Element Oxygen, O, Non Metal

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Joseph Priestley was generally acknowledged as the discoverer of oxygen. He separated oxygen on August 1, 1774 decomposing mercury (II) oxide by heating it via the sun rays focused on it by powerful lens.

2HgO (t)=> 2Hg + O₂^

However Priestley first did not realize that he discovered a new substance. He supposed that he just separated one of the components. Priestley informed Antoine Laurent Lavoisier about his discovery.

Karl Wilhelm Scheele, the Swedish pharmacist extracted oxygen some time before 1773 (perhaps in 1770) by baking saltpeter with sulphuric acid with subsequent decomposing yielded nitrogen oxide. Scheele called the gas "fire air" because it was the only known supporter of combustion. Scheele published his discovery in 1777.

Lavoisier, who received the information from Priestley and Scheele, interpreted the results and clarified the nature of the discovered gas. He made a great contribution because his observations brought about a re-evaluation of the phlogiston theory and its eventual abandonment.

Oxygen is the most abundant element on the Earth; it accounts for 47.4% by mass of Earth's crust. World's oceans and fresh water consists of enormous quantity, 88.8 mass %, of bound oxygen. Oxygen is the second most common component of the Earth's atmosphere (20.947% by volume), second to nitrogen. Elementary oxygen is the part of more than 1500 of the Earth's crust compounds.

Oxygen is the main biogenic element which is the component of molecules of compounds with functions crucially most important for life: proteins, nucleic acids, carbohydrates and lipids as well as a great number of low-molecular compounds. Oxygen dominates in living organisms (70%). Muscular tissue consists of 16 % oxygen, bone tissue - 28.5 %; the total mass of oxygen in human body equals 43kg. Living organisms of animals and human beings are supplied with free oxygen through the respiratory system) and water (bound oxygen). The oxygen requirement is determined from the level or rate of metabolism, which depends on the body mass and surface, as well as on sex, feeding habits, environment and so on. The ratio of total respiration (or total oxidizing processes) and the total biomass is a very important parameter in ecology.