the letter on 15 October and seems not to have replied. It was published only in 1890, by Édouard Grimaux. Scheele was elected to the Royal Swedish Academy of Sciences on 4 February 1775, an unusual honour for a pharmacy assistant.

Fire air: the analysis of the atmosphere

For the general reader. Before Scheele, most chemists treated air as a single element. He sealed air in bottles with substances that slowly “eat” part of it and found that about a quarter disappears and the rest will not support a flame. He then made the missing part from at least a dozen different starting materials, called it fire air, and put the two parts back together to get ordinary air again.

Analysis by absorption

The first part of Chemische Abhandlung von der Luft und dem Feuer (Chemical Treatise on Air and Fire) begins with closed-vessel experiments. Scheele sealed air over a solution of liver of sulphur (a potassium polysulfide), over linseed oil, over a moist iron precipitate, and measured how far water rose when the vessel was opened under water. Liver of sulphur took up 6 of 20 parts in fourteen days; the iron precipitate took up 12 of 40. The residue extinguished candles and killed animals.

The modern composition of dry air is 78.08% N\(_2\), 20.95% O\(_2\), 0.93% Ar and about 0.04% CO\(_2\) by volume. Scheele’s synthetic mixture, 25% fire air, is close.

Making fire air

Scheele obtained the gas from manganese dioxide heated with concentrated oil of vitriol, from saltpetre (“the cheapest and best method”, he wrote), from red mercury calx, from silver and gold precipitates, from magnesium nitrate and from arsenic acid. In modern notation, some of these are

He also tested the gas biologically. Peas germinated and grew in it. Bees and a rat shut in ordinary air died, and the air they left would not support a flame; fresh blood had the same effect on air. He breathed fire air himself.

Phlogiston and priority

Scheele read his results through the phlogiston theory. Combustion released phlogiston, which combined with fire air to form heat, and the compound escaped through the glass; this is why the air shrank. The theory is wrong, but his observations were exact and they stand independent of it. Lavoisier’s interpretation, in which the burning body takes up oxygen, explains the same data and the weight gains as well.

On priority, the notebooks place Scheele’s preparations in 1771–72. Joseph Priestley obtained the gas from mercury calx on 1 August 1774 and published in 1775. Scheele’s book, at the printer from late 1775, appeared only in 1777. Lavoisier gave oxygen its role in combustion. Historians now credit Scheele and Priestley as independent discoverers, with Scheele first in the laboratory and Priestley first in print.

Chlorine from pyrolusite

For the general reader. In 1774 Scheele warmed a black mineral, manganese dioxide, with “spirit of salt”, hydrochloric acid. A yellow-green, choking gas came off. It bleached coloured paper and killed insects. He thought it was a compound of the acid. Thirty-six years later Humphry Davy showed that it is an element and named it chlorine, from the Greek for pale green.

The observation

In the 1774 memoir on magnesia nigra, Scheele heated pyrolusite with muriatic acid on a warm sand bath and collected a yellow-green gas with a smell like warm aqua regia. It turned litmus paper white and killed insects. Since in his view the manganese calx had taken phlogiston away from the acid, he called the gas dephlogisticated muriatic acid. Followers of Lavoisier assumed it contained oxygen and called it oxymuriatic acid. In 1810 Davy, unable to extract oxygen from it by any means, concluded that it was an element; he proposed the name chlorine to the Royal Society on 15 November 1810.

Why it needs strong acid

The half-reactions and standard potentials at 25 °C are

Under standard conditions the cell potential is \(1.23-1.36=-0.13\) V, so the reaction does not run. The manganese couple consumes four protons, and the chloride couple’s potential falls as chloride concentration rises, so concentrated hydrochloric acid, heat and removal of the gas drive the reaction forward. This is a clean example of Le Chatelier’s principle acting through the Nernst equation.

Afterlife

Claude Louis Berthollet used the gas to bleach textiles from 1785 and in 1789, at Javel near Paris, absorbed it in alkali to make the hypochlorite solution known as eau de Javel. Chlorine became one of the great industrial chemicals of the nineteenth century, and Scheele’s pyrolusite method remained the standard laboratory route.

New earths and metals

For the general reader. Scheele could seldom isolate the new metals he found: the furnaces of a pharmacy were not hot enough to strip oxygen from them. What he could do was show, by careful reactions in solution, that a mineral contained an earth or acid unlike any known one. Four elements entered chemistry that way: manganese, barium, molybdenum and tungsten.

