In 1774, Joseph Priestley discovered the oxygen released by heating mercuric oxide(21908-53-2), although he did not identify the gas as oxygen. Rather, Priestly called it "dephlogisticated air", as that was the paradigm that he was working under at the time. Lavoisier identified this "dephlogisticated air" as "oxygen" due to the acidic compounds that the gas produced. This is why the textbook account of the discovery of oxygen is inaccurate in the sense that it is really impossible to answer who "discovered" oxygen. This was, however, one of the major milestones of chemistry.

Before Priestly, oxygen had been discovered by the Swedish chemist Carl Wilhelm Scheele some time before 1773, by the same method as Priestly. However, Priestly's discovery was published already in 1775 and Scheele's not until 1777, which is claimed to be because of a very long delay on the part of the publisher.

The Mercuric oxide, also known as Montroydite, is an organic compound with the formula HgO. It belongs to the product category of Inorganics. Its EINECS registry number is 244-654-7. With the CAS registry number 244-654-7, its IUPAC name is oxomercury.

Physical properties of Mercuric oxide: (1)H-Bond Donor: 0; (2)H-Bond Acceptor: 1; (3)Rotatable Bond Count: 0; (4)Exact Mass: 217.965541; (5)MonoIsotopic Mass: 217.965541; (6)Topological Polar Surface Area: 17.1; (7)Heavy Atom Count: 2; (8)Formal Charge: 0; (9)Complexity: 2; (10)Isotope Atom Count: 0; (11)Defined Atom StereoCenter Count: 0; (12)Undefined Atom StereoCenter Count: 0; (13)Defined Bond StereoCenter Count: 0; (14)Undefined Bond StereoCenter Count: 0; (15)Covalently-Bonded Unit Count: 1.

Preparation: The red form of HgO can be made by heating Hg on oxygen at roughly 350 °C, or by pyrolysis of Hg(NO₃)₂. The yellow form can be obtained by precipitation of aqueous Hg²⁺ with alkali. The difference in colour is due to particle size, both forms have the same structure consisting of near linear O-Hg-O units linked in zigzag chains with an O-Hg-O angle of 108°.

Uses of Mercuric oxide: HgO is sometimes used in the production of mercury as it decomposes quite easily. When it decomposes, oxygen gas is generated. It is also used as a material for cathodes for mercury batteries.

When you are using this chemical, please be cautious about it as the following:
This chemical that at very low levels can cause damage to health. It may present an immediate or delayed danger to one or more components of the environment. In addition, it is very toxic by inhalation, in contact with skin and if swallowed. You should keep it away from food, drink and animal feeding stuffs. After contact with skin, you should wash immediately with plenty of ... (to be specified by the manufacturer). In case of accident or if you feel unwell seek medical advice immediately (show the label where possible).

You can still convert the following datas into molecular structure:
(1)Canonical SMILES: O=[Hg]
(2)InChI: InChI=1S/Hg.O
(3)InChIKey: UKWHYYKOEPRTIC-UHFFFAOYSA-N

The toxicity data is as follows: