,transcrib]'s ,note ,9 ! ,pla9 ,text v]sion ( ?is e,book1 sup]scripts are indicat$ by 1 subscripts by 1 italics by pair$ und]scores1 & boldface by pair$ equals signs4 ,und]l9+ 9 ! adv]tisem5t at ! end ( ! book is indicat$ by pair$ und]scores1 n di/+ui%$ f italics4 ,! 8,we/m9/]0 ,s]ies ,,glass ,,manufacture ,,glass ,,manufacture ,,by ,,walt] ,,ros5ha9 ,b4,a4 ,b4,c4,e4 ,,sup]9t5d5t ,,( ,,! ,,dep>tm5t ,,( ,,metallurgy ,,& ,,metallurgical ,,*emi/ry ,,at ,,! ,,national ,,physical ,,laboratory ,illu/ration ,,new ,,york ,d4 ,,van ,,no/r& ,,company #bc ,,murray ,,& #bg ,,w>r5 ,,/reets #aijh ,,bradbury1 ,,agnew1 ,,co4 ,,ld41 ,,pr9t]s1 ,,london ,,& ,,tonbridge4 ,,preface ,! pres5t volume on ,glass ,manufacture has be5 writt5 *iefly = ! b5efit ( ^? :o are us]s ( glass1 & !re=e makes no claim to be an adequate guide or help to ^? engag$ 9 glass manufacture itself4 ,= ?is reason ! acc\nt ( manufactur+ processes has be5 kept z non-te*nical z possible2 no detail$ draw+s ( plant or appliances h be5 giv51 & only a few illu/rative diagrams h be5 introduc$ = ! purpose ( avoid+ l5g?y v]bal descriptions4 ,9 describ+ ea* process ! object 9 view has be5 to give an insight into ! rationale ( ea* /ep1 s f> z x is kn[n or und]/ood1 & ?us to indicate ! possibilities & limitations ( ! process & ( its result+ products r ?an to provide a detail$ guide to ! te*nique ( ! v>i\s op]ations4 ,! practical aim ( ! book has fur!r be5 safegu>d$ by ! fact t ! processes describ$ 9 ^! pages are1 ) ! exception ( ^? describ$ z obsolete1 to ! au?or's def9ite k1 9 comm]cial use at ! pres5t "t4 ,= ?is reason _m app>5tly +5i\s & beautiful processes describ$ 9 e>li] books on glass h n be5 m5tion$ "h1 s9ce ! au?or c\ld f9d no trace ( _! employm5t beyond ! records ( ! v>i\s pat5ts involv$4 ,on ! o!r h& ! read] mu/ be w>n$ to be> 9 m9d t ! peculi> conditions ( ! glass manufactur+ indu/ry h l$ to ! practice on ! "p ( manufactur]s ( keep+ _! processes z secret z possible1 s t ! task ( ! au?or :o w\ld give an accurate acc\nt ( ! be/ mod]n processes us$ 9 any giv5 dep>tm5t ( ! indu/ry is beset ) great difficulties4 ,! au?or has endeav\r$ to /e] ! be/ c\rse op5 to him "u ^! circum/ances1 & he w\ld appeal to ! paucity ( glass lit]ature 9 ! ,engli% language z evid5ce ( ! difficulty to :i* he ref]s4 ,9 addition to ^! difficulties1 :i* arise l>gely f consid]ations ( a comm]cial nature1 ! writ] ( a book on glass is fur!r confront$ ) te*nical difficulties ( no inconsid]able ord]4 ,z already indicat$1 ! aim ( ! pres5t au?or has be5 to describe processes f ! po9t ( view ( pr9ciples & me?ods r ?an z m]e rule-(-?umb descriptions ( manufactur+ manipulations1 b 9 do+ ?is he is met at e turn by ! fact t f ! sci5tific side ! great] "p ( ! field ( glass manufacture is a 8t]ra incognita40 ,9 mak+ ?is /atem5t ! lab\rs ( _m em95t sci5tific work]s are by no means =gott51 b ! entire field is s l>ge & beset ) su* great exp]im5tal difficulties t ev5 ! lab\rs ( a li/ ( inve/igators t includes ! names ( ,fraunh(] & ,f>aday1 ,/okes1 ,hopk9son1 ,abb & ,s*ott1 h result$ 9 little m ?an an accumulation ( empirical data :i*1 :ile !y h be5 productive ( great direct practical results1 h left ! sci5ce ( glass /ill 9 a v elem5t>y condition4 ,to take two examples 9 illu/ration ( ?is fact we may m5tion ! "q ( ! connection betwe5 *emical composition & any ( ! physical prop]ties ( glass1 su* z refraction & disp]sion ( light1 & on ! m me*anical side ! "q :y all processes1 su* z roll+ or m\ld+1 :i* involve ! contact ( hot glass ) metal result 9 a r\gh5+ ( ! glass surface4 ,! =m] "q has be5 /udi$ by sev]al ( ! inve/igators nam$ above1 ,s*ott & ,abb hav+ p>ticul>ly devot$ an enorm\s am\nt ( lab\r & money to ! /udy ( ! "q ) results :i* h prov$ disappo9t+ f ! sci5tific po9t ( view4 ,by prolong$ exp]im5t+ & ! employm5t ( a co/ly sy/em ( trial & error an important s]ies ( novel & useful glasses has be5 produc$ by ^! work]s1 b no law by ^: aid ! optical prop]ties ( a glass ( giv5 *emical composition c\ld be pr$ict$ has yet be5 discov]$1 & z a summ>y ( ! kn[n facts only ! vague/ g5]al pr9ciples are available = ! guidance ( ^? :o wi% to produce glasses ( def9ite prop]ties4 ,! same applies 9 a simil> degree to mo/ ( ! o!r prop]ties ( glass1 ) ! exception1 p]haps1 ( d5sity & !rmal expansion2 attempts to g5]alise f ! kn[n data ( a limit$ numb] ( glasses g5]ally meet ) unqualifi$ failure4 ,! conclusion :i* "o is =c$ to admit is t ! fundam5tal pr9ciples und]ly+ ! nature & con/itution ( glasses h yet to be discov]$4 ,a /udy ( ! o!r "q m5tion$ above z an example ( ! limitations ( our k leads to ! same conclusion2 an almo/ endless succession ( inv5tors h busi$ !mselves ) devices = ov]com+ ! r\gh5+ action ( roll]s & m\lds ^u glass1 b )\t any real success4 ,a long li/ ( o!r examples ( ! same k9d c\ld be giv51 our k ( ! physical & *emical pr9ciples und]ly+ _m ( ! ph5om5a met ) 9 glass manufacture be+ deplorably defici5t4 ,x w ?us be se5 t to write a truly sci5tific acc\nt ( glass manufacture is at ! pres5t "t impossible1 & ! read] is ask$ to be> ?is 9 m9d if he %\ld f9d ! *emical or physical explanations giv5 9 ?is book less frequ5t or less adequate ?an c\ld be desir$4 ,hav+ dwelt some:at emphatically on ! limitations ( our pres5t sci5tific k z appli$ to glass manufacture1 x is p]haps sc>cely necess>y at ! pres5t "t to emphasise ! fact t ?is /ate ( affairs %\ld act z ! /ronge/ inc5tive to fur!r inve/igation ( ! :ole subject4 ,! difficulty1 h[ev]1 lies 9 ! fact t su* inve/igation c sc>cely be c>ri$ on by volunt>y work]s 9 ord9>y laboratories1 b mu/ be und]tak5 ) ! active help ( glass manufactur]s at _! works4 ,glass is ess5tially a sub/ance t _c be satisfactorily h&l$ 9 small quantities1 p>ticul>ly s f> z all ! ph5om5a connect$ ) its production & manipulation :ile hot are conc]n$2 ! influ5ces ( conta9+ vessels1 ( furnace gases & ( rapid cool+ are all enorm\sly exagg]at$ if ounces in/ead ( hundr$weights or tons ( glass are us$ = exp]im5tal purposes1 & ^! influ5ces & o!rs ( ! same nature vitally affect all ! results ( small-scale laboratory op]ations4 ,! progress ( our sci5tific k ( glass--& ! consequ5t developm5t ( ! glass indu/ry f its pres5t /ate :]e rule-(-?umb & 8practical exp]i5ce0 /ill hold excessive sway--lies 9 ! h&s ( ^? conc]n$ 9 ! indu/ry itself4 ,x mu/ be admitt$ t to und]take su* "w involves ! exp5diture ( mu* "t & money on ! "p ( a manufactur]1 :ile ! field is s l>ge & ! problems s complicat$ t any adequate return _c be promis$ = ! imm$iate future2 on ! o!r h& ! v size ( ! field & ! difficulty ( ! problems (f]s ! promise ( ! greate/ ultimate rew>d2 a really important sci5tific discov]y 9 connection ) glass w\ld be c]ta9 to br+ 9 its tra9 indu/rial developm5ts ^: limits x is impossible to =esee4 ,! indu/rial success ( ! glass-works ( ,s*ott 9 ,j5a is (t5 quot$ z a brilliant example ( comm]cial success result+ f purely sci5tific inve/igations 9 ?is actual field2 an example ( /ill great] magnitude is furni%$ by ! success ( ! anil9e dye works ( ,g]many :i* are built up on purely sci5tific a*ievem5ts4 ,! glass indu/ry z a :ole1 supply+ "s ( ! absolute necess>ies ( mod]n life1 %\ld be capable ( (f]+ ! greate/ rew>ds to success1 & ! example ( o!r indu/ries has %[n t ultimate success is b\nd to rew>d prop]ly-conduct$ & p]sev]ant sci5tific rese>*4 ,n[h]e is ?is m urg5tly ne$$ ?an 9 ! :ole field ( glass manufacture4 ,! au?or is indebt$ to ,mr4 ,w4 ,c4 ,hancock = valuable assi/ance 9 ! read+ ( pro(s & v>i\s sugge/ions 9 connection ) ! cont5ts ( ?is book4 ,,table ,,( ,,cont5ts ,,page ,,preface v ,,*apt] ,i4 ,,! ,,physical ,,& ,,*emical ,,prop]ties ,,( ,,glass4 ,def9ition ( ! t]m 8,glass0--,amorph\s /ructure ! common feature ( all vitre\s bodies--,glass a congeal$ fluid--,glasses n def9ite *emical comp\nds b complex solutions--,range ( *emical composition available = glass-mak+--,consid]ations gov]n+ *emical composition--,influ5ce ( composition on physical prop]ties--,*emical /ability ( glass-- ,p]man5ce ( glass surfaces--,action ( wat]1 acids1 & alkalies on glass--,action ( light on glass p4 #a ,,*apt] ,,ii4 ,,! ,,physical ,,prop]ties ,,( ,,glass4 ,me*anical prop]ties3 t5sile /r5g?1 cru%+ /r5g?1 ela/icity1 ductility1 & h>dness--,!rmal prop]ties ( glass3 !rmal endurance1 coeffici5t ( expansion1 !rmal conductivity--,!rmomet] glass--,electrical prop]ties ( glass--,transp>5cy & col\r ( glass p4 #ah ,,*apt] ,,iii4 ,,! ,,raw ,,mat]ials ,,( ,,glass ,,manufacture4 ,g5]al consid]ations--,*emical purity1 moi/ure1 & physical condition1 con/ancy ( quality--,s\rces ( silica1 s& & s&/one--,felsp>--,s\rces ( alkali3 ,soda a% 7c>bonate ( soda71 salt-cake 7sulphate ( soda71 pe>l a% 7c>bonate ( pota%7--,alkali nitrates--,natural m9]als conta9+ alkalies--,s\rces ( o!r bases3 ,lime1 *alk1 lime/one1 slak$ lime-- ,gypsum 7sulphate ( lime7--,b>ium comp\nds--,magnesia & z9c--,lead oxide1 r$ lead--,alum9ium1 manganese1 ars5ic--,c>bon--,coke1 *>coal1 an?racite coal p4 #ce ,,*apt] ,,iv4 ,,crucibles ,,& ,,furnaces ,,= ,,! ,,fusion ,,( ,,glass4 ,fire-clay & silica-brick--,manufacture ( glass-melt+ pots--,dry+ & fir/ heat+ ( pots--,blocks = tank & o!r furnaces--,uses ( silica brick--,furnaces-- ,coal-fir$ & gas-fir$ furnaces--,gas produc]s-- ,reg5]ative furnaces1 pr9ciples & con/ruction ( ,siem5s' furnaces--,recup]ative furnaces--,g5]al arrangem5ts ( mod]n tank furnaces--,relative advantages ( tank & pot furnaces p4 #ed ,,*apt] ,v4 ,,! ,,process ,,( ,,fusion4 ,mix+ ( raw mat]ials by h& & by ma*9]y--,! *>g+ op]ation--,*emical reactions dur+ melt+ ( c>bonate mixtures1 & ( sulphate mixtures--,influ5ce ( c>bon on ! reactions--,! f9+ process p4 #gc ,,*apt] ,,vi4 ,,processes ,,us$ ,,9 ,,! ,,work+ ,,( ,,glass4 ,ladl+1 ga!r+1 & ca/+--,limitations ( ladl+-- ,ladl+ us$ = roll$ glass1 ga!r+ = bl[n glass--,roll+ ( glass--,bl[+ processes & op]ations--,use ( m\lds--,press+--,m\ld+ p4 #hd ,,*apt] ,,vii4 ,,bottle ,,glass4 ,raw mat]ials--,furnaces--,pr$om9ance ( tank furnaces-- ,process ( bl[+ bottles by h&--,ga!r+1 m>v]+1 bl[+--,use ( fire-clay & metal m\lds-- ,=mation ( neck--,improv$ appliances1 m\lds & tools--,manufacture ( bottles by ma*9]y--,! 8,b\*]0 bottle-bl[+ ma*9e--,anneal+ ( bottles-- ,l>ge bottles1 c>boys--,aids to ! bl[]--,siev]t's process--,l>ge %all[ vessels1 ba?-tubs p4 #ie ,,*apt] ,,viii4 ,,bl[n ,,& ,,press$ ,,glass4 ,raw mat]ials--,bohemian glass & fl9t glass--,ga!r+ & bl[+--,*air "w--,h& "w--,production ( tumbl]s by h&--,application ( col\r$ glass to bl[n articles--,use ( m\lds z aids to bl[+--,r\gh5+ effect ( m\lds--,fire-poli%+ by reheat+--,use ( compress$ air--,press$ glass--,m\lds & presses-- ,capacity & limitations ( press+ process p4 #ajh ,,*apt] ,,ix4 ,,roll$ ,,or ,,plate ,,glass4 ,roll$ plate glass--,furnaces--,raw mat]ials--,process ( ladl+--,! roll+ table--,anneal+--,cutt+ & sort+--,patt]ns on roll$ plate--8,figur$0 roll$ plate--,ma*9e us$ = d\ble-roll+--,poli%$ plate--,raw mat]ials--,ca/+ f melt+ pots-- ,special ca/+ pots--,! roll+ table--,importance ( flatness--,anneal+ kilns--,gr9d+ & poli%+ processes--,ma*9es us$ = gr9d+ & poli%+-- ,me?od ( hold+ ! glass--,abrasives & poli%+ mat]ials--,!ory ( ! poli%+ process--,limit+ sizes ( poli%$ plate--,homog5eity ( poli%$ plate-- ,uses ( plate glass--,b5t poli%$ plate--,mirrors-- ,bevell+1 process & ma*9es--,wir$ plate glass1 roll$ & poli%$--,difficulties & limitations-- ,advantages ( wir$ glass p4 #abb ,,*apt] ,x4 ,,%eet ,,& ,,cr[n ,,glass4 ,comp>ison ( %eet ) poli%$ plate--,raw mat]ials = %eet--,furnaces3 v>i\s =ms ( tank furnaces-- ,bl[+ process--,ga!r+1 =m+ ! ga!r+ on blocks1 =m+ ! %\ld] ( ! cyl9d]1 bl[+ ! cyl9d]1 op5+ ! end ( ! cyl9d]1 deta*+ cyl9d] f pipe--,cutt+ (f ! 8cap0--,splitt+ ! cyl9d]--,flatt5+ & anneal+--,cutt+ & sort+ %eet-glass--,defects ( %eet-glass--,v>iations ( ! process--,attempts to produce 8%eet0 glass by roll+--,siev]t's process--,direct draw+ processes-- ,! ,am]ican process = draw+ cyl9d]s--,f\rcault's processes--,difficulties & limitations--,cr[n glass-- ,! bl[+ process--,limitations p4 #adi ,,*apt] ,,xi4 ,,col\r$ ,,glasses4 ,def9ition ( col\r$ glass--,physical causes ( col\r-- ,col\r+ sub/ances3 copp]1 silv]1 gold1 c>bon1 t91 ars5ic1 sulphur1 *romium1 uranium1 fluor9e1 manganese1 iron1 nickel1 cobalt--,range & dep?s ( t9ts available--,int5sely col\r$ glasses--,! process ( 8fla%+0--,"* ( 8fla%$0 glass--,col\rs produc$ on glass by pa9t+3 use ( col\r$ 8glazes0 z pa9ts--,anci5t /a9$ glass & mod]n glass-- ,te*nical uses ( col\r$ glass1 photography1 railway & m>9e signals p4 #agh ,,*apt] ,,xii4 ,,optical ,,glass4 ,nature & prop]ties ( optical glass--,homog5eity-- ,=mation & removal ( /ri 9 solutions & 9 glass--,transp>5cy & col\r--,absorption ( light 9 8decol\ris$0 glasses--,refraction & disp]sion-- ,def9itions--,refractive index1 disp]sion1 m$ium disp]sion1 ! quantity --,specification ( optical prop]ties 9 t]ms ( c]ta9 spectrum l9es--,table ( typical optical glasses & _! optical con/ants-- ,cr[n & fl9t glasses--,relation betwe5 refraction & disp]sion 9 ! old] & new] glasses--,"w ( ,abb & ,s*ott--,applications ( ! new glasses-- ,non-proportionality ( disp]sion 9 diff]5t types ( glass--,result+ imp]fections ( a*romatism-- ,! relative p>tial disp]sions ( glasses--,pairs ( glasses giv+ p]fect a*romatism n yet fully available--,con/ants ( ,s*ott's telescope cr[n & fl9t--,n>r[ range ( optical glasses1 consequ5t limitations 9 l5s design--,causes ( ^! n>r[ limits--,possible directions ( ext5sion--,*emical /ability ( optical glasses--,d\ble refraction 9 optical glass aris+ f imp]fect anneal+ p4 #bje ,,*apt] ,,xiii4 ,,optical ,,glass4 ,! manufacture ( optical glass--,raw mat]ials-- ,mix+--,furnaces & crucibles--,kilns = heat+ pots--,transf] ( pots f kiln to melt+ furnace-- ,introduction ( cullet & raw mat]ials--,! f9+ process1 difficulties & limitations--,! /irr+ process--,! f9al cool+ ( ! glass--,r\gh sort+ ( ! glass fragm5ts--,m\ld+ & f9al anneal+ ( ! m\ld$ glass--,gr9d+ & poli%+ ( plates & discs = exam9ation2 smallness ( yield obta9$-- ,difficulty ( obta9+ l>ge blocks ( p]fect glass p4 #bbc ,,*apt] ,,xiv4 ,,miscellane\s ,,products4 ,glass tub+--,ga!r+ & draw+ ( ord9>y tubes-- ,special v>ieties ( tube--,combu/ion tubes--,tubes ( vitre\s silica--,v>ieties ( vitre\s silica-- ,transp>5t1 glass-l silica w>e--,great co/ ( production--,transluc5t 8milky0 silica w>e produc$ electrically--,great !rmal endurance ( vitre\s silica--,s5sitiv5ess to *emical action ( all basic sub/ances at high temp]atures--,glass rod & fibre-- ,glass wool--,qu>tz fibres--,glass beads--,artificial gems--,use ( v d5se fl9t glass col\r$ to imitate preci\s /ones--,means ( di/+ui%+ imitations-- ,preci\s /ones produc$ by artificial means--,*ill$ glass--,great /r5g? & fragility ( *ill$ glass-- ,rup]t's drops--,manufacture ( 8temp]$0 glass by ,siem5s--,de ,la ,ba/ie's process--,massive glass1 us$ = h\se con/ruction & pav+ blocks--,wat]-glass 7silicate ( soda or pota%71 manufacture 9 tank furnaces--,glass = ligh?\se l5ses & se>*light mirrors--,production by ca/+ glass 9 iron m\lds-- ,sizes & types ( l5ses & prisms produc$ p4 #bch ,,app5dix--,bibliography ( ,glass ,manufacture p4 #bec ,,glass ,,manufacture ,,*apt] ,i4 ,,! ,,physical ,,& ,,*emical ,,prop]ties ,,( ,,glass4 ,al?\gh ! t]m 8glass0 d5otes a gr\p ( bodies :i* possess 9 common a numb] ( well-def9$ & *>act]i/ic prop]ties1 x is difficult to frame a satisfactory def9ition ( ! t]m itself4 ,?us :ile ! prop]ty ( transp>5cy is at once sugge/$ by ! ^w 8glass10 !re are a numb] ( true glasses :i* are n transp>5t1 & "s ( :i* are n ev5 transluc5t4 ,h>dness & brittl5ess also are prop]ties m or less *>act]i/ic ( glasses1 yet v wide diff]5ces are to be f\nd 9 ?is respect also1 & bodies1 bo? h>d] & m fragile ?an glass1 are to be f\nd among m9]als & metals4 ,p]haps ! only really univ]sal prop]ty ( glasses is t ( possess+ an amorph\s /ructure1 s t vitre\s bodies z a :ole may be reg>d$ z typical ( 8/ructureless0 solids4 ,all bodies1 :e!r liquid or solid1 mu/ possess an ultimate /ructure1 be x atomic1 molecul> or electronic 9 "*1 b ! /ructure "h ref]r$ to is n t ( individual molecules b r ! mann] ( gr\p+ or aggregation ( molecules4 ,9 ! great majority ( m9]al or inorganic bodies ! molecules 9 ! solid phase are arrang$ 9 a def9ite gr\p+ & ! body is said to h a cry/all9e /ructure2 evid5ces ( ?is /ructure are g5]ally visible to ! unaid$ eye or c be reveal$ by ! microscope4 ,vitre\s bodies on ! o!r h& are *>act]is$ by ! entire abs5ce ( su* a /ructure1 & ! me*anical1 optical & *emical behavi\r ( su* bodies is consi/5t only ) ! assumption t _! molecules possess ! same arrangem5t1 or r lack ( arrangem5t1 t is f\nd 9 liquids4 ,! intimate resemblance betwe5 vitre\s bodies & true liquids is fur!r emphasis$ :5 x is realis$ t true liquids c 9 _m in/ances pass into ! vitre\s /ate )\t und]go+ any critical *ange or exhibit+ any discont9uity ( behavi\r1 su* z is exhibit$ dur+ ! freez+ ( a cry/all9e body4 ,9 ! latt] class ( sub/ances ! passage f ! liquid to ! cry/all9e /ate takes place at "o def9ite temp]ature1 & ! *ange is accompani$ by a consid]able evolution ( heat1 s t ! cool+ ( ! mass is tempor>ily arre/$4 ,9 ! case ( glasses1 on ! o!r h&1 ! passage f ! liquid to ! app>5tly solid condition is gradual & p]fectly cont9u\s1 no evolution ( heat or ret>dation ( cool+ be+ obs]v$ ev5 by ! aid ( ! mo/ delicate in/rum5ts4 ,we are ?us ju/ifi$ 9 speak+ ( glasses z 8congeal$ liquids10 ! process ( congeal+ 9 ?is case involv+ no *ange ( /ructure1 no re-arrangem5t ( ! molecules1 b simply implies a gradual /iff5+ ( ! liquid until ! viscosity becomes s great t ! body behaves l a solid4 ,x is1 h[ev]1 j ?is p[] ( becom+ exce$+ly /iff or visc\s :5 cool$ d[n to ord9>y temp]atures t r5d]s ! exi/5ce ( vitre\s bodies possible4 ,all glasses are capable ( und]go+ ! *ange to ! cry/all9e /ate :5 kept = a suffici5t "t at a suitable temp]ature4 ,! process :i* !n takes place is kn[n z 8devitrification10 & sometimes gives rise to s]i\s manufactur+ difficulties4 ,molt5 glass may be reg>d$ z a mutual solution ( a numb] ( *emical sub/ances--usually silicates & borates4 ,:5 cool$ 9 ! ord9>y way ^! bodies rema9 mutually dissolv$1 & ord9>y glass is ?us simply a congeal$ solution4 ,! dissolv$ sub/ances h1 h[ev]1 natural freez+-po9ts ( _! own1 & if ! molt5 mass be kept = any l5g? ( "t at a temp]ature a little bel[ "o ( ^! freez+-po9ts1 t p>ticul> sub/ance w beg9 to solidify sep>ately 9 ! =m ( cry/als4 ,! facility ) :i* ?is w occur dep5ds ^u ! prop]ties ( ! +r$i5ts & ^u ! proportions 9 :i* !y are pres5t 9 ! glass4 ,9 "s cases ?is devitrification sets 9 s readily t x c sc>cely be prev5t$ at all1 :ile 9 o!r cases ! glass mu/ be ma9ta9$ at ! prop] temp]ature = h\rs be=e cry/allisation c be induc$ to set 94 ,9 ei!r ( ^! cases1 provid$ t ! glass is cool$ suffici5tly rapidly to prev5t cry/allisation1 ! sequ5ce ( ev5ts dur+ ! subsequ5t cool+ ( ! mass is ?is3 z ! temp]ature falls fur!r & fur!r bel[ ! natural freez+-po9t ( "o or o!r ( ! dissolv$ bodies1 ! t5d5cy ( t body to cry/allise out at fir/ rapidly increases2 z ! temp]ature falls1 h[ev]1 ! resi/ance :i* ! liquid pres5ts to ! motion ( ! molecules increases at a /ill great] rate1 s t two oppos+ =ces are at "w1 "o ( !m an increas+ t5d5cy t[>ds cry/allisation1 ! o!r a /ill m rapidly increas+ resi/ance to any *ange4 ,!re is ?us = e glass a c]ta9 critical range ( temp]ature dur+ :i* ! greate/ t5d5cy exi/s = ! cry/allis+ =ces to ov]come ! int]nal resi/ance2 ?r\gh ?is range ! glass mu/ be cool$ at a relatively rapid rate if devitrification is to be avoid$2 at l[] temp]atures ! cry/allis+ =ces require increas+ly long] p]iods ( "t to produce any s5sible effect1 until1 z ! ord9>y temp]ature is approa*$1 ! =ces ( int]nal resi/ance entirely prev5t all t5d5cy to cry/allisation4 ,! ph5om5a j describ$ 9 reality con/itute ! natural limit to ! range ( bodies :i* c be obta9$ 9 ! vitre\s /ate3 z we approa* ?is limit ! glass requires m & m rapid cool+ ?r\gh ! critical range ( temp]ature1 & is ?us m & m liable to devitrify dur+ ! manufactur+ processes1 until f9ally ! limit is set :5 no indu/rially feasible rapidity ( cool+ suffices to reta9 ! mass 9 ! vitre\s /ate4 ,:ile ! range ( bodies t c be obta9$ 9 ! vitre\s /ate is v l>ge1 only a comp>atively small numb] ( sub/ances are ord9>ily incorporat$ 9 indu/rial glasses4 ,) ! exception ( c]ta9 special glasses us$ = sci5tific purposes1 su* z ! con/ruction ( optical l5ses1 !rmomet]s & vessels int5d$ to resi/ unusual treatm5t1 all indu/rial glasses are ( ! nature ( mix$ silicates ( a few bases1 viz41 ! alkalies1 sodium & potassium1 ! alkal9e e>?s1 calcium1 magnesium1 /rontium1 & b>ium1 ! oxides ( iron & alum9ium 7g5]ally pres5t 9 m9or quantities71 & lead oxide4 ,! mann] 9 :i* ^! v>i\s elem5ts ent] into comb9ation & solution ) "o ano!r has be5 mu* inve/igat$1 & ! m g5]al conclusions h be5 anticipat$ 9 :at has be5 said above4 ,x is abundantly evid5t t glasses are n def9ite *emical comp\nds1 b r solutions1 9 v>y+ proportions1 ( a s]ies ( def9ite comp\nds 9 "o ano!r4 ,9 _m cases ! actual con/itution ( indu/rial glasses is s complex z1 = ! pres5t at all ev5ts1 to baffle adequate *emical expression4 ,"o ( ! factors t limit ! range ( possible compositions ( glasses has already be5 indicat$1 & two o!rs mu/ n[ be discuss$4 ,= indu/rial purposes1 ! co/ & r>ity ( ! +r$i5ts becomes a vital b> at a c]ta9 /age2 ?us ! use ( su* elem5ts z li?ium1 ?allium1 etc41 is prohibitively co/ly4 ,9 ano!r direction ! glass-mak] is v effectively re/ra9$ by ! limitations ( 8 furnaces z reg>ds temp]ature4 ,! pres5ce ( excessive proportions ( silica1 lime1 alum9a1 etc41 t5ds to raise ! temp]ature requir$ = ! free fusion ( ! glass1 & :5 ?is temp]ature s]i\sly exce$s #afjj ,c41 ! manufacture ( ! glass 9 ord9>y furnaces becomes impossible4 ,?us pure silica c be conv]t$ into a glass possess+ v valuable prop]ties1 b ! requisite temp]ature _c be atta9$ 9 reg5]ative gas-fir$ furnaces su* z are ord9>ily us$ by glass manufactur]s4 ,! production ( ?is glass has accord+ly be5 c>ri$ on ^u a small scale only by means ( laboratory furnaces heat$ by oxy-acetyl5e flames1 :ile latt]ly a less p]fect v>iety ( silica glass-w>e has be5 produc$ on a l>ge scale by ! aid ( electric furnaces4 ,su* me?ods are1 h[ev]1 obvi\sly limit$ to v special products comm&+ special prices4 ,a fur!r limitation 9 ! *oice ( *emical compon5ts is plac$ ^u ! manufactur] by ! actual *emical behavi\r ( ! glass bo? dur+ manufacture & 9 use4 ,z reg>ds *emical behavi\r dur+ manufacture1 x mu/ be borne 9 m9d t1 al?