Heat Exchanger

Lore & Background

The modern concept of the element oxygen developed over five centuries and included many related discoveries and unsuccessful theories. Multiple people made different contributions to the concept; no one person discovered oxygen. One of the first known experiments on combustion and air was conducted by the 2nd-century BCE Greek writer Philo of Byzantium, who observed water rising into the neck of an inverted vessel over a burning candle. Polish alchemist Michael Sendivogius, writing in 1604, described a substance contained in air, referring to it as 'cibus vitae' ('food of life'), identical with oxygen. He recognized it as the gaseous byproduct released by the thermal decomposition of potassium nitrate. Unaware of Sendivogius's work, John Mayow wrote about a portion of air that provided heat in a fire and the human body, publishing his ideas in 1668 in his work 'Tractatus duo' in the tract 'De respiratione'.

In Their Own Story

Swedish pharmacist Carl Wilhelm Scheele produced oxygen gas by heating mercuric oxide (HgO) and various nitrates in 1771–1772, calling the gas 'fire air' because it was the only known agent to support combustion. On August 1, 1774, British clergyman Joseph Priestley focused sunlight on mercuric oxide contained in a glass tube, liberating a gas he named 'dephlogisticated air'. He noted that candles burned brighter in the gas and that a mouse was more active and lived longer while breathing it. After breathing the gas himself, Priestley 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 in a paper titled 'An Account of Further Discoveries in Air'. French chemist Antoine Lavoisier conducted the first adequate quantitative experiments on oxidation, discrediting the phlogiston theory and proving that the substance discovered by Priestley and Scheele was a chemical element. In one experiment, Lavoisier observed that there was no overall increase in weight when tin and air were heated in a closed container, noting that air rushed in when he opened the container, indicating part of the trapped air had been consumed.

Reader's Guide

Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic activities of autotrophs such as cyanobacteria, chloroplast-bearing algae, and land plants. All eukaryotic organisms, including plants, animals, fungi, algae, and most protists, need oxygen for cellular respiration, a process that extracts chemical energy by the reaction of oxygen with organic molecules and releases carbon dioxide as a waste product. Many major classes of organic molecules in living organisms contain oxygen atoms, such as proteins, nucleic acids, carbohydrates, and fats, as do the major constituent inorganic compounds of animal shells, teeth, and bone. Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms. Common industrial uses of oxygen include production of steel, plastics and textiles, brazing, welding and cutting of steels and other metals, rocket propellant, oxygen therapy, and life-support systems in aircraft, submarines, spaceflight, and diving.

Did You Know?

• Oxygen is the most abundant element in Earth's crust, making up almost half of it in the form of various oxides.
• Dioxygen gas currently constitutes approximately 20.95% molar fraction of the Earth's atmosphere.
• Ozone (O3) strongly absorbs UVB and UVC wavelengths and forms a protective ozone layer at the lower stratosphere.
• Polish alchemist Michael Sendivogius described oxygen as 'cibus vitae' ('food of life') in 1604, properly recognizing it as the gaseous byproduct of decomposing potassium nitrate.
• Antoine Lavoisier first recognized oxygen as a chemical element in 1777 and correctly characterized the role it plays in combustion.