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2. (Chem.) A poisonous nonmetallic element of the nitrogen group, obtained as a white, or yellowish, translucent waxy substance, having a characteristic disagreeable smell. It is very active chemically, must be preserved under water, and unites with oxygen even at ordinary temperatures, giving a faint glow, -- whence its name. It always occurs compined, usually in phosphates, as in the mineral apatite, in bones, etc. It is used in the composition on the tips of friction matches, and for many other purposes. The molecule contains four atoms. Symbol P. Atomic weight 31.0.

3. (Chem.) Hence, any substance which shines in the dark like phosphorus, as certain phosphorescent bodies.

Bologna phosphorus (Chem.), sulphide of barium, which shines in the dark after exposure to light; -- so called because this property was discovered by a resident of Bologna. The term is sometimes applied to other compounds having similar properties. -- Metallic phosphorus (Chem.), an allotropic modification of phosphorus, obtained as a gray metallic crystalline substance, having very inert chemical properties. It is obtained by heating ordinary phosphorus in a closed vessel at a high temperature. -- Phosphorus disease (Med.), a disease common among workers in phosphorus, giving rise to necrosis of the jawbone, and other symptoms. -- Red, or Amorphous, phosphorus (Chem.), an allotropic modification of phosphorus, obtained as a dark red powder by heating ordinary phosphorus in closed vessels. It is not poisonous, is not phosphorescent, and is only moderately active chemically. It is valuable as a chemical reagent, and is used in the composition of the friction surface on which safety matches are ignited. -- Solar phosphori (Chem.), phosphorescent substances which shine in the dark after exposure to the sunlight or other intense light.

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Phos"phor*yl (?), n. [Phosphorus + -yl.] (Chem.) The radical PO, regarded as the typical nucleus of certain compounds.

Phos"phu*ret (?), n. (Chem.) A phosphide. [Obsoles.]

Phos"phu*ret`ed (?), a. (Chem.) Impregnated, or combined, with phosphorus. [Obsoles.] [Written also phosphuretted.]

Phosphureted hydrogen. (Chem.) See Phosphine.

Pho"tic (?), a. [Gr. fw^s, fwto`s, light.] (Physiol.) Relating to the production of light by the lower animals.

Pho"tics (?), n. (Physics) The science of light; -- a general term sometimes employed when optics is restricted to light as a producing vision. Knight.

Pho"to (?), n.; pl. Photos (&?;). A contraction of Photograph. [Colloq.]

Pho"to- (?). A combining form from Gr. fw^s, fwto`s, light; as, photography, phototype, photometer.

Pho`to*bi*ot"ic (?), a. [Photo- + biotic.] (Biol.) Requiring light to live; incapable of living without light; as, photobiotic plant cells.

Pho`to*chem"ic*al (?), a. [Photo- + chemical.] (Chem.) Of or pertaining to chemical action of light, or produced by it; as, the photochemical changes of the visual purple of the retina.

Pho`to*chem"is*try (?), n. [Photo- + chemistry.] (Chem.) The branch of chemistry which relates to the effect of light in producing chemical changes, as in photography.

{ Pho`to*chro"mic (?), Pho`to*chro*mat"ic (?), } a. Of or pertaining to photochromy; produced by photochromy.

Pho*toch"ro*my (?), n. [Photo- + Gr. &?; color.] The art or process of reproducing colors by photography.

Pho"to*drome (?), n. [Photo- + Gr. &?; to run.] (Physics) An apparatus consisting of a large wheel with spokes, which when turning very rapidly is illuminated by momentary flashes of light passing through slits in a rotating disk. By properly timing the succession of flashes the wheel is made to appear to be motionless, or to rotate more or less slowly in either direction.

Pho`to-e*lec"tric (?), a. [Photo- + electric.] Acting by the operation of both light and electricity; -- said of apparatus for producing pictures by electric light.

Pho`to-e*lec"tro*type (?), n. (Print.) An electrotype plate formed in a mold made by photographing on prepared gelatine, etc.

Pho`to-en*grav"ing (?), n. [Photo- + engraving.] The process of obtaining an etched or engraved plate from the photographic image, to be used in printing; also, a picture produced by such a process.

Pho`to-ep"i*nas`ty (?), n. [See Photo-, and Epinastic.] (Bot.) A disproportionately rapid growth of the upper surface of dorsiventral organs, such as leaves, through the stimulus of exposure to light. Encyc. Brit.

Pho`to*gal`va*nog"ra*phy (?), n. [Photo- + galvanography.] The art or process of making photo-electrotypes. Sir D. Brewster.

Pho"to*gen (?), n. [Photo- + - gen.] (Chem.) A light hydrocarbon oil resembling kerosene. It is obtained by distilling coal, paraffin, etc., and is used as a lubricant, illuminant, etc. [Written also photogene.]

Pho"to*gene (?), n. [See Photogen.] 1. A photograph. [Obsoles.]

2. A more or less continued impression or image on the retina. H. Spencer.

Pho`to*gen"ic (?), a. Of or pertaining to photogeny; producing or generating light.

Pho*tog"e*ny (?), n. [See Photogen.] See Photography. [Obsoles.]