The 2^nd century BC Greek writer, Philo of Byzantium, observed that inverting a jar over a burning candle and surrounding the jar’s neck with water resulted in some water rising into the neck. He incorrectly ascribed this to the idea that part of the air in the vessel were converted into the element fire and thus were able to escape through pores in the glass. Much later Leonardo da Vinci (Figure 1) suggested that this effect was actually due to a portion of air being consumed during combustion.

Figure 1: Italian painter, sculptor, architect, musician, scientist, mathematician, engineer, inventor, anatomist, geologist, cartographer, botanist and writer Leonardo di ser Piero da Vinci (1452 - 1519).

By the late 17^th century, Robert Boyle (Figure 2) showed that air is necessary for combustion. His work was expanded by English chemist John Mayow (Figure 3) by showing that fire requires only a part of air that he called spiritus nitroaereus or just nitroaereus.

Figure 2: British natural philosopher, chemist, physicist, and inventor Robert Boyle (1627 - 1691).

Figure 3: English chemist, physician, and physiologist John Mayow FRS (1641–1679).

The reactive nature of nitroaereus was implied by Mayow from his observation that antimony (Sb) increased in weight when heated in air. He also suggested that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body; both concepts that were proven to be correct.

Robert Hooke (Figure 4), Ole Borch (Figure 5), Mikhail Lomonosov (id1168366758158), and Pierre Bayen (Figure 7) all produced oxygen in experiments in the 17^th and the 18^th century but none of them recognized it as an element, probably since the prevalence at that time of the phlogiston, and their attempts to fit their experimental observations to that theory.

Figure 4: Portrait of English natural philosopher, architect Robert Hooke FRS (1635 - 1703).

Figure 5: Danish scientist, physician, grammarian, and poet Ole Borch (1626 - 1690).

Figure 6: Russian scientist and writer Mikhail Vasilyevich Lomonosov (1711 - 1765).

Figure 7: French chemist and pharmacist Pierre Bayen (1725 - 1798).

Oxygen was first discovered by Carl Wilhelm Scheele (Figure 8) by heating mercuric oxide (HgO). Scheele called the gas fire air because it was the only known supporter of combustion. He wrote an account of this discovery in a manuscript (Treatise on Air and Fire) submitted in 1775. Unfortunately for Scheele his work was not published until 1777. In August 1774, an experiment conducted by Joseph Priestley (Figure 9) sunlight on mercuric oxide (HgO) inside a glass tube, which liberated a gas he named dephlogisticated air. Priestley noted that candles burned brighter in this gas. He even went as far as breathing the gas himself, after which he wrote: "The feeling of it to my lungs was not sensibly different from that of common air, but I fancied that my breast felt peculiarly light and easy for some time afterwards." Priestley published his findings in 1775. Because he published his findings first, Priestley is usually given credit for the discovery of what became known as oxygen.

Figure 8: Swedish chemist Carl Wilhelm Scheele (1742 – 1786). Isaac Asimov called him "hard-luck Scheele" because he made a number of chemical discoveries before others who are generally given the credit.

Figure 9: Portrait (by Ellen Sharples) of British clergyman natural philosopher, educator, and political theorist Joseph Priestley (1733 - 1804).

Interestingly, Lavoisier (Figure 10) claimed to have discovered this new substance independently. However, Priestley visited Lavoisier in October 1774 and told him about his experiment and how he liberated the new gas. Furthermore, Scheele also posted a letter to Lavoisier on September 30, 1774 that described his own discovery. Lavoisier never acknowledged receiving it, however, a copy of the letter was found in Scheele's belongings after his death.

Figure 10: Line engraving (by Louis Jean Desire Delaistre) of the French chemist and biologist Antoine-Laurent de Lavoisier (1743 - 1794) often refereed to as the father of modern chemistry due to his extensive contributions.

Raoul Pictet (Figure 11) showed that by the evaporation of liquid sulfur dioxide (SO₂), carbon dioxide could be liquefied, which in turn was evaporated to cool oxygen gas enough to liquefy it. Pictet reported his results on December 22, 1877. Two days later, Louis Cailletet (Figure 12) announced his own method of liquefying oxygen. In both cases only a few drops could be produced, making analysis difficult. In 1891 James Dewar (Figure 13) was able to produce enough liquid oxygen to study. However, it was the process developed independently by Carl von Linde (Figure 14) and William Hampson (1854 - 1926).

Figure 11: Swiss chemist and physicist Raoul Pierre Pictet (1846 - 1929).

Figure 12: French physicist Louis Paul Cailletet (1832 - 1913).

Figure 13: Scottish chemist and physicist Sir James Dewar FRS (1842 - 1923).

Figure 14: German engineer Carl Paul Gottfried von Linde (1842 - 1934).

