PHOTIUS 



Parker, and Robinson process 

 phosphate is converted directly 

 into phosphorus by means of an 

 electric furnace. 



Phosphorus is a pale yellow 

 waxy-looking solid which readily 

 takes fire when exposed to the 

 air. It is converted into another 

 variety known as red phosphorus 

 by heating to a temperature of 

 between 240 to 250 C. for a time. 

 It is this variety which is used in 

 the manufacture of matches. Phos- 

 phorus is also used in the prepara- 

 tion of vermin-killers, phosphor- 

 bronze, and in the preparation of 

 certain organic compounds. (See 

 Phosphoric acid.) 



Acute poisoning by phosphorus 

 has occurred from taking rat- 

 poison, and among children from 

 sucking match-heads. From one 

 to two grains are likely to be fatal. 

 When swallowed, the poison causes 

 a garlic -like taste in the mouth and 

 odour in the breath. Pain, vomit- 

 ing, and diarrhoea follow in from 

 a quarter of an hour to several 

 hours. Sometimes the symptoms 

 become steadily worse, and de- 

 lirium, coma, and convulsions pre- 

 cede death. Treatment consists in 

 washing out the stomach, or giving 

 copper sulphate as an emetic. 

 Fatty material, such as milk, 

 should not be given. 



Photius (c. 820-891). Byzan- 

 tine scholar and prelate. Born at 

 Constantinople of a distinguished 

 family, he became captain of the 

 imperial bodyguard and secretary 

 of state under Michael III. Al- 

 though a layman, he was appointed 

 patriarch of Constantinople, 857, 

 deposed 867, reinstated 876, again 

 deposed and banished 886. He 

 died in exile in Armenia. During 

 his second patriarchate the breach 

 between the eastern and western 

 Churches became complete. 



Photius rendered great service 

 to classical scholarship by two 

 works, both extant in more or less 

 complete form: (1) Bibliotheca 

 or Myriobiblos, containing a de- 

 scription of 280 works by Greek 

 theological, historical, medical, 

 and miscellaneous writers, together 

 with abstracts of the same, of vary- 

 ing length, accompanied by shrewd 

 literary criticisms. It is curious 

 that the poets are entirely omitted. 

 The Bibliotheca is especially valu- 

 able as containing specimens of 

 works, the originals of which are 

 in many cases entirely lost ; (2) a 

 lexicon, in alphabetical order, of 

 the words occurring in the Greek 

 orators and historians. The first 

 vol. of an Eng. trans., by J. H. 

 Freese, appeared in 1920. 



Photo-chemistry. Branch of 

 chemistry which deals with chemi- 

 cal changes due to the action of 



6123 



light. If a mixture of chlorine and 

 hydrogen is kept in the dark, rib 

 chemical combination takes place, 

 but if a beam of light be allowea 

 to fall ort the glass vessel cbritaining 

 the mixture, Chemical combination 

 takes place with explosive vio^ 

 lence, hydrochloric acid being 

 formed. Light also " reduces " 

 many chemical salts, especially in 

 the presence of organic substances. 

 This fact is the basis of the opera- 

 tions of photography. The silver 

 haloids, i.e. the bromide, iodide, 

 and chloride of silver, are particu- 

 larly sensitive to light, and these 

 are used for the sensitive portion 

 of photographic plates and papers. 



Many other substances are sen- 

 sitive to light, and some of these 

 are employed also in photography. 

 Light-sensitive iron salts form the 

 basis of the ferro-prussiate paper 

 devised by Herschel in 1840, and 

 largely employed for making blue- 

 prints in engineering workshops. 

 Platinum salts sensitive to light 

 form the basis of platinotype. 

