Ozone
in chemistry, a modification of oxygen existing as a triatomic molecule. It is nearly always present in the atmosphere, apparently as the result of electrical action, and is formed by passing electric sparks into dry air. It and filtration through charcoal, and yields, by this treatment, a white waxy substance known as cerasin, used in the odor, and seems to have all the properties of oxygen, in an enhanced degree, P P, p, the 16th letter and the 12th consonant of the English alphabet is a labial sound, formed by a compression of the anterior part of the lips, as in pull, papa, ap. As a sharp labial it is classed with f, and corresponds to the flat labial b. Phas but one sound in English, except when in combination with h it forms the digraph ph, which is as f, and occurs in words derived from the Greek. In the case of many words derived from the Greek, initial p is not sounded, as in pneumatics, psalm, psalter, pterodactyl. It is sometimes, but rarely, silent in the middle of a word, as in receipt. P repreof a word, as in receipt. Prepresents the Latin post = after; as p. m.= post meridiem = after noon; p. s. postscript, etc.; in music for piano = softly.
As a symbol, P was formerly used:
In numerals: To denote 400, and with a dash over it, to denote 400,000.