Chromium

Siberia may be said to be the birthplace of chromium as we shall see later; in the 18^th century the mineral crocoite, known at the time as red lead ore, was found there. Some other chromium ores had been known much earlier. And this is not surprising since chromium is one of abundant elements (0.02 per cent of the total mass of the earth’s crust). But it is not easy to separate chromium even in the form of oxide and for the time being this task was beyond the power of chemists. Although chromium compounds have different colours, this peculiar fact did not attract the attention of scientists to chromium minerals.

The only exception was crocoite. For the first time it was analysed in 1766 by the German chemist I. Lehmann who lived at the time in St. Petersburg. Treating the mineral with hydrochloric acid the chemist obtained a beautiful emerald–coloured solution. But his conclusion was erroneous: crocoite contained lead contaminated with impurities. These impurities could only be chromium since crocoite is lead chromate PbCrO₄. I. Lehmann was not destined to establish the composition of the mineral.

For the second time crocoite became the object of study in 1770 when P. S. Pallas, a St. Petersburg Academician, was describing the Berezov mines in the Urals: “This lead ore comes in different colours but more often looks like cinnabar. The crystals of this heavy mineral shaped as irregular pyramids are imbedded in quartz like little rubies”.

1. S. Pallas was a traveller, geographer and mineralogist, and not a chemist. But it was he who introduced crocoite to laboratories in Western Europe. A sample of the mineral fell into the hands of the well–known chemist L. Vauquelin. Three decades passed since I. Lehmann had studied crocoite. During this time the scientists repeatedly tried to determine its composition but failed to find any new elements in it. The results obtained were very contradictory. For instance, there was an analyst who reported that lead ore contained molybdic acid, nickel, cobalt, iron and copper. In his first experiments L. Vauquelin also made mistakes and found lead dioxide, iron and alumina in crocoite.

In 1797 the French chemist decided to study crocoite more thoroughly. Step by step Vauquelin refuted the results of all the previous analyses and at last drew a conclusion that crocoite contained a new metal with properties quite different from those of other metals.

1. Vauquelin boiled powdered crocoite with potassium carbonate. The product was lead carbonate and a yellow solution which contained, in the scientist’s opinion, a potassium salt of an unknown acid. The solution acquired bright and diverse colours when various reagents were added: mercuric salts yielded a red sediment, lead salts gave a yellow sediment, tin chloride turned the solution green all these results convinced Vauquelin that he was dealing with a new element. Its separation in the form of oxide was rather simple after that.

Many years later D.I. Mendeleev wrote in his Principles of Chemistry that the Uralian red chromium ore, or chromium–lead salt, had given Vauquelin the means to discover chromium. Vauquelin derived this name from the Greek chroma meaning “colour” because of the bright colouring of its compounds. For the sake of justice we should note that the name “chromium” for the new element was proposed by Vauquelin’s compatriots A. Fourcroy and R. Haüy. Independently of Vauquelin and almost simultaneously with him the presence of a new metal in crocoite was established by M. Klaproth who, however, did not prove it as clearly as his French colleague. Numerous attempts to obtain pure chromium were unsuccessful. L. Vauquelin himself tried to prepare it but most likely it was chromium carbide that he obtained.

Titanium

W. Gregor was not a chemist. But sometimes this English clergyman did chemical experiments since his hobby was mineralogy. From time to time W. Gregor studied the composition of various minerals and so succeeded in the work that afterwards J. Berzelius respected him as a prominent mineralogist. One day W. Gregor became interested in the composition of black sand whose deposit he found in the Menaccin valley on the territory of his parish. This black sand, resembling very much gunpowder, mixed with dingy–white sand of a different kind attracted W. Gregor’s attention. Having separated specks of black sand, he analysed them; you will judge the carefulness of this analysis from the following figures:

per cent (these 9/16 is especially impressive) is iron oxides; 3  per cent is silica, and 45 per cent is accounted for by the compound described by Gregor as reddish–brown lime. And 4  per cent was lost during the analysis. In this list it is the reddish–brown lime that is of interest. It dissolved in sulphuric acid yielding a yellow solution. Under the action of zinc, tin, or iron, the solution turned purple. Gregor wrote an article, reporting his findings. Being very modest, he believed that his investigation was incomplete. He only set forth some facts the explanation of which was the privilege of more knowledgeable scientists.