Manganese and baryta (1774)

The pyrolusite memoir showed that the black mineral was the calx of a distinct metal, not of iron or of the white earth magnesia with which it shared a name. Gahn reduced the oxide with charcoal in 1774 and obtained impure manganese. Scheele had determined in 1772 that the mineral baryte (barium sulfate) contained a new earth, whose sulfate is insoluble even in acids; Gahn isolated the same oxide two years later. The earth was named baryta, from the Greek for heavy, and Davy isolated barium by electrolysis in 1808.

Molybdenum (1778) and tungsten (1781)

The soft grey mineral molybdena was confused with graphite and with galena, a lead ore; its name comes from the Greek for lead. In 1778 Scheele showed that it was neither, and that roasting and acid treatment gave a white earthy acid, molybdic acid (MoO\(_3\)), the oxide of a new element. Peter Jacob Hjelm reduced it with carbon and obtained the metal in 1781.

The Swedes called a very dense white mineral tungsten, “heavy stone”. In 1781 Scheele obtained from it a new acid, tungstic acid (WO\(_3\)), and with Bergman suggested that reducing it might give a new metal. In 1783, at Bergara in Spain, the brothers Juan José and Fausto Elhuyar found the same acid in wolframite and reduced it with charcoal to the metal. The mineral became scheelite (CaWO\(_4\)); the English name of the element, tungsten, comes from the Swedish name of the mineral, and its symbol W from wolfram.

Fluorspar, arsenic and phosphorus

For the general reader. Some of Scheele’s most important acids were also his most dangerous. From fluorspar he made an acid that eats glass. From arsenic he made arsenic acid, the poisonous gas arsine and a brilliant green pigment that later coloured, and poisoned, Victorian wallpapers. With Gahn he found how to get phosphorus from bones, which made the element cheap.

Fluor acid (1771)

Heating fluorspar (calcium fluoride) with concentrated sulfuric acid releases hydrogen fluoride, which attacks silica:

Scheele showed that fluorspar is the lime salt of a peculiar acid, long called the Swedish acid, and developed glass etching as a test for it. The acid’s element resisted isolation until Henri Moissan obtained fluorine by electrolysis in 1886.

Arsenic

Scheele prepared arsenic acid, H\(_3\)AsO\(_4\). In 1775 he reported arsine, AsH\(_3\), made by reducing arsenic(III) oxide with zinc in acid:

In 1836 James Marsh turned the reaction into the first sensitive test for arsenic: the arsine from a suspect sample is decomposed in a heated tube, leaving a mirror of metallic arsenic. Scheele invented a copper arsenite pigment in 1775 and published it in 1778. Scheele’s green, roughly CuHAsO\(_3\), was widely used in paints and wallpapers until the 1860s, when deaths drew attention to arsenic in household goods. Damp, mouldy wallpaper could release volatile arsenic compounds, and dust from it was a hazard in its own right.

Phosphorus from bones (1769)

Phosphorus had been made since 1669 by evaporating and strongly heating urine, a slow and smelly process. In 1769 Gahn and Scheele showed that bones contain calcium phosphate by obtaining phosphorus from bone ash. The method that became standard was to dissolve the ash in sulfuric acid, filter off calcium sulfate, concentrate the phosphoric acid and reduce it with charcoal.

Bone ash remained the main industrial source of phosphorus until the 1840s.

Acids of plants and animals

For the general reader. Fruits taste sour and milk turns sour, but in 1770 nobody knew which substances caused this. Scheele isolated pure crystalline acids from grapes, lemons, apples, sorrel, sour milk, gall nuts and urinary stones, and found the sweet substance hidden in fats. Organic chemistry as a separate science began some decades after his death, but its first pure compounds were largely his.

The lime method

An acid in a juice is mixed with sugars, proteins and colouring matter. Scheele neutralized the juice with chalk or lime, which precipitated the sparingly soluble calcium salt of the acid; he washed the salt, then decomposed it with dilute sulfuric acid, which precipitated calcium sulfate and left the free acid in solution to crystallize. For tartaric acid,

Lead salts served the same purpose for other acids. Industrial citric acid was made in exactly this way until fermentation took over in the twentieth century.