\gh glasses are ( ! nature ( solutions r ?an ( comp\nds1 yet ^! solutions t5d t[>ds a /ate ( saturation2 ?us a glass ri* 9 silica & defici5t 9 bases w readily dissolve any basic mat]ials ) :i* x may come 9 contact1 :ile1 on ! o!r h&1 a glass ri* 9 bases & poor 9 acid con/itu5ts su* z silica1 boric acid or alum9a1 w readily absorb acid bodies f its surr\nd+s4 ,dur+ ! process ( melt+1 glass is univ]sally conta9$ 9 fire-clay vessels4 ,^! are *os51 z reg>ds _! own *emical composition1 s z to (f] to ! molt5 glass a few ( ^? mat]ials 9 :i* ! glass itself is defici5t2 yet a limit arises 9 ?is respect also1 s9ce glasses v ri* 9 bases1 su* z ! v d5se lead & b>ium glass made = optical purposes1 rapidly attack any fire-clay ) :i* !y may come 9 contact4 ,! f9i%$ glass also betrays its *emical composition by its *emical behavi\r t[>ds ! atmosph]ic ag5ts1 su* z moi/ure & c>bonic acid1 ) :i* x comes 9 contact2 glasses conta9+ an excessive proportion ( alkali1 = example1 are f\nd to be s]i\sly hygroscopic & to und]go rapid decomposition1 especially 9 a damp atmosph]e4 ,)9 ! limits set by ^! consid]ations1 ! glass manufactur] *ooses ! *emical composition ( 8 glass accord+ to ! purpose = :i* x is int5d$2 = mo/ indu/rial products ! *eape/ & mo/ accessible raw mat]ials t w yield a glass ( ! requisite appe>ance are employ$1 :ile = special purposes ! dep5d5ce ( physical prop]ties ^u *emical composition is utilis$1 z f> z possible1 9 ord] to atta9 a glass specially suit$ to ! p>ticul> requirem5ts 9 "q4 ,?us ! fl9t & b>ium glasses us$ = table & ornam5tal w>e d]ive f ! d5se & /rongly refract+ oxides ( lead & b>ium _! prop]ties ( brilliancy & weight4 ,! fusibility & s(tness imp>t$ to ! glass by ! pres5ce ( ^! bases fur!r adapts x to its purpose by facilitat+ ! complicat$ manipulations to :i* ! glass mu/ be subject$ 9 ! manufactur+ processes4 ,tak+ our next example at almo/ ! opposite extreme1 ! h>de/ 8combu/ion tub+10 :i* is int5d$ to resi/ a r$ heat )\t appreciable s(t5+1 is manufactur$ by r$uc+ ! basic cont5ts ( ! glass to ! l[e/ possible degree1 especially m9imis+ ! alkali cont5t1 & us+ ! mo/ refractory bases available1 su* z lime1 magnesia1 & alum9a 9 ! highe/ possible proportions4 ,su* glass is1 ( c\rse1 difficult to melt1 & special furnaces are requir$ = its production1 b on ! o!r h& ?is mat]ial meets requirem5ts :i* ord9>y soda-lime or fl9t glass tub+ c\ld nev] approa*4 ,ano!r in/ance ( ^! refractory glasses is to be f\nd 9 ! ,j5a special !rmomet] glasses & 9 ! ,fr5* 7,tonnelot7 8,v]re dur02 ! be/ ( ^! glasses %[ little or no pla/icity at temp]atures approa*+ #ejj ,c41 & h ?us r5d]$ possible a consid]able ext5sion ( ! range ( ! m]cury !rmomet]4 ,fur!r modification ( *emical composition has result$ 9 ! production ( glasses :i* are f> less subject to ^? gradual *anges :i* occur 9 ord9>y glass :5 us$ = ! manufacture ( !rmomet]s--*anges :i* vitiat$ ! accuracy ( mo/ e>ly !rmomet]s4 ,a /ill m ext5sive adaptation ( *emical composition to ! atta9m5t ( desir$ physical prop]ties has be5 rea*$ prim>ily z a result ( ! lab\rs ( ,s*ott & ,abb1 9 ! case ( optical glasses4 ,! "w ( ^! m51 & ! developm5ts :i* h foll[$ f x1 bo? at ! works f\nd$ by !m at ,j5a & else:]e1 h s pr(\ndly modifi$ our k ( ! range ( possibilities embrac$ by ! class ( vitre\s bodies1 t x is n at all easy at ! pres5t "t to realise ! =m] n>r[ & re/rict$ mean+ ( ! t]m 8glass40 ,! subject ( ! dep5d5ce ( ! optical prop]ties ( glass ^u *emical composition w be ref]r$ to 9 detail 9 ,*apt] ,,xii4 on 8,optical ,glass10 b ! outl9e ( ! influ5ce ( composition on prop]ties "h giv5 c\ld n be clos$ )\t "s ref]5ce to ?is pione] "w ( ! ,g]man inve/igators4 ,! *emical behavi\r ( glass surfaces1 to :i* we h already ref]r$1 is ( ! utmo/ importance to all us]s ( glass4 ,! relatively neutral *emical behavi\r ( glass is1 9 fact1 "o ( its mo/ useful prop]ties1 &1 next to its transp>5cy1 mo/ frequ5tly ! gov]n+ factor 9 its employm5t = v>i\s purposes4 ,?us ! entire use ( glass = table-w>e dep5ds prim>ily ^u ! fact t x does n appreciably affect ! composition & flav\r ( edible solids or liquids ) :i* x is br\ght into contact--a prop]ty :i* is only v p>tially %>$ ev5 by ! noble metals4 ,aga91 ! use ( glass w9d[s 9 places expos$ to ! wea!r w\ld n be feasible if w9d[-glass 7 appreciably attack$ by ! action ( wat] or ( ! gases ( ! atmosph]e4 ,= ^! g5]al purposes1 x is true1 mo/ ord9>y glasses are adequately resi/ant1 b ?is degree ( p]fection 9 ?is respect is only ! outcome ( ! c5turies ( exp]i5ce :i* ! practical glass-mak] has beh9d him 9 ! manufacture & behavi\r ( su* glass4 ,:51 h[ev]1 a high] degree ( *emical resi/ance is requir$ = special purposes1 z = in/ance :5 glass is call$ ^u to resi/ exposure to hot1 damp climates1 or is int5d$ to conta9 corrosive liquids1 ! rules :i* are an adequate guide to ! glass-mak] 9 meet+ ord9>y requirem5ts are no long] suffici5t1 p>ticul>ly :5 ! glass is expect$ to meet o!r /r+5t requirem5ts z well4 ,x has1 9 fact1 frequ5tly happ5$ t a glass-mak]1 9 /riv+ to improve ! col\r or quality ( 8 glass1 z reg>ds fre$om f defects1 brilliancy ( surface1 etc41 has spoilt ! *emical durability ( 8 products4 ,! reason lies 9 ! fact1 long kn[n 9 g5]al t]ms1 t an increas$ alkali cont5t r$uces ! *emical resi/ance ( glass1 :ile at ! same "t su* an increase ( alkali is ! readie/ means :]eby ! glass-mak] c improve 8 glass 9 o!r respects by mak+ x m fusible & easi] to "w 9 e way4 ,?is subject ( ! *emical /ability ( glass surfaces attract$ mu* att5tion dur+ ! lat] "p ( la/ c5tury1 & c>eful inve/igations on ! subject 7 c>ri$ out1 p>ticul>ly at ! ,g]man ,rei*san/alt 7,imp]ial ,physical ,laboratory7 at ,*>lott5burg4 ,"h also ! lab\rs ( ,s*ott & ,abb prov$ helpful1 until at ! pres5t "t su* glass z t us$ by ! ,j5a firm 9 ! production ( laboratory w>e1 & c]ta9 o!r special glasses ( t k9d1 are fitt$ to meet ! mo/ /r+5t requirem5ts4 ,leav+ aside ! inf]ior glasses1 conta9+1 g5]ally1 m ?an #ae p] c5t4 ( alkali1 ! behavi\r ( glass surfaces to ! pr9cipal *emical ag5ts may be summ$ up 9 ! foll[+ /atem5ts4 ,pure wat] attacks all glass to a great] or less] ext5t2 9 ! be/ glasses ! prolong$ action ( cold wat] m]ely extracts a m9ute trace ( alkalies1 b 9 less p]fect k9ds ! extraction ( alkali is consid]able on prolong$ exposure ev5 9 ! cold1 & becomes rapidly m s]i\s if ! temp]ature is rais$4 ,sup]heat$ wat]1 i4e41 wat] "u /eam pressure1 becomes an active corrod+ ag5t1 & ! be/ glasses c only resi/ its action = a limit$ "t4 ,= ! gauge-glass tubes ( /eam boil]s work+ at ! high pressures1 :i* are cu/om>y at ! pres5t "t1 specially durable glasses are requir$ & c be obta9$1 al?\gh _m ( ! gauge-tubes ord9>ily sold are q unfit = ! purpose1 bo? f ! pres5t po9t ( view & f t ( /r5g? & 8!rmal endurance40 ,9 c]ta9 classes ( glass1 ! action ( wat]1 especially :5 hot1 is n entirely conf9$ to ! surface1 "s wat] p5etrat+ into ! mass ( ! glass to an appreciable dep?4 ,! exact me*anism ( ?is action is n kn[n1 b ! writ] incl9es to ! view t x arises f a p>tial hydration ( "s ( ! silica or silicates pres5t 9 ! glass4 ,if su* glasses be dri$ 9 ! ord9>y way & subsequ5tly heat$1 ! surface w be riddl$ ) m9ute cracks1 "s glass may ev5 flake (f1 & ! :ole surface w be dull$4 ,z su* p5etrat+ action sometimes takes place--9 ! poor] k9ds ( glass--by ! action ( atmosph]ic moi/ure :5 ! glass is m]ely /or$ 9 a damp place1 x is (t5 mi/ak5 = 8devitrification40 ,?is latt] action1 h[ev]1 is n kn[n to occur at ! ord9>y temp]ature1 al?\gh glass :5 heat$ 9 a flame frequ5tly %[s ! ph5om5on2 x is1 h[ev]1 entirely di/9ct f ! surface 8corrosion0 j describ$4 ,wat] conta9+ alkal9e sub/ances 9 solution acts ^u all glasses 9 a relatively rapid mann]2 x acts by fir/ ab/ract+ silica f ! glass1 ! alkali & lime be+ dissolv$ or me*anically remov$ at a lat] /age4 ,wat] conta9+ acid bodies 9 solution--i4e41 dilute acid--on ! o!r h& acts ^u mo/ v>ieties ( glass decid$ly less en]getically ?an ev5 pure wat]1 & mu* less vigor\sly ?an alkal9e solutions2 ?is peculi> behavi\r probably dep5ds ^u ! t5d5cy ( acids to prev5t ! hydration ( silica1 ?is sub/ance be+ !reby enabl$ to act z a b>ri] to ! solv5t action ( ! wat] ^u ! alkal9e con/itu5ts ( ! glass4 ,! bett] v>ieties ( glass are also practically imp]vi\s to ! action ( /rong acids1 al?\gh c]ta9 ( ^!1 su* z phosphoric & hydr(luoric1 ex]t a rapid action on all k9ds ( glass4 ,only c]ta9 special glasses1 conta9+ an excessive proportion ( basic con/itu5ts & ( su* sub/ances z boric or phosphoric acid1 are capable ( be+ completely decompos$ by ! action ( /rong acids1 su* z hydro*loric or nitric1 ! bases ent]+ into comb9ation ) ! acids1 :ile ! silicic & o!r acids are lib]at$4 ,9 connection ) ! action ( acids ^u glass1 m5tion %\ld be made ( c]ta9 special actions t are ( practical importance4 ,! dissolv+ action ( hydr(luoric acid ^u glass is1 ( c\rse1 well kn[n4 ,x is us$ 9 practice bo? 9 ! liquid & gase\s =m1 & also 9 t ( comp\nds f :i* x is readily lib]at$ 7su* z ammonium or sodium fluoride71 = ! purpose ( 8et*+0 glass1 & also 9 decompos+ glass = purposes ( *emical analysis4 ,next 9 importance ranks ! action ( c>bonic acid gas ^u glass1 especially 9 ! pres5ce ( moi/ure4 ,! action 9 "q is probably indirect 9 "*2 ! moi/ure ( ! air1 cond5s+ ^u ! surface ( ! glass1 fir/ ex]ts its dissolv+ action1 & ?us draws f ! glass a c]ta9 quantity ( alkali1 :i* almo/ c]ta9ly at fir/ goes into solution z alkali hydrate 7potassium or sodium hydroxide72 ?is alkal9e solution1 h[ev]1 rapidly absorbs c>bonic acid f ! air1 & ! c>bonate ( ! alkali is =m$4 ,if ! glass dries1 ?is c>bonate =ms a coat+ ( m9ute cry/als on ! surface ( ! glass1 giv+ x a dull1 dimm$ appe>ance2 ?is1 h[ev]1 only occurs ord9>ily ) soda glasses1 s9ce ! c>bonate ( potassium is too hygroscopic to rema9 9 ! dry solid /ate 9 any ord9>y atmosph]e4 ,pota% glasses are1 z su*1 no m /able *emically ?an soda glasses1 b !y are = ! reason j giv5 less liable to exhibit a dim surface4 ,if ! dimm+ process1 9 ! case ( a soda glass1 has n gone too f>1 ! brightness ( ! surface ( ! glass may be practically re/or$ by wa%+ x ) wat]1 9 :i* ! m9ute cry/als ( c>bonate ( soda readily dissolve1 :ile sep>at$ silica is remov$ me*anically4 ,an attempt made to clean ! same dimm$ surface by dry wip+ w\ld only result 9 f9ally ru9+ ! surface1 s9ce ! small %>p cry/als ( c>bonate ( soda w\ld be rubb$ ab\t ov] ! surface1 scrat*+ x 9 all directions4 ,! dimm+ process 9 ! case ( ! less resi/ant glasses is n only conf9$ to ! =mation ( alkal9e c>bonates2 ! films ( alkal9e solution :i* are =m$ on ! surface ( glass =m a ready bre$+-gr\nd = c]ta9 =ms ( bact]ia & fungi1 ^: gr[? occurs p>tly at ! exp5se ( ! glass itself2 ! precise nature ( ^! actions has n be5 fully /udi$1 b !re c be little d\bt t silicate m9]als--& glass is to be reckon$ among ^!--are subject to bact]ial decomposition1 a well-kn[n example 9 ano!r direction be+ ! 8matur+0 ( clays by /orage 9 ! d>k1 ! *ange 9 ! clay be+ accompani$ by an evolution ( ammonia gas4 ,9 ! case ( glass x has be5 %[n t specks ( organic du/ fall+ ^u a surface give rise to local decomposition4 ,9 ?is connection x is int]e/+ to note ! effect ( ! pres5ce ( a small proportion ( boric acid 9 "s glasses4 ,! pres5ce ( ?is +r$i5t 9 small proportions is kn[n to r5d] ! glass m resi/ant to atmosph]ic ag5cies1 & m especially to r5d] x less s5sitive to ! effects ( organic du/ p>ticles ly+ ^u ! surface4 ,x has be5 sugge/$--probably rightly--t ! boric acid1 ent]+ into solution 9 ! film ( surface moi/ure1 ex]ts its well-kn[n antiseptic prop]ties1 ?us protect+ ! glass f bact]ial & fungoid activity4 ,! durability ( glass "u ! action ( atmosph]ic ag5ts is a matt] ( su* importance t num]\s ef=ts h be5 made to e/abli% a satisfactory te/ :]eby ?is prop]ty ( a giv5 glass may be asc]ta9$ )\t actually await+ ! results ( exp]i5ce obta9$ by actual use "u unfav\rable conditions4 ,"o ( ! e>lie/ ( ! te/s propos$ consi/$ 9 expos+ surfaces ( ! glass to ! vap\r ( hydro*loric acid4 ,= ?is purpose "s /rong hydro*loric acid is plac$ 9 a glass or porcela9 bas91 & /rips ( ! glass to be te/$ are plac$ across ! top ( ! bas91 ! :ole be+ cov]$ ) a bell-j>4 ,aft] sev]al days ! glass is exam9$1 & z a rule ! less /able glasses %[ a dull1 dimm$ surface z comp>$ ) ! m /able ones4 ,a m satisfactory =m ( te/ dep5ds ^u ! fact t aque\s e!r solutions react readily ) ! less /able k9ds ( glass2 if a suitable dye1 su* z iod-eos91 be dissolv$ 9 ! wat]-e!r solution1 !n ! effect ^u ! less /able glasses :5 imm]s$ 9 ! solution is ! =mation ( a /rongly adh]5t p9k film4 ,! d5sity or dep? ( col\r ( ?is film may be reg>d$ z measur+ ! /ability ( ! glass2 ! be/ k9ds ( glass rema9 practically free f col\r$ film ev5 on prolong$ exposure4 ,a te/ ( a some:at diff]5t k9d is "o devis$ 9 its orig9al =m by ,dr4 ,zs*imm]1 ( ! ,j5a glass works2 ?is dep5ds ^u ! fact t ! dis9tegrat+ action ( moi/ air c be v mu* accel]at$ if bo? ! moi/ure & ! temp]ature ( ! air surr\nd+ ! glass be consid]ably increas$4 ,= ?is purpose ! samples ( glass are expos$ to a curr5t ( air saturat$ ) moi/ure at a temp]ature ( ab\t #hj ,c4 9 a specially arrang$ incubator = "o or m days1 means be+ provid$ = secur+ a con/ant /ream ( moi/ air dur+ ! :ole "t4 ,on exam9+ ! glass surfaces aft] ?is exposure--any wip+ or o!r clean+ ( ! surfaces be+ avoid$--v>i\s qualities ( glass are f\nd to %[ widely v>y+ appe>ances4 ,! be/ & mo/ /able glasses rema9 entirely unaffect$2 less /able k9ds %[ small specks1 :i* m]ge into a g5]ally dull$ surface 9 un/able k9ds4 ,!re is no d\bt t ?is te/ gives a %>p classification ( glasses1 b x yet rema9s to be prov$ t ?is classification agrees ) _! true relative durability 9 practice2 ! writ] is incl9$ to d\bt :e!r ?is is really ! case1 s9ce c]ta9 glasses t h prov$ v satisfactory 9 ?is respect 9 practical use all ov] ! _w 7 class$ among ! less /able k9ds by ?is te/4 ,be=e leav+ ! subject ( ! *emical behavi\r ( glass1 a ref]5ce %\ld be made to ! *anges :i* glass und]goes :5 act$ ^u by light & o!r radiations4 ,"u ! influ5ce ( prolong$ exposure to /rong light1 p>ticul>ly to sunlight1 & /ill m s to ultra-violet light1 or ! light ( ! sun at high altitudes1 practically all k9ds ( glass und]go *anges :i* g5]ally take ! =m ( *anges ( col\r4 ,glasses conta9+ manganese especially are apt to assume a purple or br[n t+e "u su* circum/ances1 al?\gh ! p[]ful action ( radium radiations is capable ( produc+ simil> discoloration 9 glasses free f manganese4 ,ap>t f ^! latt] effects1 ( :i* v little is kn[n z yet1 !re c be no d\bt t ! action ( light br+s ab\t *emical *anges )9 ! glass1 b x is by no means easy to asc]ta9 ! true nature ( ^! *anges1 al?\gh !y mo/ probably consi/ 9 a transf] ( oxyg5 f "o to ano!r ( ! oxides pres5t 9 ! glass4 ,al?\gh x has n be5 def9itely prov$1 x seems v unlikely t ! glass ei!r loses or ga9s 9 any con/itu5t dur+ ^! *anges4 ,good examples ( ! *anges und]gone by glass "u ! action ( sunlight are frequ5tly f\nd 9 skylights1 :]e ! olde/ panes sometimes %[ a decid$ purple t9t :i* !y did n possess :5 fir/ put 9 place4 ,! glass sph]es ( ! in/rum5ts us$ = obta9+ records ( ! duration ( sun%9e at meteorological /ations also %[ signs ( ! *anges due to light--! glass ( ^! sph]es :5 new has a light gre5i% t9t1 b aft] prolong$ use ! col\r *anges to a decid$ yell[4 ,! col\r$ glass 9 /a9$-glass w9d[s also %[s signs ( hav+ und]gone *anges ( t9t 9 consequ5ce ( prolong$ exposure to light2 glass remov$ f anci5t w9d[s usually %[s a deep] t9t 9 ^? portions :i* h be5 protect$ f ! direct action ( light by ! lead+ 9 :i* ! glass 0 set1 & x is at lea/ an op5 "q :e!r ! beauty ( anci5t glass may n be1 9 "p1 due to ! mell[+ effect ( light ^u "s ( ! t9ts ( ! design4 ,?is photo-s5sitiv5ess ( glass is also ( "s importance 9 connection ) ! manufacture ( photographic plates4 ,x has be5 f\nd t if ! glass plate ( a /rongly-develop$ negative be clean$1 a decid$ trace ( ! =m] image is reta9$ by ! glass1 & ?is image is apt to re-appe> z a 8gho/0 if ! same glass be aga9 coat$ ) s5sitive emulsion & aga9 expos$ & develop$4 ,! be/ mak]s ( plates recognise ?is fact & d n re-coat glass t has once be5 us$ = ! production ( a negative4 ,,*apt] ,,ii4 ,,! ,,physical ,,prop]ties ,,( ,,glass4 ,! ,me*anical ,prop]ties ( ,glass are ( consid]able importance 9 _m directions4 ,al?\gh glass is r>ely us$ 9 su* a mann] t x is directly call$ ^u to su/a9 s]i\s me*anical /resses1 ! ord9>y uses ( glass 9 ! glaz+ ( l>ge w9d[s & skylights dep5d ^u ! /r5g? ( ! mat]ial to a v consid]able ext5t4 ,?us 9 ! h&l+ ( plate-glass 9 ! l>ge/ %eets1 ! me*anical /r5g? ( ! plates mu/ be reli$ ^u to a consid]able ext5t1 & x is ?is factor :i* really limits ! size ( plate t c be safely h&l$ & in/all$4 ,! same limitation applies to %eet-glass also1 =1 al?\gh its light] weight r5d]s x less liable to break "u its own weight1 its ?9n] section r5d]s x mu* m liable to accid5tal fracture4 ,9 special cases1 also1 ! me*anical /r5g? ( glass mu/ be reli$ ^u to a consid]able ext5t4 ,gauge tubes ( high-pressure boil]s1 port-hole glasses 9 %ips1 ! glass prisms ins]t$ 9 pavem5t lights1 & ! glass bricks :i* h f\nd "s use 9 ,france1 z well z *ampagne bottles & m9]al wat] bottles & syphons1 are all examples ( uses 9 :i* glass is expos$ to direct /resses4 ,x is1 !re=e1 a little surpris+ t :ile ! me*anical prop]ties ( metals1 timb]s1 & all mann] ( o!r mat]ials h be5 /udi$ 9 ! fulle/ possible mann]1 ^? ( glass h receiv$ v little att5tion1 at all ev5ts s f> z publi%$ data g4 ,"o reason = ?is /ate ( affairs is probably to be f\nd 9 ! fact t x is by no means easy to det]m9e ! /r5g? ( s brittle & h>d a body z glass4 ,z a consequ5ce ev5 ! scanty data available c only be reg>d$ z fir/ approximations4 ,! foll[+ data are only int5d$ to give an idea ( ! g5]al ord] ( /r5g? to be look$ = 9 glass3-- ,t5sile /r5g?3 ,f #a to #d tons p] sq4 94 7,trautw9e74 0 to #a 0 0 0 7,h5rivaux74 0 #b to #e 0 0 0 7,w9kelmann & ,s*ott74 0 #e to #f 0 0 0 7,k[alski74 ,cru%+ /r5g?3 ,f #i to #af tons p] sq4 94 7,trautw9e74 0 #c to #h 0 0 0 7,w9kelmann & ,s*ott74 0 #bj to #bg 0 0 0 7,k[alski74 ,( ! above figures ! exp]im5ts ( ,w9kelmann & ,s*ott are probably by f> ! mo/ reliable1 b ^! ref] to a s]ies ( special ,j5a glasses1 select$ ) a view to det]m9+ ! influ5ce ( *emical composition on me*anical prop]ties1 &1 un=tunately1 ?is s]ies does n include glasses at all closely resembl+ ^? ord9>ily us$ = practical purposes4 ,! attempt to connect t5sile & cru%+ /r5g? ) *emical composition 0 also only v p>tially successful2 b ! results s]ve to %[ t ! *emical composition has a pr(\nd influ5ce on ! me*anical /r5g? ( glass1 s t by sy/ematic rese>* x w\ld probably be possible to produce glasses ( consid]ably great] me*anical /r5g? ?an ^? at pres5t kn[n4 ,x mu/ be not$ 9 ?is connection t ! me*anical prop]ties ( glass dep5d to a v consid]able ext5t ^u ! rate ( cool+ :i* ! specim5 9 "q has und]gone4 ,x is well kn[n t by rapid cool+1 or qu5*+1 ! h>dness ( glass c be consid]ably increas$2 su* treatm5t also increases ! /r5g? bo? z aga9/ t5sion & compression1 & num]\s processes h be5 put =w>d = ! purpose ( utilis+ ^! effects 9 practice4 ,un=tunately ! 8h>d5$0 glass ?us obta9$ is extremely s5sitive to m9ute scrat*es1 & flies to pieces z soon z ! surface is brok51 & ! great int]nal /ress :i* always exi/s 9 su* glass is !reby reliev$4 ,all ^! peculi>ities are1 ( c\rse1 dep5d5t z to _! degree ^u ! rapidity ) :i* ! glass has be5 cool$1 & ! aim ( inv5tors 9 ?is field has be5 to devise a rapid cool+ process :i* %\ld /rike ! happy mean betwe5 ! increas$ /r5g? & ! induc$ brittl5ess result+ f qu5*+4 ,?us processes = 8temp]+0 glass by cool+ x 9 a bla/ ( /eam or 9 a ba? ( hot oil or grease h be5 br\ght =w>d2 b1 al?\gh "s su* glass is manufactur$1 no v ext5sive practical application has result$4 ,ela/icity & ,ductility ( ,glass4--,9 a s]ies ( glasses inve/igat$ by ,w9kelmann & ,s*ott1 ! modulus ( ela/icity 7,"y's ,modulus7 v>i$ f #c1ejj to #e1ajj tons p] sq4 941 ! value be+ l>gely dep5d5t ^u ! *emical composition ( ! glass4 ,measurable ductility has n be5 obs]v$ 9 glass "u ord9>y conditions except 9 ! case ( *ampagne bottles "u te/ by int]nal hydraulic pressure2 9 ^! te/s x 0 f\nd t a p]man5t increase ( volume ( a few t5?s ( a cubic c5timetre c\ld be obta9$ by ! application ( an int]nal pressure j %ort ( t requir$ to bur/ ! bottle--pressure ( ! ord] ( #ah to #cj atmosph]es be+ involv$4 ,?is small p]man5t set has be5 ascrib$ to incipi5t fissur+ ( ! glass1 & ?is explanation is probably correct4 ,on ! o!r h&1 x is 9 ! writ]'s op9ion v probable t glass is capable ( decid$ fl[ "u ! prolong$ action ( relatively small =ces2 ! behavi\r ( l>ge discs ( work$ optical glass sugge/s "s su* action1 b ! view z yet lacks full exp]im5tal confirmation4 ,! ,h>dness ( glass is a prop]ty ( "s importance 9 mo/ ( ! applications ( glass4 ,! durability ( glass objects :i* are expos$ to h&l+ or to p]iodical clean+ mu/ l>gely dep5d ^u ! p[] ( ! glass to resi/ scrat*+2 ?is applies to su* objects z plate-glass w9d[s & mirrors1 spectacle & o!r l5ses1 & 9 a m9or degree to table-w>e4 ,on ! o!r h&1 ! exact def9ition & means ( measur+ h>dness are n yet satisfactorily settl$4 ,exp]im5t]s h f\nd x v difficult to measure ! direct resi/ance to scrat*+1 s9ce x is f\nd1 = example1 t two glasses ( v diff]5t h>dness are yet capable ( decid$ly scrat*+ ea* o!r "u suitable conditions4 ,resort has !re=e be5 _h to o!r me?ods ( measur+ h>dness2 ! me?od :i*1 f ! exp]im5tal po9t ( view1 is1 p]haps1 ! mo/ satisfactory1 dep5ds ^u pr9ciples laid d[n by ,h]tz & elaborat$ exp]im5tally by ,au]ba*4 ,?is dep5ds ^u measur+ ! size ( ! circul> area ( contact produc$ :5 a sph]ical l5s is press$ aga9/ a flat plate ( ! same glass ) a kn[n pressure4 ,au]ba* himself f\nd "s difficulty 9 decid+ ! exact connection betwe5 ! 8ind5tation modulus0 ?us det]m9$ & ! actual h>dness ( ! glass4 ,?is me?od is1 !re=e1 ( !oretical int]e/ r ?an ( use 9 te/+ glasses = h>dness4 ,a te/ ( a m practical k9d consi/s 9 expos+ specim5s ( ! glasses to be te/$ to abrasion aga9/ a revolv+ disc ( ca/-iron f$ ) em]y or o!r abrasive1 & to measure ! loss ( weight :i* results f a giv5 am\nt ( abrad+ action "u a kn[n contact pressure4 ,if a numb] ( specim5s ( diff]5t glasses are expos$ to ?is te/ at "o "t1 a v good comp>ison ( _! p[] ( resi/+ abrasion c be obta9$4 ,x is n q c]ta9 t ?is te/ measures ! actual 8h>dness0 ( ! glass1 b x af=ds "s in=mation z to its p[] ( resi/+ abrasion1 & = _m purposes ?is p[] is ! important factor4 ,h>dness be+1 z indicat$ above1 a some:at indef9ite t]m1 x is n possible to give any precise /atem5t z to ! influ5ce ( *emical composition ^u ! h>dness ( glass4 ,9 g5]al t]ms x may be said t glasses ri* 9 silica & lime w be f\nd to be h>d1 :ile glasses ri* 9 alkali1 lead or b>ium1 are likely to be s(t4 ,x mu/1 h[ev]1 be borne 9 m9d t rapid cool+1 or ev5 ! lack ( c>eful anneal+1 w produce a v great increase ( h>dness 9 ev5 ! s(te/ glasses4 ,! actual behavi\r ( a giv5 specim5 ( glass w1 !re=e1 dep5d at lea/ z mu* ^u ! nature ( ! processes :i* x has und]gone z ^u its *emical composition4 ,! ,!rmal ,prop]ties ( ,glass1 al?