His friend, mineralogist D. Hawkins, convinced Gregor that the black sand was a new unknown mineral. Such an opinion from a man who knew about mineralogy not less than Gregor, suggested to the latter that the black sand contained a new metallic substance. Gregor proposed to name it “menaccin” in honour of the place where the sand had been found, and the sand itself menaccite (or menacconite). Now this black sand is named ilmenite and has the formula FeTiO₃. All this goes to show that titanium was discovered in 1791 by W. Gregor.

But many historians of science believe that M. Klaproth was the discoverer of titanium although the merit of Gregor’s work is unquestionable. But the English clergyman was too unambitious. Klaproth chose another way. Of course, he read Gregor’s report but did not immediately grasp its meaning. In 1795 Klaproth succeeded in separating an oxide of the new element from the mineral brought from Hungary. Now this mineral is known as rutile (TiO₂). The oxide separated by Klaproth and the menaccin earth found by Gregor turned out to be very much alike. Soon Klaproth established that he and Gregor had discovered the same element.

The German scientist named the element “titanium” from mythological “Titans”– the sons of Ge (the goddess of Earth). Pure metallic titanium was obtained only in 1910.

Uranium

There is hardly another chemical element that from near oblivion sprang to instant fame. This is uranium occupying box No. 92 in the periodic table. Discovered in 1789, uranium did not interest chemists for a long time and even its atomic mass was determined incorrectly. Its practical use was confined to making coloured glass. But in 1906 in the eighth edition of Principle of Chemistry Mendeleev appealed to those who were searching for new subjects of investigation to pay close attention to uranium compounds. The reason Mendeleev gave was that two most important events at the end of the 19^th century science were related to uranium: the discovery of helium and the discovery of radio activity. And, finally is it a mere chance that uranium is the last in the series of naturally occurring chemical elements, the heaviest of them?

Some scientists have referred to the ninety second element as element No. 1 of our century.

And yet, there was nothing extraordinary about the  discovery of uranium about two hundred years ago. It was like many others during the emergence of analytical chemistry. There is no doubt about the name of the discoverer–M. Klaproth. True, the actual extraction of uranium is associated with the name of another scientist (we shall come back to it later).

Pitchblende had been known to man for ages. When chemical analysis was still in its infancy, pitchblende was considered to be an ore of zinc and iron. More accurate knowledge of its composition was to come later.

When a pitchblende sample fell into the hands of Klaproth, he dissolved a piece of the mineral in nitric acid and added potash to the solution. Yellow precipitate was formed which was soluble in the excess of potash. The precipitate was small greenish–yellow crystals in the form of hexagonal prisms. Gradually the scientist made the conclusion that he had obtained a salt of a new element. Having prepared an oxide, the scientist tried to separate pure metal. And when a lustrous black powder was formed on the bottom of the crucible, the German scientist decided that the aim was attained. But Klaproth was mistaken. At the most he obtained a mixture of oxide with a small amount of the metal. Indeed, chemists were yet to see how difficult it is to extract pure uranium.

Confident of success, M. Klaproth proposed the name “uranium” for the element discovered. The chemist wrote: “In old times only seven planets were known and thought to correspond to seven metals, and according to this tradition the new metal should rightfully be named after the planet which has been recently discovered”. It was the planet Uranus discovered in 1781 by the English astronomer Herschel. After that it became fashionable to name newly discovered chemical elements after celestial bodies. Uranium had been included in the list of simple substances and made its way to chemical textbooks, but metallic uranium remained unobtainable for a long time to come. There were even scientists who were doubtful about the discovery of the German chemist. Six years after Klaproth’s death (1817), J. Arfvedson, the pupil of Berzelius, decided, perhaps, following his teacher’s advice, to remove these doubts. He tried to reduce dark–green uranium oxide with hydrogen. Arfvedson believed that the initial material was the lower oxide (we know now that the Swedish scientist worked with U₃O₈). The reaction yielded a brown powder (UO₂). J. Arfvedson, however, thought that he extracted metallic uranium.