Several of these acids later carried chemistry forward. Friedrich Wöhler made oxalic acid from cyanogen in 1824, an early synthesis of a natural product. Louis Pasteur separated the mirror-image crystals of a tartrate salt in 1848, the discovery of molecular chirality. Jöns Jacob Berzelius found lactic acid in muscle in 1808. Michel Eugène Chevreul named glycerol (as glycérine) in his studies of fats.

Prussian blue and prussic acid

For the general reader. Prussian blue was the first modern synthetic pigment, made in Berlin early in the eighteenth century, and nobody knew what gave it its colour. In 1782–83 Scheele extracted from it a volatile acid with a smell of bitter almonds. It was hydrogen cyanide, one of the fastest-acting poisons known. He studied it, as usual, by smell and taste, and survived.

The pigment

Insoluble Prussian blue is iron(III) hexacyanoferrate(II), ideally Fe\(_4\)[Fe(CN)\(_6\)]\(_3\cdot x\)H\(_2\)O. Each cyanide bridges an Fe(II) bound to carbon and an Fe(III) bound to nitrogen. The intense blue comes from an intervalence charge transfer: red light near 700 nm moves an electron from Fe(II) to Fe(III). Scheele showed that the colouring matter could be separated from the iron and carried as a distinct acid, which he called the colouring matter of Berlin blue; in German it became Blausäure, blue acid.

Because the p\(K_a\) is far above physiological pH, cyanide in the body and in neutral water is present almost entirely as the neutral molecule, which crosses membranes and evaporates easily. Solutions of cyanide salts smell of HCN for the same reason.

Light, silver chloride and radiant heat

For the general reader. Two short parts of Air and Fire belong to physics. Scheele spread sunlight into a spectrum with a prism and found that violet light blackens silver chloride much faster than red light: different colours do different chemical work. He also argued that the heat felt in front of a hot stove is a different thing from the warm air rising above it. Both observations were early steps toward the physics of radiation.

Horn silver and the violet ray

Johann Heinrich Schulze had shown in 1727 that light darkens silver salts. Scheele went further in 1777. He placed paper coated with horn silver (silver chloride) in the spectrum from a prism fixed at a window and found that it grew black sooner in the violet than in any other colour, while red light had little effect. He also found that ammonia dissolved the unchanged chloride but not the black particles, which were metallic silver.

Scheele had in hand a way to fix a light image, though neither he nor anyone else used it for that. In 1801 Johann Wilhelm Ritter, testing silver chloride beyond the violet end of the spectrum, discovered ultraviolet light. The principle that only absorbed light causes chemical change, later the Grotthuss–Draper law, and Albert Einstein’s photochemical equivalence law of 1912, made the wavelength dependence Scheele saw quantitative.

Radiant heat

In Air and Fire Scheele distinguished three ways heat travels: by contact through bodies, by currents of heated air, and by a radiating heat that moves in straight lines from a fire like light, through air without warming it. The idea was taken further by Marc-Auguste Pictet’s mirror experiments (1790), Pierre Prévost’s theory of exchanges (1791) and William Herschel’s discovery of infrared radiation beyond the red (1800). The quantitative laws came a century later.

Köping, 1775–1786

In 1775 Scheele moved to Köping, a small town on Lake Mälaren, to manage the pharmacy of the late Hindrich Pascha Pohl for his widow, Sara Margaretha Pohl. Between late 1776 and early 1777 he bought the business. On 11 November 1777 he passed the apothecary examination before the Royal Medical College with the highest honours. On 29 October 1777 he took his seat at the Academy of Sciences in Stockholm, the only time he did so.

Air and Fire finally appeared in 1777 in Uppsala and Leipzig, after delays at the printer, and an English edition followed in 1780. By then Priestley’s and Lavoisier’s papers on oxygen had been read across Europe.

Offers declined

His reputation brought offers. He declined a well-paid post as chemical consultant to the mines at Falun, and he declined the invitation to succeed Andreas Sigismund Marggraf as chemist of the Berlin Academy. Nineteenth-century accounts add an invitation from England. He preferred his own pharmacy, which paid for his experiments and left him free. In 1782 he moved it into a new building with a larger laboratory.