\gh n ( su* g5]al importance z ! me*anical prop]ties1 are yet ( consid]able int]e/ 9 a l>ge numb] ( ! practical uses to :i* glass is con/antly appli$4 ,p]haps ! mo/ important ( ^! prop]ties is t kn[n z !rmal endurance1 :i* measures ! am\nt ( sudd5 heat+ or cool+ to :i* glass may be expos$ )\t risk ( fracture2 ! *imneys employ$ 9 connection ) inc&esc5t gas burn]s1 boil] gauge glasses1 laboratory vessels1 & ev5 table & dome/ic ut5sils are all expos$ at times to sudd5 *anges ( temp]ature1 & 9 _m cases ! value ( ! glass 9 "q dep5ds pr9cipally ^u its p[] ( und]go+ su* treatm5t )\t breakage4 ,! prop]ty ( 8!rmal endurance0 itself dep5ds ^u a consid]able numb] ( m or less indep5d5t factors1 & _! influ5ce w be readily und]/ood if we foll[ ! mann] 9 :i* sudd5 *ange ( temp]ature produces /ress &1 sometimes1 fracture 9 glass objects4 ,if we suppose a hot liquid to be p\r$ into a cold vessel1 ! fir/ effect ^u ! mat]ial ( ! vessel w be to raise ! temp]ature ( ! inn] surface4 ,"u ! influ5ce ( ?is rise ( temp]ature ! mat]ial ( ?is inn] lay] exp&s1 or endeav\rs to exp&1 be+ re/ra9$ by ! resi/ance ( ! c5tral & out] lay]s ( mat]ial :i* are /ill cold2 ! result ( ?is conte/ is1 t :ile ! inn] lay] is ?r[n into a /ate ( compression1 ! out] & c5tral lay]s are ?r[n into a /ate ( t5sion4 ,accord+ly1 if ! t5sion s produc$ is suffici5tly great1 ! out] lay]s fracture "u t5sion & ! :ole vessel is %att]$ by ! propagation ( ! crack ?us initiat$4 ,f ?is description ( ! process x w be se5 t a high coeffici5t ( expansion & a l[ modulus ( ela/icity w bo? fav\r fracture1 :ile high t5sile /r5g? w t5d to prev5t x4 ,! !rmal conductivity ( ! glass w also affect ! result1 because ! int5sity ( ! t5sile /ress set up 9 ! cold] lay]s ( glass w dep5d ^u ! temp]ature gradi5t :i* exi/s 9 ! glass2 ?us if glass 7 a good conductor ( heat x w\ld nev] be possible to set up a suffici5t diff]5ce ( temp]ature betwe5 adjac5t lay]s to produce fracture2 = ! same reason1 vessels ( v ?9 glass are less apt to break "u temp]ature *anges ?an ^? hav+ ?ick walls1 s9ce ! greate/ diff]5ce ( temp]ature t c be set up betwe5 ! inn] & out] lay]s ( a ?9-wall$ vessel c nev] be v consid]able4 ,x also foll[s f ^! consid]ations1 t if a cold glass vessel be simultane\sly heat$ or cool$ f bo? sides1 x c be safely expos$ to a mu* m sudd5 *ange ( temp]ature ?an x c\ld )/& if heat$ f "o side alone2 on ! o!r h&1 :5 v ?ick masses ( glass h to be heat$1 ?is mu/ be done v gradually1 z a consid]able "t w necess>ily elapse be=e an increm5t ( temp]ature appli$ to ! outside w p5etrate to ! c5tre ( ! mass4 ,x %\ld also be not$ "h1 t 9 addition to ! !rmal conductivity ( ! glass1 its heat capacity or specific heat also ent]s into ?is "q1 s9ce heat w obvi\sly p5etrate m sl[ly ?r\gh a glass ^: own rise ( temp]ature absorbs a great] quantity ( heat4 ,x w ?us be se5 t 8!rmal endurance0 is a some:at complicat$ prop]ty1 dep5d+ ^u ! factors nam$ above1 viz43 coeffici5t ( expansion1 !rmal conductivity1 specific heat1 ,"y's modulus ( ela/icity1 & t5sile /r5g?4 ,! coeffici5t ( !rmal expansion v>ies consid]ably 9 diff]5t glasses1 & we c "h only /ate ! limit+ values betwe5 :i* ^! coeffici5ts usually lie2 ^! are #cg #aj-g z ! l[]1 & #abb #aj-g z ! upp] limit4 ,^! figures express ! cubical expansion ( ! glass p] degree ,c5tigrade1 ! correspond+ figures = /eel & brass respectively be+ ab\t #cfj #aj-g & #fdh #aj-g respectively4 ,x %\ld be not$ t vitre\s bodies ( extremely l[ expansibility are obta9able by ! suitable *oice ( +r$i5ts1 b 9 "s cases ^! 8glasses0 are :ite opaque bodies1 & 9 all cases !y pres5t great difficulty 9 manufacture1 ow+ to ! fact t alkalies & lime mu/ be avoid$ 9 _! composition4 ,q ap>t f ! "q ( !rmal endurance1 ! expansive prop]ties ( glass are ( "s importance4 ,?us :5 sev]al k9ds ( glass h to be unit$1 z1 = example1 9 ! process ( produc+ 8fla%$0 col\r$ glass1 x is ess5tial t _! coeffici5ts ( expansion %\ld be z ne>ly z possible ! same2 o!rwise consid]able /resses w be set up :5 ! glasses1 :i* h be5 jo9$ at a r$ heat1 are all[$ to cool4 ,on ! o!r h&1 ?is mutual /ress+ ( two glasses ow+ to diff]5ces 9 _! !rmal expansion has be5 utilis$ = ! production ( tubes & o!r glass objects possess+ special /r5g?4 ,if a tube be drawn out ( glass consi/+ ( two lay]s1 "o consid]ably m expansible ?an ! o!r1 & ! cool+ process be rightly conduct$1 x is possible to produce a tube 9 :i* bo? ! inn] & out] lay]s ( glass are "u a consid]able compressive /ress4 ,n only is glass1 z we h se5 above1 enorm\sly /rong] z aga9/ compression ?an x is aga9/ t5sion1 b glass "u compressive /ress behaves z ?\gh x 7 a mu* t\gh] mat]ial1 be+ less liable to injury by scrat*es or bl[s4 ,moreov]1 if a tube 9 ?is condition be heat$ & !n expos$ to sudd5 cool+1 ! fir/ effect ( ! application ( cold w be a contraction ( ! surface lay]s1 result+ 9 a relief ( ! initial condition ( compression4 ,^! tubes are1 !re=e1 rem>kably indiff]5t to sudd5 cool+1 al?\gh !y are naturally m s5sitive to sudd5 heat+4 ,9 ?is respect !y diff] entirely f ord9>y glass1 :i* is consid]ably m s5sitive to sudd5 cool+ ?an to sudd5 heat+1 p>ticul>ly :5 ! heat or cold is appli$ to all ! surfaces ( ! object at ! same "t4 ,! special tubes made ( two lay]s ( glass above ref]r$ to are manufactur$ by ! ,j5a ,glass ,works = special purposes1 among :i* boil] gauge glasses are ! mo/ important4 ,x %\ld be also m5tion$ "h t ! rem>kable !rmal endurance ( vitrifi$ silica1 :i* c be rais$ to a r$ heat & !n imm]s$ 9 cold wat] )\t risk ( breakage1 is *iefly due to its v l[ coeffici5t ( expansion4 ,9 ano!r direction ! expansive prop]ties ( glass are ( importance :]ev] glass is rigidly atta*$ to metal4 ,at ! pres5t "t ?is is done 9 sev]al indu/rial products1 su* z inc&esc5t electric lamps & 8wir$0 plate glass4 ,9 c]ta9 v>ieties ( inc&esc5t lamps1 metallic wires are seal$ into ! glass bulbs1 & ! only metal available = ?is purpose1 at all ev5ts until rec5tly1 has be5 plat9um1 ^: coeffici5t ( expansion is l[ z comp>$ ) mo/ metals1 & ^: fre$om f oxidation :5 heat$ to ! necess>y temp]ature makes x easy to produce a clean jo9t betwe5 glass & metal4 ,m rec5tly ! use ( c]ta9 v>ieties ( nickel /eel has be5 pat5t$ = ?is purpose1 s9ce x is possible to obta9 nickel /eel alloys ( almo/ any desir$ coeffici5t ( expansion f t ( ! alloy kn[n z 8inv>10 hav+ a negligibly small expansion comp>$ ) t ( ord9>y /eel4 ,by *oos+ a suitable memb] ( ?is s]ies a metal c\ld be obta9$ ^: coeffici5t ( expansion corresponds exactly ) t ( ! glass to :i* x is to be unit$4 ,! oxidation ( ! nickel /eel :5 heat$ to ! temp]ature necess>y = effect+ its union ) ! glass pres5t$ s]i\s difficulties to ! production ( a tight jo9t1 & sev]al devices = avoid+ ?is oxidation h be5 pat5t$4 ,9 ! inc&esc5t electric lamp1 al?\gh ! jo9t betwe5 glass & metal is requir$ to be p]fectly air-tight1 ! two bodies are only atta*$ to "o ano!r ov] a v %ort l5g?4 ,9 wir$ plate glass1 h[ev]1 an entire lay] ( wire nett+ is int]pos$ betwe5 two lay]s ( glass1 ! wire be+ ins]t$ dur+ ! process ( roll+4 ,"h a c]ta9 am\nt ( oxidation ( ! wire is n ( any s]i\s importance1 z x only appe>s to give rise to a few bubbles1 ^: pres5ce does n int]f]e ) ! /r5g? & usefulness ( ! glass2 b any consid]able diff]5ce ( coeffici5t ( expansion w produce ! mo/ s]i\s results on acc\nt ( ! great l5g?s ( glass & metal t are atta*$ to ea* o!r4 ,?is factor has be5 neglect$ by "s manufactur]s1 ) ! result t mu* ( ! wir$ glass ( comm]ce is liable to crack spontane\sly "s "t aft] x has left ! manufactur]'s h&s1 :ile !re is also mu* loss by breakage dur+ ! process ( manufacture4 ,!rmal expansion is a vital factor 9 yet ano!r ( ! uses ( glass4 ,our ord9>y in/rum5t = measur+ temp]ature--! m]cury !rmomet]--is v consid]ably affect$ by ! expansive behavi\r ( glass4 ,:5 a m]cury !rmomet] is w>m$ ! m]cury column rises 9 ! /em because ! m]cury exp&s ^u w>m+ to a great] ext5t ?an ! glass vessel1 bulb & /em1 9 :i* x is conta9$4 ,! subject ( ! graduations & corrections ( ! m]cury glass !rmomet] is a v l>ge "o & some:at outside ! scope ( ! pres5t volume2 b att5tion %\ld be drawn 9 ?is place to ! peculi>ities ( ! behavi\r ( glass t h be5 discov]$ 9 ?is connection4 ,"o ( ^! is t :5 fir/ bl[n ! bulb ( a !rmomet] takes a v consid]able "t to acquire its f9al volume1 ! result be+1 t if a fre%ly made !rmomet] is graduat$1 aft] "s "t ! z]o ( ! in/rum5t w be f\nd consid]ably *ang$1 g5]ally 9 a direction :i* indicates t ! volume ( ! bulb has slightly increas$4 ,by a special anneal+ or 8age+0 process ?is *ange c be complet$ 9 a comp>atively %ort "t be=e ! in/rum5t is graduat$4 ,!re is1 h[ev]1 a fur!r peculi>ity :i* is prom95t 9 "s !rmomet]s1 al?\gh v greatly r$uc$ 9 ! be/ mod]n glasses4 ,?is becomes app>5t 9 a decid$ *ange ( z]o :5ev] ! !rmomet] has be5 expos$ = any l5g? ( "t to a high temp]ature1 ! z]o gradually return+ m or less to its orig9al position 9 ! c\rse ( "t4 ,) !rmomet]s made ( glasses liable to ^! ab]rations1 ! read+ = a giv5 temp]ature dep5d$ l>gely ^u ! imm$iate pa/ hi/ory ( ! in/rum5t2 b1 ?anks to ! ,j5a ,works1 !rmomet] glasses are n[ available :i* are almo/ entirely free f ?is defect4 ,9 ?is connection ! curi\s fact has be5 obs]v$ t glass conta9+ bo? ! alkalies 7pota% & soda7 %[s ^! !rmal effects mu* m m>k$ly ?an a glass conta9+ "o ( ! alkalies only4 ,! !rmal conductivity ( glass1 except 9 s f> z x affects ! !rmal endurance1 is n a matt] ( any great direct practical importance1 al?\gh ! fact t glass is always a comp>atively poor conductor ( heat is utilis$ 9 _m ( its applications1 z1 = example1 ! con/ruction ( cons]vatories & hot-h\ses1 al?\gh ev5 9 t case ! opacity ( glass to !rmal radiations ( long wave-l5g?s is ( m importance ?an its l[ !rmal conductivity4 ,simil> /atem5ts apply1 9 a /ill m m>k$ degree1 to ! subject ( ! specific heat ( glass4 ,! electrical prop]ties ( glass are ( mu* great] practical importance1 glass be+ frequ5tly us$ 9 electrical appliances z an insulat+ m$ium4 ,! insulat+ prop]ties ( glass1 z well z ! prop]ty kn[n z ! specific inductive capacity1 v>y greatly accord+ to ! *emical composition ( ! mat]ial4 ,g5]ally speak+1 ! h>d] glasses1 i4e41 ^? ri*e/ 9 silica & lime1 are ! be/ insulators1 :ile s(t glasses1 ri* 9 lead or alkali1 are mu* poor] 9 ?is respect4 ,9 practice1 p>ticul>ly :5 ! glass insulator is expos$ to ev5 a mod]ately damp atmosph]e1 ! nature ( ! glass affects ! result+ insulation or abs5ce ( insulation1 9 ano!r way4 ,almo/ all v>ieties ( glass h ! prop]ty ( cond5s+ ^u _! surfaces a decid$ film or lay] ( moi/ure f ! atmosph]e1 &1 z we h se5 above1 glasses diff] v consid]ably 9 ! degree to :i* !y display ?is hygroscopic t5d5cy4 ,! s(t] glasses are mu* m hygroscopic ?an ! h>d ones1 & ! result+ film ( surface moi/ure s]ves to less5 or ev5 to break d[n ! insulat+ p[] ( ! glass1 ! electricity leak+ away along ! film ( moi/ure4 ,9 ! case ( appliances = /atic electricity1 :]e v high voltages h to be dealt )1 an endeav\r is sometimes made to avoid ?is leakage by v>ni%+ ! surface ( ! glass ) %ellac or o!r simil> sub/ance1 & ?is proves a satisfactory rem$y up to a c]ta9 po9t4 ,q rec5tly a v>iety ( glass has be5 br\ght =w>d :i* is peculi> 9 hav+ a comp>atively l[ electrical resi/ance1 s t = c]ta9 purposes x c be us$ z an electric conductor4 ,al?\gh int]e/+ 9 itself1 ?is glass is n v likely to prove useful ev5 = ! limit$ numb] ( applications t c\ld be f\nd = an electrically conduct+ glass1 s9ce x is v ri* 9 alkali1 & is1 !re=e1 likely to be un/able *emically1 ev5 "u ! action ( atmosph]ic ag5cies alone4 ,! mo/ valuable & 9 _m ways ! mo/ int]e/+ ( ! prop]ties ( glass--its transp>5cy--has n be5 dealt ) z yet1 & all m5tion ( ?is subject has be5 po/pon$ to ! end ( ! pres5t *apt]1 because ! :ole subject ( ! optical prop]ties ( glass w be dealt ) m fully 9 ! *apt] on optical glass 7,*ap4 ,,xii471 s t a v brief ref]5ce only ne$ be made to ! matt] "h4 ,!re c be no d\bt t1 9 mo/ ( its practical applications1 transp>5cy is ! fundam5tal & ess5tial prop]ty :i* leads to ! employm5t ( glass 9 ! place ( ei!r /rong] or *eap] mat]ials4 ,by transp>5cy1 9 ?is s5se1 we wi% to include m]e transluc5ce also1 s9ce v frequ5tly x is z necess>y to avoid undi/urb$ visibility z x is to secure ! admission ( light4 ,x is inde$ h>d to f9d any use to :i* glass is ext5sively put into :i* ! function ( transmitt+ light does n v l>gely ent]4 ,almo/ ! only su* example ( use is ! mod]n application ( opal glass to ! cov]+ ( walls1 & ! use--n z yet widely ext5d$--( press$ glass blocks z bricks & pav+ /ones2 9 ^! cases x is ! h>dness & smoo?ness ( surface t gives to ! vitre\s body its sup]iority ov] o!r mat]ials1 b ap>t f ^! special cases1 ! fact rema9s t well ov] #ie p] c5t4 ( ! glass us$ 9 ! _w is employ$ = purposes :]e transmission ( light is ess5tial to ! atta9m5t ( ! desir$ result1 ei!r f ! po9t ( view ( utility or f t ( beauty4 ,x is int]e/+ to note t ! p[] ( transmitt+ light is n %>$ by _m solid bodies4 ,"s colloidal organic bodies1 su* z gelat9e & celluloid1 possess ! prop]ty to a degree comp>able ) glass1 :ile c]ta9 m9]al cry/als1 su* z qu>tz & fluor-sp>1 may ev5 surpass ! f9e/ glass 9 ?is respect2 :ile "s ( ! o!r optical prop]ties ( glass are greatly exce$$ by su* natural sub/ances z ! diamond & ! ruby4 ,b ! v brevity ( ?is li/ is 9 itself /rik+1 because x mu/ be borne 9 m9d t transp>5cy by no means con/itutes ! only common *>act]i/ic ( vitre\s bodies4 ,al?\gh ! transp>5cy ( glass is s valuable & inde$ s ess5tial a prop]ty ( t sub/ance1 x mu/ be rememb]$ t no k9d ( glass is p]fectly transp>5t4 ,q ap>t f ! fact t ( ! light t falls ^u a glass surface1 h[ev] p]fectly poli%$1 a consid]able proportion is turn$ back by reflection at ! surface ( entry & aga9 by reflection at ! surface ( exit f ! glass1 a c]ta9 proportion ( light is absorb$ dur+ its passage ?r\gh ! glass itself1 & ! transmitt$ beam is correspond+ly weak5$4 ,9 ! pure/ & be/ glasses ?is absorption is s small t 9 any mod]ate ?ickness v delicate in/rum5ts are requir$ to %[ t !re has be5 any loss ( light at all2 b ev5 ! be/ glass1 :5 exam9$ ?r\gh a ?ickness ( #bj 94 or m1 always %[s ! effects ( ! absorption ( light q unmi/akably4 ,9 fact1 n only does all glass absorb light1 b x does ?is to a diff]5t degree accord+ to ! col\r ( ! light1 s t 9 pass+ ?r\gh ! glass a beam ( :ite light becomes weak5$ 9 "o ( its con/itu5t col\rs m ?an 9 ! o!rs1 ) ! result t ! em]g5t light is slightly col\r$4 ,?us ! pure/ & :ite/ ( glasses1 :5 exam9$ 9 v ?ick pieces1 always %[ a decid$ blue or gre5 t9t1 al?\gh ?is t9t is q invisible on look+ ?r\gh a few in*es ( ! glass4 ,! ord9>y glass ( comm]ce1 h[ev]1 is f> remov$ f ev5 ?is approa* to p]fect transp>5cy4 ,! be/ plate glass %[s a slight gre5i%-blue t9t1 :i* is j p]ceptible to ! tra9$ eye :5 a s+le %eet ( mod]ate ?ickness is laid d[n ^u a piece ( :ite pap]4 ,:5 a %eet ( ?is glass is view$ edgewise1 9 su* a way t ! light rea*+ ! eye has trav]s$ a consid]able ?ickness1 ! gre5i%-blue t9t ( ! glass becomes m app>5t4 ,by hold+ /rips ( v>i\s k9ds ( glass1 cut to an equal l5g?1 close toge!r & comp>+ ! col\r exhibit$ by _! ends1 a means ( comp>+ ! col\rs ( app>5tly 8:ite0 glasses is readily obta9$4 ,x w be f\nd t diff]5t specim5s ( glass diff] mo/ m>k$ly 9 ?is respect4 ,%eet glass is1 z a rule1 decid$ly deep] 9 col\r ?an poli%$ plate1 b roll$ plate is z a rule mu* gre5]--! col\r ( ?is glass c1 9 fact1 9 mo/ cases be se5 q pla9ly 9 look+ ?r\gh or at ! %eets 9 ! ord9>y way4 ,! "q ( h[ f> ! col\r ( glass affects ! value ( ! light :i* x transmits dep5ds = its answ] ^u ! purpose to :i* ! light$ space is to be put4 ,:]e delicate comp>isons ( col\r are to be made1 or o!r delicate "w involv+ ! use ( ! col\r s5se is to be c>ri$ on1 x is ess5tial t all col\ration ( ! ent]+ daylight %\ld be avoid$1 & ! use ( ! mo/ col\rless glass obta9able w be desirable4 ,aga91 9 photographic /udios x is important to secure a glass :i* %all absorb z small a proportion ( ! *emically active rays conta9$ 9 daylight z possible1 & special glasses = ?is purpose are available4 ,al?\gh = ! pres5t ! price ( ^! special glasses may prove prohibitive = ! glaz+ ( /udio lights1 _! use is f\nd highly advantage\s :]e artificial light is to be us$ to ! be/ advantage4 ,on ! o!r h&1 = e-day purposes1 ! slight t+e ( col\r introduc$ into ! light by ! col\r ( ord9>y %eet & plate glass1 or ev5 ( gre5i% roll$ plate glass1 has no delet]i\s effect :atev]1 ! majority ( p]sons be+ entirely unconsci\s ( its pres5ce4 ,! transmission ( light by glass1 its absorption1 refraction1 disp]sion1 etc41 are1 h[ev]1 be/ gr\p$ toge!r z ! 8optical0 prop]ties ( glass1 & "u t head+ !y w receive a full] treatm5t 9 connection ) ! subject ( ! manufacture ( glass = optical purposes4 ,,*apt] ,,iii4 ,,! ,,raw ,,mat]ials ,,( ,,glass ,,manufacture4 ,! *oice ( raw mat]ials = all bran*es ( glass manufacture is a matt] ( vital importance4 ,z a rule all 8fix$0 bodies t are once introduc$ into ! glass-melt+ pot or furnace appe> 9 ! f9i%$ glass1 :ile volatile or combu/ible bodies are m or less completely elim9at$ dur+ ! process ( fusion4 ,?us :ile ! *emical manufactur] c purify 8 products by filtration1 cry/allisation or "s o!r process ( sep>ation1 ! glass-mak] mu/ elim9ate all undesirable +r$i5ts be=e !y are p]mitt$ to ent] ! furnace1 & ! /r+5cy ( ?is condition is increas$ by ! fact t ! transp>5cy ( glass makes ! detection ( defects ( col\r or quality exce$+ly easy4 ,= ! production ( ! be/ v>ieties ( glass1 !re=e1 an exact+ /&>d ( purity is appli$ to ! sub/ances us$ z raw mat]ials4 ,z ! quality ( ! product decreases1 s also d ! dem&s ^u ! purity ( raw mat]ials1 until f9ally = ! manufacture ( common gre5 bottles1 ev5 su* v het]og5e\s sub/ances z basaltic rock & ! miscellane\s residues ( brok51 defective & half-melt$ glass =m+ ! refuse ( o!r glassworks may be utilis$ m or less satisfactorily4 ,= ! be/ k9ds ( glass ! mo/ desirable quality 9 raw mat]ials is ?us z ne> an approa* to purity z possible "u comm]cial conditions1 & next to t1 z great a con/ancy ( composition z possible4 ,= in/ance1 ! quantity ( moi/ure conta9$ 9 a ton ( s& appreciably affects ! result+ composition ( ! glass1 & if ! s& _c be obta9$ p]fectly dry1 x %\ld at lea/ conta9 a con/ant proportion ( moi/ure1 o!rwise x becomes necess>y to det]m9e1 by *emical te/s1 ! p]c5tage ( moi/ure 9 ! s& t is us$ f day to day1 & to adju/ ! quantity us$ 9 accordance ) ! results ( ^! te/s1 a proce$+ :i*1 ( c\rse1 mat]ially complicates ! :ole process4 ,9 o!r cases1 v>iable composition is n s readily all[$ =1 & uncontrollable v>iations 9 ! composition ( ! glass result--at times ! quality falls (f unacc\ntably1 or ! glass refuses to melt freely at ! usual temp]ature4 ,! sy/ematic employm5t ( *emical analysis 9 ! sup]vision ( bo? ! raw mat]ials & ( v>i\s products w frequ5tly enable ! manufactur] to trace ! causes ( su* undesirable occurr5ces2 b h[ev] necess>y su* control und\bt$ly is1 x _c entirely comp5sate = ! use ( raw mat]ials liable to too great a v>iation 9 composition or physical "*4 ,= n only ! *emical composition1 b also ! physical condition & prop]ties ( ! mat]ial are ( importance 9 glass manufacture4 ,?us x is ess5tial t mat]ials to be us$ = glass-melt+ %\ld be obta9able 9 a reasonably f9e /ate ( division1 & 9 ?is connection x mu/ be rememb]$ t bo? exce$+ly h>d bodies & s(t pla/ic sub/ances c only be gr\nd ) v great difficulty4 ,fur!r1 :]e a sub/ance occurs naturally z a p[d]1 ?is p[d] %\ld be ( uni=m & n too f9e a gra91 m especially if x belongs to ! class ( refractory r ?an ( flux+ +r$i5ts4 ,9 t case ! pres5ce ( co>s] gra9s w result 9 _! pres5ce 9 ! undissolv$ /ate 9 ! f9i%$ glass1 unless excessive heat & duration ( 8f\nd+0 be employ$ to p]mit ( _! dissolution4 ,?is applies *iefly to silice\s & calc>e\s +r$i5ts1 b h>d5$ nodules ( salt-cake may behave 9 a simil> mann]4 ,a fur!r consid]ation 9 ! *oice ( raw mat]ials is facility ( /orage4 ,?us lime/one 9 ! %ape ( l>ge lumps ( /one :i* are only gr\nd to p[d] z requir$1 is readily /or$1 & und]goes no delet]i\s *ange ev5 if expos$ to ! wea!r2 on ! o!r h&1 sulphate ( soda 7salt-cake71 if /or$ ev5 9 mod]ately dry places1 rapidly agglom]ates into h>d masses1 at ! same "t absorb+ a c]ta9 p]c5tage ( moi/ure4 ,su* prop]ties are n always to be avoid$1 salt-cake = example be+ at ! pres5t "t an indisp5sable +r$i5t 9 _m k9ds ( glass-mak+1 b ! value ( a sub/ance is 9 "s cases mat]ially less5$ by su* causes4 ,! raw mat]ials ord9>ily employ$ 9 glass-mak+ may be gr\p$ into ! foll[+ classes3-- 7#a7 ,s\rces ( silica4 7#b7 ,s\rces ( alkalies4 7#c7 ,s\rces ( bases o!r ?an alkalies4 7#a7 ,s\rces ( ,silica4--,! pr9cipal s\rce ( silica is s&4 ,?is sub/ance occurs 9 nature 9 geological deposits1 (t5 ( v consid]able area & dep?4 ,^! deposits ( s& h always be5 =m$ by ! dis9tegration ( a silice\s rock1 & ! fragm5ts s =m$ h be5 sift$ & transport$ by ! ag5cy ( wat]1 be+ f9ally deposit$ by a riv] ei!r 9 ! sea 7m>9e deposits7 or 9 lakes 7lacu/r9e deposits71 :ile ! action ( ! wat]1 ei!r dur+ transport or aft] deposition1 has frequ5tly worn ! individual p>ticles into ! %ape ( r\nd$ gra9s4 ,9 consequ5ce ( ?is orig91 ! *emical composition ( s& v>ies v greatly ) ! nature ( ! rock ^: d5udation gave rise to ! deposit4 ,:]e rocks v ri* 9 silica1 or ev5 consi/+ ( ne>ly pure silica1 h be5 ?us d5ud$1 ! result+ s& is (t5 v pure1 deposits conta9+ up to #iii p] c5t4 silica be+ kn[n4 ,m frequ5tly1 h[ev]1 ! s& conta9s fragm5ts ( m or less decompos$ felsp>1 :i* introduce alum9a1 iron & alkalies into its composition4 ,f9ally1 8s&s0 ( all ranges ( composition f ! pure v>ieties j ref]r$ to d[n to ! clay m>ls1 v ri* 9 iron & alum9a1 are kn[n4 ,= ! be/ v>ieties ( glass1 viz41 optical glass1 fl9t glass & ! :ite/ %eet-glass1 z well z = ! be/ ,bohemian glass1 a v pure v>iety ( s& is requir$1 pref]ably conta9+ less ?an #jje p] c5t4 ( iron1 & n m ?an #jje p] c5t4 ( o!r impurities su* z alum9a1 lime or alkali4 ,z a matt] ( fact1 s&s conta9+ s little iron r>ely conta9 any o!r impurity except alum9a 9 measurable quantities4 ,! be/-kn[n deposit ( su* s& 9 ,europe is t at ,fonta9ebleau ne> ,p>is1 b equally good s& is f\nd at ,lippe 9 ,g]many1 :5ce s& is deliv]$ comm]cially ) a gu>ante$ silica cont5t ( #iiih p] c5t4 ,s& ( excell5t quality1 al?\gh n q s good z ! above1 is obta9$ at ,hoh5bocka 9 ,g]many 7,saxony7 & at a few o!r places 9 ,europe4 ,9 ,engl& no deposit ( s& ( su* purity is at pres5t be+ exploit$4 ,next 9 ord] ( value to ^! exce$+ly pure s&s1 come ! glass-mak+ s&s ( ,belgium1 notably ( ,ep9al4 ,^! usually conta9 f #jb to #jc p] c5t4 ( iron & r m alum9a1 b !y are us$ v l>gely = ! manufacture ( %eet & plate-glass4 ,:5 ! /&>d ( quality is fur!r relax$1 a l>ge numb] ( s& deposits become available1 & ! manufactur]s ( ea* di/rict avail !mselves ( m or less local supplies2 ?us 9 ,engl& ! s&s ( ,leighton 9 ,b$=d%ire & ( ,lynn on ! ,ea/ ,coa/1 are l>gely us$4 ,f9ally1 = ! manufacture ( ! *eape/ class ( bottles1 s&s conta9+ up to #b p] c5t4 ( iron & a consid]able proportion ( o!r sub/ances are employ$4 ,silica1 9 v>i\s /ates ( purity1 occurs 9 nature 9 a numb] ( o!r =ms ?an t ( s&4 ,by f> ! commone/ ( ^! is t ( m or less compact s$im5t>y rock1 kn[n z 8s&/one40 ,z f> z *emical composition is conc]n$1 "s ( ^! /ones are admirably suit$ = mak+ ! be/ k9ds ( glass1 al?