It was only in 1841 that the French chemist E. Peligot succeeded with the aid of a new reduction method. He heated anhydrous uranium chloride mixed with metallic potassium in a closed platinum crucible and obtained a black metallic powder. Its properties noticeably differed from those which M. Klaproth used to ascribe to metallic uranium. Therefore, some historians of science associate the real discovery of uranium with name of E. Peligot.

Ingots of the metal were produced by the French chemist A. Moissan who melted it in an electric furnace invented by him in which a very high temperature could be attained. The scientist produced the first ingot in May. 1896, and gave it to Bacquerel. With the aid of the sample A. Bacquerel established that radioactivity is a property of the elemental uranium. This property attracted everybody’s attention to uranium for the first time.

At one time uranium gave a lot of trouble to D.I. Mendeleev when the scientist was working on his periodic table. The atomic mass of uranium was considered to be 120 and, therefore, uranium was placed in the third group as a heavy analogue of aluminium. But this allocation by no means agreed with the properties of uranium. Mandeleev concluded that the atomic weight had been determined incorrectly and proposed to increase it by 100 per cent. This put uranium in Group VI under tungsten and made it the last element in the periodic table.

Zirconium

Zirconium oxide closely resembles aluminium oxide or alumina. For a long time the letter effectively concealed the presence of the former. Nobody suspected an unknown element in zirconium minerals known as early as the Middle Ages. Thus, zirconium, one of the most abundant metals on Earth (0.02%) remained “invisible” up to the end of the 18^th century. Today the mineral zircon is the main source of zirconium; it occurs in two varieties: hyacinth and jargoon. Already in old times hyacinth was known as a precious stone owing to its beautiful colours ranging from yellow–brown to smoky green.

It was believed that the composition of hyacinth was similar to that of ruby and topaz.

Zircon was analysed more than once and every time erroneously. In 1787 the German chemist J. Wiegleb, when analysing Ceylon zircon, found only silicon dioxide and small admixtures of lime, magnesia, and iron. Earlier such a skilled chemist as T. Bergman had established that Ceylon hyacinth contained 25% silicon dioxide, 40% aluminium oxide, 13% iron oxide, and 20% lime. The element known subsequently as zirconium was safely “hidden” in aluminium oxide.

This natural camouflage was revealed in 1789 by M. Klaproth. He heated zircon powder (a sample similar to that used by T. Bergman) with alkali in a silver crucible. The alloy was then dissolved in sulphuric acid and from the solution M. Klaproth separated a new earth which he named zirconium. His analytical results demonstrated 25 per cent silica, 0.5 per cent iron oxide, 70 per cent zirconium earth. As we see, there is nothing in common with Bergman’s results. In the same year Guyton de Morveau, separating zirconium from hyacinth found in France, confirmed Klaproth’s results.

Preparing metallic zirconium turned out to be not so simple. In 1808 H. Davy tried in vain to decompose zirconium earth with electric current. It was not before 1824 that Berzelius obtained contaminated zirconium by heating a dry mixture of potassium, potassium fluoride, and zirconium in a platinum crucible. Zirconium received its name from the mineral.

Strontium

In 1787 a new mineral, strontianite, was found in a lead mine near the village of Strontian in Scotland. Some mineralogists classified it as a variety of fluorite (CaF₂). The majority of scientists, however, believed that strontianite was a variety of witherite (barium mineral BaCO₃).

In 1790 the Scottish physician A. Crawford thoroughly studied the mineral and came to conclusion that the salt obtained by the action of hydrochloric acid in strontianite differed from barium chloride. It dissolved in water more readily and its crystals were of different shape. Crawford decided that strontianite contained a previously unknown earth.

