146 



PHOT1US 



PIIOToi.i: APMY 



phoric acid. II. I'" P.O. + 2H.O), tctraliasic, 



iditained by acting II|KIII Ica.l pyrophosphate with 

 sulphuretted hydrogen, the lead salt being pre- 

 ttied fr -.la pyrophosphale, which is obtained 



I iy heating such a phosphate as Na_.IIP<> 4 , of 

 which two molecule- give off one of water and 

 form Na,!',! > r ; phosphoric or orthophosphoric acid, 

 HjP 4 , nifi.-i.-ic. prepared by iMiiling P ; ( ) 5 in water, 

 or from bODA-MB and sulphuric acid ; the l.-u-t 

 iiameil acid has thn-e sets of salts, the hydrogen 



in the acid lieing ic 01 less comjdetely replaced 



\ HJTO VUIPO,. and Na,P0 4 , which are 

 obtained by more or less completely neutralising 

 phosphoric acid with soda. 



The discovery of phosphoric acid was made in 

 1740 by Marggraf; the discovery of its true 

 chemical nature is, however, due to Lavoisier, and 

 that of it.s various modifications and its poly- 

 ha-irity to the investigations of C.rah.-un. The 

 salts of phosphoric acid are phosphates ; and they 

 are of great value, when in a soluble form or 

 when they can In-come soluble through weather 

 ing, UK manures (see M AM-KKI. Of late years 

 mineral phosphates have been largely worked 

 up: and a new source of phosphatic manure has 

 become available in the alkaline slag of the 

 Thomas (.'ilchrist process, whereby the phosphorus 

 is removed from iron by means of lime. 



Phosphorus combines with hydrogen in three 

 proportions to form phosphuretted hydrogen gas, 

 PH.,: liquid phosphide of hydrogen, 1\.H 4 ; and 

 solid phosphide of hydrogen, P,1L. Of these the 

 liist alone requires notice in these i.ages. There 

 are various processes for obtaining the gas, one of 

 the simplest lieing by liiling fragments of phos- 

 phorus HI a concentrated solution of hyd rated 



potash, in which i-a.se hypophosphite of ]iotAsh is 

 formed, while phosph melted hydrogen gas is 

 extricated. The reaction is explained hy the 



equation 4P + 3KHO t- :l.f) = 3KPO.,H, +' PH,. 

 The g.-Ls thus evolved is colourless, possesses a 

 characteristic fwtid odour, and has the remarkable 

 property of taking lire spontaneously in atmo- 

 spheric air or in oxygen gas, with the production 

 of anhydrous mctaiiliosphoric acid and water. 

 There is reason to lielicve that /" i-j'ftli/ /mn phos 

 phuretted hydrogen ^a- iloes not possess the power 

 of igniting s|M>iitaiieous!y, and that the self-light- 

 ing gas always contains n minute quantity of the 

 vapour of the liquid phosphide, PJ1 4 . The 

 luminous phenomenon known as Ignis Katuus ( <|.v.) 

 has IM-CII refci red to tin- natural evolution of the 

 gas. The com|M>iinds of phosphorus with sulphur, 

 chloiinc, iiMline, bromine, \c. are not of practical 

 importance. 



I'liosphoriis is rarely employed in medicine as a 

 nervoii- stimulant, in consei|iience of ii- poisonou- 

 plop -i lies. The svmptoms induced by this poi-on 

 are those of acnle inlliimmation of the stomach and 

 Iniwels ; the treatment is the administration of 

 lar^-e quantities of mild demulcent fluids, ami of 

 neia. Dilute phosphoric acid is included in 

 the Hiitish l'liarmaco|Hi-ia. but in not very iniirli 

 i-mployed. It may IK- pn-,,-1 ilied in much the same 

 as those in which sulphuric and nitric acids 

 an- employed, and is less likely to disturb tin- 

 live t'linciioiis. if employed for a long period, 

 than the oilier mineral acids. It has also been 

 iimended, when prujierly diluted, as a -i-rvice. 

 able acidulated drink for assuaging tin- thirst in 

 diahetc*. It may IM- iirc-crilied in half-dnu-hm 

 dunes, l-'or miHlicinal phosphates. -,-,- Svitup. 