\gh z a rule a /one is n s homog5e\s z ! mat]ial ( a good s&-b$4 ,! /one has ! fur!r disadvantage t x requires to be cru%$ to p[d] be=e x c be us$ = glass-mak+1 & ! cru%$ product is g5]ally a mixture ( gra9s ( all sizes rang+ f a f9e du/ to ! l>ge/ size ( gra9 pass$ by ! sieves atta*$ to ! cru%+ ma*9e4 ,! pres5ce ( ! v f9e p>ticles is a di/9ct objection f ! glass-mak]'s po9t ( view1 s t x w\ld probably be necess>y to wa% ! s& s z to remove ?is du/--a process t 9 itself adds to ! co/ ( ! cru%$ /one & at ! same "t leads to ! loss ( a s]i\s p]c5tage ( ! mat]ial4 ,objections ( ! same k9d apply1 b ) /ill great] =ce1 to ! use ( p[d]$ qu>tz or fl9t z s\rces ( silica = ! glass-mak]2 fur!r1 ^! mat]ials are exce$+ly h>d & !re=e difficult to cru%1 s t ! price ( ! mat]ials is prohibitive = glass-mak+ purposes4 ,! use ( gr\nd qu>tz & fl9t is !re=e conf9$ to ! c]amic indu/ries 9 :i* ^! sub/ances s]ve z s\rces ( silica = bo? bodies & glazes2 9 =m] times1 h[ev]1 gr\nd fl9t 0 ext5sively us$ 9 ! manufacture ( ! be/ k9ds ( glass1 z ! /ill surviv+ "n ( 8fl9t glass0 te/ifies4 ,m9]als ( ! felsp> class1 consi/+ ess5tially ( silicates ( alum9a & "o or m ( ! alkalies1 are ext5sively us$ 9 glass-mak+ & %\ld be m5tion$ "h1 s9ce _! high silica-cont5t 7up to #gj p] c5t47 con/itutes an effective s\rce ( silica4 ,z a s\rce ( ?is sub/ance1 h[ev]1 mo/ felsp>s w\ld be f> too exp5sive1 & _! use is due to _! cont5t ( alum9a & alkali4 7#b7 ,s\rces ( ,alkali4--,orig9ally ! alkal9e con/itu5ts ( glass 7 d]iv$ f ! a%es ( plants & ( seawe$ or 8kelp02 9 bo? cases ! alkali 0 obta9$ 9 ! =m ( c>bonate & 0 ord9>ily us$ 9 a v impure =m2 at ! pres5t "t1 h[ev]1 ! orig9al s\rce ( alkali = indu/rial purposes is f\nd 9 ! natural deposits & o!r s\rces ( ! *lorides ( sodium & potassium4 ,at ! pres5t "t x is n yet indu/rially possible to introduce ! alkalies into glass mixtures 9 ! natural =m ( *lorides4 ,! pr9cipal difficulty 9 do+ ?is arises f ! fact t ! *lorides are volatile at ! temp]ature ( glass-melt+ furnaces & are only act$ ^u by hot silica 9 ! pres5ce ( wat] vap\r4 ,introduc$ into an ord9>y glass furnace1 !re=e1 ^! salts w\ld be driv5 (f z vap\r be=e !y c\ld comb9e ) ! o!r +r$i5ts 9 ! desir$ =m ( d\ble silicates4 ,alkalies are1 !re=e1 introduc$ into ! glass mixture 9 less volatile & m readily attackable =ms4 ,( ^! ! c>bonate is hi/orically ! e>li]1 :ile ! sulphate is at ! pres5t "t indu/rially by f> ! m important4 ,! ,c>bonate ( ,soda1 or soda a%1 :i* is us$ 9 ! production ( "s special glasses1 & is an +r$i5t ( ,engli% fl9t glasses1 is produc$ by ei!r ( two well-kn[n *emical processes4 ,"o ( ^! is ! 8black a%10 or 8,le ,blanc0 process1 9 :i* ! *loride is fir/ conv]t$ into sulphate by ! direct action ( sulphuric acid1 & ! sulphate ?us =m$ is conv]t$ into ! c>bonate by calc9ation ) a mixture ( calcium c>bonate & coal4 ,! sodium c>bonate ?us =m$ is sep>at$ by solution & subsequ5t evaporation4 ,a pur] =m ( sodium c>bonate c be obta9$ ) great regul>ity by ! 8ammonia soda0 process1 9 :i* a solution ( sodium *loride is act$ ^u by ammonia & c>bonic acid "u pressure4 ,soda a% produc$ by ?is process is n[ suppli$ regul>ly = glass-mak+ purposes 9 a /ate ( great purity & con/ancy ( composition4 ,x is ^u ^! qualities t ! great advantages ( ?is sub/ance dep5d1 s9ce its relatively high co/ precludes its use except = special k9ds ( glass1 & = ^! purposes ! qualities nam$ are ( great value4 ,= mo/ purposes ( glass-mak+1 su* z ! production ( %eet & plate-glass ( all k9ds1 ! alkali is introduc$ 9 ! =m ( salt-cake--i4e41 sulphate ( soda4 ,?is product is obta9$ z ! result ( ! fir/ /ep ( ! ,le ,blanc process ( alkali manufacture--i4e41 by ! action ( sulphuric acid on sodium *loride2 salt-cake is ?us a relatively crude product1 & its use is due to ! fact t x is by f> ! *eape/ s\rce ( alkali available = glass-mak+4 ,!re are1 h[ev]1 c]ta9 disadvantages connect$ ) its use4 ,! *ief ( ^! is ! fact t silica _c decompose salt-cake )\t ! aid ( a r$uc+ ag5t2 su* a r$uc+ ag5t is p>tly suppli$ by ! flame-gases 9 ! atmosph]e ( ! furnace1 b 9 addition to ^! a c]ta9 proportion ( c>bon1 9 ! =m ( coke1 *>coal or an?racite coal mu/ be add$ to all glass mixtures conta9+ salt-cake4 ,! use ( a slightly incorrect quantity ( c>bon = ?is purpose leads to disa/r\s results1 :ile ev5 "u ! be/ conditions x is n easy to remove all traces ( sulphur comp\nds f glass made 9 ?is way4 ,a fur!r risk ( tr\ble arises 9 connection ) salt-cake f ! fact t x is nev] entirely free f m or less delet]i\s impurities4 ,accord+ to ! exact mann] 9 :i* x has be5 prep>$1 ! sub/ance always conta9s a small excess ei!r ( undecompos$ sodium *loride or ( free sulphuric acid1 or ! latt] may be pres5t 9 ! =m ( sulphate ( lime4 ,a good salt-cake1 h[ev]1 %\ld conta9 at lea/ #ig p] c5t4 ( anhydr\s sodium sulphate1 & n m ?an #aj p] c5t4 ( ei!r sodium *loride or sulphuric acid4 ,:ile pure sodium sulphate is readily soluble 9 wat]1 ord9>y salt-cake always leaves an insoluble residue1 consi/+ frequ5tly ( m9ute p>ticles ( clay or o!r mat]ial d]iv$ f ! l9+ ( ! furnace 9 :i* x 0 prep>$1 or f ! tools ) :i* x 0 h&l$2 & ^! impurities are liable to become delet]i\s to ! glass if pres5t 9 any quantity4 ,! insoluble residue %\ld n exce$ #je p] c5t4 9 am\nt1 & 9 ! be/ salt-cake is g5]ally "u #jb p] c5t4 ,salt-cake possesses c]ta9 o!r prop]ties t make x some:at tr\blesome to deal ) z a glass-mak+ mat]ial4 ,?us1 on prolong$ exposure1 p>ticul>ly to moi/ air1 ! p[d]$ salt-cake absorbs moi/ure f ! atmosph]e & und]goes p>tial conv]sion into ! cry/all9e =m ( 8,glaub]'s ,salt10 a process :i* results 9 ! =mation ( exce$+ly h>d masses4 ,gr\nd salt-cake1 !re=e1 _c be /or$ = any l5g? ( "t )\t incurr+ ! necessity ( regr9d+1 & ?is accretive action ev5 comes into play :5 mixtures ( glass-mak+ mat]ials1 conta9+ salt-cake z "o +r$i5t1 are /or$4 ,9 practice1 !re=e1 salt-cake c only be gr\nd z x is want$1 & its physical prop]ties make x difficult to gr9d x at all f9e1 :ile ! du/ aris+ f ?is process is peculi>ly irritat+1 al?\gh n s]i\sly injuri\s to heal?4 ,pota% is utilis$ 9 glass-mak+ almo/ entirely 9 ! =m ( c>bonate1 g5]ally call$ 8pe>l-a%40 ,orig9ally d]iv$ f ! a%es ( wood & o!r l& plants1 ?is sub/ance is n[ manufactur$ by processes simil> to ^? describ$ 9 ! case ( soda1 ! raw mat]ial be+ potassium *loride d]iv$ f natural deposits su* z ^? at ,/assfur?4 ,! pe>l-a% ?us comm]cially obta9able is a fairly pure sub/ance1 b its use is complicat$ by ! fact t x is /rongly hygroscopic & rapidly absorbs wat] f ! atmosph]e4 ,:]e x is desir$ to produce pota% glasses ( con/ant composition1 frequ5t analytical det]m9ations ( ! moi/ure cont5ts ( ! pe>l-a% are necess>y1 & ! composition ( ! glass mixture requires adju/m5t 9 accordance ) ! results ( ^! det]m9ations4 ,! alkalies are also introduc$ into glass 9 ! =m ( nitrates 7potassium nitrate1 or saltpetre1 & sodium nitrate1 or nitre72 b al?\gh ^! sub/ances act z s\rces ( alkali 9 ! glass1 !y are employ$ ess5tially = ! sake ( _! oxyg5 cont5ts4 ,su* oxidis+ ag5ts are n1 ( c\rse1 add$ to glass mixtures conta9+ sulphates & c>bon1 b are employ$ to purify ! mixtures conta9+ alkali c>bonates1 & m especially to oxidise ! fl9t glasses4 ,s9ce ^! sub/ances are only introduc$ into glass 9 small quantities _! extreme purity is n ( su* great importance to ! glass-mak]1 & ! ord9>y 8ref9$0 qualities ( bo? nitrates are f\nd amply pure en\gh to answ] ! highe/ requirem5ts4 ,a c]ta9 numb] ( natural m9]als :i* conta9 an appreciable quantity ( alkali are sometimes utilis$ z raw mat]ials = glass manufacture4 ,! mo/ important ( ^! are ! m9]als ( ! felsp> class already ref]r$ to4 ,^!1 h[ev]1 conta9 a consid]able proportion ( alum9a1 :ile all b ! pure/ v>ieties also conta9 m or less consid]able quantities ( iron4 ,"s glass-mak]s reg>d alum9a z an undesirable con/itu5t1 :ile o!rs take ! opposite view1 & ^u ?is view _! use ( felspa?ic m9]als w dep5d4 ,= ! *eap] v>ieties ( glass1 h[ev]1 su* z bottle glass1 felspa?ic m9]als & rocks1 su* z granite & basalt1 are freely us$ z raw mat]ials4 ,ano!r m9]al 9 :i* bo? alkali & alum9a are f\nd is cryolite4 ,?is m9]al is a d\ble fluoride ( soda & alum9a1 ^: prop]ties are p>ticul>ly valuable 9 ! production ( opal & opalesc5t glasses4 ,z a m]e s\rce ( alkali1 h[ev]1 cryolite is mu* too exp5sive4 7#c7 ,s\rces ( ,bases o!r ?an ,alkalies4--,! mo/ important ( ^! are lime & lead oxide1 ! =m] be+ requir$ = ! production ( all v>ieties ( plate & %eet-glass1 z well z = bottles & a l>ge proportion ( press$ & bl[n glass1 :ile lead is an ess5tial +r$i5t ( all fl9t glass4 ,! only o!r base hav+ any consid]able comm]cial importance 9 connection ) glass-mak+ is b>ium oxide1 :ile oxide ( z9c1 magnesia1 & a few o!r sub/ances are us$ 9 ! manufacture ( special glasses = sci5tific1 optical or te*nical purposes1 :]e glass ( special prop]ties is requir$4 ,! metallic oxides :i* are us$ = ! production ( col\r$ glass are1 ( c\rse1 also basic bodies4 ,^! w be treat$ 9 connection ) col\r$ glasses1 ) ! exception ( manganese dioxide1 :i* is us$ 9 l>ge quantities 9 ! manufacture ( _m ord9>y 8:ite0 glasses4 ,calcium ,oxide 7lime7 is g5]ally introduc$ into glass mixtures 9 ! =m ( ei!r ! c>bonate or ! hydrat$ oxide 7slak$ lime74 ,! c>bonate may be d]iv$ ei!r f natural s\rces1 or x may be ( *emical orig91 :ile ! hydrate is always obta9$ by ! calc9ation ( ! c>bonate1 foll[$ by 8slak+0 ! lime ?us produc$4 ,natural calcium c>bonate occurs 9 great quantities 9 ! =m ( *alk & lime/one rocks4 ,bo? v>ieties are us$ = glass-mak+4 ,*alk is a s(t friable mat]ial :i* is apt to clog dur+ ! gr9d+ op]ations1 p>ticul>ly z ! natural product is g5]ally some:at moi/4 ,z reg>ds ! great] "p ( its mass1 *alk is (t5 f\nd 9 a /ate ( great purity1 b x is frequ5tly contam9at$ by ! pres5ce ( scatt]$ masses ( fl9t4 ,*emically ?is impurity is n v objectionable to ! glass-mak]1 s9ce x m]ely introduces a small proportion ( silica ^: pres5ce ne$ sc>cely be all[$ = 9 lay+ d[n ! mixture4 ,on ! o!r h&1 if any fragm5ts ( fl9t rema9 9 ! mixture :5 put into ! furnace1 !y prove v refractory1 & are apt to be f\nd z opaque enclosures 9 ! f9i%$ glass4 ,natural lime/one c also be obta9$ 9 great purity 9 _m p>ts ( ! _w4 ,x is g5]ally a h>d & r brittle rock t c be readily gr\nd to p[d] ( ! requisite degree ( f95ess4 ,fl9t concretions are n s frequ5tly f\nd 9 ?is mat]ial1 b1 on ! o!r h&1 x is (t5 contam9at$ ) magnesia & iron4 ,! =m] +r$i5t1 :5 pres5t 9 small quantities1 t5ds to make ! glass h>d & visc\s1 s t lime/one ( ! l[e/ possible magnesia cont5t %\ld be us$1 especially = ! h>d] k9ds ( glass1 su* z plate & %eet-glass1 etc4 ,! iron cont5ts ( ! lime/one us$ mu/ also be l[ :]e a :ite glass is requir$2 b s9ce a small] quantity ( lime/one is us$ = a giv5 weight ( glass produc$ ?an ! quantity ( s& us$ = ! same purpose1 ! pres5ce ( a some:at high] p]c5tage ( iron is p]missible 9 ! lime/one z comp>$ ) ! s&2 = ! bett] v>ieties ( glass1 h[ev]1 ! iron %\ld n exce$ #jc p] c5t4 ( ! lime/one4 ,slak$ lime is sometimes us$ z ! s\rce ( lime = special glasses :]e ! process ( manufacture r5d]s x desirable to avoid ! evolution ( c>bonic acid gas :i* takes place :5 ! c>bonate is heat$ & attack$ by silica4 ,:5 slak$ lime is us$ only ! wat] vap\r ( ! hydrate is driv5 (f1 & ?is occurs at a mu* l[] temp]ature4 ,= ! production ( slak$ lime1 an adequately pure =m ( lime/one1 pref]ably 9 ! =m ( l>ge lumps1 is burnt 9 a kiln until ! c>bonic acid is entirely driv5 (f2 aft] cool+1 ! lime s =m$ is slak$ by h&4 ,! product s obta9$ is1 h[ev]1 apt to v>y bo? z reg>ds cont5ts ( moi/ure & c>bonic acid1 :i* latt] is readily absorb$ f ! atmosph]e2 ! use ( ?is mat]ial1 !re=e1 requires frequ5t analytical det]m9ations ( ! lime cont5ts & correspond+ adju/m5ts ( ! mixture if con/ant results are requir$4 ,x is possible to introduce lime into glass mixtures 9 ! =m ( gypsum or calcium sulphate1 b ! decomposition ( ?is comp\nd1 l t ( sodium sulphate1 requires ! int]v5tion ( a r$uc+ ag5t su* z c>bon1 & ! difficulties aris+ f ?is s\rce 9 connection ) ! use ( salt-cake are /ill fur!r increas$ 9 ! case ( ! calcium comp\nd4 ,s9ce lime/ones ( consid]able purity are m or less pl5tiful 9 _m di/ricts1 ! comm]cial value ( calcium sulphate = glass-mak+ is probably slight4 ,! ,comp\nds ( ,b>ium may be/ be dealt ) at ?is /age1 s9ce !y are *emically s closely alli$ to ! comp\nds ( lime j describ$4 ,b>ium occurs 9 nature 9 consid]able quantities 9 ! m9]als kn[n z b>ytes 7heavy sp>7 & )]ite respectively4 ,! =m] is ess5tially sulphate ( b>ium1 :ile ! latt] is a c>bonate ( b>ium4 ,! use ( ! sulphate meets ) ! same objection "h z 9 ! case ( calcium sulphate discuss$ above1 except t ! b>ium comp\nd is mu* m easily r$uc$ & decompos$ ?an ! lime comp\nd4 ,! natural m9]al )]ite is us$ to a consid]able ext5t 9 ! production ( b>ium glasses1 & ^! h be5 f\nd capable ( replac+ lead glasses = c]ta9 purposes4 ,on ! o!r h&1 = ! be/ k9ds ( b>ium glasses1 viz41 ^? requir$ = optical purposes1 ! elem5t is introduc$ 9 ! =m ( artificially prep>$ salts4 ,( ^! ! mo/ important is ! c>bonate1 comm]cially describ$ z 8precipitat$ c>bonate ( b>ium02 ?is precipitat$ comp\nd1 h[ev]1 does n ord9>ily correspond to ! *emically pure sub/ance1 b conta9s m or less consid]able quantities ( sulphur comp\nds4 ,! "q :e!r ^! impurities are or are n objectionable c only be det]m9$ = ea* p>ticul> case1 s9ce mu* dep5ds ^u ! special "* ( ! glass to be produc$4 ,bo? ! nitrate & ! hydrate ( b>ium are comm]cially available1 b !y are v co/ly +r$i5ts = use 9 ! production ( ev5 ! mo/ exp5sive k9ds ( glass2 ^! sub/ances are1 h[ev]1 obta9able 9 a /ate ( consid]able purity1 al?\gh ! hydrate has ! inconv5i5t prop]ty ( rapidly absorb+ c>bonic acid f ! atmosph]e1 ?us becom+ conv]t$ into ! c>bonate4 ,magnesia is ano!r glass-=m+ base t is closely relat$1 *emically1 to calcium & b>ium4 ,?is elem5t is usually introduc$ into glass mixtures 9 ! =m ( ei!r ! c>bonate or ! oxide4 ,! c>bonate occurs 9 nature 9 a m or less pure /ate 9 ! =m ( magnesite1 & by calc9ation1 ! oxide is obta9$4 ,! natural m9]al & its product are1 ( c\rse1 by f> ! *eape/ s\rces ( magnesia1 b z ! elem5t is only us$ 9 comp>atively small quantities1 ! artificial precipitat$ c>bonate or calc9$ magnesia are frequ5tly pref]r$4 ,magnesia is only introduc$ int5tionally 9 notable quantities 9 special glasses :]e ! prop]ties x conf]s are ( special value2 9 ord9>y lime glasses ?is elem5t1 z has already be5 m5tion$1 is to be reg>d$ z an undesirable impurity4 ,z9c oxide lies1 *emically1 betwe5 ! bases already discuss$ on ! "o h&1 & lead oxide on ! o!r4 ,?is elem5t is only introduc$ into special optical glasses1 a special 8z9c cr[n0 hav+ f\nd "s application4 ,*emically prep>$ z9c oxide is almo/ ! only =m 9 :i* ! elem5t is us$1 b ! v volatile "* ( ?is sub/ance mu/ be borne 9 m9d :5 x is introduc$ into glass mixtures4 ,lead is "o ( ! mo/ widely-us$ +r$i5ts ( glass2 ! glasses conta9+ ?is sub/ance 9 notable quantity are all *>act]is$ to a great] or less degree by simil> prop]ties1 su* z consid]able d5sity & high refractive p[]1 & are class$ toge!r "u ! "n 8fl9t glasses40 ,lead is n[ almo/ univ]sally introduc$ into glass mixtures 9 ! =m ( r$ lead1 al?\gh ! o!r oxides ( lead might be employ$ almo/ equally well4 ,r$ lead is a mixture ( two oxides ( lead 7,pb,o & ,pb#b,o#c7 9 approximately su* proportions z to correspond to ! =mula ,pb#c,o#d4 ,x is prep>$ by ! roa/+ ( metallic lead 9 suitable furnaces1 :]e ! molt5 lead is expos$ to curr5ts ( hot air4 ,! product is obta9able 9 consid]able purity1 v small proportions ( silica1 d]iv$ f ! furnace b$1 & ( iron d]iv$ f ! tools ) :i* ! lead is h&l$1 be+ ! pr9cipal =eign sub/ances f\nd 9 good r$ lead4 ,silv] w\ld be an objectionable impurity1 b ow+ to ! mod]n p]fect me?ods ( de-silv]+ lead1 t elem5t is r>ely f\nd 9 lead products4 ,analytical control ( r$ lead z us$ 9 ! glass mixtures1 & consequ5t adju/m5ts ( ! mixture1 are1 h[ev]1 necess>y :]e exact con/ancy 9 ! glass produc$ is desir$4 ,! reason = ?is necessity lies 9 ! fact t ! oxyg5 cont5t1 & !re=e ! lead-oxide 7,pb,o7 cont5t1 v>ies decid$ly f bat* to bat*1 :ile ! mat]ial z actually deliv]$ & us$ frequ5tly conta9s notable proportions ( moi/ure4 ,a ^w %\ld p]haps be said "h z to me?ods ( h&l+ r$ lead on acc\nt ( ! injuri\s effects :i* ! inhalation ( lead du/ produces ^u ! workm5 expos$ to x4 ,= glass-mak+ purposes x is n feasible to adopt ! me?od adopt$ by pott]s ( fir/ 8fritt+0 ! lead & ?us r5d]+ x comp>atively insoluble & innocu\s2 ev5 if ?is 7 done1 ! difficulty w\ld only be mov$ "o /ep fur!r back1 & w\ld h to be ov]come by ^? :o und]took ! prep>ation ( ! frit4 ,! prop] solution ( ! problem1 9 ! writ]'s op9ion1 is to be f\nd 9 prop]ly prev5t+ ! =mation ( lead du/1 or at all ev5ts 9 protect+ ! workm5 f ! risk ( inhal+ x4 ,:]e only small quantities ( lead glass are made1 & !re=e only small quantities ( lead are h&l$ & mix$ at a "t1 x is no d\bt suffici5t to provide ! workm5 engag$ on ?is task ) "s effici5t =m ( respirator to be worn dur+ ! :ole ( ! "t t !y are engag$ on su* "w1 & to take ! fur!r precautions necess>y--by way ( cleanl9ess & ! provision ( prop] mess-rooms--to avoid any risk ( lead du/ ei!r directly or indirectly contam9at+ _! food4 ,:]e1 h[ev]1 l>ge quantities ( fl9t-glass are made e day1 x is possible & prop] to make m p]fect arrangem5ts = ! me*anical h&l+ & mix+ ( ! lead ) ! o!r +r$i5ts by ! provision ( suitable mix+ & transport+ ma*9]y1 s arrang$ z to be du/-tight4 ,x is only fair to /ate1 h[ev]1 t p>tly "u _! own initiative1 p>tly "u pressure f ! au?orities1 glass mak]s 9 ?is c\ntry are comply+ ) ^! requirem5ts 9 an adequate mann]4 ,alum9ium4--,!re are sev]al v>ieties ( glass into :i* alum9a ent]s 9 notable quantities1 ! pr9cipal examples be+ c]ta9 optical & _m opal glasses1 :ile mo/ ord9>y glasses conta9 ?is sub/ance 9 great] or less degree4 ,9 ! latt]1 ! alum9a is d]iv$ by ! inevitable processes ( solution1 f ! fire-clay vessels or walls )9 :i* ! molt5 glass is conta9$1 :ile 9 "s cases ! elem5t is int5tionally introduc$ 9 small proportions 7ab\t #b p] c5t4 to #c p] c5t4 ( ,al#b,o#c7 by ! use ( felsp> z an +r$i5t ( ! mixture4 ,:]e l>g] proportions ( alum9a are requir$1 ! sub/ance is introduc$ 9 ! =m ( ! hydrate1 :i* is obta9able comm]cially 9 a /ate ( almo/ *emical purity1 b ( c\rse at a correspond+ly high co/4 ,9 opal glasses alum9a is d]iv$ p>tly or :olly f felsp>s1 or 9 "s cases f ! use ( ! m9]al cryolite4 ,?is is a d\ble fluoride ( alum9ium & sodium :i* is f\nd 9 great natural masses1 *iefly 9 ,gre5l&4 ,ow+ to ! high price ( ?is m9]al1 h[ev]1 artificial sub/itutes ( ne>ly id5tical composition & prop]ties h be5 introduc$ & are us$ successfully 9 ! glass & enamell+ indu/ries4 ,manganese4--,al?\gh ! oxides ( ?is elem5t really belong to ! class ( col\r+ comp\nds1 !y are s widely us$ 9 ! manufacture ( ord9>y 8:ite0 glasses t x is desirable to deal ) !m "h4 ,! elem5t manganese is mo/ usually introduc$ into glass mixtures 9 ! =m ( ! p]-oxide 7,mn,o#b71 al?