At the end of 1791 the Scottish chemist T. Hope concerned himself with studying strontianite, and established the difference between witherite and strontianite. Hope also noted that the strontium earth reacted with water more vigorously than quicklime; it dissolved in water much more readily than barium oxide, and all strontium compounds turned the flame red. T. Hope proved that the new earth could not be a mixture of calcium and barium earths. Lavoisier suggested that the new earth was of metallic nature but only H. Davy succeeded in proving it in 1808.

The history of the discovery of strontium would be incomplete if we did not mention another scientist to whom, undoubtedly, a great deal of credit for studying strontianite should be given. He was the Russian chemist T. E. Lovits who concluded, independently of other scientists, that strontianite contained an unknown element. Lovits was the first to discover strontium in heavy spar. The method of preparing metallic strontium suggested by H. Davy did not yield a sufficiently pure product. It was only in 1924 that P. Danner (USA) obtained pure strontium by reducing its oxide with metallic aluminium or magnesium.

Tungsten

Although tungsten is also a rare element, it was discovered (in the form of its oxide) as early as the last quarter of the 18^th century. To some extent it was a matter of chance but progress in analytical chemistry also contributed to the discovery of tungsten.

The name “tungsten” appeared much earlier. In German it means “wolf’s froth”. The point is that in smelting of tin from some ores a part of smelted metal was irretrievably lost. Medieval miners believed that tin was “devoured” by the mineral that was contained in the ore like a sheep is devoured by a wolf. This mineral was named tungsten or wolframite. As time passed, tungsten attracted ever increasing attention of the scientists. In 1761 the German mineralogist I. Lemann analysed wolframite but did not find any new components in it. His compatriot P. Wolf for his part said that wolframite contained “something”. Another strange mineral, “tungsten” or “heavy stone”, was also known. It was found in 1751 by A. Cronstedt. In 1781 this mineral attracted the attention of C. Scheele who treated tungsten (calcium wolframate) with nitric acid and obtained a white substance resembling molybdic acid. An analyst par excellence, Scheele showed the difference between the two acids and, consequently, he is considered to be the discoverer of tungsten.

At the same time T. Bergman, Scheele’s compatriot, was also at the threshold of discovery. In his opinion, tungsten, due to its high density, could contain baryta earth. Studying the mineral, the scientist found a white substance in it which he called tungstic acid. But after that Bergman followed a wrong path, believing that both tungstic and molybdic acids were arsenic derivatives; however, he did not check this assumption. In 1783 two Spanish chemists, the F. and H. D’ Egluar (brothers), separated a while acid from wolframite which proved to be similar to tungstic acid. Like Bergman and Scheele, the Spanish chemists succeeded in extracting metallic tungsten.

Molybdenum

The molybdenum story is not rich in events. It is even trivial. Only one detail is of interest: this rare element was discovered very early, namely, in 1778, when the chemical analysis was just coming of age. Molybdenum was first separated in the form of oxide. The name “molybdenum” had appeared long before the new element was discovered. It originates from the Greek names molybdena for a lead mineral (lead glance) and molybdos for “lead”, the two resembling each other. There was another mineral which also resembled these two very much; later it became known as molybdenite (molybdenum sulphide). 

In 1754 the Swedish mineralogist A. Cronstedt differentiated these minerals, saying that molybdenite possessed some peculiar properties. But proof of that was required. By a lucky coincidence, the report of the molybdenite study fell into Scheele’s hands. In 1778 he performed and analysis of molybdenite. The treatment of molybdenite with strong nitric acid resulted in the formation of a bulky white mass which Scheele described as a peculiar white earth. At the same time nitric acid had no effect on graphite. Thus, the difference between graphite and molybdenite became evident. Scheele named the white earth “molybdic acid” since it had acid properties. Having calcinated molybdic acid, the swedish chemist obtained molybdenum oxide, i.e. an oxide of a new metal. This is what Scheele believed and his belief was shared by his compatriot T. Bergman.

After that it was important to extract the metal from the molybdic earth. To do that Scheele planned to calcinate the earth with coal. But for some reason he could not perform the reaction himself and asked his friend P. Hjelm to do it. In 1790 Hjelm complied with the request. However, molybdenum obtained by him was contaminated with carbon and molybdenum carbide. The credit for preparing pure molybdenum (by reduction of the oxide with hydrogen) went to J. Berzelius (1817).

