Occlusion is the property possessed by certain solids, notably some metals, of retaining gases either within the solid or on the surface. There is no chemical combination in the accepted sense.
Oligocene — The Oligocene was the fifteenth geological period, 42,000,000 years ago.
Osmium — Osmium is a blue-white metal element with the symbol Os. It is volatile and very poisonous.
Ounce — The ounce is a unit of measurement of the avoirdupois scale equivalent to 16 drams or 28.350 grams.
Oxidation — Oxidation is the chemical combination of atoms with oxygen atoms to form oxides. In metals, the process appears as rust, iron rust being iron oxide, a molecule formed of iron atoms combined with oxygen atoms.
Oxidize — The term oxidise refers to the chemical reaction of oxidation.
Oxygen — Oxygen is a gaseous element with the symbol O that is partly soluble in water. It is the only gas able to sustain respiration.
Palaeontology — Palaeontology is a branch of biology and geology which deals with fossils. It is divided into palaeozoology and palaeobotany, which respectively have animals and plants as their subject matters.
Pewter — Pewter is an alloy of tin and lead.
PH — pH is a mesurement of acidity or alkalinity in terms of hydrogen ion content.
Phosphate — A phosphate is any salt of phosphorus oxy acids.
Pinchbeck — Pinchbeck is an alloy of 80 percent copper and 20 percent zinc once used for making cheap watch cases, and more recently as a substitute for the more expensive bronze. It was invented by a London watchmaker in the 18th century.
Pleistocene — The Pleistocene (ice age) was the seventeenth geological period, 500,000 years ago. It marked the evolution of tool-making man.
Pliocene — The Pliocene was the sixteenth geological period, 8,000,000 years ago. It marked the modern formation of the continents.
Plutonium — Plutonium is an artificial radioactive metal element with the sumbol Pu.
Polonium — Polonium is a metal radioactive element with the symbol Po.
Potassium Bromate — Potassium bromate is a white, crystalline, water-soluble powder used chiefly as an oxidising agent and as an analytical reagent.
Potassium Bromide — Potassium bromide (bromide) is a white, crystalline, water-soluble powder. It has a bitter, saline (salty) taste and is used in the manufacture of photographic papers and plates and as a sedative.
Potassium Carbonate — Potassium carbonate is a white, granular, water-soluble substance used chiefly in the manufacture of soap, glass and potassium salts.
Potassium nitrate — Potassium nitrate is a white bitter tasting substance used in gunpowder, as an oxidising agent, for pickling meat and in medicine.
Potassium Oxalate — Potassium oxalate is a colourless, crystalline water-soluble substance. It is toxic, and is used as a bleaching agent and in medical tests as an anticoagulant.
Potassium Thiocyanide — Potassium Thiocyanide is a sulphocyanate. It is colourless, easily dissolvable crystals used in dyeing.
Pre-Cambrian — The Pre-Cambrian period was the second geological period. It was the time when the first animal life appeared, about 1,125,000,000 years ago.
Protactinium — Protactinium is a rare actinide element with the symbol Pa.