\gh ! l[] oxide 7,mn#c,o#d7 c also be us$4 ,! mat]ial ord9>ily us$ is ! natural manganese ore1 m9$ *iefly 9 ,russia2 ! pure/ =ms ( ?is ore consi/ almo/ entirely ( ! p]-oxide1 b 8br[n0 ores1 conta9+ m or less ( ! l[] oxide1 are also us$ ) success4 ,^! ores always conta9 small am\nts ( iron & silica1 b provid$ ! iron is n pres5t 9 any consid]able quantity1 ! value ( ! ore is measur$ by ! p]c5tage ( manganese :i* x conta9s4 ,! col\r+ & 8decol\ris+0 action ( manganese w be discuss$ 9 a lat] *apt]4 ,c]ta9 o!r sub/ances1 :i* h be5 sugge/$ z ei!r sub/itutes =1 or improvem5ts ^u1 manganese = ?is purpose ne$ only be m5tion$ "h1 viz41 nickel1 sel5ium & gold4 ,ars5ic is ano!r sub/ance frequ5tly introduc$ into 8:ite0 glass mixtures4 ,?is elem5t is univ]sally introduc$ 9 ! =m ( ! :ite ars5ic ( comm]ce 7i4e41 ars5i\s acid1 ,z#b,o#c7 :i* is obta9$ 9 a pure =m by a process ( sublimation4 ,ow+ to ! v poison\s nature ( ?is mat]ial1 special precautions mu/ be tak5 9 its use = glass-mak+ purposes to avoid all risk ( poison+4 ,c>bon4--,z has already be5 indicat$1 an admixture ( c>bon 9 "s suitable =m is ess5tial 9 ! case ( c]ta9 glass mixtures4 ,! c>bon = ?is purpose may be us$ 9 ! =m ( ei!r *>coal1 coke1 or an?racite coal4 ,( ^!1 *>coal is und\bt$ly ! pure/ =m ( c>bon1 b x is excessively exp5sive 9 ?is c\ntry4 ,coke v>ies v mu* 9 quality accord+ to ! coal f :i* x has be5 produc$1 b x always conta9s notable proportions ( a% ri* 9 iron1 & also "s sulphur4 ,an?racite coal c be obta9$ 9 a v pure =m1 conta9+ consid]ably less a% ?an t f\nd 9 mo/ k9ds ( coke1 & ?is is !re=e probably ! mo/ conv5i5t =m ( c>bon = ?is purpose4 ,,*apt] ,,iv4 ,,crucibles ,,& ,,furnaces ,,= ,,! ,,fusion ,,( ,,glass4 ,= ! successful production ( sub/ances :i* are =m$ by a process ( fusion1 ! use ( refractory mat]ials ( a prop] k9d is ( great importance4 ,9 ! production ( glass ! d\ble difficulty has to be ov]come ( f9d+ sub/ances capable ( be+ =m$ into furnaces & crucibles :i* %all n only resi/ ! s(t5+ & melt+ action ( ! furnace heat = long p]iods ( "t1 b %all also resi/ ! dissolv+ action ( ! molt5 glass itself4 ,! refractory mat]ials employ$ 9 connection ) glass-mak+ ?us fall into two di/9ct gr\ps1 memb]s ( "o gr\p be+ ^? :i* meet bo? ( ! above requirem5ts & c !re=e be us$ 9 positions expos$ to direct contact ) molt5 glass1 :ile memb]s ( ! second gr\p are mat]ials :i* resi/ ! action ( ! heat & flame gases b _c resi/ ! dissolv+ effect ( ! glass itself2 ^!1 ( c\rse1 c only be plac$ :]e molt5 glass is n liable to t\* !m4 ,we %all deal ) ! =m] gr\p fir/4 ,^? portions ( glass-melt+ plant :i* come into contact ) molt5 glass are almo/ univ]sally made ( "s =m ( fire-clay4 ,to discuss 9 detail ! composition & prop]ties ( ! v>ieties ( fire-clay be/ suit$ to ?is purpose w\ld exce$ ! entire limits ( ?is book1 s t only a few lead+ pr9ciples c be /at$4 ,tak+ fir/ ! clays int5d$ = ! production ( crucibles or 8pots10 we f9d t = ! purposes ( ! production ( su* objects ! prep>$ clay mu/ possess a c]ta9 degree ( pla/icity :ile damp & a consid]able degree ( /r5g? :5 dri$4 ,! dri$ & burnt mat]ial mu/ be s refractory z to resi/ ! high temp]atures us$ 9 glass-melt+ )\t und]go+ fusion or ev5 s]i\s s(t5+4 ,clays ( v>i\s composition & physical nature also diff] v widely 9 _! p[] ( resi/+ ! *emical attack ( molt5 glass2 all clays are m or less dissolv$ "u ^! circum/ances1 b n only ! rate1 b also ! mann]1 ( dissolution is ( importance1 s t frequ5tly a clay :i* dissolves rapidly b uni=mly is pref]r$ to "o :i* dissolves m sl[ly b 9 su* an irregul> mann] z to ?r[ (f p>ticles ( undissolv$ mat]ial :i* contam9ate ! glass 9 ! =m ( opaque enclosures or 8/ones40 ,x is also to be not$ t ! be/ results 9 ?is direction c only be obta9$ by c>eful adaptation ( ! clay employ$ to ! p>ticul> k9d ( glass :i* is to be melt$ 9 ! crucibles 9 "q4 ,9 ,engl& ?is "q has n receiv$ ! am\nt ( att5tion x des]ves1 b 9 ,g]many & ,am]ica ! available fire-clays ( ! c\ntry h be5 sy/ematically /udi$ & exploit$4 ,z a result ! glass-mak] has at 8 disposal a l>ge selection ( mat]ials ( accurately kn[n physical & *emical prop]ties4 ,by c>efully correlat+ ^! ) ! p]=mance ( 8 8pots0 9 ! furnaces1 ! manufactur] is able to select ! mo/ suitable mat]ial1 & is1 moreov]1 9 a position to "k 9 :at direction to look = improvem5t or = replacem5t if ! supply ( a satisfactory br& %\ld cease4 ,we may n[ foll[ briefly ! process ( manufacture ( a fire-clay pot or crucible4 ,! size & %ape ( ! crucible w dep5d ^u ! p>ticul> purpose = :i* x is int5d$4 ,crucibles v>y+ 9 capacity f #d cwt4 to #b tons ( glass are us$ = v>i\s k9ds ( glass1 b ! m usual sizes lie betwe5 #cj 94 & #ej 94 9 diamet]4 ,= _m k9ds ( glass ! %ape ( ! pot is simply t ( an op5 bas91 circul> or oval 9 plan & l>g] 9 diamet] at ! brim ?an at ! base 7,fig4 #a71 b = ! production ( fl9t glass1 & ( o!r glasses :i* are to be protect$ f contact ) ! flame & gases ( ! furnace1 s-call$ 8cov]$0 pots are us$4 ,9 ^! ! bas9--"h ( a m ne>ly cyl9drical %ape--is cov]$ ov] by a dome1 & access is all[$ only by a relatively small hood$ op5+ 7,fig4 #b74 ,cov]$ pots are built up on wood5 m\lds1 :i* are made collapsible1 & are remov$ be=e ! dry+ ( ! pot is begun4 ,illu/ration3 ,,fig4 #a4--,op5 8pot0 or crucible = glass melt+4 ,illu/ration3 ,,fig4 #b4--;,cov]$ pot = glass melt+1 z us$ = fl9t glass & optical glass4 ,! mat]ial = pot-mak+ is fir/ prep>$ ) great c>e4 ,! prop] v>iety ( clay hav+ be5 select$1 x is gr\nd to a f9e p[d] 9 suitable mills & c>efully siev$2 ) ?is f9e clay p[d] is mix$1 9 accurately det]m9$ proportions1 a quantity ( cru%$ burnt fire-clay4 ,9 "s works ?is burnt mat]ial is obta9$ by simply gr9d+ up fragm5ts ( old us$ pots1 b ! bett] practice is to burn specially-select$ fire-clay sep>ately = ?is purpose4 ,! quantity ( su* burnt mat]ial add$ to ! mixture dep5ds ^u ! *emical nature & especially on ! pla/icity ( ! virg9 clay employ$2 ) s-call$ 8fat0 or v pla/ic clays up to #ej p] c5t4 ( burnt mat]ial is add$1 b ) ! lean] clays1 su* z ^? ( ! ,/\rbridge di/rict 9 ,engl&1 v mu* small] proportions are us$4 ,! object ( ?is addition ( burnt mat]ial is to facilitate ! safe dry+ ( ! f9i%$ pots & to dim9i%--by dilution--! total am\nt ( contraction :i* takes place bo? :5 pla/ic clay is all[$ to dry1 & fur!r :5 ! dry mass is subsequ5tly burnt2 ! burnt mat]ial or 8*amotte10 hav+ already und]gone ^! %r9k+ processes1 acts bo? z a neutral dilu5t & also z a skeleton /r5g!n+ ! :ole mass & r$uc+ ! t5d5cy to =m cracks4 ,! virg9 clay & *amotte hav+ be5 intimately mix$1 ! :ole mass is 8wet up0 by ! addition ( a prop] proportion ( wat] & prolong$ & vigor\s knead+1 usually 9 a suitable pug mill4 ,! mass leaves ?is mill z a fairly /iff1 pla/ic d\gh1 b ! full t\ghness & pla/icity ( su* clay mixtures c only be develop$ by prolong$ /orage ( ! damp mass4 ,9 ! next /age ( ! process1 ! pla/ic clay is pass$ to ! 8pot mak]0 9 ! =m ( ?ick rolls1 & ) ^! he gradually builds up ! pots or crucibles f day to day1 all[+ ! l[e/ p>ts to dry suffici5tly to enable !m to be> ! weight ( ! upp] p>ts )\t giv+ way4 ,! build+ ( l>ge pots 9 ?is way occupies sev]al weeks1 & dur+ ?is "t ! premature dry+ ( any "p ( ! pot mu/ be c>efully avoid$4 ,aft] ! completion ( ! pot1 dry+ is all[$ to take place1 sl[ly at fir/1 b m vigor\sly aft] a "t :5 ! risk ( crack+ is small]2 :5 x is tak5 into use1 ! pot is usually _m mon?s old & is ?or\ghly air-dry4 ,! clay1 h[ev]1 is /ill hydrat$1 i4e41 conta9s *emically comb9$ wat]1 & ?is is only expell$ dur+ ! e>ly /ages ( ! burn+ process4 ,?is process is c>ri$ out 9 small] furnaces or kilns plac$ ne> ! melt+ furnaces4 ,9 ^! ! pot or pots are expos$ to a v gradually increas+ temp]ature1 until a bright r$ heat is f9ally atta9$4 ,?is is a delicate process 9 :i* great c>e is requir$ to secure gradual & uni=m heat+1 especially dur+ ! e>li] /ages1 o!rwise ! pots are apt to crack & become useless4 ,f9ally1 :5 a bright r$ heat has be5 ma9ta9$ = at lea/ a day1 ! pots are ready to be plac$ 9 ! furnace1 & ?is is ord9>ily done :ile bo? pots & furnace are at a r$ heat1 ! pots nev] be+ all[$ to cool d[n aga9 once !y h be5 burnt4 ,fire-clay is also us$ 9 ! manufacture ( bricks & blocks ( v>i\s sizes requir$ = ! con/ruction ( glass-melt+ furnaces4 ,"h fire-clay is only us$ 9 positions :]e contact ) molt5 glass is expect$1 z 9 ! walls ( ! bas9 or tank prop] 9 8tank0 furnaces1 or at a level bel[ t ( ! pot or crucible 9 pot furnaces2 9 ! latt] position leakage ( glass f brok5 pots or ov]fl[ be+ liable to result 9 an accumulation ( molt5 glass on ! floors or walls ( ! furnace & passages4 ,! fire-bricks us$ 9 ^! latt] positions are usually ( a mu* poor] quality ( fire-clay ?an t us$ = ! manufacture ( pots1 & ?is is ju/ifi$ 9 s f> z c]ta9 ( ! requirem5ts t apply to crucibles d n apply "h--b on ! o!r h& ! use ( m refractory bricks w\ld result 9 a long] life = ! furnace4 ,su* bricks1 x %\ld be not$1 are n laid 9 mort> :5 us$ = furnace con/ruction1 b are set 9 a ?9 pa/e ( fire-clay 9 wat]1 & ^! jo9ts are kept z ?9 z possible4 ,! "p ( ! furnace kn[n z ! 8siege0 7,fr5* 8sige071 i4e41 ! floor ( ! furnace ^u :i* ! pots are plac$1 is usually built ( v l>ge blocks ( fire-clay1 made ( co>se mat]ials calculat$ to give great /r5g?4 ,at or ne> ! po9ts :]e ! flame ent]s ! furnace1 ^! blocks rapidly we> away1 p>tly by melt+ b *iefly by a process ( abrasion1 = x seems t a rapidly mov+ flame has an abrad+ action ( a v m>k$ k9d4 ,! actual tanks or bas9s :i* conta9 ! molt5 glass 9 tank furnaces are also built ( l>ge blocks ( fire-clay1 b ^! are made ( ! be/ procurable mat]ials1 & %\ld receive at lea/ z mu* c>e 9 e respect z crucibles2 x is true t _! %ape & size gives !m great] /r5g?1 b on ! o!r h& ^! blocks are expect$ to resi/ ! contact ( molt5 glass = v mu* long] p]iods ( "t ?an ! av]age crucible4 ,to und]/& ! requirem5ts = tank-blocks x is necess>y to anticipate ! next section to ! ext5t ( /at+ t 9 tank furnaces ! glass is conta9$1 dur+ melt+1 ref9+ & work+1 9 a bas9 built up ( l>ge blocks4 ,^! blocks are n cem5t$ toge!r 9 any way1 b are built up 8dry0 & are support$ on ! outside by a sy/em ( iron b>s & rods4 ,! molt5 glass p5etrates betwe5 ! blocks to a c]ta9 ext5t1 b z ! outside ( all su* blocks is int5tionally kept z cold z possible ! glass rapidly /iff5s z x p5etrates fur!r into ^! int]/ices1 & ?is /iff5$ glass effectually b9ds ! blocks toge!r & prev5ts all leakage4 ,x w ?us be se5 t ! blocks are expos$ to ! full heat ( ! furnace & to ! corrod+ action ( ! glass on ! inn] side1 b are kept cold on ! out] side4 ,z ?is /ate ( affairs t5ds to produce cracks1 ^! blocks are necess>ily made ( r co>se mat]ial4 ,on ! o!r h&1 ! mat]ial ( a block nev] gets s hot z ! wall ( a crucible1 :i* is heat$ f bo? sides1 s t extreme refractor9ess is n s ess5tial4 ,x is impossible1 )9 ! limits ( ?is *apt]1 to g into ! details ( ! *oice ( mat]ials = tank-blocks2 x is a subject ^u :i* no f9ally satisfactory conclusion has yet be5 rea*$1 & :at has be5 said above w suffice to %[ ! nature ( ! consid]ations ^u :i* su* *oice mu/ be bas$4 ,we n[ turn to ! second class ( refractory mat]ials us$ 9 ! con/ruction ( glass-melt+ furnaces1 viz41 ^? :i* are s plac$ z n to come into contact ) molt5 glass4 ,"h me*anical /r5g? & refractor9ess are almo/ ! only consid]ations1 b 9 ! ro(-vaults or 8cr[ns0 ( tank furnaces & also ( furnaces 9 :i* glass is melt$ 9 op5 pots1 !re is ! fur!r consid]ation t ! mat]ial ( ! bricks us$ %all n conta9 notable quantities ( any col\r+ oxide1 s9ce small flakes1 etc41 are apt to drop d[n into ! molt5 glass1 & w\ld ?us be liable to cause s]i\s discol\ration4 ,su* a mat]ial z *rome-ore brick is !re=e exclud$4 ,z a matt] ( fact1 "s =m ( 8silica brick0 is 9 univ]sal use4 ,bricks ( ?is mat]ial1 o!rwise kn[n z 8,d9as bricks0 f ! place ( _! fir/ orig91 9 ,wales1 consi/ ( ab\t #ih p] c5t4 ( silica 7,si,o#b74 ,pure silica _c be bak$ or burnt into coh]5t bricks entirely by itself1 s9ce x possesses nei!r pla/icity :5 wet nor any b9d+ p[] :5 burnt1 b an admixture ( ab\t #b p] c5t4 ( lime & a little alum9a makes x possible fir/ to m\ld ! bricks :5 wet & !n to burn !m s z to =m fairly /rong1 coh]5t blocks4 ,^! are ( amply adequate refractor9ess = ! highe/ temp]atures t c be atta9$ 9 indu/rial gas-fir$ furnaces1 & _! me*anical /r5g? is suffici5t to make x possible to build vaults ( consid]able span1 b on ! o!r h& ?is mat]ial requires v gradual heat+ & con/ant wat*+ :ile ! temp]ature is ris+ or fall+ to any consid]able ext5t2 ! reason = ?is difficulty lies 9 ! fact t silica bricks swell v m>k$ly dur+ heat+1 s t unless a vault built ( ?is mat]ial is giv5 room to spread some:at1 x w rise s]i\sly & may ev5 break up completely4 ,?is risk is avoid$ by gradually slack5+ ! tie-bolts t hold ! vault toge!r1 & correspond+ly 8tak+ up ! slack0 z ! vault cools :5 ! furnace is let out4 ,sudd5 local heat also has a disa/r\s effect on ?is mat]ial1 produc+ s]i\s flak+4 ,= positions :]e int5se heat is to be borne1 & at ! same "t me*anical /r5g? is requir$1 silica brick is a mo/ valuable mat]ial1 b ow+ to its *emical composition x is rapidly attack$ by molt5 glass or by any mat]ial conta9+ a notable proportion ( basic con/itu5ts1 s t ! silica bricks c only be employ$ out ( contact ) glass4 ,we n[ turn to consid]1 v briefly1 ! g5]al design & arrangem5t ( "s typical glass-melt+ furnaces4 ,! olde/ & simple/ =m ( furnace is1 9 effect1 simply a box built ( fire-brick1 9 ! c5tre ( :i* /&s ! crucible1 :ile a fire ( wood or coal is plac$ ^u ei!r side4 ,to atta9 any great degree ( heat by su* means1 h[ev]1 ! size ( ! box or *amb] & especially ( ! grates 9 :i* ! fires are ma9ta9$ mu/ be prop]ly proportion$ bo? to ! dim5sions ( ! crucible & to ea* o!r4 ,! grates are g5]ally wide & deep1 :ile draught is provid$ by means ( a tall conical *imney :i* /&s ov] ! entire *amb] & communicates ) x by a numb] ( small op5+s4 ,9 a m ref9$ furnace1 ! *amb] itself is d\ble1 & ! flame1 aft] play+ ar\nd ! crucible 9 ! inside ( ! *amb]1 is made to pass ?r\gh ! space betwe5 ! out] & inn] *amb] be=e pass+ to ! *imney or cone4 ,we ne$ n give any great] att5tion to ^! primitive furnaces1 s9ce !y are practically obsolete at ! pres5t "t4 ,9 mod]n furnaces ! process ( combu/ion is c>ri$ on 9 two di/9ct /ages2 ! fir/ /age takes place 9 a subsidi>y appliance kn[n z a 8gas produc]10 :]e "p ( ! heat :i* ! fuel is capable ( g5]at+ is utilis$ = ! production ( a combu/ible gas2 ?is gas passes into ! furnace prop]1 ei!r direct1 :ile x is /ill hot f ! produc]1 or aft] be+ convey$ "s di/ance1 :5 x is aga9 heat$ up by ! wa/e heat ( ! furnace4 ,9 ei!r case ! gas is hot :5 x ent]s ! furnace prop]1 & !re x meets a curr5t ( air1 also heat$ by ! aid ( ! wa/e heat ( ! furnace4 ,hot gas & hot air burn rapidly & completely1 & if prop]ly proportion$ yield exce$+ly high temp]atures4 ,see+ t 9 ?is process a "p ( ! heat ( combu/ion yield$ by ! fuel is g5]at$ 9 a subsidi>y appliance & is ?us lo/ to ! furnace1 x appe>s at fir/ sight some:at surpris+ t ?is sy/em ( fir+ is v consid]ably m effici5t ?an ! old 8direct0 sy/em :]e ! :ole ( ! fuel is burnt 9 ! furnace itself4 ,b ! advantage arises f ! fact t 9 ! new] sy/em ! fuel is h&l$ 9 ! gase\s =m4 ,?is has ! advantage1 fir/ & mo/ important1 t ! heat escap+ f ! furnace 9 ! hot products ( combu/ion 7*imney gases7 c be transf]r$ to ! incom+ unburnt gas & air & c ?us be return$ to ! furnace4 ,! mann] 9 :i* ?is is accompli%$ w be consid]$ bel[1 b x may be not$ "h t 9 "s furnaces ! escap+ products ( combu/ion are s ?or\ghly cool$ t !y are unable to produce an effective draught 9 ! *imney ( ! furnace4 ,ano!r advantage ( ! use ( gase\s fuel is ! fact t complete combu/ion c be obta9$ )\t ! use ( s great excess ( air1 su* z is requir$ :5 solid fuels are to be burnt completely4 ,= ?is reason mu* high] temp]atures c be readily obta9$ ) gase\s fuel1 :ile ! pre-heat+ ( bo? gas & air also facilitates ! atta9m5t ( high temp]atures2 fur!r1 ! great facility ) :i* ! fl[ ( ei!r gas or air c be regulat$ by means ( suitable valves1 makes x possible to secure mu* great] regul>ity 9 ! work+ ( ! furnaces4 ,f9ally1 9 mod]n gas-produc]s1 ! am\nt ( s5sible heat g5]at$ & !re=e lo/ to ! furnace1 is kept v l[1 ! great] "p ( ! heat set free by ! p>tial combu/ion ( coal 9 ! produc] be+ absorb$ by ! decomposition ( a correspond+ quantity ( /eam into hydrog5 & c>bonic oxide gas4 ,! gas z x leaves "o ( ^! produc]s is n v hot1 & ! p]c5tage ( heat lo/ 9 ?is way is !re=e mu* small] ?an 9 ! old] =ms ( gas-produc]4 ,x is aga9 impossible1 )9 ! limits ( ?is *apt]1 to ent] into ! details ( con/ruction & work+ ( gas-produc]s4 ,we mu/ cont5t ourselves ) say+ t mo/ mod]n produc]s are ( ! =m ( a t[] 9 :i* a ?ick b$ ( fuel is p>tially burnt & p>tly gasifi$ "u ! action ( a bla/ ( air mix$ ) /eam4 ,! *emical actions t take place are complicat$1 b ! f9al result is ! production ( a gas conta9+ f #b to #h or #aj p] c5t4 ( c>bonic acid1 #aj to #bj p] c5t4 ( hydrog51 #h to #be p] c5t4 ( c>bonic oxide 7,,co71 #a to #c p] c5t4 me?ane 7,,*#d71 & #de to #fj p] c5t4 ( nitrog51 ) v>y+ quantities ( moi/ure1 t>ry matt]1 & ammonia4 ,9 good produc] gas1 ! combu/ible con/itu5ts 7hydrog51 c>bonic oxide & me?ane7 %\ld total f #cj to #dh p] c5t4 ( ! :ole by volume1 b ! exact composition to be expect$ dep5ds v mu* on ! type ( produc] & ! class ( fuel us$4 ,"s produc]s are capable ( deal+ ) exce$+ly l[-grade fuels1 & ! gas :i* !y yield c /ill be utilis$ = obta9+ ! highe/ temp]atures--a proce$+ t w\ld h be5 impossible if x _h be5 attempt$ to burn ^! fuels directly 9 ! furnace4 ,illu/ration3 ,,fig4 #c4--;,diagram ( ! arrangem5ts ( a reg5]ative furnace4 ,! gas on leav+ ! produc] passes along fire-brick flues or passages to ! furnace prop]2 ! pa? :i* x is n[ caus$ to take v>ies some:at accord+ to ! arrangem5t ( ! furnace 9 "q4 ,mod]n gas-fir$ furnaces usually belong to "o ( two di/9ct types accord+ to ! mann] 9 :i* ! heat ( ! escap+ products ( combu/ion is utilis$ = heat+ ! incom+ gas & air2 ^! two types are kn[n z ! 8reg5]ative0 & ! 8recup]ative0 respectively4 ,9 reg5]ative furnaces ! hot products ( combu/ion1 aft] leav+ ! furnace *amb] prop]1 & be=e rea*+ ! *imney1 pass ?r\gh *amb]s :i* are loosely /ack$ ) fire-bricks2 ^! *amb]s absorb ! heat ( ! escap+ gases1 & ?us rapidly become hot4 ,z soon z a suffici5tly high temp]ature is atta9$ 9 ^! *amb]s or 8reg5]ators10 ! pa? ( ! gas-curr5ts is alt]$2 ! escap+ products ( combu/ion are made to pass ?r\gh1 & ?us to heat a second set ( reg5]at+ *amb]s1 :ile ! incom+ gas & air are drawn ?r\gh ! heat$ reg5]ator *amb]s be=e ent]+ ! furnace *amb] prop]4 ,! incom+ gas & air are ?us heat$1 absorb+ 9 turn ! heat /or$ 9 ! brickwork ( ! reg5]ators4 ,x is evid5t t two sets ( su* reg5]ators are suffici5t1 ! "o set und]go+ ! heat+ process at ! h&s ( ! escap+ products ( combu/ion1 :ile ! o!r set is giv+ up its heat to ! incom+ gas & air2 :5 ?is process has gone f> en\gh1 x is only necess>y to int]*ange ! two sets ( *amb]s1 by ! op]ation ( suitable valves1 & ?is s]ies ( alt]nations may be cont9u$ indef9itely4 ,! arrangem5t is %[n diagrammatically 9 ,fig4 #c4 ,9 recup]ative furnaces ! same pr9ciple is utilis$ 9 a some:at diff]5t mann]2 ! outgo+ products ( combu/ion pass ?r\gh tubul> *annels =m$ 9 fire-clay blocks1 :ile ! +o+ gas & air pass ar\nd ! outside ( ^! same blocks2 ! heat ( ! outgo+ gases is ?us transf]r$ to ! incom+ gases by ! process ( conduction ?r\gh ! fire-clay walls ( ! recup]ator tubes4 ,! relative m]its ( ! two sy/ems h be5 hotly conte/$2 ! reg5]ative sy/em has ! advantage ( avoid+ all reliance on ! heat conductivity ( fire-clay1 :ile x also avoids ! some:at complicat$ special tubul> blocks requir$ = ! o!r sy/em2 on ! o!r h&1 ! recup]ative sy/em avoids ! necessity = all 8rev]s+0 valves & _! regul> p]iodical work+1 :ile x also occupies some:at less space4 ,temp]atures suffici5tly high = all glass-melt+ purposes c be atta9$ by bo? means4 ,9 bo? sy/ems ( furnace1 heat$ gas & heat$ air are admitt$ to ! furnace by sep>ate fire-brick flues or passages1 air & gas be+ all[$ to mix j be=e !y ent] ! furnace *amb] prop]4 ,! economy & effici5cy ( ! furnace dep5d to a v great ext5t ^u ! mann] 9 :i* ?is mix+ is accompli%$4 ,rapid & complete mix+ ( air & gas results 9 an int5sely hot1 b %ort & local flame1 :ile sl[] mix+ t5ds to l5g!n ! flame & spread ! heat ?r\gh ! entire furnace *amb]2 on ! o!r h& if ! mix+ ( gas & air is too sl[1 combu/ion may n h be5 complet$ 9 ! %ort "t occupi$ by ! gases 9 pass+ ?r\gh ! furnace1 & combu/ion may ei!r cont9ue 9 ! outfl[ flues & reg5]ators1 or x may be prev5t$ by ! n>r[ness ( ^! passages1 & unburnt gases may pass to ! *imney4 ,:5 ! op5+s or 8ports0 are prop]ly proportion$1 & ! draught ( ! *imney is prop]ly regulat$1 combu/ion %\ld be j complete z ! gases leave ! furnace *amb]1 & "u ^! circum/ances small tongues ( ke5 flame w escape f e op5+ 9 ! furnace2 l>ge smoky flames issu+ f a gas-fir$ furnace indicate incomplete combu/ion4 ,illu/ration3 ,,fig4 #d4--,sectional diagram ( a reg5]ative pot furnace work+ ) cov]$ pots4 ,z has already be5 indicat$1 glass is melt$ ei!r 9 pots or crucibles ( v>i\s %apes & sizes1 or 9 op5 tank furnaces4 ,! g5]al arrangem5t ( a pot furnace work+ ) clos$ or 8cov]$0 crucibles is %[n 9 ,fig4 #d4 ,9 ?is p>ticul> furnace1 ! 8ports0 or ap]tures by :i* ! gas & air ent] ! furnace *amb]1 are plac$ 9 ! floor ( ! *amb]1 b ^! ap]tures are (t5 plac$ 9 ! side or end walls1 or ev5 9 a c5tral column1 ! object be+ 9 all cases to heat all ! pots z uni=mly z possible & to avoid any int5se local heat+1 :i* w\ld m]ely endang] ! p>ticul> crucible expos$ to x1 )\t greatly aid+ ! real "w ( ! furnace4 ,9 pot furnaces1 h[ev]1 9 :i* ! m refractory k9ds ( glass are to be melt$1 x is g5]ally consid]$ desirable t ! flame %\ld be made to play ab\t ! pots 9 su* a way z to heat ! l[] p>ts ( ! pots mo/ /rongly4 ,9 connection ) ! "q ( ! uni=mity ( heat di/ribution 9 a gas-fir$ furnace x mu/ fur!r be borne 9 m9d t 9 ! case ( reg5]ative furnaces ! direction ( ! flame is rev]s$ e "t ! valves are ?r[n ov]1 & 9 practice ?is is done ab\t once e half-h\r2 ?is proce$+1 ( c\rse1 t5ds v mu* to equalise ! temp]ature ( ! two sides ( ! furnace4 ,9 recup]ative furnaces1 on ! o!r h&1 ! direction ( ! flame is n *ang$1 & = t reason a flame return+ ^u itself1 usually call$ a horse-%oe flame1 is (t5 employ$2 ?is is obta9$ by plac+ ! entry & exit ports side by side at "o end ( ! furnace2 ! impetus ( ! flame gases & _! rapid expansion dur+ combu/ion c>ry ! flame out across ! furnace1 :ile ! *imney draught ultimately sucks x back to ! exit ports1 ! %ape ( ! flame be+ %[n 9 ,fig4 #e4 ,illu/ration3 ,,fig4 #e4--;,diagram ( a furnace ) 8horse-%oe0 flame4 ,9 g5]al arrangem5t1 a tank furnace = glass melt+ resembles an op5-he>? /eel furnace4 ,! tank or bas91 z already indicat$1 is built up ( a numb] ( l>ge fire-clay blocks1 =m+ a ba? v>y+ 9 dep? f #bj 94 to #db 94 accord+ to ! design ( ! furnace & ! k9d ( glass to be melt$ 9 x4 ,! ports = entry ( gas & air & = exit ( ! products ( combu/ion are 9 mo/ mod]n furnaces plac$ 9 ! side walls ( ! furnace j above ! level ( ! glass1 ! :ole be+ cov]$ by a vault built ( silica brick4 ,figs4 #f & #g %[ ! g5]al arrangem5t ( a simple =m ( tank-furnace su* z t us$ 9 ! manufacture ( roll$ plate glass4 ,! furnace indicat$ 9 ! diagram is int5d$ = reg5]ative work+ ) alt]nat+ directions ( flame2 9 recup]ative furnaces ! horse-%oe flame is always us$ 9 tanks1 :ile ?is arrangem5t ( ports is sometimes adopt$ = reg5]ative tanks also1 p>ticul>ly 9 ! manufacture ( bottles4 ,= ! production ( %eet glass1 tank furnaces are g5]ally sub-divid$ into two comp>tm5ts & are also provid$ ) v>i\s con/rictions int5d$ to arre/ impurities & to all[ only cle> glass to pass1 b z reg>ds ! arrangem5t ( flues & ports !re is a v g5]al simil>ity betwe5 v>i\s furnaces ( ?is type4 ,illu/ration3 ,,fig4 #f4--,longitud9al sectional diagram ( tank furnace4 ,illu/ration3 ,,fig4 #g4--,transv]se sectional diagram ( tank furnace1 %[+ reg5]ators & gas & air passages4 ,x is beyond ! scope ( ?is book to discuss ! relative m]its ( tank & pot melt+ furnaces2 :]ev] ! =m] c be made to produce glass ( adequate quality = ! purpose desir$1 ! great economy ( ! tank furnace inevitably c>ries all be=e x1 s t bottle glass1 = example1 is n[ made exclusively 9 tanks1 & ! same applies also to roll$ plate ( ! ord9>y k9d1 & to ! great majority ( %eet glass4 ,on ! o!r h&1 :]e special qualities ( glass are requir$ 9 relatively small quantities1 or :]e ! requirem5ts z to quality are v extreme1 ! pot furnace rema9s indisp5sable4 ,optical glass & col\r$ glasses are examples ( ?is k9d1 al?\gh "s t9t$ glasses are us$ 9 suffici5t quantity to ju/ify ! use ( small tank furnaces = _! production4 ,! causes ( ! great] economy ( ! tank furnace are num]\s1 & complicat$ by ! detail$ requirem5ts ( ea* p>ticul> manufacture1 b ! mo/ important factors 9 ! "q may be summ$ up ?us3-- 7#a7 ,! tank furnace utilises ! heat ( ! flame m effici5tly1 z ! glass is expos$ to ! heat 9 a bas9 ^: surface cov]s ! entire area ( ! furnace1 :ile 9 a pot furnace !re is mu* vacant1 unus$ space4 7#b7 ,! tank furnace p]mits ( cont9u\s work+1 ! raw mat]ials be+ introduc$ at "o end :ile ! glass is be+ )drawn & work$ at ! o!r end4 ,!re are ?us no idle p]iods1 & ea* "p ( ! furnace rema9s at or ne> ! same temp]ature dur+ ! :ole "t t a furnace is alight4 ,= a giv5 size ( plant1 !re=e1 a tank furnace yields a mu* l>g] output1 ) a relatively small] fuel consumption4 7#c7 ,! tank furnace obviates ! ne$ = pots or crucibles1 :i* are n only co/ly & tr\blesome to produce1 b are liable to premature failure & require p]iodical r5ewal1 :i* involves a s]i\s loss ( "t = ! furnace4 7#d7 ,f9ally1 ! molt5 glass 9 a tank furnace c be always ma9ta9$ at or ne> "o con/ant level & is1 !re=e1 always conv5i5t = )drawal by means ( ! ga!r]'s pipe or ! ladle4 ,9 pot furnaces1 on ! o!r h&1 ! composition ( ! glass c be m accurately regulat$1 & ! molt5 glass itself c be m effectively protect$ f contam9ation ei!r by matt] dropp+ into x or by ! action ( ! furnace gases1 :ile 9 pots x is also possible to effectually melt toge!r mat]ials :i*1 9 ! op5 bas9 ( a tank1 c\ld n be kept toge!r long en\gh to comb9e4 ,,*apt] ,v4 ,,! ,,process ,,( ,,fusion4 ,x has already be5 indicat$ t1 = glass-mak+ purposes1 ! raw mat]ials are requir$ 9 a /ate ( reasonably f9e division4 ,! exact degree ( f95ess requir$ dep5ds v mu* ^u ! nature ( ! +r$i5t 9 "q1 ! g5]al rule be+ t ! m refractory & *emically resi/ant mat]ials require to be mo/ f9ely gr\nd1 :ile sub/ances :i* melt & react readily1 su* z soda a% & salt-cake1 d n require v f9e gr9d+4 ,assum+ t ! mat]ials are available 9 a suitable /ate ( f95ess1 ! fir/ /ep 9 ! process ( glass melt+ consi/s 9 secur+ _! admixture 9 ! prop] proportions4 ,?is may be done by h& entirely1 by h& aid$ by "s ma*9]y1 or entirely automatically4 ,! process ( h& mix+ is only available = relatively small quantities ( mat]ial & requires v c>eful sup]vision if inadequate mix+ is to be avoid$4 ,9 mo/ cases ! actual weigh+ out is done by h&1 :ile ! mix+ is done by ma*9]y4 ,9 ?is process ! sep>ate +r$i5ts are weigh$ out f b>r[s or skips & are tipp$ into a l>ge hopp] :5ce ea* bat*1 z soon z x is complet$1 passes into ! mix+ *amb] ( ! mix+ ma*9e4 ,?is may consi/ ( no?