Barium

Barium, as well as his analogues in the second group of the periodic table, is not encountered in nature in the native state. Sulphates and carbonates are the most typical barium minerals. One of barium minerals attracted attention of alchemists back in the early 17^th century (in 1602, to be exact).

In that year V. Casciaralo, a shoemaker from Bologna, noted that heavy spar (barium sulphate), heated with coal and drying oil and then cooled to room temperature began to emit a reddish glow. The mineral, named Bologna stone, Bologna phosphorus, sunstone, and so on, was barium sulphide BaS. The unusual luminescence was immediately interpreted in many different ways. For instance, the French chemist N. Lémery wrote in his “Chemistry Course” that the ability of Bologna stone to luminesce in the dark is due to the presence of sulphur. Another mineral displaying this property is Bolduin phosphorus (anhydrous calcium nitrate).

For a long time (up to 1774) heavy spar was confused with limestone; they were believed to be two varieties of the same compound. In 1774 Scheele, studying pyrolusite together with Gahn, discovered a new compound which gave a white precipitate under the action of sulphuric acid. Scheele established that heavy spar contained an unknown earth which was named “baryta” one. By the last quarter of the 18^th century barium oxide was known rather well; it was suggested that it contained an unknown metal. This belief was supported by A. Lavoisier in his “Textbook of Chemistry”. In “The Table of Simple Bodies” barite is considered a simple substance. However, only in 1808 did H. Davy succeed in preparing the new metal by the method which he had used for obtaining calcium (see chapter 5).

The name of barium originates from the Greek baros (heavy) since barium oxide and its minerals were primarily characterized by their great mass.

Manganese

Manganese compounds and, in particular, its oxidepyrolusite (MnO₂)–have been known from ancient times and used for making glass and pottery. In 1540 V. Biringuccio, an Italian metallurgist, wrote that pyrolusite was brown, did not melt, and gave a violet colour to glass and ceramic when added to them. Another characteristic of pyrolusite was observed–its ability to make clear yellow and green glasses.

The Austrian scientist I. Kaim seems to be the first to have obtained a small amount of metallic manganese in 1770. He heated a mixture consisting of one part of pyrolusite powder and two parts of black flux (i.e. a mixture of coal with K₂CO₃) and obtained bluish–white brittle crystals. Apparently, it was contaminated manganese but the scientist only concluded that the metal obtained was iron–free and did not complete his studies.

The subsequent story of manganese is associated with T. Bergman who by that time had already confirmed the discovery of nickel. He characterized pyrolusite in the following way: the mineral called “black magnesium” is a new earth; it should not be confused either with roasted lime or with “magnesium alba” (i.e. magnesium oxide). However, T. Bergman failed to separate the metal from pyrolusite, in contrast to I. Kaim.

1. Scheele was the third chemist who tried to separate a new element form this mineral. In 1774 he submitted his paper “On Manganese and Its Properties” to the Stockholm Academy of Sciences; in it he summed up the three years of studies of pyrolusite. In this extremely informative paper he reported the discovery of two metals (barium and manganese) and described two gaseous elements (later identified as chlorine and oxygen). Scheele established that manganese oxide differed from all earths known at the time.

There are two significant dates in the history of manganese: May 16 and June 27, 1774. On May 16 Scheele sent I. Gahn, his friend and compatriot, a sample of purified pyrolusite and asked him to decompose it. Gahn placed a mixture of pyrolusite powder, oil, and ground coal into a coal crucible and calcinated it for an hour. On the bottom of the crucible he found a regulus of the metal whose weight was only one third that of the initial pyrolusite. On June 27, having received from Gahn the sample of the new metal, Scheele wrote to his colleague that he considered the regulus obtained from pyrolusite a new semi–metal different from all other semi–metals and closely resembling iron. The term “semi–metal” was retained in chemistry and metallurgy for some time. Thus, Gahn succeeded in separating metallic manganese. It may be said that he completed the discovery of this element, although manganese obtained by him had a high carbon content (pure metal was obtained later).

In 1785 the German chemist J. Ilsemann obtained metallic manganese independently of Gahn and Scheele by heating a mixture of pyrolusite, fluorspar, lime, and coal powder. The product was intensely calcinated. The resulting manganese was, moreover, even less pure. At first the metal was named in Latin “manganesium” which derived from the old name of pyrolusite “Lapis manganesis”. When in 1808 magnesium was obtained, to avoid confusion the Latin name of manganese was changed for “manganum”.

Cobalt

The history of the discovery of cobalt can conveniently be started with the history of its name. Cobalt owes its name to the mineral which medieval Saxony miners named “cobold” after the evil spirit who was assumed to inhabit the mineral. This mineral closely resembled silver ore but all attempts to produce silver from it were unsuccessful.

Blue cobalt glasses, enamels, and pigments were known as early as 5,000 years ago in ancient Egypt. In pharaoh Tutankhamen’s tomb archaeologists found  fragments of blue glass. It is not known whether the preparation of blue glasses and paints on the basis of cobalt compounds was due to chance or whether it was a conscious effort. At any rate the method of their preparation remained unknown for a long time. Its first mention dates back to 1679.

Cobalt was discovered by the Swedish chemist G. Brandt in 1735. In his “Dissertation on Semi–metals” Brandt wrote about a new semi–metal, cobold, discovered by him. By semi–metals the scientist meant compounds whose properties resemble those of known metals but which are not malleable. He described six semi–metals: mercury, bismuth, zinc, antimony, cobalt, and arsenic. Since the majority of bismuth ores contain cobalt, G. Brandt proposed several methods to distinguish between cobalt and bismuth.

In 1744 G. Brandt found a new mineral which contained cobalt, iron, and sulphur. It proved to be cobalt sulphide Co₃S₄.

Later G. Brandt studied cobalt in detail. At the turn of the 18^th century cobalt and its compounds were studied by T. Bergman, L. Thenard, L. Proust, and J. Berzelius, which made cobalt a well–investigated element. It must be added that for a long time many chemists did not believe in the discovery of cobalt. In 1776 the Hungarian chemist P. Padaxe said that cobalt was a compound of iron and arsenic; but he considered nickel, which had already been discovered by that time, to be a chemical element. Only by the end of the 18^th century, the efforts of many scientists confirmed the discovery of G. Brandt.

Cobalt, as well as nickel, is often present (and sometimes in great amounts) in meteorites. In 1819 the Germa chemist F. Stromeyer reported the discovery of cobalt in a meteorite and somewhat later S. Tennant found nickel in the same meteorite.

Oxygen

One can safely say that none of the chemical elements played such an important role in the development of chemistry as oxygen. This life–giving gas enabled chemistry to make such great progress at the end of the 18^th century which had never been possible before. First of all, oxygen overturned the phlogistic theory which had seemed immovable. Erroneous as it was, this theory was undoubtedly of some historical usefulness. For the time being the theory of phlogiston made it possible somehow to systematize the existing chemical conceptions and to consider various processes in nature and laboratory from a common (though erroneous) standpoint. This gave a certain purposefulness to the research. Hydrogen and nitrogen were found from the phlogistic conceptions but the study of these “varieties of air” made it possible to accumulate new facts whose explanation demanded a different approach. Figuratively speaking, chemistry needed a new look at itself, and oxygen made it possible.

In defiance of the theory of phlogiston, vague conjectures were repeatedly made that combustion of inflammable compounds and calcination of metals drew a “substance” form the air. In 1673 R. Boyle concluded that when lead and antimony are calcinated a very fine “materia ignea” passes into the metals and combines with them, increasing their weight. “…the good Robert Boyle’s opinion is false,” Lomonosov wrote 80 years later. The famous Russian scientist said that air participates in the processes of combustion–particles form the air mix with the compound being calcinated and increase its mass.

In the period when pneumatic chemistry was gaining ground, the French Chemist P. Bayan wrote a paper (1774) in which he discussed the causes for an increase in the mass of metals during calcination. He believed that a peculiar variety of air–an expansible fluid, heavier than ordinary air–was added to a metal in the process of calcination. Bayen obtained this fluid by thermal decomposition of mercury compounds. And conversely, acting on metallic mercury, the fluid transformed it into a red compound.

