Ō'zo-nŏm'e-try or P, n.

n. The determination of the amount of ozone in the atmosphere.

P, the twelfth consonant, and the sixteenth letter in the order of the English alphabet, is formed by closely compressing the lips, and separating them suddenly with an explosive emission of breath, as in part, pap. P is called a pure mute, because it has no sound. Like the other pure mutes, k and t, it gives an abruptness to the sound which immediately precedes or follows it, according as it is itself final or initial in the syllable, as in imp, play. P is closely related to b and m, all three of these letters representing labial sounds, p being the labial mute, b the labial sonant, and m the labial nasal. P is convertible into b and f, and sometimes into v. The combination ph has the same sound as f, as in philosophy, being equivalent to the Gr. φ. See Principles of Pronunciation, §§ 84, 85.