+ m ?an a cyl9drical *amb] 9 :i* /eel arms revolve & /ir up ! cont5ts1 b m mod]n appliances take ! =m ( rotat+ b>rels or cyl9d]s1 set up on an incl9$ axis & provid$ ) suitable %elves & baffles2 9 ^! ! mat]ials are v ?or\ghly %ak5 ov] & mix$4 ,:]e h& mix+ is adopt$1 ! v>i\s +r$i5ts ( ea* bat* are ?r[n into a l>ge b9 & are !re turn$ ov] sev]al times ) %ovels1 ! entire mat]ial be+ ultimately siev$ ?r\gh a wire sieve ( suitable me%4 ,9 all cases ! result+ mixture %\ld be p]fectly uni=m 9 col\r & texture1 & analyses ( diff]5t samples %\ld %[ only small v>iations4 ,) ! mixture ?us prep>$ ! 8cullet0 or brok5 glass :i* is to be re-melt$ is n[ incorporat$2 ideally ?is %\ld also be uni=mly di/ribut$1 b ?is is r>ely attempt$ 9 practice on ! l>ge scale4 ,! next /ep 9 ! process is ! introduction ( ! mixture into ! furnace4 ,9 ! case ( tank furnaces ?is is a simple matt]1 s9ce 9 ^! ! temp]ature is kept z ne>ly con/ant z possible1 & raw mat]ials may1 !re=e1 be introduc$ at almo/ any "t1 ! am\nt introduc$ be+ s regulat$ z to keep ! level ( ! molt5 glass or 8metal0 z ne>ly con/ant z possible4 ,! actual introduction is manag$ by means ( a l>ge op5+ or door at :at is kn[n z ! 8melt+ end0 ( ! furnace4 ,normally ?is op5+ is cov]$ by a l>ge fire-brick block susp5d$ by a *a9 runn+ ov] pulleys & c\nt]balanc$ by a c\nt]poise weight4 ,:5 *>g+ is to beg91 ?is block is rais$ & ! op5+ is uncov]$4 ,! raw mat]ials are !n introduc$ ei!r by h&1 by ! aid ( long-h&l$ %ovels1 or !y are fir/ fill$ into a long scoop mov$ by me*anical means =w>d into ! furnace1 :]e x is giv5 a half-turn1 :i* empties ! cont5ts out1 & is !n rapidly )drawn4 ,?is *>g+ process may be repeat$ e half-h\r1 or l>g] quantities may be introduc$ once e f\r h\rs1 accord+ to ! practice t may be adopt$ at any p>ticul> furnace4 ,9 ! case ( pot furnaces ! *>g+ process is n s simple4 ,"h ! fir/ *>ge ( raw mat]ials has to be introduc$ into a pot :i* has be5 almo/ entirely empti$ dur+ ! work+-out process1 & ! temp]ature ( ! furnace has also fall5 v consid]ably dur+ ?is "t4 ,be=e new mat]ial is introduc$1 ! heat ( ! furnace mu/ fir/ be adequately re/or$4 ,if ?is is n done1 ! fusion ( ! glass takes an abnormal c\rse & v imp]fect results arise4 ,fur!r1 ! quantity ( mat]ial introduc$ at "o "t mu/ be c>efully adju/$ to ! capacity ( ! pot4 ,dur+ ! e>li] /ages ( fusion mo/ glass mixtures =m l>ge masses ( foam1 & if ! crucible has be5 too heavily *>g$ ?is foam ov]fl[s1 ) ! result t valuable mat]ial is lo/ & ! floor & passages ( ! furnace are clogg$ ) glass4 ,a c]ta9 am\nt ( ov]fl[1 z well z leakage f defective crucibles1 is1 h[ev]1 unavoidable1 & = ?is purpose e pot furnace is provid$ ) a *amb] s plac$ t ! glass w fl[ into x & s be prev5t$ f f9d+ its way into ! reg5]ators or o!r p>ts :]e its pres5ce w\ld h9d] ! work+ ( ! furnace4 ,^! receptacles or 8pockets0 mu/1 h[ev]1 be p]iodically cle>$ ( _! cont5ts f outside1 & ?is con/itutes "o ( ! mo/ irksome op]ations connect$ ) glass manufacture4 ,ow+ to ! occurr5ce ( foam+ & to ! fact t ! raw mat]ials occupy mu* m space ?an ! glass =m$ f !m1 x is necess>y to fill ! pot ) fre% bat*es ( raw mat]ials sev]al times1 ! quantity :i* c be introduc$ decreas+ ea* "t4 ,! numb] ( times t ?is mu/ be done dep5ds ^u ! p>ticul> circum/ances1 b f f\r to eight 8fill+s0 are commonly us$ = v>i\s k9ds ( glass & size ( pot4 ,! precise /age at :i* a fre% bat* ( raw mat]ials %\ld be introduc$ is ano!r matt] requir+ c>eful att5tion4 ,= "s purposes x is necess>y to wait until ! previ\s bat* is completely melt$1 :ile 9 o!r cases raw mat]ial may be add$ :il/ "s ( ! previ\s bat* is /ill float+ on ! surface ( ! glass 9 ! pot4 ,we h n[ to consid] ! *emical reactions :i* take place 9 ! mixture ( raw mat]ials t are introduc$ into ! hot furnace4 ,! exact c\rse ( ^! reactions is n kn[n 9 v great detail1 z ?is c\ld only be asc]ta9$ by an elaborate rese>* on ! nature ( ! int]m$iate products t result "u v>i\s circum/ances4 ,a rese>* ( ?is k9d w\ld ?r[ mu* light on ! :ole ( ! melt+ processes b is 9 itself s difficult t x has n yet be5 c>ri$ out at all fully4 ,we c !re=e only give an acc\nt ( ! *emical *anges f our k ( ! end-results & ( a few int]m$iate products t are kn[n4 ,to take ! simple/ case1 we may consid] a mixture consi/+ ( s&1 c>bonate ( lime & c>bonate ( soda mix$ 9 suitable proportions4 ,9 su* a case we "k t ! m]e action ( heat alone w produce two *anges--! c>bonate ( soda w melt & ! c>bonate ( lime w lose its c>bonic acid & be 8burnt0 or conv]t$ into cau/ic lime4 ,! fir/ /age ( ! fusion process ?us probably results 9 a mass consi/+ ( s& gra9s & gra9s ( c>bonate ( lime und]go+ decomposition1 all cem5t$ toge!r by molt5 c>bonate ( soda4 ,?is mass w be full ( bubbles1 "s d]iv$ f ! air enclos$ betwe5 ! gra9s ( ! orig9al mixture & ?us trapp$ by ! melt+ mass1 & o!rs =m$ by ! c>bonic acid :i* is be+ driv5 (f 9 ! =m ( gas by ! decomposition ( ! c>bonate ( lime4 ,at ! temp]ature ( ! furnace1 h[ev]1 silica has ! prop]ties ( a /rong acid1 & n only attacks ! c>bonate ( lime mu* 9 ! same mann] z1 = in/ance1 hydro*loric acid w\ld d 9 ! cold1 b ! silica also attacks ! c>bonate ( soda1 :i* heat alone c sc>cely decompose4 ,! exact ord] 9 :i* ^! reactions take place w dep5d ^u ! temp]ature ( ! furnace & ! degree ( mix+ atta9$ 9 ! prep>ation ( ! raw mat]ials4 ,al?\gh 9 ! long run ! f9al result w probably be ! same z reg>ds purely *emical con/itution1 mu* ( ! te*nical success ( ! process mu/ dep5d ^u ! exact sequ5ce ( ! *anges involv$1 z ?is mu/ gov]n ! numb] & size ( ! bubbles t are =m$ 9 ! glass & ! fluidity ( ! mass f :i* ^! bubbles h to free !mselves4 ,9 ! pres5t /ate ( our k1 h[ev]1 we c only say t ! f9al result is ! complete expulsion ( all c>bonic acid f ! comp\nds pres5t 7al?\gh x may rema9 entangl$ 9 ! glass 9 ! =m ( bubbles7 & ! =mation ( silicates ( bo? lime & soda :i* rema9 9 ! f9i%$ glass 9 a /ate p>tly ( mutual *emical comb9ation1 p>tly ( mutual solution4 ,! description ( ! process ( fusion j giv5 applies1 ) slight modifications1 to ! melt+ ( ord9>y fl9t-glass mixtures z well z to lime glasses1 ) ! "o modification t ! c>bonate ( lime ( ! lime-soda glass is replac$ by r$-lead1 & ! gas evolv$ by ! decomposition ( ! r$-lead is oxyg5 9 place ( ! c>bonic acid evolv$ f ! decomposition ( ! c>bonate ( lime4 ,9 ! case ( bo? lime & fl9t glasses1 h[ev]1 c]ta9 o!r sub/ances besides ^? m5tion$ are usually introduc$ 9 small quantities4 ,al?\gh ^! sub/ances d n v mat]ially affect ! end-products ( ! *emical reactions1 !y v mat]ially affect ! int]m$iate /ages1 & ?us s]ve ! purpose = :i* !y are introduc$ by affect+ ! c\rse ( ! *emical *anges 9 a fav\rable mann]4 ,! sub/ances usually employ$ = ?is purpose are ars5ic & nitrate ( ei!r soda or pota%4 ,! mann] 9 :i* ! ars5ic acts is v obscure & _c be discuss$ 9 detail "h2 ! *ief factors 9 its action are1 h[ev]1 its volatility & its p[] ( ei!r absorb+ oxyg5 or p>t+ ) x accord+ to circum/ances4 ,! action ( ! nitrates is *iefly dep5d5t ^u ! oxyg5 :i* !y yield on decomposition by heat4 ,?is oxyg5 is 9 "s cases /or$ up by o!r +r$i5ts ( ! mixture & only giv5 (f at a mu* lat] /age1 :5 ! evolution ( ?is gas assi/s 9 ! removal ( ! la/ small bubbles ( in]t air or c>bonic acid gas /ill left 9 ! glass4 ,! oxidis+ action ( ! nitrates1 h[ev]1 s]ves *iefly = ! de/ruction ( organic matt] & ! full oxidation ( any iron pres5t2 bo? processes :i* t5d to improve ! col\r ( ! glass1 :ile 9 ! case ( fl9t glasses ! pres5ce ( ^! oxidis+ additions is necess>y to avoid all risk ( r$uction ( lead1 s9ce ?is w\ld result 9 ! complete black5+ ( ! glass4 ,a mu* m complicat$ set ( reactions occur :5 ! alkali ( a soda-lime glass is introduc$ ei!r p>tly or :olly 9 ! =m ( sulphate ( soda 7salt-cake74 ,we h already po9t$ out t ! unaid$ action ( heat & ( silica is n suffici5t to br+ ab\t ! rapid decomposition ( sulphate ( soda :i* is requir$ = successful glass manufacture1 & t ! int]v5tion ( r$uc+ ag5ts is requir$4 ,= ?is purpose a c]ta9 am\nt ( c>bon 9 ! =m ( coke1 *>coal or an?racite coal1 is introduc$ into all salt-cake mixtures1 b ! r$uc+ gases ( ! furnace atmosph]e also play an important "p 9 ! reactions t take place4 ,"h aga9 x is n possible to give any?+ b an incomplete acc\nt ( :at takes place4 ,! rationale ( ! :ole process lies1 no d\bt1 9 ! fact t sulphite ( soda 7,na#b,,s#c7 is mu* m readily decompos$ by ! action ( hot silica ?an ! sulphate 7,na#b,,s#d7 itself1 s t ! ess5tial action ( ! r$uc+ ag5ts consi/s 9 robb+ ! sulphate ( "p ( its oxyg51 ?us r$uc+ x to ! condition ( sulphite & r5d]+ x accessible to ! attack ( silicic acid4 ,b if we attempt to express su* a reaction 9 ! usual mann] by a *emical equation f :i* ! quantity ( c>bon requir$ to effect ! r$uction 9 "q c be calculat$1 we f9d t ! am\nt ( c>bon requir$ 9 practice is v consid]ably less ?an t giv5 by ?is !ory2 x foll[s !re=e t ei!r ?is v l>ge am\nt ( r$uc+ action mu/ be ascrib$ to ! furnace gases1 or t ! actual reactions are n /rictly ( ! k9d we h describ$4 ,bo? explanations are probably p>tly correct1 & 9 practice ! am\nt ( c>bon to be us$ 9 a giv5 mixture & furnace c only be f\nd by actual trial1 9 :i* ! manufactur] is1 ( c\rse1 guid$ by ! results obta9$ ) o!r furnaces ( a simil> type4 ,! end-product ( ! reactions is aga9 a mixture ( silicates1 b a c]ta9 am\nt ( undecompos$ sulphate is always f\nd 9 su* glasses1 :ile gase\s oxides ( sulphur escape f ^! furnaces 9 consid]able quantity4 ,"u exceptional circum/ances ! glass may ev5 conta9 sulphides ( soda or ( lime1 & sometimes ev5 susp5d$ c>bon1 b ^! are abnormal con/itu5ts & result 9 ! s]i\s discol\ration ( ! glass4 ,x is obvi\s t to a mixture conta9+ c>bon z a r$uc+ ag5t su* oxidis+ mat]ials z nitrates _c be add$1 b small quantities ( ars5ic & ( manganese dioxide are add$ because _! o!r prop]ties are suffici5tly valuable to outweigh _! disadvantages z oxidis+ ag5ts4 ,hav+ n[ briefly consid]$ ! process ( fusion prop]1 we pass to ! second /age 9 ! melt+ ( glass4 ,9 a prop]ly conduct$ glass-furnace1 :5 ! la/ trace ( undecompos$ raw mat]ials has disappe>$1 we f9d ! glass z a transp>5t mass ?r\gh\t :i* gas bubbles are ?ickly dissem9at$4 ,= ! majority ( purposes x is necess>y to free ! glass z p]fectly z possible f ^! bubbles be=e x is work$ into its f9al =m4 ,?is free+ or 8f9+0 process is c>ri$ out by fur!r & m int5se heat+ ( ! molt5 glass1 :i* is !reby r5d]$ m fluid & all[s ! bubbles to dis5gage !mselves by ris+ to ! surface4 ,?is occurs mu* m readily :5 ! bubbles are l>ge2 v m9ute bubbles1 9 fact1 %[ no incl9ation to rise ?r\gh ! fluid mass4 ,! glass-mak] accord+ly comp\nds 8 mixtures ( raw mat]ials 9 su* a way z to yield l>ge bubbles1 or1 fail+ t1 he adds to ! molt5 mass "s sub/ance t evolves a great _m l>ge bubbles1 & ^! 9 _! upw>d c\rse ?r\gh ! glass sweep ! small ones away ) !m4 ,! add$ sub/ance may be an inorganic volatile body1 su* z ars5ic1 or m frequ5tly "s vegetable sub/ance conta9+ mu* moi/ure is introduc$ into ! glass4 ,! mo/ usual me?od is to place a potato 9 ! crook ( a =k$ iron rod & !n to dip ! rod ) ! atta*$ potato into ! molt5 glass2 ! heat at once beg9s to drive (f ! moi/ure & to decompose ! potato1 s t !re is a viol5t ebullition ( ! :ole mass4 ,?is 8boil+ up0 process assi/s ! f9+ consid]ably & also s]ves to mix ! :ole cont5ts ( ! pot v ?or\ghly1 b x has "s att5dant disadvantages1 su* z ! introduction ( oxide ( iron into ! glass f ! rod :i* is us$ 9 ! op]ation1 :ile ! contam9at$ mat]ial adh]+ to ! walls ( ! pot itself is dragg$ (f & mix$ ) ! re/ ( ! glass by ! viol5t /irr+ action t takes place4 ,x is1 ( c\rse1 fur!r obvi\s t ?is process c only be usefully appli$ to glass melt$ 9 pots1 s9ce ! bulk ( ! molt5 glass 9 a tank furnace c\ld n be rea*$ at all 9 ?is mann]4 ,mixtures t are to be melt$ 9 tanks mu/ !re=e be capable ( free+ !mselves ( _! enclos$ bubbles )\t su* outside aid4 ,9 a tank1 9 fact1 ! :ole melt+ process proce$s on some:at diff]5t l9es1 s9ce ! temp]ature ( ! furnace is nev] int5tionally v>i$1 :ile on ! o!r h& ! melt+ glass travels d[n ! furnace into regions ^: temp]ature c be regulat$ to fav\r ! v>i\s /ages ( ! process t take place 9 ea* "p ( ! furnace4 ,on ! :ole1 h[ev]1 x is an und\bt$ fact t :ile ! runn+ ( a pot furnace c be v>i$1 )9 wide limits1 to suit ! requirem5ts ( :atev] mixture x is desir$ to melt1 9 ! case ( tank furnaces ! mixture mu/ be closely adju/$ to ! requirem5ts ( ! furnace1 ^: g5]al 8run0 _c be v readily alt]$4 ,! completion ( ! 8f9+0 process is g5]ally det]m9$ by tak+ samples ( ! glass out ( ! pot or tank & exam9+ !m = enclos$ bubbles4 ,su* samples may be obta9$ 9 a v>iety ( ways1 ! mo/ usual me?od be+ to dip a flat iron rod j bel[ ! surface ( ! glass & to lift x out v]tically upw>ds1 ?us reta9+ on ! flat surface ( ! rod "s ( ! glass t lay !re at ! mom5t :5 ! rod 0 imm]s$4 ,^! te/ samples or 8pro(s0 are exam9$ v c>efully1 & if no trace ( bubbles c be obs]v$ ! glass is g5]ally reg>d$ z 8f9e10 b x is by no means c]ta9 t ! abs5ce ( bubbles f su* a small sample w prove t ! :ole mass is free2 t1 h[ev]1 is a po9t :]e ! melt]'s exp]i5ce enables him to judge h[ f> he may rely ^u ! indications giv5 by ! 8pro(s40 ,:5 ! glass is 8f9e0 x frequ5tly happ5s t ! surface ( ! molt5 mass is contam9at$ by specks ( =eign matt] float+ on ! glass2 = ! purpose ( remov+ ^!1 ! surface ( all glass is skimm$ be=e "w is begun ^u x4 ,?is is done by remov+ ! surface sk9 ( glass by means ( suitably %ap$ iron rods1 ^u :i* small masses ( molt5 glass are fir/ 8ga!r$40 ,f9ally1 x only rema9s to r$uce ! temp]ature ( ! glass f t ( ! melt+ & f9+ process to ! mu* l[] temp]ature at :i* ! v>i\s me?ods ( work+ ! glass are c>ri$ out4 ,9 pot furnaces ?is is accompli%$ by l[]+ ! temp]ature ( ! entire furnace1 :ile 9 tank furnaces ! f9e glass fl[s into ! work+ *amb] ( ! tank :i* is always kept at ! work+ temp]ature4 ,,*apt] ,,vi4 ,,processes ,,us$ ,,9 ,,! ,,work+ ,,( ,,glass4 ,9 ! previ\s *apt] we h foll[$ 9 outl9e ! process ( fusion & f9+ ( glass1 leav+ ! molt5 mat]ial ready = work+ up into ! f9al %ape4 ,up to t po9t ! process is v simil> 9 all k9ds ( glass1 al?\gh ! furnaces1 pots & ut5sils employ$ v>y consid]ably1 z d also ! temp]atures to :i* ! mat]ials are heat$ at v>i\s /ages4 ,! work+ processes1 h[ev]1 diff] entirely f "o class ( product to ano!r1 z obvi\sly ! process employ$ = ! production ( a %eet ( plate-glass c h little 9 common ) t us$ 9 ! manufacture ( a w9e-glass4 ,on ! o!r h&1 ! modes ( work+ hot glass are n s num]\s z ! products t are produc$1 s t we f9d v simil> appliances & manipulation recurr+ 9 v>i\s bran*es ( ! indu/ry4 ,= t reason we propose to deal "h ) ! pr9cipal me?ods ( manipulat+ glass1 leav+ ! details ( ea* me?od z appli$ to special purposes to be discuss$ 9 connection ) ! special product 9 "q4 ,! fir/ /age 9 ! work+ ( all glass is ! removal ( a suitable quantity ( molt5 glass f ! furnace4 ,practically only ?ree me?ods are available1 viz41 ladl+1 p\r+ & ga!r+4 ,if we ?9k ( a famili> sub/ance ( physical prop]ties some:at resembl+ ^? ( glass1 we may take ?ick treacle & suppose x conf9$ 9 a j> or bottle2 !re are ?ree obvi\s ways ( extract+ x f ! bottle3 we may ladle x out ) a spoon1 or we may p\r x out by tilt+ ! :ole bottle1 or we may dip a spoon or =k into ! ?ick liquid1 sl[ly draw x out & turn x r\nd z we d s1 ?us br++ out on ! spoon or =k a r\nd adh]5t mass or 8ga!r+0 ( treacle4 ,9 ! case ( molt5 glass1 ! process ( ladl+ is by f> ! simple/1 b x has c]ta9 v decid$ limitations & disadvantages4 ,^! arise f ! fact t a ladle _c be introduc$ into molt5 glass )\t contam9at+ ! :ole mass ( glass1 at any rate ) num]\s air bubbles4 ,! metal ( ! ladle c>ries ) x a consid]able am\nt ( closely adh]5t air :i* is p>tially deta*$ :ile 9 contact ) ! hot glass1 s t bo? ! cont5ts ( ! ladle & ! glass rema9+ 9 ! furnace are contam9at$4 ,^! bubbles might p]haps be avoid$ if hot ladles 7 us$1 b 9 t case ! glass w\ld adh]e to ! surface ( ! metal1 & ea* ladle w\ld require labori\s clean+ aft] ea* "t t x 0 us$4 ,9 practice1 !re=e1 ladl+ is only us$ = ! production ( ^? classes ( glass :]e ! pres5ce ( a c]ta9 numb] ( air-bells is n injuri\s1 & ! ladles are kept cold by imm]sion 9 wat] aft] ea* "t ( use4 ,! use ( ! cold ladle has1 h[ev]1 ! fur!r disadvantage t a c]ta9 quantity ( ! glass )drawn 9 ! ladle is v consid]ably *ill$ by contact ) ! cold metal1 & is ?us too /iff to und]go ! fur!r processes satisfactorily--?is *ill$ glass has1 !re=e1 to be reject$ f ea* ladleful2 ?is n only involves loss ( glass1 b also necessitates ! sep>ation ( ?is spoilt glass f ! re/4 ,! g5]al process ( roll+ requires little treatm5t "h4 ,two ess5tially diff]5t processes are us$2 9 "o ! glass is ?r[n on a flat table & roll$ out by a mov+ roll] pass+ along ! table2 9 ! o!r ! glass passes betwe5 two mov+ roll]s1 & ! %eet s =m$ is receiv$ on a mov+ table or slab4 ,! =m] mode ( roll+ is us$ = ! production ( ! ord9>y roll$ plate glass2 if ! surface ( bo? table & roll] is smoo?1 ! glass also has a comp>atively smoo? surface1 b ! surface is f> f be+ level or free f irregul>ities4 ,x has be5 f\nd t x is q impossible to prev5t ^! irregul>ities1 :i* appe> to arise f ! buckl+ ( ! glass aga9/ ! iron surfaces ) :i* x comes into contact2 :5 roll$1 ! glass is too /iff to recov] its true1 smoo? surface "u ! influ5ce ( surface t5sion1 s t x reta9s all ! m>ks ( roll] & table--nor c ! roll] be made p]fectly smoo?1 s9ce 9 t case x appe>s to slip ov] ! glass & does n roll x out prop]ly4 ,all ef=ts1 !re=e1 to produce a glass hav+ a true & smoo? surface by direct roll+ h fail$1 & are likely to fail1 s long z tables & roll]s are made ( mat]ials simil> to ^? n[ 9 use4 ,! process ( roll+ on a /ation>y table is1 h[ev]1 us$ = ! manufacture ( plate-glass2 b "h ! slab z roll$ has /ill ! r\gh1 unev5 surface simil> to t ( ord9>y 8roll$ plate10 & ?is is remov$ & replac$ by a true poli%$ surface by ! me*anical processes ( gr9d+ & poli%+4 ,! second mode ( roll+1 i4e41 ) two or m 8/ation>y0 roll]s & a mov+ table1 is us$ = ! production ( roll$ plate hav+ special surface features or patt]ns2 ! v>iety ( roll$ glass kn[n z 8figur$ roll$ plate10 hav+ a deeply impr9t$ patt]n1 is produc$ 9 ?is way4 ,?is me?od requires mu* m complicat$ me*anical appliances1 "s ( :i* are /ill protect$ by pat5t rights4 ,ladl+ be+ ?us limit$ to ! production ( inf]ior k9ds ( glass1 ! bett] v>ieties are dep5d5t ^u ei!r ga!r+ or p\r+4 ,! =m] process is limit$ z reg>ds ! quantity ( glass t c be dealt ) 9 "o piece1 al?\gh surpris+ly l>ge quantities c be ga!r$ ^u a s+le pipe2 ! great masses ( glass1 h[ev]1 t are requir$ = ! production ( mod]n poli%$ plate c\ld n be h&l$ 9 ?is way1 & ! me?od ( p\r+ is accord+ly adopt$4 ,= ?is purpose ei!r ! pots 9 :i* ! glass has be5 orig9ally melt$1 or o!rs specially design$ = ?is purpose1 & into :i* ! molt5 glass has be5 transf]r$1 are remov$ bodily f ! furnace by ! aid ( p[]ful me*anical appliances2 !y are !n c>ri$ by ov]head cranes to ! place :]e ! glass is to be roll$ into ! =m ( a plate1 & !re ! pot is tilt$ & ! molt5 glass is all[$ to run out & to =m a pool on ! roll+ table1 ! passage ( ! great roll] ultimately roll+ ! pool out into a %eet mu* z d\gh is roll$ out ) a roll+-p94 ,?is process is obvi\sly only possible ) pots or crucibles ( a suitable size1 & is1 moreov]1 v de/ructive to ^! pots1 s9ce !y are expos$ to su* great v>iations ( temp]ature4 ,9 ! case ( tank furnaces1 num]\s devices h be5 pat5t$ = all[+ ! glass to fl[ out ov] a sill or weir ( suitable size1 ready to be roll$ or drawn into ! =m ( %eets or slabs2 b none ( ^! devices h1 s f> z ! writ] is aw>e1 f\nd _! way into practice2 ! reason = ?is probably lies 9 ! fact t x is n easy to f9d a mat]ial :i* w pres5t a smoo? face to ! outfl[+ glass1 su* mat]ials z fire-clay lead+ to contam9ation f deta*$ fragm5ts1 :ile *ill$ metal leads to local *ill+ ( ! glass4 ,unless1 !re=e1 ! v>i\s processes ( draw+ glass into %eets direct f ! furnace und]go v mat]ial improvem5t1 ! labori\s process ( ga!r+ is likely to reta9 its importance ev5 9 ! production ( su* l>ge objects z %eets ( w9d[ glass4 ,9 its ess5ce ! process ( ga!r+ consi/s 9 introduc+ into ! glass a heat$ iron rod or tube to :i* a small quantity ( glass is all[$ to adh]e2 rod & glass are remov$ f ! furnace toge!r1 & ! small adh]5t ball ( glass is all[$ to cool s f> z to become /iff en\gh to c>ry its own weight4 ,! rod ) its adh]5t ball is !n aga9 dipp$ into ! glass1 :]e a fre% lay] ( glass atta*es itself to ! ball already on ! rod4 ,! :ole is aga9 )drawn1 all[$ to cool d[n1 & !n dipp$ into ! molt5 glass aga9 to ga!r a fre% quantity4 ,?is cycle ( op]ations is repeat$ until ! desir$ quantity ( glass is atta*$ to ! rod or tube4 ,^! op]ations1 p>ticul>ly :5 weights ( ?irty or =ty p\nds ( glass h to be ga!r$1 require ! ex]cise ( a great deal ( skill & c>e2 ! introduction ( ! ga!r+ into ! molt5 glass is ea* "t liable to produce air-bells :i* w\ld spoil ! :ole mass ( glass or w\ld contam9ate ! cont5ts ( ! crucible1 :ile subsequ5tly ! mass ( hot glass adh]+ to ! rod or pipe t5ds to run d[n & ev5 to drop (f entirely if n prop]ly *eck$ by suitable rotation ( ! pipe4 ,fur!r1 ! manual lab\r & exposure to heat involv$ = ! op]ator all t5d to increase ! co/ ( su* "w4 ,me*anical aids h be5 inv5t$1 & "s ( ^! are 9 actual use1 b !y are *iefly conf9$ to me*anism = reliev+ ! op]ator ( ! great weight ( ! ga!r+ 9 its lat] /ages4 ,j z ladl+ is ne>ly always prelim9>y to roll+1 s ga!r+ is usually ! prelim9>y to "s bl[+ process1 al?