Discovery of Oxygen

Oxygen was discovered in 1774 by Joseph Priestley in England and two years earlier, but unpublished, by Carl W. Scheele in Sweden.

Scheele heated several compounds including potassium nitrate, manganese oxide, and mercury oxide and found they released a gas which enhanced combustion.

Priestley heated mercury oxide, focusing sunlight using a 12-inch ‘burning lens’ – a very large magnifying glass – to bring the oxide to a high temperature. Priestley’s lens was smaller than the enormous one used by Antoine Lavoisier in his investigation of carbon. (Shown on Chemicool’s carbon page.)

Totally unexpectedly, the hot mercury oxide yielded a gas that made a candle burn five times faster than normal. Priestley wrote: “But what surprised me more than I can well express was that a candle burned in this air with a remarkably vigorous flame. I was utterly at a loss how to account for it.” ⁾

In addition to noticing the effect of oxygen on combustion, Priestley later noted the new gas’s biological role. He placed a mouse in a jar of oxygen, expecting it would survive for 15 minutes maximum before it suffocated. Instead, the mouse survived for a whole hour and was none the worse for it.⁾

Antoine Lavoisier carried out similar experiments to Priestley’s and added to our knowledge enormously by discovering that air contains about 20 percent oxygen and that when any substance burns, it actually combines chemically with oxygen.

Lavoisier also found that the weight of the gas released by heating mercury oxide was identical to the weight lost by the mercury oxide, and that when other elements react with oxygen their weight gain is identical to the weight lost from the air.

This enabled Lavoisier to state a new fundamental law: the law of the conservation of matter; “matter is conserved in chemical reactions” or, alternatively, “the total mass of a chemical reaction’s products is identical to the total mass of the starting materials.”

In addition to these achievements, it was Lavoisier who first gave the element its name oxygen. 

The word oxygen is derived from the Greek words ‘oxys’ meaning acid and ‘genes’ meaning forming.

Before it was discovered and isolated, a number of scientists had recognized the existence of a substance with the properties of oxygen:

In the early 1500s Leonardo da Vinci observed that a fraction of air is consumed in respiration and combustion.

In 1665 Robert Hooke noted that air contains a substance which is present in potassium nitrate [potassium nitrate releases oxygen when heated,] and a larger quantity of an unreactive substance [which we call nitrogen].

In 1668 John Mayow wrote that air contains the gas oxygen [he called it nitroarial spirit], which is consumed in respiration and burning.

Mayow observed that: substances do not burn in air from which oxygen is absent; oxygen is present in the acid part of potassium nitrate [i.e., in the nitrate - he was right!]; animals absorb oxygen into their blood when they breathe; air breathed out by animals has less oxygen in it than fresh air.

Discovery of Hydrogen

A favorite school chemistry experiment is to add a metal such as magnesium to an acid. The metal reacts with the acid, forming a salt and releases hydrogen from the acid. The hydrogen gas bubbles up from the liquid and students collect it in small quantities for further experiments, such as the ‘pop-test.’

The first recorded instance of hydrogen made by human action was in the first half of the 1500s, by a similar method to that used in schools now. Theophrastus Paracelsus, a physician, dissolved iron in sulfuric acid and observed the release of a gas. He is reported to have said of the experiment, “Air arises and breaks forth like a wind.” He did not, however, discover any of hydrogen’s properties.

Turquet De Mayerne repeated Paracelsus’s experiment in 1650 and found that the gas was flammable. Neither Paracelsus nor De Mayerne proposed that hydrogen could be a new element. Indeed, Paracelsus believed there were only three elements – the tria prima – salt, sulfur, and mercury – and that all other substances were made of different combinations of these three. (Chemistry still had a long way to go!)

In 1670, English scientist Robert Boyle added iron to sulfuric acid. He showed the resulting (hydrogen) gas only burned if air was present and that a fraction of the air (we would now call it oxygen) was consumed by the burning.

Hydrogen was first recognized as a distinct element in 1766 by English scientist Henry Cavendish, when he prepared it by reacting hydrochloric acid with zinc. He described hydrogen as “inflammable air from metals” and established that it was the same material (by its reactions and its density) regardless of which metal and which acid he used to produce it.⁽¹⁾ Cavendish also observed that when the substance was burned, it produced water.

French scientist Antoine Lavoisier later named the element hydrogen (1783). The name comes from the Greek ‘hydro’ meaning water and ‘genes’ meaning forming – hydrogen is one of the two water forming elements.

In 1806, with hydrogen well-established as an element, English chemist Humphry Davy pushed a strong electric current through purified water.

He found hydrogen and oxygen were formed. The experiment demonstrated that electricity could pull substances apart into their constituent elements. Davy realized that substances were bound together by an electrical phenomenon; he had discovered the true nature of chemical bonding.