Bayen, unfortunately, only established the facts and did not pursue the subject further. However, you will see later that the scientist was actually dealing with oxygen. Remember two things: the data 1774 and the compound observed by Bayen–red mercury oxide. In the same year J. Priestley experimented with the same compound. Shortly before, he had discovered that in the presence of green plants fixed air, not supporting respiration, turned into ordinary air suitable for respiration by living organisms. This fact was extremely important not only for chemistry but for biology as well. Priestley proved for the first time that plants release oxygen.

In the early 1770’s so–called saltpeter gas was already known. It was liberated in the reaction of diluted nitric acid with iron shavings (it is nitrogen oxide in modern terminology). It turned out that saltpeter gas can be transformed (by its reaction with iron dust) into another variety of air supporting combustion but not supporting respiration. Thus, J. Priestley discovered another nitrogen oxide, N₂O, and named it, according to the logic of the phlogistic theory, dephlogisticated saltpeter gas.

August 1, 1774, which was to become a milestone in the history of chemistry, was a usual day of hard work for J. Priestley. He placed red mercury oxide into a sealed vessel and directed on it sunbeams, focused with a big lens. The compound began to decompose yielding bright metallic mercury and a gas (several years later this gas would be named “oxygen” and become the third elemental gas). Unlike nitrogen, oxygen was not initially isolated from the atmosphere. The new air variety was extracted from a solid. The gas discovered by Priestley proved to be suitable for respiration. A candle burnt in the atmosphere of this gas much brighter than in ordinary air. Nothing was observed when the new gas was mixed with air but, being mixed with saltpeter, the gas yielded brownish vapours (known at present to be NO₂ formed from NO). A similar, although not so pronounced, picture was observed when saltpeter was reacted with ordinary air. Priestley had only to say: “The new gas is a component of air.” But he was not ready yet to do so and named the new variety of air “dephlogisticated” air–something quite natural for a follower of the phlogistic theory.

After the discovery–and this is an important detail in the history of oxygen–Priestley left for Paris where he told Lavoisier and some other French scientists about his experiments. Lavoisier appreciated at once the importance of the experiment of his English colleague–he had a much clearer idea about it than Priestley. But Priestley kept talking about dephlogisticated air, still in the grip of his delusion (which is another proof of the vitality of the phlogistic theory). Unable to see the greatness of his own discovery, Priestley considered dephlogisticated air to be a complex substance. Only in 1786, influenced by the ideas of Lavoisier, did he began to view it as an elemental gas.

Thus, we owe the discovery of oxygen to P. Bayen and J. Priestley. However, a third name should be added–that of the famous Swedish chemist C. Scheele. It became widely known to the scientific community when Scheele published the book chemical Treatise About Air and Fire. Written in 1775, it appeared only two years later for which the publisher was to blame. This disappointing fact deprived Scheele of the right to be named the discoverer of oxygen although he described it as early as 1772 and his description was much more detailed and accurate than that of Bayen and Priestley. Scheele obtained oxygen (“fiery air”) in various ways, by decomposing inorganic compounds. Distillation of saltpeter with sulphuric acid yielded brown vapours.

Which became colourless at high temperatures. Scheele collected these vapours and named the new gas “fiery air” In this gas, like in Priestley’s, a candle burned much brighter than in ordinary air. Scheele believed that fiery air was a component of ordinary air. Mixing it with mephitic or corrupted air of Rutherford, Scheele prepared a mixture which did not differ at all from ordinary air. In fact, the scientist realized that atmospheric air is a mixture of gases which later were to be known as nitrogen and oxygen. However, this seems to be easy only with our superior knowledge. Scheele was deluded by his devotion to the phlogistic theory. Burning inflammable air (hydrogen) in a vessel with air, the scientist did not detect any products of the reaction of inflammable air with fiery one. His conclusion was that this reaction produced heat. Scheele reasoned that fiery air, combining with phlogiston, produces heat (which had, according to Scheele, a material nature) whose “decomposition” yields fiery air.