 Another class of photochemical 

 action is seen in Niepce's discovery 

 that thin films of bitumen ex- 

 posed to light become insoluble in 

 the usual solvents, such as turpen- 

 tine. Similarly gelatin impreg- 

 nated with ammonium bichromate 

 becomes insoluble in water after 

 exposure to light. The last named 

 reaction is the basis of the carbon 

 process of photography. In addi- 

 tion to the photochemical action 

 which has been referred to, there 

 are other theories involved in 

 the explanation of photographic 

 action. Two that may be men- 

 tioned are the molecular strain 

 theory put forward by Professor 

 Chunder Bose, and the ionization 

 or electron theory elaborated by 

 Professor Joly. See Chemistry ; 

 Photography. <f 



Photo-copy Paper. Paper, 

 rendered sensitive to light with 

 iron salts, and used for the making 

 of copies of drawings or tracings 

 such as engineers' and architects' 

 plans. They are of various kinds. 

 Ferro-prussiate or blue-print 

 papers, sensitised with iron am- 

 monium citrate and potassium 

 ferricyanide, yields a copy in white 

 lines on a blue ground. Ferro- 

 gallic paper, prepared with iron 

 perchloride and gallic and tartaric 

 acids, yields one in blue-black lines 

 on a white ground. With both, 

 the only manipulation is to wash 

 the exposed papers in water. See 

 Photography. 



Photo-Engraving. Process of 

 making printing blocks from pen- 

 and-ink . drawings and other line 

 originals by photographic methods. 

 It consists essentially in forming 

 on a zinc plate an image of the de- 



PHOTOGRAPHIC 



sign; consisting of material which is 

 an dbstacle or " resist " to the 

 actidri of an etching fluid. The 

 flarts df the metal representing the 

 line's of the drawing are thus left 

 standing in relief on the etched 

 metal plate. The latter, when 

 mounted on a wood block, is known 

 as a line block or zinco, and is 

 suitable for printing with type in a 

 typographic press. 



The method of preparing such 

 blocks consists in: (1) making a 

 photographic negative of the 

 original to the required scale in a 

 camera ; (2) printing from the 

 negative on to sensitised zinc ; (3) 

 converting the impression on the 

 zinc into a resist capable of with- 

 standing the acid used in (4) 

 etching the zinc plate. The nega- 

 tive is most frequently made by 

 the wet collodion process, although 

 of late years dry -plates have come 

 into use. It requires to be one in 

 which the lines of the original are 

 represented by clear glass and the 

 ground by dense deposit. For 

 printing from it on to zinc a solu- 

 tion of albumen (white of egg) and 

 bichromate of ammonium is 

 poured on the zinc plate, which is 

 whirled to leave a thin sensitive 

 coating and quickly dried over a 

 gas-ring. The sensitised plate and 

 the negative are pressed film to 

 film in a strongly made printing- 

 frame and exposed, usually to arc 

 light. The exposure renders the 

 albumen forming the lines insoluble 

 in water and also retentive of 

 greasy ink. 



The plate is then inked all over 

 very thinly with lithographic 

 printing ink, which is thus fixed 

 on the lines ; that on the ground 

 is cleared off by immersing the 

 plate in water and rubbing it with 

 cotton -wooL The thinly inked 

 lines remaining on the plate do not 

 suffice to protect the metal 

 beneath them from the etching 

 liquid, but require to be reinforced 

 before etching is begun, and also 

 by successive operations as etching 

 is done, in order to prevent the 

 etching liquid from attacking the 

 sides of the lines. Unless means 

 are taken to prevent this sideway 

 etching action or undercut, as it 

 is called the lines will be broken 

 and ragged. See Engraving; 

 Photo-Lithography ; Process. 



Photographic Society, ROYAL. 

 The leading photographic society 

 in Great Britain, founded in 1853. 

 It has numbered among its pre- 

 sidents scientists like J. Glaisher 

 and Sir W. de W. Abney. Meetings 

 are held weekly from Oct. to June, 

 and papers are read on the tech- 

 nical and artistic aspects of photo- 

 graphy. The offices are at 35, 

 Russell Square, W.C. 