\gh ! bl[+ is (t5 comb9$ ) & sometimes replac$ by ! me*anical press+ ( ! glass4 ,:]e ! glass is to be bl[n1 ! ga!r+ is always made on a glass-mak]'s pipe4 ,?is is an iron tube f #d to #f ft4 long1 provid$ at "o end ) a wood5 cas+ to s]ve z a h&le1 & ) a suitably arrang$ m\?piece = bl[+4 ,! %ape ( ! l[] or 8butt0 end ( ! pipe dep5ds ^u ! "* & size ( ! objects to be bl[n2 = small articles ! pipe mu/ be n>r[ & light1 b = heavy %eet-glass ! butt ( ! pipe is ext5d$ into a conical mass ^: base is f #b to #c 94 9 diamet]4 ,! bore ( ! pipe at bo? ends also dep5ds ^u ! class ( "w = :i* x is int5d$4 ,! fir/ /age ( all bl[+ processes consi/s 9 ! =mation ( a holl[ sph]e by bl[+ into ! pipe1 ! pressure ( ! brea? be+ z a rule suffici5t to cause ! gradual di/5sion ( ! hot mass ( glass4 ,f ?is rudim5t>y holl[ sph]e ! v>i\s %apes ( bl[n articles are !n evolv$ by a s]ies ( manipulations :i* v>y v widely 9 diff]5t bran*es ( manufacture4 ,!y g5]ally consi/1 h[ev]1 9 gradually *ang+ ! %ape ( ! mass ( glass by ! pressure ei!r ( h& tools or ( specially prep>$ m\lds or blocks aga9/ :i* ! glass is held or turn$1 ei!r ) or )\t simultane\s bl[+ into ! pipe4 ,! ext5t to :i* ! aid ( su* m\lds & blocks is invok$ v>ies cont9u\sly f ! production ( ! h&-made vase or glass to ! m\ld$ bottle2 9 ! =m]1 practically only h& tools1 ^: %ape be>s no direct resemblance to t ( ! f9i%$ article1 are employ$1 :ile 9 ! latt] ! elongat$ holl[ mass ( glass is plac$ inside a m\ld1 & int]nal air-pressure is us$ to press ! glass into contact ) ! m\ld f :i* ! %ape ( ! f9i%$ bottle is ?us directly d]iv$4 ,! art ( ! bl[] fur!r takes ! fulle/ advantages ( ! peculi> physical prop]ties ( glass :ile 9 ! heat$ visc\s condition1 ! mat]ial be+ made to fl[ "u ! action ( gravity & c5trifugal =ces1 z well z "u ! pressure ( ! brea?1 ! glass be+ held al(t1 twirl$ or swung ab\t to ensure ! production ( ! v>i\s %apes requir$4 ,= ! great majority ( su* purposes ! unaid$ manipulations ( ! op]ator are suffici5t1 b v>i\s me*anical aids are us$ to facilitate ! m labori\s /ages ( ! "w1 :ile = ! simpl] =ms t are requir$ 9 v great numb]s1 su* z bottles1 ! :ole ( ! op]ations are n[ c>ri$ out by automatic ma*9es4 ,( ! m usual me*anical aids at ! disposal ( ! glass-bl[]1 we h already m5tion$ h&-tools1 blocks1 & m\lds ( v>i\s k9ds4 ,next 9 importance to ^! is ! use ( compress$ air = bl[+ l>ge or heavy articles2 ! pressure available by ! human brea? is v limit$1 & ! volume ( air t c be ?us deliv]$ is n v l>ge1 :ile ! con/ant use ( ! lungs = su* a purpose is try+ = ! workman4 ,9 _m works1 !re=e1 air "u pressure is suppli$ to ! b5*es or /ages :]e ! bl[+ is done1 & ! bl[]s' pipes c be c\pl$ to ?is air-supply by means ( flexible connections :5 requir$4 ,! pr9cipal difficulty lies 9 ! correct regulation ( ! air-pressure = ea* special purpose2 b ?is difficulty has be5 ov]come by ! use ( delicate valves "u ! control ( ea* bl[]1 :o c ?us regulate ! pressure to 8 own exact requirem5ts4 ,su* a sy/em1 ( c\rse1 requires "s little practice on ! "p ( ! m5 us+ x1 b :5 !y h become accu/om$ to ! work+ ( ! plant ! results a*iev$ are decid$ly bett] & m regul> ?an ^? obta9$ by m\? bl[+4 ,besides ! use ( compress$ air suppli$ 9 ! way j indicat$1 sev]al o!r devices are 9 use to aid ! bl[] 9 produc+ ! requisite pressure 9 ! int]ior ( ! holl[ bodies he is produc+4 ,! simple/ ( all ^! consi/s 9 utilis+ ! expansive =ce ( ! air enclos$ 9 ! holl[ body :5 t body is expos$ to heat4 ,?us1 = in/ance1 9 bl[+ a cyl9d] ( %eet-glass1 if ! bl[] holds 8 ?umb ov] ! ap]ture ( 8 pipe1 & br+s ! clos$ end ( ! cyl9d] ne> ! hot 8bl[+ hole10 ! heat :i* s(t5s t end ( ! glass w also act ^u ! enclos$ air1 & w v rapidly produce su* an expansive effect z to bur/ op5 ! s(t5$ end ( ! cyl9d]1 & ?is means ( op5+ ! clos$ ends ( ! cyl9d] is frequ5tly employ$ 9 practice4 ,x is1 ( c\rse1 obvi\s t any o!r expansive fluid might be employ$ 9 a simil> mann]1 & 9 "s bl[+ processes x has long be5 ! practice to introduce a small quantity ( wat] into ! int]ior ( ! holl[ body1 :5 ! rapid expansion ( ! /eam produc$ !reby is utilis$ = ! purpose ( g5]at+ ! requisite int]nal pressure4 ,?is use ( ! expansive =ce ( /eam g5]at$ by ! heat ( ! hot glass body has receiv$ great developm5t at ! h&s ( ,siev]t 9 ,g]many1 ^: process is describ$ 9 ,*apt] ,,vii4 ,:atev] me*anical aids are employ$ to facilitate ! v>i\s /ages ( ! process1 all glass bl[+ involves a s]ies ( op]ations requir+ consid]able skill1 :ile ! :ole mann] ( deal+ ) ! glass is ess5tially extravagant ( mat]ial1 except p]haps 9 ! production ( bottles or flasks hav+ n>r[ m\?s4 ,! reason = ?is latt] /atem5t lies 9 ! fact t by bl[+ x is only possible to produce clos$ or ne>ly clos$ holl[ bodies or vessels2 ?us a bl[n w9e-glass or tumbl] is =m$ ) a hood or dome clos+ 9 ! op5 top ( ! glass1 & ?is hood or dome has subsequ5tly to be remov$ by subsidi>y processes1 su* z cutt+ (f by ! aid ( /rong local heat or by gr9d+1 & ! cut edge has to be provid$ ) a smoo? f9i%4 ,9 ! case ( comp>atively small articles l glasses ! loss involv$ f ?is cause is n s v great1 b 7 l>ge flat b[ls or di%es to be produc$ by bl[+1 ! loss 9 ! dome or cov]+ w\ld be v s]i\s4 ,?is difficulty is entirely avoid$ by ! process ( press+ glass4 ,we h already indicat$ ! mann] 9 :i* m\lds are us$ = ! production ( ! desir$ %ape 9 ! case ( bottles1 etc41 b 9 ^! cases1 :]e ! f9al object is to be a holl[ vessel1 ! glass is readily =c$ into contact ) ! m\ld by means ( int]nal air--or /eam--pressure2 9 ! process to :i* we are n[ ref]r+1 h[ev]1 ! hot glass is =c$ into contact ) ! ext]nal m\ld by means ( an int]nal plung] :i* is =c$ d[nw>d ) consid]able =ce4 ,by ?is means1 flat or %all[ bodies c be produc$ )\t ! prelim9>y =mation ( a completely clos$ vessel1 :ile x is obvi\s t by ! use ( suitable m\lds1 complicat$ & elaborate %apes c be produc$4 ,x is true1 ( c\rse1 t press$ articles d n %[ ! same smoo? & brilliant surface :i* is *>act]i/ic ( ! fire-poli% ( bl[n articles1 :ile ! facility ) :i* elaborate surface ornam5tation c be appli$ by ?is process has n t5d$ to arti/ic ref9em5t 9 design1 b ! great majority ( *eap & useful glass articles ( dome/ic use h be5 made available by ! developm5t ( ! press+ indu/ry4 ,9 ! ord9>y c\rse1 press$ glass is produc$ direct f ! molt5 mat]ial1 :i* is introduc$ into ! presses ei!r by ga!r+ or by means ( ladles1 b = "s special purposes glass is br\ght into its f9al %ape by me*anical pressure aft] hav+ fir/ be5 all[$ to solidify & hav+ !n be5 specially re-heat$ to und]go ! press+ or m\ld+ process4 ,?is is pr9cipally done 9 ! case ( ! be/ k9ds ( optical glass1 :]e ! molt5 glass is fir/ all[$ to cool 9 ! actual crucible & is !n brok5 up into lumps ( a suitable size1 f :i* ! m defective portions c be reject$1 ! m p]fect portions only be+ heat$ up aga9 9 special kilns & !n =c$ to take ! desir$ %ape by be+ press$--sometimes ) h& tools only & sometimes by ! aid ( p[]ful presses--into m\lds ( ! requir$ %ape4 ,small l5ses1 h[ev]1 = :i* ! requirem5ts ( quality are n s high are sometimes press$ direct f small ga!r+s tak5 f ! molt5 glass 9 ! crucible4 ,,*apt] ,,vii4 ,,bottle ,,glass4 ,al?\gh bottles are 9 "s respects ! *eape/ & crude/ products t are manufactur$ ( glass1 _! uses are s innum]able & _! numb]s s enorm\s t _! production con/itutes a mo/ important bran* ( ! indu/ry4 ,9 ! *oice ( raw mat]ials = ! production ( ord9>y bottles *eapness is necess>ily ! fir/ consid]ation4 ,natural m9]als1 bye-products ( o!r indu/ries1 & ! crude/ *emicals are utilis$ s long z x is possible by comp\nd+ ^! +r$i5ts 9 suitable proportions to obta9 a glass ^: composition meets ! some:at crude requirem5ts :i* bottles are expect$ to meet4 ,! mo/ ess5tial ( ^! requirem5ts are t ! bottles %all be /rong en\gh to resi/ ! int]nal pressure :i* may come ^u !m :5 us$ = ! /orage ( f]m5t$ or eff]vesc5t liquors z well z ! %ock ( ord9>y use1 :ile ! glass itself mu/ possess suffici5t *emical resi/ance to rema9 unattack$ by ! m or less corrosive liquids :i* x is call$ ^u to conta94 ,fur!r1 f ! po9t ( view ( ! bottle manufactur] x is desirable t ! glass %all be readily fusible1 easily work$1 & easily anneal$4 ,9 o!r bran*es ( glass manufacture increas$ fusibility is (t5 atta9$ by increas+ ! alkali cont5ts ( ! glass1 b 9 bottle mak+ ?is is inadmissible1 bo? on acc\nt ( ! prohibitive co/ ( alkali & because an increas$ alkali cont5t r5d]s ! glass m liable to *emical attack4 ,on ! o!r h&1 9 _m v>ieties ( bottle ! col\r ( ! glass is ne>ly1 or q1 immat]ial s t ! introduction ( relatively l>ge proportions ( iron oxide is p]missible4 ,?is sub/ance acts z a flux & assi/s 9 ! production ( a fusible1 workable glass conta9+ little alkali4 ,su* alkali z bottle glass does conta9 is frequ5tly d]iv$ f felspa?ic m9]als1 :i* g5]ally also conta9 consid]able proportions ( iron4 ,! use ( ^! m9]als also introduces notable proportions ( alum9a into ! glass4 ,9 c]ta9 classes ( bottles1 notably ^? us$ = special w9es1 c]ta9 %ades ( col\r are requir$--! well-kn[n 8,hock bottle0 col\r be+ an example4 ,! pres5ce ( iron 9 ! glass t5ds to ! production ( a gre5 or gre5i%-yell[ col\r deep5+ to a black opacity if ! quantity ( iron be high4 ,! light] %ades ( ?is gre5 t9t may be 8neutralis$0 by ! introduction ( manganese into ! glass1 ! result+ col\rs rang+ f light amb] to purple2 nickel oxide is also sometimes us$ z a col\r+ mat]ial 9 ^! glasses4 ,9 ! production ( ord9>y bottles ! cont9u\s tank furnace has n[ entirely sup]s$$ ! old pot furnaces1 ! "* ( ! product be+ 9 ?is case p>ticul>ly suit$ to ?is process ( production4 ,! mod]n bottle-glass tank is g5]ally an oblong bas9 hav+ "o semi-circul> end4 ,! flame is (t5 ( ! 8horse-%oe0 type1 ! gases bo? ent]+ & leav+ ! furnace at ! flat or *>g+ end ( ! furnace4 ,! raw mat]ials are ?r[n into ! furnace at ! squ>e end ( ! tank1 & ! glass fl[s un9t]rupt$ly d[n ! furnace to ! cold] semi-circul> end :]e ! work+ holes are situat$4 ,at ^! po9ts fire-clay r+s are kept float+ on ! glass1 & f )9 ^! ! ga!r] takes 8 ga!r+1 ! r+s s]v+ to reta9 ! gross] impurities c>ri$ d[n by ! glass4 ,! produc+ p[] ( su* a furnace1 ev5 :5 ! bottles are bl[n by h&1 is v consid]able2 a furnace hav+ t5 work+ holes & conta9+ normally ab\t #he tons ( molt5 glass w yield "s f\r million bottles p] annum1 & furnaces ( consid]ably l>g] capacity are 9 use4 ,! me?ods ( bottle mak+ are at ! pres5t "t pass+ ?r\gh :at is probably a /age ( transition4 ,up to ! middle ( la/ c5tury ! processes 9 use 7 little bett] ?an ^? ( ! middle ages2 ! fir/ /ep ( a m mod]n developm5t ( ! indu/ry took ! direction ( improv$ tools & implem5ts = c>ry+ out ! old op]ations4 ,m rec5tly a :ole s]ies ( inv5tions h be5 put =w>d ) ! aim ( produc+ bottles by entirely diff]5t & :olly me*anical processes ) ! object ( elim9at+ ! unc]ta9 elem5t ( skill$ lab\r entirely4 ,:ile x mu/ be admitt$ t "s ( ! e>li] ( ^! inv5tions prov$ to be brilliantly +5i\s failures1 !re is little d\bt t "h1 z 9 o!r manufactur+ processes1 ! ma*9e-made article w ultimately sup]s$e ! h&-made product4 ,ev5 n[1 me*anical processes are l>gely 9 use bo? 9 ,am]ica & ,europe1 & at "s rec5t exhibitions ma*9e-made bottles h be5 %[n :i* 9 e po9t ( quality 7 sup]ior to ! be/ h&-made goods4 ,! fir/ /age 9 ! production ( bottles by h&1 & also = mo/ ( ! ma*9e processes1 is t ( ga!r+ ! requisite quantity ( glass4 ,! bottle-bl[]'s pipe is betwe5 #e & #f ft4 long1 & is provid$ ) a slightly enl>g$ end or 8nose0 ^u :i* ! glass is ga!r$4 ,?ree ga!r+s are g5]ally suffici5t = ! production ( ord9>y bottles1 b = extra l>ge bottles1 & especially = c>boys1 heavi] ga!r+s are necess>y1 & = ^! ! ga!r] mu/ g to ! furnace f\r1 five1 or ev5 six times4 ,:5 ! requisite quantity ( glass has be5 ga!r$ on ! pipe ! ga!r+ is work$ & r\nd$ by roll+ x ei!r on a flat metal plate or 8m>v]10 or 9 a holl[$ block made ( wood or m r>ely ( metal2 by ?is process ! glass is =m$ into a well-r\nd$1 symmetrical pe>-%ap$ body4 ,! bl[] n[ di/5ds ! mass gradually by ! pressure ( 8 brea?1 at ! same "t sw++ ! pipe1 ! effect ( ^! movem5ts be+ to draw ! bulk ( ! glass d[nw>ds1 leav+ a ?9n] & cold] portion hav+ ! rudim5t>y %ape ( ! neck ( ! bottle next to ! pipe4 ,9 ! olde/ =m ( ! process ! next /age 9 ! production ( ! bottle is accompli%$ by ! aid ( a cyl9drical m\ld ( fire-clay1 ^: diamet] is t ( ! ext]nal size ( ! f9i%$ bottle4 ,! pe>-%ap$ bulb ( glass is = ?is purpose re-heat$ at ! melt+ furnace1 & is !n plac$ inside ! fire-clay m\ld4 ,by vigor\s bl[+1 & a rapid rotation ( ! pipe & glass1 ! bulb is =c$ to assume ! cyl9drical %ape ( ! m\ld1 ! glass =m+ ! neck ( ! bottle be+ at ?is /age ( ! process too cold & /iff to be fur!r de=m$4 ,! next /ep is ! =mation ( ! concavity f\nd 9 ! base ( w9e & be] bottles2 ?is is produc$ by pu%+ up ! hot pla/ic glass t =ms ! bottom ( ! bottle z x leaves ! clay m\ld4 ,?is is done by a second workman us+ an iron rod kn[n z ! 8pontil10 ^u :i* a small mass ( glass has previ\sly be5 ga!r$4 ,?is mass ( glass rema9s atta*$ to ! bottom ( ! bottle1 :i* is ?us = ! mom5t fa/5$ bo? to ! 8pontil0 & to ! bl[]'s pipe4 ,! bl[]1 h[ev]1 imm$iately deta*es ! bottle f ! pipe at ! po9t :]e ! neck ( ! bottle is int5d$ to end1 effect+ ?is by locally *ill+ ! glass--a process kn[n by ! descriptive t]m ( 8wett+ (f40 ,! unf9i%$ bottle is n[ atta*$ to & h&l$ by means ( ! 8pontil40 ,! neck is s(t5$ by re-heat+ x ov] ! furnace1 & is !n m\ld$ into ! desir$ %ape by ! aid ( specially-%ap$ tongs4 ,f9ally a ?read ( glass is w\nd r\nd ! end ( ! neck to produce ! ?ick5+ usually f\nd at t po9t4 ,! f9i%$ bottle1 /ill atta*$ to ! 8pontil10 is n[ c>ri$ to ! anneal+ kiln1 :]e x is plac$ 9 position & deta*$ f ! 8pontil0 by a %>p bl[1 :i* sev]s ! glass t _h be5 ga!r$ on ! 8pontil0 f ! bottom ( ! bottle4 ,! process1 9 ! =m describ$ above1 has be5 obsolete = _m ye>s1 improvem5ts1 consi/+ ( appliances = facilitat+ ! v>i\s op]ations1 hav+ be5 gradually introduc$4 ,! mo/ important ( ^! is ! sub/itution ( metal m\lds = ! fire-clay m\lds ( e>li] times4 ,^! metallic m\lds are made to op5 & close at w by ! action ( a p$al1 & are design$ to give ! entire bottle its f9al %ape1 except = ! ind5tation ( ! bottom1 al?\gh ?is is sometimes produc$ by a convex piece plac$ on ! bottom ( ! m\ld4 ,9 ! =mation ( ! neck ?ick5+1 also1 important me*anical aids h become almo/ univ]sal4 ,^! la/ consi/ ( tongs provid$ ) roll]s & arrang$ to rotate ab\t an axis t t]m9ates 9 a tap]$ spike :i* ent]s ! neck ( ! bottle2 by press+ ! tongs toge!r s z to br+ ! roll]s aga9/ ! outside ( ! neck & rotat+ ! :ole1 ! roll]s are made to =m ! neck ?ick5+ 9 an accurate & rapid mann]4 ,important & valuable z ^! improvem5ts ( ! anci5t process ( bottle-bl[+ und\bt$ly are1 !y d n t\* ! ma9 disadvantages ( ! process--disadvantages t s]i\sly affect ! economy ( ! process & ! well-be+ ( ! work]s employ$ ^u x4 ,x is consequ5tly n surpris+ t a great numb] ( inv5tors h lab\r$ at ! problem ( ! purely me*anical production ( bottles4 ,a l>ge numb] ( pat5ts h accord+ly be5 tak5 out 9 connection ) bottle-mak+ ma*9]y4 ,! fir/ ( ^! to atta9 any fav\r 0 t devis$ by ,a%ley1 b al?\gh great claims 7 made = x1 its use has n ext5d$4 ,at ! pres5t "t1 h[ev]1 !re are a numb] ( bottle-works actually at "w produc+ bottles by me*anical means2 "o ( ! mo/ successful ( ^! ma*9es is t devis$ by ,b\*]1 ( ,cognac4 ,! products ( ?is ma*9e1 exhibit$ 9 ,p>is at ! exhibition ( #aijj1 7 equal1 & possibly sup]ior1 to ! be/ h&-made bottles4 ,! ,b\*] ma*9e1 al?\gh by no means entirely automatic1 requires no highly-skill$ lab\r beyond t ( a workman ^: duty x is to op]ate ! v>i\s lev]s ( ! ma*9e at ! "r in/ant & 9 ! prop] ord]4 ,! details ( ! ma*9e1 z set =? 9 ! pat5ts & o!r publi%$ descriptions1 are some:at complicat$1 & v>y some:at 9 ! diff]5t models2 ! g5]al pr9ciple & mode ( op]ation is1 h[ev]1 ! same 9 all v>ieties ( ! ma*9e1 & we %all !re=e give a brief acc\nt ( x "h4 ,9 ! ,b\*] process1 ! glass is fir/ ga!r$ f ! furnace1 b z no bl[+-pipes are requir$1 ! ga!r+ is done on a light iron rod1 ?us sav+ ! ga!r] mu* ( ! lab\r ( c>ry+ ! heavy pipes4 ,! requisite quantity ( ! glass s ga!r$ is !n dropp$ into ! fir/ or 8measur+0 m\ld ( ! ma*9e1 ! 8?read0 be+ cut by h& by ! op]ator4 ,f ! measur+ m\ld1 ! glass is next caus$ to pass into ! 8neck0 m\ld2 ! glass fl[s into ?is m\ld1 & is fur!r press$ into x by ! aid ( compress$ air1 appli$ above ! free surface ( ! glass4 ,at ?is /age ! /ill liquid glass has ! ext]nal %ape ( ! neck ( ! bottle1 b ! mass ( glass is solid1 i4e41 no cavity has yet be5 produc$ 9 x4 ,! =mation ( ! cavity is next begun by ! action ( a plung] :i* is driv5 into ! 8solid0 mass ( glass fill+ ! neck m\ld1 ?is plung] ?us pun*+ out ! passage ?r\gh ! neck ( ! bottle4 ,z soon z ! plung] is )drawn1 compress$ air is admitt$ into ! cavity s =m$1 & ! mass ( glass is at ! same "t inv]t$1 & t "p occupy+ ! position ( :at is to be ! %\ld] ( ! bottle is all[$ to desc5d :ile be+ bl[n out by ! compress$ air4 ,?is process ( di/5sion is limit$1 & ! desir$ %ape is imp>t$ to ! mass by br++ t[>ds x a ?ird m\ld1 by contact ) :i* ! glass is consid]ably /iff5$--a r[ ( jets ( compress$ air1 imp++ on ! outside ( ! glass =m+ ! %\ld] ( ! bottle1 be+ fur!r us$ to /iff5 ! glass1 once ! requisite ext5sion has be5 atta9$4 ,! mass has n[ a %ape v simil> to t kn[n z a 8p>ason0 9 h& bottle-bl[+1 & is by ?is "t decid$ly /iff4 ,x is n[ introduc$ into ! f9i%+ m\ld & is bl[n into p]fect contact ) ! m\ld by p[]ful air-pressure1 ?us atta9+ ! prop] %ape ( b>rel & base2 ! ind5tation ( ! base is1 h[ev]1 sometimes produc$ on a sep>ate ma*9e or press4 ,dur+ all ^! op]ations ! neck ( ! bottle1 :i* 0 ! fir/ "p to be =m$1 has rema9$ firmly held 9 ! neck m\ld1 & all ! movem5ts t h be5 describ$ are p]=m$ by means ( lev]s actuat+ movem5ts ( ?is m\ld z a :ole1 :i*1 ( c\rse1 c>ry ! glass ) !m4 ,! la/ movem5t ( ! lev]s1 :i* releases ! bottle f ! f9i%+ m\ld1 also op5s ! neck m\ld1 & ?us leaves ! bottle f9i%$ & entirely free4 ,x w be se5 t ! process adopt$ 9 ?is ma*9e foll[s z closely z possible ! v>i\s /ages ( h& bl[+1 b t ! me*anical movem5ts ( ! ma*9e replace ! labori\s & difficult te*nique ( ! bl[]4 ,"o su* ma*9e is capable ( produc+ z _m z #abj bottles1 ea* weigh+ #a lbs41 p] h\r1 b ?is is accompli%$ only by hav+ "s ( ! m\lds 9 duplicate & s arrang$ z to come into use alt]nately4 ,! ma*9e itself is att5d$ by "o 8m\ld]10 :o op]ates ! lev]s1 & by a y\?1 :o c>ries ! f9i%$ bottles to ! anneal+ kiln1 :ile1 ( c\rse1 ! s]vices ( a ga!r] are also requir$4 ,! appe>ance ( a bottle works equipp$ ) ^! ma*9es is 9 /rik+ contra/ to t ( a h&-bl[+ works1 :]e ! /ages ar\nd ! work+-holes are cr[d$ ) m5 do+ ardu\s "w "u v sev]e conditions ( temp]ature & atmosph]e4 ,f9ally1 x mu/ be po9t$ out t ! use ( ! ,b\*] ma*9e is by no means conf9$ to ! production ( ! *eape/ k9ds ( bottles1 b t x has %[n itself especially well suit$ to ! production ( *ampagne & o!r bottles t are requir$ to )/& a high int]nal pressure1 ! ma*9e-made bottles %[+ excell5t results "u pressure te/s4 ,! ma*9e is also us$ = ! production ( m\ld$ glass-w>e ( :ite glass1 s9ce x c be adapt$ to ! production ( any k9d ( glass vessel t c be produc$ by bl[+ into a m\ld4 ,! anneal+ ( bottles 0 =m]ly c>ri$ out 9 l>ge *amb]s or kilns ( v simple con/ruction1 9 :i* ! bottles 7 /ack$ z made1 ! kiln be+ previ\sly heat$ to ! requisite temp]ature3 :5 full1 ! kiln 0 clos$ up 9 a r\gh tempor>y mann] & all[$ to cool naturally1 ?us anneal+ ! bottles /ack$ )9 x4 ,9 ?is bran* ( glass-mak+ also1 h[ev]1 ! cont9u\s anneal+ kiln has sup]s$$ ! old] k9ds1 & cont9u\s kilns are n[ almo/ univ]sal 9 bottle-mak+4 ,9 ^! kilns1 :i* consi/ ( long tunnels1 kept hot at "o end & hav+ a gradually decreas+ temp]ature z ! o!r end is approa*$1 ! bottles are /ack$ on trucks :i* are sl[ly drawn ?r\gh ! kiln f ! hot to ! cold end4 ,at ! cold end ! trucks are unload$ & are !n return$1 by an outside r\te1 to ! *>g+ end1 b ( c\rse ! bottles _c be /ack$ on ! truck until x has actually ent]$ ! hot end ( ! tunnel & acquir$ ! temp]ature !re prevail+4 ,9 a slightly diff]5t =m ( kiln1 ! bottles are c>ri$ d[n ! kiln on a species ( convey] belt =m$ ( iron plates1 b ! pr9ciple ( all ^! appliances is simil> ev5 :5 us$ = v diff]5t k9ds ( glass4 ,9 ! acc\nt ( bottle manufacture giv5 above we h ref]r$ almo/ exclusively to ! mode ( production ( ! ord9>y bottles us$ = ! /orage ( su* liquids z w9e1 be]1 spirits1 etc41 & we w n[ deal ) "s o!r bran*es ( manufacture closely alli$ to ^!4 ,an important bran* ( glass manufacture is ! production ( vessels ( l>ge dim5sions4 ,^? mo/ closely alli$ to ord9>y bottles are ! vessels kn[n z c>boys1 us$ = ! /orage & transportation 9 bulk ( *emical liquids1 & especially ( acids4 ,=m]ly ^! 7 bl[n by h& 9 a mann] closely resembl+ t us$ = ord9>y bottles1 b ! weight ( ! mass ( glass to be h&l$ by ga!r] & bl[] is v great1 :ile ! lung-p[] ( a bl[] is n suffici5t to produce ! great expansion requir$4 ,=m]ly ! only aid available to ! bl[] 0 ! device ( inject+ into ! hot1 holl[ glass body1 at an e>ly /age ( ! process1 a quantity ( wat] or alcohol2 ?is liquid 0 imm$iately vap\ris$ by ! heat ( ! glass1 & if ! bl[] clos$ ! m\?piece end ( 8 pipe by plac+ 8 ?umb ov] x1 ! expansive =ce ( ! vap\r s g5]at$ s]v$ to bl[ out ! glass to ! desir$ ext5t4 ,m rec5tly me*anical aids to ! production ( ^! l>ge vessels h become available1 fir/ 9 ! %ape ( me*anical arrangem5ts = reliev+ ! workm5 ( ! full weight ( ! glass & pipe by provid+ suitable arms ^u :i* ! :ole c be support$ )\t int]f]+ ) ! bl[]'s fre$om ( manipulat+ ! pipe & glass 9 ! desir$ way2 fur!r1 a supply ( compress$ air1 :i* c be readily connect$ ) ! pipe at any desir$ mom5t1 facilitates ! bl[+ process4 ,a process ( produc+ holl[ glass vessels ( v l>ge size by purely me*anical means has1 h[ev]1 be5 introduc$ dur+ rec5t ye>s by ,p4 ,siev]t1 ( ,dresd54 ,by ! me?ods ( ?is inv5tor1 glass vessels ( q unprec$5t$ size--su* z ba?-tubs freely accommodat+ full-gr[n m5--c be produc$4 ,= ?is purpose ! glass is spread out on ! surface ( a l>ge ca/-iron plate1 provid$ ) num]\s small holes ?r\gh :i* /eam or compress$ air may be bl[n :5 desir$4 ,! slab ( visc\s glass1 :5 prop]ly spread ov] ?is plate1 is clamp$ d[n aga9/ x all ar\nd ! outside edge by means ( a suitably-%ap$ iron coll>1 :i* holds ! glass 9 air-tight contact aga9/ ! plate b5ea?4 ,! :ole iron plate1 ) ! slab ( glass clamp$ to x1 is n[ turn$ ov]1 s t ! glass hangs d[n "u ! plate4 ,! glass imm$iately beg9s to sag "u its own weight1 & is assi/$ 9 ?is t5d5cy by a suitable bl[+ ( /eam or air into ! space betwe5 ! plate & ! glass4 ,9 bl[+ ba?