Scheele discovered fiery air knowing nothing about Priestley’s experiments and informed Lavoisier about it on September 30, 1774. Regretfully, Scheele’s results were published too late. Had they appeared earlier, the difficult and contradictory process of elucidating the nature of elemental gases would have been accelerated.

Their real understanding was made possible by Lavoisier, one of the most outstanding chemists of all times. During the period dominated by the phlogistic theory, vast experimental material was accumulated which led to revolutionary changes in chemistry. The main credit for this goes to A. Lavoisier owing to whom oxygen was properly understood. F. Engels wrote: “Lavoisier was able to discover in the oxygen obtained by Priestley the real antipode to the fantastic phlogiston and thus could throw overboard the entire phlogistic theory. But this did not in the least do away with the experimental results of phlogistics. On the contrary, they persisted, only their formulation was inverted, was translated from the phlogistic into the now valid chemical language and thus they retained their validity.”

Lavoisier’s road to the discovery of oxygen was much straighter than that of his contemporaries. At first the French scientist also appealed to the phlogistic theory, but the more experimental facts he obtained, the more inclined he became to discard it. By November1, 1772, he had finished the description of his experiments on the combustion of various compounds in air. He concluded that the mass of all substances, including metals, increases upon combustion and calcination.  

Since these processes require a great amount of air, A. Lavoisier made another conclusion: air is a mixture of gases with different properties. A certain part of it supports combustion and becomes bonded to the burning substance. At first A. Lavoisier assumed that this type of air is similar to the fixed air of J. Black but soon he saw his error. In February 1774, the French scientist discovered that air which interacts with a substance during combustion is most suitable for respiration. Thus, A. Lavoisier met face to face with oxygen but refrained from announcing the discovery of a new gas since he was going to perform some additional experiments.

In October 1774, Priestley reported to Lavoisier about his discovery revealing to the French chemist the real significance of his own findings. He immediately began to experiment with red mercury oxide which was the most suitable “generator” of oxygen. In April 1775, Lavoisier made a report to the Academy of sciences: “Memoir on the Nature of the Substance Which Combines with metals upon calcination and Increases their weight”–the announcement of the discovery of oxygen. Lavoisier wrote that this type of air had been discovered almost simultaneously by Priestley, Scheele, and by him. At first he said that it was “very easily inhaled air” but then changed the name for “life–giving” or invigorating” air.

This fact alone shows how far behind Lavoisier left his contemporaries in understanding the nature of oxygen. Invigorating air became the subject of comprehensive studies. At a later stage the scientist came to the conclusion that “the most easily inhaled air” is an acid–forming principle, the most important part of all acids. Later it was shown that this belief was erroneous (when oxygen–free acids were described with hydrohalic acids as an example). But in 1779 Lavoisier thought it possible to reflect this property of the new gas in its name of “oxygen” derived from the Greek for “producing acid”.

Determination of the water composition became a major advance of the oxygen theory. In 1781 H. Cavendish observed that inflammable air upon combustion is transformed almost completely (together with dephlogisticated air) into pure water. But he published his results only in 1784. Lavoisier knew about these experiments and, after repeating them, he concluded that water is not a simple substance but a mixture of inflammable and invigorating air. Since the conclusion was made in 1783, Lavoisier is held by many to be the first one to have established the composition of water. In reality, however, H. Cavendish was the first. Determination of the composition of water made it possible to get an insight into the nature of hydrogen.

What makes the history of the discovery of oxygen interesting is that the process was not a single event. Several stages were passed: from an empirical observation of oxygen to a proper understanding of its nature as a gaseous chemical element. It should also be mentioned that the discovery of oxygen (as well as of other elemental gases) was not the doing of one man. Engels wrote: “Priestley and Scheele had produced oxygen without knowing what they had laid their hands on …. And although Lavoisier did not produce oxygen simultaneously and independently of the other two, as he claimed later on, he nevertheless is the real discoverer of oxygen vis–à–vis other who had only produced it without knowing what they had produced.”