The Köping years were his most productive. Molybdenum, Scheele’s green, lactic acid, tungstic acid, hydrogen cyanide, glycerol, citric acid, malic acid and gallic acid all came from there, together with a method of preserving vinegar by heating it in sealed bottles, an early form of pasteurization (1782). His papers appeared mainly in Swedish in the Academy’s Handlingar, although he wrote in German. Bergman, his patron, died on 8 July 1784. In 1785 the Société de Médecine in Paris elected Scheele a member.

Death, priority, legacy

From the autumn of 1785 Scheele suffered from symptoms that his doctors attributed to the kidneys, and early in 1786 from a skin disease. In February 1786 he sent his memoir on gallic acid to the Academy. A few days before his death (sources give 18 or 19 May 1786) he married Sara Margaretha Pohl, so that the pharmacy and his possessions would pass to her. He died at home in Köping on 21 May 1786, aged 43. The cause is uncertain; his long exposure to mercury, arsenic, lead compounds and hydrogen cyanide is usually blamed.

Priority

Scheele published late and through others, and much of his credit arrived slowly. The 1774 letter to Lavoisier, printed in 1890, and the laboratory notebooks studied in the nineteenth century established his independent and earlier discovery of oxygen. For chlorine, manganese, barium, molybdenum and tungsten, the credit is shared with those who isolated the elements: Gahn, Davy, Hjelm and the Elhuyar brothers. For hydrogen fluoride, hydrogen cyanide, arsine and the organic acids, it is his alone.

Legacy

• Elements: oxygen, chlorine, manganese, barium, molybdenum and tungsten all trace their recognition to his analyses.
• Compounds: HF, H\(_2\)S, AsH\(_3\), HCN, arsenic acid and the first pure organic acids and glycerol.
• Physics: the wavelength dependence of photochemistry and the separation of radiant heat from convection.
• Method: a model of qualitative analysis by precipitation and solubility, done with simple apparatus and great skill.
• Names: the mineral scheelite, the pigment Scheele’s green, the lunar crater Scheele and the asteroid 12356 Carlscheele. A monument stands in Köping, and a plaque marks his birthplace at Fährstraße 23 in Stralsund.

Connections

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

Influenced by

• Andreas Sigismund Marggraf

Influenced

• Humphry Davy
• Fausto Elhuyar
• Peter Jacob Hjelm

Colleagues and collaborators

• Antoine Lavoisier
• Johan Gottlieb Gahn 1769-1786
• Peter Jonas Bergius
• Torbern Bergman 1770-1784

Rivals

• Antoine Lavoisier 1774
• Joseph Priestley

Friends

• Anders Jahan Retzius 1765-1786

Also mentioned in this life

• Jöns Jacob Berzelius
• Ludwig Boltzmann
• Albert Einstein
• Joseph Louis Gay-Lussac
• Louis Pasteur
• William Herschel
• Friedrich Wöhler

Fields

• chemistry 21 lives

Sources and further reading

Biography

1. Carl Wilhelm Scheele, Wikipedia; German Wikipedia.
2. Neue Deutsche Biographie, Scheele, Carl Wilhelm (with genealogy).
3. Sketch of Karl Wilhelm Scheele, Popular Science Monthly 31 (1887).
4. On the discovery of oxygen and Scheele’s letter to Lavoisier, Redalyc.
5. É. Grimaux, Une lettre inédite de Scheele à Lavoisier, Revue générale des sciences (1890).
6. Carl Wilhelm Scheele, New World Encyclopedia.

Chemistry and physics

1. C. W. Scheele, Chemische Abhandlung von der Luft und dem Feuer, Uppsala and Leipzig, 1777. The Discovery of Oxygen, Part 2, Alembic Club Reprints (Project Gutenberg).
2. C. W. Scheele, Anmärkning om Citron-saft, samt sätt at crystallisera densamma, Kungl. Vetenskaps Academiens Nya Handlingar 5 (1784) 105–109.
3. C. W. Scheele, Examen chemicum calculi urinarii, Opuscula 2 (1776).
4. History of chlorine, Wikipedia.
5. Scheele’s green and Arsine, Wikipedia.
6. Tungsten, Molybdenum and Barium: history sections, Wikipedia.
7. History of photography, Wikipedia (Schulze and Scheele on silver salts).
8. J. R. Partington, A History of Chemistry, vol. 3, Macmillan, 1962, chapter on Scheele.