Sulfur was known in ancient times and is referred to in the Bible. English translations of the Bible commonly referred to burning sulfur as brimstone, giving rise to the name of fire-and-brimstone sermons, in which listeners are reminded of the fate of eternal damnation that await the unbelieving and unrepentant. It is from this part of the Bible that Hell is implied to smell of sulfur (likely due to its association with volcanic activity). Sulfur ointments were used in ancient Egypt, while it was used for fumigation in Greece. A natural form of sulfur known as shiliuhuang was known in China since the 6^th century BC. However, it was not until 1777 that Lavoisier (Figure 10) convinced the scientific community that sulfur was an element and not a compound.

The element was discovered in 1817 by Berzelius (Figure 15), who found the element associated with tellurium. It was discovered as a byproduct of sulfuric acid production.

Figure 15: Swedish chemist Jöns Jacob Berzelius (1779 - 1848).

Tellurium was discovered in the 18^th century in gold ore from the mines in Zlatna, Transylvania. In 1782 Müller von Reichenstein (Figure 16), the Hungarian chief inspector of mines in Transylvania, concluded that the ore was bismuth sulfide. However, the following year, he reported that this was erroneous and that the ore contained mostly gold and an unknown metal very similar to antimony. After three years of work Müller determined the specific gravity of the mineral and noted the radish-like smell of the white smoke evolved when the new metal was heated. Nevertheless, he was not able to identify this metal and gave it the names aurum paradoxium and metallum problematicum, as it did not show the properties predicted for the expected antimony.

Figure 16: A stamp showing Hungarian mineralogist Franz-Joseph Müller von Reichenstein (1742 - 1825).

In 1789 Kitaibel (Figure 17) also discovered the element independently in an ore from Deutsch-Pilsen which had been regarded as argentiferous molybdenite, but later he gave the credit to Müller. In 1798, the name was chosen by Klaproth (Figure 18) who earlier isolated it from the mineral calaverite.

Figure 17: Hungarian botanist and chemist Pál Kitaibel (1757 - 1817).

Figure 18: Figure. German chemist Martin Heinrich Klaproth (1743 –1817).

Temporarily called radium F, polonium was discovered by Marie Curie and her husband Pierre Curie (Figure 19) in 1898, but it was later named after Marie Curie's native land of Poland. At the time Poland was not an independent country, but partitioned under Russian, Prussian, and Austrian. It was Curie's hope that naming the element after her native land would publicize its lack of independence. Polonium was the first chemical element named to highlight a political controversy.

Figure 19: Pierre (1859 - 1906) and Marie Skłodowska-Curie (1867 - 1934) in their Paris laboratory.

Ever since the early 1960s, the presence of polonium-210 in tobacco smoke has been known. The world's biggest tobacco firms spent over 40 years trying to find ways to remove the polonium-210 without success: even to this day. However, they also never published the results, keeping the facts of the radioactive hazards from the consumer.

Radioactive polonium-210 is contained in phosphate fertilizers and is absorbed by the roots of plants (such as tobacco) and stored in its tissues. Tobacco plants fertilized by rock phosphates contain polonium-210, which emits alpha radiation estimated to cause about 11,700 lung cancer deaths annually worldwide.

First used in Sicily from where it takes its name, the Sicilian process was used in ancient times to get sulfur from rocks present in volcanic regions. The sulfur deposits are piled and stacked in brick kilns built on sloping hillsides, and with airspaces between them (Figure 20). Then powdered sulfur is put on top of the sulfur deposit and ignited. As the sulfur burns, the heat melts the sulfur deposits, causing the molten sulfur to flow down the sloping hillside. The molten sulfur can then be collected in wooden buckets. The sulfur produced by the Sicilian process must be purified by distillation.

Figure 20: Extraction of sulfur by the Sicilian process.

In 1867, sulfur was discovered in the caprock of a salt dome in Louisiana; however, it was beneath quicksand, which prevented mining. In 1894 Herman Frasch (Figure 21), devised a method of sulfur removal using pipes to bypass the quicksand. The process proved successful, but the high cost of fuel needed to heat the water made the process uneconomic until the 1901 discovery of the Spindletop oil field in Texas (Figure 22) provided cheap fuel oil to the region.

Figure 21: German-born American chemist Herman Frasch (1851 - 1914).

Figure 22: Spindletop oil field in Beaumont, Texas.

In the Frasch process three concentric pipes to extract sulfur at high purity directly out of the ground (Figure 23). Superheated steam (160 °C) is pumped down the outermost pipe, which melts the sulfur. Hot compressed air is pumped down the innermost pipe, which serves to create foam and pressure. The resulting molten sulfur foam is then expelled through the middle pipe. The Frasch process produces sulfur with 99.5% purity, which needs no further purification.

Figure 23: Schematic diagram of the Frasch process.

Most of the world's sulfur was obtained using the Frasch process until the late 20^th century, when sulfur recovered from petroleum sources (recovered sulfur) became more commonplace.