I'holllls. Patriarch .if Constantinople at a 

 critical |N-iio.l, was a memlier of a patrician family 



of < 'oiislaiitinople. ami wiis Imrn in tl arly part 



of the !lth century. I >is| in^nislied by his abilities, 

 he served in various im|K>itant public offices, and 

 secured the favour of the Hnijieror Michael and bis 



powerful favourite llardas. The patriarch Ignatius. 

 having in vain tried to correct the vices of the 

 profligate emperor, was de|Hise<l and banished. 

 I'hotiiis, although a layman, was appointed in In- 

 stead. hniTied in a few successive days through all 

 the stages of sacied orders, and llnallv installed a- 

 patriarch. Two successive councils of bishops under 

 court influence conlirmed the deposition of Ignatius 

 and the election of I'hotiiis. In Sii-J, ho\\e\ei. 

 Pope Nicholas I. (q.v.) called a new council at 

 Uome, which declared I'hotiiis' election nm-iinon- 

 ical and invalid, de)K>sc<l and e\con ..... inicat<-d him 

 and reinstated Ignatius in his see. lleing sup 

 porteil. however, by the emperor, Plmtiiis retained 

 possession, and retaliated on the pope by assembling 

 a council ai Constantinople in K67, in which lie 

 raised a controversy of doctrine and discipline 

 lietween the churches of the Kast ami \\esi them 

 selves. In all these doctrinal differences the 



Council colidemneil the \\esteril Church. e\com 



iimnicated Nicholas and his abettors, and with 

 drew from the communion of the sec of Home. 

 Michael being put to death bv llosiltus the Maci- 

 (Ionian in Mi7, Photius was banished to C\ pills, 

 and Ignatius reinstated: and in 8(i!) the eighth 

 general council, at which Po|ie Adrian ll.'s legates 

 presided, was assembled at Constantinople. Photiu- 

 was iigKin condemned and excommunicated, and 

 the intercommunion of the churches restored. Yei 

 on the death of Ignatius Photius was rcappojnled 

 to the patriarchate. In 87!) lie assembled a new 

 c ..... icil ut Consiaiitinople. renewed the charge 

 against the \Vc-tcrn Churrh, and erased from the 

 creeil in the article on the Procession of the Holy 

 (ihost the word ///./. (see Sl-IHIT). The sepaia- 

 tioli of the churches, however, was not completed 

 till the time of Michael Ccrulaiius i see C, I:KKK 

 ('lit HCII ). Photius was linally dejirived, and exiled 

 to Armenia by I.eo. the son of Ititsiliiis. in 880, and 

 ilied soon afterwards, probably in MM. His chief 

 remains are MynobMo*, called also /.'/////<///<.- 

 Biiinniary n-\iew of -'7!t works which Photius Imd 

 read, many of which are now In-l ; .-i l.i.iii-nn : the 

 .\IIIIIIII-IIHIIH, which is a collection of the acts and 

 decrees of the councils mid ecclesiastical lav 

 the emperois : several minor theological treat; 

 and a collection of letters, many of them cMremeU 



, 



interesting iinil elegant. See liergenriithei 's mono 

 69). 

 the art of pro<lucing |iicture 



graph 



restng iin 

 h on Pho 



tius ( 1869). 



by means of the action of light on sensitised sur- 

 faces. It is usual to regard the obseivation by 

 the alchemists of the li'ith century that ].iui 

 Curiii n or Horn Silver (native chloride of silver) 

 is blackened on exposure to light, a.s the first 

 chemical step in the history of jiliotography, while 

 the foundation of photographic optic- was laid 

 by Delhi Porta in the invention of the camera 

 ob.-ciira i I ."!!() at a s,, mew hat earlier period. This 

 |iropert\ of chloiide of silver, and also the darken 

 ing of nitrate of silver by light in the presence of 

 organic matter, con-titute the leading facts on 

 which the science of photography is based. In 

 1777 the fatuous Swedish chemist Scheele found. 

 by expeiiment, that H ..... Silver was blackened 

 quickest at the violet end of the solar spectrum. 

 thus proving that the ra\s ol light are not all 

 alike chemically active. A quarter of n century 

 later Hitter of .b-na demonstrated the existence 

 of chemically active non-visible rays beyond the 

 violet rays of the spectrum. 



The honour of having lieen the first to produce 

 pictures by the action of light on a sensitive sur- 

 face is now very generally conceded to Thomas 

 Wedgwood, an account of whose researches was 

 published in 1802 in the ././// nf >/,* 1,'m/n/ 

 limHtiilinii, under the title. 'An Account of a, 

 Method of copying Paintings ti|>on Class, and of 