-tubs 9 ?is way ! glass is all[$ to di/5d d[nw>ds until ! desir$ dep? is atta9$1 :5 fur!r di/5sion is arre/$ by br++ a flat support+ plate "u ! glass1 :i* is press$ aga9/ ?is flat plate by ! pressure ( ! air1 ?us =m+ ! flat bottom ( ! tub4 ,9 ?is process ! outl9e ( ! object is det]m9$ by ! %ape ( ! clamp+ b>s or plate t fix ! edges ( ! hot glass aga9/ ! iron plate describ$ above1 & by ?is means almo/ any desir$ %ape c be giv5 to objects ( simple =m4 ,x is obvi\s t ?is process c also be employ$ = bl[+ a holl[ body into contact ) a m\ld ( any desir$ =m & =c+ ! hot glass to take ! exact %ape ( ! m\ld2 = small] bodies1 h[ev]1 ! bl[+ 9 ( sep>ately g5]at$ /eam is n requir$1 ! heat ( ! molt5 glass itself be+ us$ to g5]ate ! necess>y /eam4 ,= ?is purpose ! requisite quantity ( glass is dropp$ on ! surface ( a wet slab ( asbe/os4 ,on ?is surface ! glass rema9s float+ ^u a lay] ( /eam1 :i* is con/antly r5ew$ by ! int5se heat+ action ( ! hot glass on ! wat] conta9$ 9 ! asbe/os bel[4 ,! m\lds us$ 9 ?is process are provid$ ) a %>p edge or lip1 & z soon z ! glass has spread into a slab ( suffici5t size1 ! inv]t$ m\ld is br\ght d[n ^u ! glass & press$ aga9/ x4 ,! %>p lip or edge ( ! m\ld =ces ! glass into close contact ) ! asbe/os "u x all ar\nd ! edge ( ! m\ld1 !reby enclos+ ! space exi/+ betwe5 ! re/ ( ! glass & ! wet asbe/os4 ,! heat ( ! glass cont9ues to g5]ate /eam at a rapid rate1 b n[ ! /eam c no long] escape f "u ! glass ar\nd ! edges1 & !re=e bl[s ! glass upw>ds into ! m\ld1 ultimately =c+ ! glass into intimate contact ) ! surface ( ! m\ld2 :5 ?is is accompli%$1 ! pressure ( ! /eam rises rapidly1 & ultimately lifts ! entire m\ld & glass suffici5tly to all[ ! excess /eam to escape--& ?is is ! sign t ! bl[+ is complete4 ,! :ole process takes only a v few seconds1 & is v successful :5 appli$ to suitable glass & us$ ) m\lds ( prop] %ape4 ,x is1 ( c\rse1 obvi\s t ord9>y n>r[-m\!d bottles c\ld n be produc$ 9 ?is way1 b wide-m\!d bottles & j>s are made 9 ?is mann]1 al?\gh ! *ief utility ( ! process lies 9 ! production ( comp>atively %all[ articles1 :i* are n ( a %ape t l5ds itself to press+4 ,,*apt] ,,viii4 ,,bl[n ,,& ,,press$ ,,glass4 ,9 _m ways v simil> to ! processes employ$ 9 ! production ( bottles are ^? us$ 9 ! manufacture ( all holl[ glass vessels t are produc$ by bl[+1 ei!r ) or )\t ! aid ( m\lds4 ,ap>t f ! actual %apes ( ! articles !mselves1 h[ev]1 ! pr9cipal diff]5ce betwe5 bottles & ! bett] classes ( holl[ glass-w>e lies 9 ! composition & quality ( ! glass itself4 ,9 ?is respect all grades ( manufacture are to be met )1 f ! light-col\r$ gre5i% or blui% glass us$ = m$ic9e bottles to ! mo/ p]fectly col\rless & brilliant 8cry/al0 or fl9t glass4 ,?is gradation 9 ! p]fection ( ! glass repres5ts a correspond+ gradation 9 ! c>e be/[$ ^u ! *oice ( raw mat]ials & ! v>i\s manipulations ( melt+ ! glass4 ,z we h se51 = ! commone/ k9ds ( bottles1 :]e col\r & quality are immat]ial1 all k9ds ( fusible mat]ials c be utilis$1 loamy or f]rug9\s s&s & refuse glass ( all k9ds be+ employ$4 ,:]e some:at high] requirem5ts h to be met1 r pur] s&s h to be us$ z s\rces ( silica1 :ile lime & alkali mu/ be introduc$ 9 pur] =ms1 ! alkali 9 ! %ape ( ! *eape/ qualities ( salt-cake & ! lime 9 t ( lime-/ones reasonably free f iron & magnesia4 ,f9ally1 = ! be/ qualities ( glass ! pure/ s& obta9able is us$1 be+ (t5 specially wa%$ to remove all loamy matt]1 :ile ! alkali is introduc$ 9 ! =m ( c>bonate1 a *emical product :i* 9 its bett] qualities is practically free f injuri\s impurities4 ,9 ^! high-class products two v di/9ct k9ds ( glass are met )4 ,"o class1 ( :i* ! ,bohemian 8cry/al0 is ! highe/ example1 is *emically ( ! nature ( an alkali-lime silicate1 ! alkali 9 ! case ( ! ,bohemian glass be+ pota%2 ! o!r v>iety ( glass conta9s no lime1 its place be+ tak5 by lead1 typical ( ?is class be+ ,engli% fl9t glass4 ,9 "s v>ieties ( glass1 lead is also replac$1 p>tially or entirely1 by b>ium1 b ?is mat]ial is *iefly us$ = ! manufacture ( press$ glass4 ,! high] grades ( quality 9 glass1 :i* ?us require increas$ ref9em5t 9 ! raw mat]ials1 also dem& increas$ ref9em5t 9 ! furnaces & appliances employ$ 9 _! melt+4 ,! tank-furnace1 :i* holds ! field 9 bottle manufacture1 is sc>cely met ) 9 ! production ( ! bett] qualities ( holl[ glass-w>e2 m$ic9e bottles & o!r articles ( mod]ate quality might be produc$ 9 tanks1 b ! quantity ( glass requir$ = su* purposes is seldom l>ge en\gh to ju/ify su* l>ge plant4 ,= ! be/ qualities ( col\rless glass-w>e1 h[ev]1 ! tank-furnace c\ld n be us$ on acc\nt ( ! fact t bo? z reg>ds col\r & fre$om f defects1 ! product ( a tank-furnace is nev] equal to ! be/ product ( pot-furnaces4 ,= fl9t-glass1 inde$1 cov]$ pots or crucibles mu/ be us$ 9 ord] to adequately protect ! molt5 glass f ! r$uc+ action ( ! furnace gases & f contam9ation by du/4 ,! mat]ials ( :i* ! pots are con/ruct$ are also *os5 ) a view to avoid+ all risk ( introduc+ col\r+ or o!rwise injuri\s impurities f t s\rce4 ,9 all processes = ! production ( holl[ glass-w>e1 ! glass or 8metal0 is tak5 f ! pot by ! process ( ga!r+ :i* has already be5 describ$2 :]e bl[n articles are to be produc$1 z di/9ct f press$ goods1 ! initial /age is always ! =mation ( a small holl[ globe or bulb at ! end ( ! glass-bl[]'s pipe4 ,! subsequ5t manipulations dep5d ^u ! nature ( ! article to be produc$4 ,! article may ei!r be made entirely by h& "w1 or r 8*air0 "w1 z x is usually call$1 or ! manipulations may be facilitat$ & ! product *eap5$--:ile its "* is1 ( c\rse1 also modifi$--by ! aid ( m\lds1 :i* are us$ to br+ ! object to its prop] %ape & to impress ^u x c]ta9 decorative m\ld+s or m>k+s4 ,z we h already se51 ord9>y bottles are n[ always bl[n ) ! aid ( m\lds1 & ! same applies to m$ic9e bottles1 lamp *imneys1 & ! bulbs = electric light2 9 connection ) lamp-*imneys x %\ld be not$ t !y are bl[n 9 m\lds 9 ! =m ( cyl9drical bottles ) a flat bottom & a dom$ top1 ! ends be+ subsequ5tly cut (f4 ,_m ( ! *eap] v>ieties ( tumbl]s & glasses are also bl[n 9 m\lds1 b !y c be1 & sometimes are1 produc$ by h&1 & z _! manufacture is typical ( t ( all h&-bl[n holl[ w>e1 we %all n[ describe x 9 "s detail z an example ( ?is class ( "w4 ,! implem5ts us$ by ! glass-bl[] & 8 assi/ants = ?is "w are few & simple4 ,! l>ge/ item is ! glass-bl[]'s b5* or *air1 :i* is simply a r\gh wood5 b5* provid$ ) two project+ side-rails or arms4 ,:5 f9i%+ a piece ( "w ! bl[] sits on ?is b5*1 & ! pipe lies across ! two rails 9 front ( him 9 su* a position t by roll+ x backw>ds & =w>ds along ! rails he c readily keep ! pipe 9 g5tle rotation4 ,9 addition to ! ord9>y bl[]'s pipe & a 8pontil0 or rod = atta*+ small quantities ( glass :]eby ! piece 9 h& c be held1 ! only o!r tools us$ by ! bl[] are a numb] ( %e>s & p9c]s ( v>i\s %apes :i* s]ve = cutt+ (f1 press+ 91 & di/5d+ ! glass z requir$1 a flat bo>d & a /one or metal plat or 8m>v]0 be+ also us$ = ! purpose ( m\ld+ ! glass4 ,z already indicat$1 ! fir/ /ep 9 ! production ( su* an object z a tumbl] consi/s 9 ga!r+ a suitable quantity ( glass on ! pipe & bl[+ x into a small bulb4 ,?is bulb is bl[n out to ! prop] size & is !n elongat$ by g5tly sw++ ! pipe4 ,! next /ep is ! flatt5+ ( ! l[] end ( ! bulb by g5tly press+ x on ! 8m>v]0 or flat plate provid$ = su* purposes2 9 ?is way ! flat bottom ( ! glass is =m$1 & ! bulb n[ has ! %ape ( ! f9i%$ glass1 b rema9s atta*$ to ! pipe by a %\ld] & neck4 ,! e>lie/ practice 0 to sep>ate ! tumbl] f ! pipe at su* a po9t z to leave ! tumbl] ( ! correct l5g?1 ! rema9+ op]ation consi/+ 9 hold+ ! glass1 fir/ fix$ to a pontil = ! purpose1 into ! furnace s z to heat ! brok5 edge2 ?is edge 0 !reby r\nd$ (f1 & ! brim ( ! glass c\ld be wid5$ or o!rwise %ap$ by rotat+ ! glass or press+ x 9 or out by ! aid ( pieces ( wood4 ,9 mod]n practice1 h[ev]1 ?is is n usual1 ! glass be+ sep>at$ f ! pipe well above ! %\ld] & anneal$ 9 ?is %ape4 ,subsequ5tly ! glass is f9i%$ 9 a trimm+ room or work%op by be+ cut (f at ! desir$ po9t & hav+ ! r\gh edge r\nd$ (f by ! aid ( a bl[pipe flame4 ,! cutt+-(f op]ation is c>ri$ out 9 a great v>iety ( ways1 ! mo/ usual be+ by ! action ( heat appli$ locally & sudd5ly1 ei!r by ! aid ( specially-%ap$ flat bl[pipe flames or by an electrically-heat$ wire4 ,ma*9es = c>ry+ out ?is op]ation1 z well z ! subsequ5t r\nd+ ( ! edge automatically1 are 9 use1 b ! latt] process is sometimes replac$ by slightly gr9d+ & poli%+ ! edges4 ,illu/ration3 ,,fig4 #h4--,sectional diagram ( ! evolution ( a tumbl]4 ,! evolution ( an ord9>y tumbl]1 z j describ$1 & z illu/rat$ diagrammatically 9 ,fig4 #h1 is typical ( ! :ole process ( holl[-glass bl[+1 b ( c\rse ! numb] ( op]ations1 z well z ! c>e & skill involv$ 9 ea* /ep1 increases rapidly z ! =m ( ! vessel becomes m complex2 9 ! highe/ class ( "w a v consid]able elem5t ( arti/ic ta/e & judgm5t on ! "p ( ! op]ative also becomes ess5tial1 =1 al?\gh ! =m ( ! object z well z ! *oice ( col\r & ornam5tation are *os5 by ! design]1 ! bl[] has to translate ! draw+ ( ! design] into glass1 & al?\gh 8 skill enables him to atta9 a consid]able degree ( fidelity 9 8 r5d]+1 _m details rema9 at 8 own option1 & ! prop] managem5t ( ^! is no small factor 9 ! success ( ! :ole "w4 ,9 ?is connection m5tion %\ld p]haps be made ( ! application ( col\r & o!r decorations to ?is k9d ( glass4 ,a v consid]able range ( effects ( ?is k9d is n[ available to ! glass-work]4 ,9 ! fir/ place ! body ( ! glass us$ = ! production ( ! articles 9 "q may be col\r$ by ! addition ( suitable col\r+ mat]ials to ! molt5 glass or raw mat]ials1 z expla9$ 9 ,*apt] ,,xi41 b ?is proc$ure has v obvi\s limitations2 :]e ! article is built up ( glass f sev]al ga!r+s--z1 = example1 is ! case 9 an ord9>y w9e-glass1 :]e ! b[l1 leg & foot are ea* made ( sep>ate ga!r+s--x is possible to use glass ( diff]5t col\rs = ^! diff]5t p>ts1 & ?is is commonly done 9 ! production ( w9e glasses hav+ ruby or gre5 b[ls & :ite legs & feet4 ,a fur!r modification 9 ! application ( col\r is obta9able by tak+ up two or m ga!r+s on ! same pipe & sup]pos+ a l>ge ga!r+ ( :ite glass on a small] "o ( col\r$ glass2 ?is is analog\s to ! process ( 8fla%+0 %eet glass1 describ$ 9 ,*apt] ,x4 & ?is process l5ds itself to a v>iety ( manipulations result+ 9 ! di/ribution ( ! col\r$ lay] ( glass 9 almo/ any desir$ mann] ov] ! object 9 h&4 ,! pr9cipal objection to ?is process1 h[ev]1 lies 9 ! fact t pots ( molt5 glass ( all ! col\rs desir$ mu/ be kept available to ! bl[] at ! same "t1 & ?is is n easily arrang$ = 9 any reasonably economical mann]4 ,= ?is reason1 & also because ! manipulations are simpl]1 col\r$ glass int5d$ = application to bl[n glass-w>e is g5]ally us$ 9 ! =m ( %ort rods previ\sly prep>$2 ^! rods are suitably heat$1 & ! col\r$ glass c !n be appli$ to ! article 9 h& at any desir$ place & 9 z small or l>ge a quantity z requir$4 ,if ! two glasses ?us br\ght into contact are prop]ly relat$ to "o ano!r z reg>ds *emical composition & physical prop]ties1 !y bl5d v readily & p]fectly1 & ! result is q z good z c\ld be obta9$ by us+ ! col\r$ glass 9 ! molt5 condition4 ,o!r decorations1 su* z gild+ or o!r metallic lu/res & also v>i\s k9ds ( iridesc5ce1 are produc$ ^u ! f9i%$ glass4 ,metallic lu/res are obta9$ by plac+ ^u ! surface ( ! glass1 & slightly fus+ into x a lay] ( p>ticles ( ! actual metal4 ,9 "s cases ?is is done by roll+ ! glass vessel1 :ile /ill hot1 9 a mass ( metallic foil ( ! k9d desir$1 :5 a suffici5t quantity readily adh]es2 9 o!r cases ! metal is appli$ 9 ! =m ( a flux or glaze conta9+ a l>ge proportion ( an easily-r$uc$ comp\nd ( ! metal1 & ?is is aft]w>ds r$uc$ to ! metallic /ate by ! action ( heat1 sometimes aid$ by t ( smoke or o!r r$uc+ gases4 ,an iridesc5t surface is produc$ ^u c]ta9 v>ieties ( glass by ! corrosive action ( acid vap\rs2 9 fact1 9 localities :]e ! atmosph]e is ta9t$ ) sulphur fumes x is q usual to see an iridesc5t lu/re on ! surface ( ord9>y w9d[ glass4 ,!re are1 ( c\rse1 num]\s o!r means ( decorat+ bl[n & o!r glass1 su* z cutt+1 engrav+1 et*+1 silv]+1 etc41 b x w\ld lie beyond ! scope ( ! pres5t volume to deal ) ^!1 s9ce !y are outside ! field ( actual glass manufacture4 ,9 ! production ( holl[ glass-w>e by h&1 ! glass-bl[] avails himself to ! full ( ! prop]ty s *>act]i/ic ( glass ( assum+ a pa/y or visc\s condition :5 suitably heat$2 by rais+ or l[]+ ! temp]ature ( 8 mat]ial1 ! bl[] c at w r5d] x /iff] or m fluid2 by bl[+ he c di/5d x1 draw x out by ! aid ( gravity or c5trifugal action1 or he c m\ld x ) ! aid ( rods & tongs ( suitable %ape1 :ile at times he all[s x to fall or fe/oon "u its own weight :ile held al(t4 ,) all ^! manipulations at 8 disposal1 ! skilful op]ative is able to "w ! glass to 8 w & to fa%ion objects ( great v>iety & beauty1 b x %\ld be not$ t objects produc$ by h& 9 ?is way w be> ! m>k ( ! processes employ$ 9 _! production 9 ! fact t !y d n possess ! extreme regul>ity ( size & %ape :i* are associat$ ) ma*9e-made articles2 !re is a c]ta9 natural v>iability 9 ! exact %ape ( curves & fe/oons t is =eign to ! products ( me*anical processes4 ,= "s purposes ?is v>iability is a disadvantage1 :ile to "s m9ds x appe>s z a defect1 & me?ods h be5 devis$ = facilitat+ ! production ( /rictly uni=m glass-w>e by ! use ( m\lds z an aid to ! "w ( ! glass-bl[]4 ,:ile und\bt$ly r$uc+ ! value & beauty ( ! w>e f ! purely arti/ic /&po9t1 ^! aids to h&-"w h r5d]$ possible an imm5se expansion ( ! entire indu/ry1 s9ce1 ) ! use ( m\lds1 pres5table glass-w>e c be produc$ by h&s f> less skill$ ?an ^? requir$ = pure h&-"w4 ,9 ! description giv5 above ( bottle-bl[+ by h& we h already se5 an example ( ! use ( m\lds 9 aid+ ! bl[] to =m 8 object to ! desir$ size & %ape4 ,mu* m complicat$ & decorative objects c1 h[ev]1 be produc$ by ! use ( m\lds4 ,su* objects z globes & %ades = gas1 oil & electric lamps1 :5 ( a light sub/ance & suitable %ape1 are usually produc$ by bl[+ bulbs ( glass into m\lds1 :]e !y acquire ! g5]al %ape z well z ! detail$ decorat$ surface configuration :i* !y aft]w>ds pres5t4 ,"h aga9 ! body rema9s a clos$ vessel1 & is only op5$ & trimm$ to ! f9al %ape at ! end ( ! op]ation :5 all ! bl[+ & m\ld+ h be5 done4 ,articles bl[n 9 ?is way v frequ5tly %[ 8m\ld m>ks10 s9ce ! contact ( ! hot glass ) ! relatively cold surface ( ! m\ld results 9 a c]ta9 cr9kl+ or r\gh5+ ( ! glass1 mu* z 9 ! process ( roll+4 ,?is effect c be m9imis$ by dress+ ! int]ior surfaces ( ! m\lds ) suitable greasy dress+s1 ^: *ief prop]ty %\ld be t !y d n /ick to ! hot glass & leave little or no residue :5 gradually burnt away 9 ! m\ld2 ! prop] c>e ( ! m\lds & _! ma9t5ance is 9 fact ! fir/ ess5tial to successful manufacture 9 ?is z well z 9 ! press$-glass indu/ry4 ,ev5 "u ! mo/ fav\rable conditions1 h[ev]1 ! surface ( glass bl[n into m\lds is n s good z t ( h&-bl[n articles :i* h nev] come into contact ) cold mat]ials1 & !re=e reta9 undim9i%$ ! natural 8fire poli%0 :i* glass possesses :5 all[$ to cool freely f ! molt5 /ate4 ,an ef=t at produc+ a simil> brilliance ( surface on m\ld$ & press$ articles is (t5 made by expos+ !m1 aft] !y h atta9$ _! f9al =m1 to ! heat ( a furnace to su* an ext5t z to s(t5 ! surfaces & all[ ! glass to re-solidify "u ! undi/urb$ influ5ce ( surface-t5sion mu* z x w\ld d 9 solidify+ freely 9 ! fir/ place4 ,un=tunately ?is process _c be c>ri$ out )\t m or less s(t5+ ! entire article1 s t skilful manipulation is requir$ to prev5t s]i\s de=mation ( ! object1 :ile a c]ta9 am\nt ( r\nd+ (f 9 all %>p corn]s & angles _c be avoid$4 ,! air-pressure requir$ to br+ ! :ole ( ! surfaces ( a l>ge & possibly complicat$ piece ( glass into contact ) ! surfaces ( ! m\ld is sometimes v consid]able1 & ! lung-p[] ( ! bl[] is (t5 insuffici5t = ! purpose2 9 _m works1 !re=e1 compress$ air is suppli$ = ! purpose1 arrangem5ts be+ employ$ :]eby ! op]ative c quickly connect ! m\?piece ( 8 pipe ) ! air-ma91 :ile he c accurately control ! pressure by means ( a suitable valve4 ,! ,siev]t process ( m\ld+ by ! aid ( /eam pressure has already be5 describ$4 ,al?\gh ! evolution ( ! indu/ry sc>cely foll[$ ?is pa?1 x is n a l>ge /ep to pass f a process 9 :i* air-pressure is us$ to drive visc\s glass into contact ) a m\ld to a process 9 :i* ! pressure ( ! air is replac$ by ! pressure ( a suitably-%ap$ solid plung]1 & ?is is ess5tially ! widely-us$ process ( glass press+4 ,9 ! fir/ in/ance ?is mode ( manufacture is obvi\sly applicable to solid or flat & %all[ articles :i* c\ld n be conv5i5tly evolv$ f ! sph]ical bulb :i* /&s z embryo ( all bl[n glass2 at fir/ sight x w\ld seem 9 fact z ?\gh ! process mu/ be limit$ to articles ( su* a %ape t a plung] c readily ent] & leave ! concave portions4 ,by ! +5i\s device1 h[ev]1 ( press+ two halves ( a clos$ or ne>ly clos$ vessel simultane\sly 9 two adjac5t m\lds & !n press+ ! two halves toge!r :ile /ill hot en\gh to unite1 x has be5 made possible to produce by ! press alone su* objects z wat]-jugs1 = example1 into :i* a plung] c\ld n possibly be introduc$ :5 f9i%$4 ,! process ( press+ be+ a purely me*anical "o & requir+ no v elaborate plant & little skill$ lab\r1 has plac$ ^u ! m>ket a ho/ ( *eap & extremely useful articles1 ?us s]v+ to wid5 v consid]ably ! useful applications ( glass4 ,on ! o!r h&1 ! process has be5 & is /ill us$ to "s ext5t = ! production ( articles int5d$ to imitate ! products ( o!r processes su* z h&-bl[n & cut glass1 ) ! result t a great deal ( glass has be5 produc$ :i* _c possibly be class$ z beautiful & mu* ( :i* c lay z little claim to utility4 ,! ess5tial feature ( ! process ( glass press+ consi/s1 z already indicat$1 9 =c+ a lay] ( glass into contact ) a m\ld by ! pressure ( a me*anically actuat$ plung]4 ,= ?is purpose a suitable m\ld & plung] z well z a press = hold+ ! =m] & actuat+ ! latt] are requir$4 ,! m\lds are g5]ally made ( a special quality ( close-gra9$ ca/-iron1 & !y are kept trimm$ & dress$ 9 mu* ! same mann] z ! m\lds us$ = bl[+ 7except t ! latt] are sometimes made ( wood74 ,= ! purpose ( facilitat+ ! removal ( ! f9i%$ article1 ! m\lds are g5]ally made 9 sev]al pieces :i* fit into "o ano!r & c be sep>at$ by means ( h+es4 ,a v important po9t ab\t ^! m\lds is t ! v>i\s pieces %\ld fit accurately into "o ano!r1 s9ce o!rwise a m9ute 8f90 ( glass w be =c$ into e int]/ice1 & ! traces ( ^! f9s w always rema9 visible on ! f9i%$ article2 ! v p]fect fit requir$ to entirely prev5t ! =mation ( su* f9s is1 ( c\rse1 sc>cely atta9able 9 practice except 9 ! case ( new m\lds1 s t ! traces ( f9s are g5]ally to be f\nd on all press$ articles1 & s]ve z a ready means ( id5tify+ ^! products :5 an attempt is made to imitate bett] classes ( glass-w>e by _! means4 ,! presses us$ 9 ?is process are g5]ally ( ! h&-lev] type2 p[] presses c\ld no d\bt be us$1 b x is cont5d$ t ! h&-press has a v great advantage 9 all[+ ! op]ator to judge by t\* :5 suffici5t pressure has be5 ex]t$1 & ?is is an important consid]ation1 s9ce an excessive pressure w\ld ei!r =ce ! glass out ( ! m\ld altoge!r or w\ld be liable to bur/ or injure ! m\ld s]i\sly4 ,! actual presses consi/ ( v]tical guides & lev]s = controll+ ! movem5t ( ! plung] & a table = hold+ ! m\lds1 & 9 "s cases a sy/em ( cranks & lev]s = op5+ & clos+ ! m\lds4 ,! process ( press+ is exce$+ly simple4 ,! prop] quantity ( glass is ga!r$ f ! pot on a solid rod & dropp$ into ! m\ld4 ,! ?read ( glass :i* rema9s betwe5 ! glass 9 ! m\ld & t rema9+ on ! iron is cut (f ) a pair ( %e>s1 & !n ! plung] is l[]$ into ! m\ld & all[$ to rema9 !re until ! glass has /iff5$ suffici5tly to reta9 its %ape1 :5 ! plung] is )drawn4 ,9 ?is proce$+ x w be se5 t ! glass is =c$ into intimate contact ) ! relatively cold surfaces ( m\ld & plung]1 & :ile und]go+ ?is treatm5t ! glass mu/ rema9 suffici5tly pla/ic to readily adapt itself to ! configuration ( ! m\ld4 ,x is !re=e n surpris+ to f9d t ! press+ process c only be us$ successfully ) glass ( a k9d specially adapt$ = x4 ,c]ta9 v>ieties ( fl9t glass & "s b>ium glasses are us$ = ?is purpose1 b ! great] quantity ( press$ glass1 p>ticul>ly z produc$ on ! ,cont95t1 is made ( a lime-alkali silicate conta9+ consid]able quantities ( bo? soda & pota% & relatively little lime2 :ile suffici5tly resi/ant = mo/ purposes1 ?is glass is p>ticul>ly s(t & adaptable :ile 9 ! visc\s condition4 ,! delet]i\s effect produc$ ^u glass surfaces :5 br\ght into contact ) relatively cold metal has already be5 ref]r$ to above1 & x only rema9s to add t ?is is ! pr9cipal difficulty ) :i* ! glass-press+ process has to cont5d4 ,x is ov]come to "s ext5t by ! aid ( ! reheat+ process describ$ above2 b ?is is only a p>tial rem$y1 & 9 ! majority ( press$ glass products ! surface is 8cov]$0 z f> z possible by ! application ( relief decorations su* z grooves1 spirals1 & ribb+s4 ,an attempt is sometimes made to imitate ! appe>ance ( cut glass1 b ! r\nd+ ( ! angles dur+ ! reheat+ process de/roys ! %>pness ( ! effect & all[s ( ! ready detection ( ! imitation1 :ile ! *eapness ( ! decoration :5 appli$ 9 ! m\ld has frequ5tly l$ manufactur]s to grossly ov]-decorate1 &1 !re=e1 de/roy all claim to beauty 9 _! w>es4 ,,*apt] ,,ix4 ,,roll$ ,,or ,,plate-,,glass4 ,9 ! pres5t *apt] we propose to deal ) all ^? processes ( glass manufacture 9 :i* ! fir/ /age consi/s 9 conv]t+ ! glass into a slab or plate by "s process ( roll+4 ,we h already consid]$ ! g5]al "* ( ! roll+ process1 & h se5 t1 al?\gh hot1 visc\s glass l5ds itself readily to be+ roll$ into %eets or slabs1 ^! _c be turn$ out ) a smoo?1 flat surface4 ,9 practice ! surface ( roll$ glass is always m or less dimm$ by contact ) ! m9ute irregul>ities ( table or roll]1 & l>g] irregul>ities ( ! surface arise f ! buckl+ t occurs at a great _m places 9 ! %eet4 ,^! limitations gov]n ! v>ieties ( glass t c be produc$ by processes t involve roll+1 & h l$ to ! some:at curi\s result t bo? ! *eape/ & r\ghe/1 z well z ! be/ & mo/ exp5sive k9ds ( flat glass1 are produc$ by roll+ processes4 ,ord9>y r\gh 8roll$ plate10 su* z t us$ 9 ! skylights ( work%ops & ( railway /ations1 is ! extreme on ! "o h&1 :ile poli%$ plate-glass repres5ts ! o!r end ( ! scale4 ,! app>5t p>adox is1 h[ev]1 solv$ :5 x is not$ t 9 ! production ( poli%$ plate-glass ! "* ( ! surface ( ! glass z x leaves ! roll]s is ( v m9or importance1 s9ce x is entirely oblit]at$ by ! subsequ5t processes ( gr9d+1 smoo?+1 & poli%+4 ,int]m$iate betwe5 ! r\gh 8roll$0 & ! 8poli%$0 plate-glass we h a v>iety ( glasses 9 :i* ! appe>ance ( ! roll$ surface is hidd5 or disguis$ to a great] or less] ext5t by ! application ( a patt]n t is impress$ ^u ! glass dur+ ! roll+ process2 ?us we h roll$ plate hav+ a ribb$ or loz5ge-patt]n$ surface1 or ! well-kn[n v>iety ( 8figur$ roll$0 plate1 sometimes kn[n z 8,muranese10 ^: elaborate & deeply-impr9t$ patt]ns give a v brilliant effect4 ,roll$ plate-glass be+ practically ! r\ghe/ & *eape/ =m ( glaz+1 is pr9cipally employ$ :]e appe>ance is n consid]$1 & its *ief requirem5t is1 !re=e1 *eapness1 al?\gh bo? ! col\r & quality ( ! glass are ( importance z affect+ ! quantity & "* ( ! light :i* x admits to ! build+ :]e ! glass is us$4 ,on ! gr\nd ( *eapness x w be obvi\s f :at we h said above 7,*apt] ,,iv471 t su* glass c only be produc$ economically 9 l>ge tank furnaces1 & ^! are univ]sally us$ = ?is purpose4 ,! requirem5ts z reg>ds fre$om f enclos$ =eign bodies ( small size & ( enclos$ air-bells are n v high 9 su* glass1 &1 !re=e1 tanks ( v simple =m are g5]ally us$4 ,no ref9em5ts = regulat+ ! temp]ature ( v>i\s p>ts ( ! furnace 9 ord] to ensure p]fect f9+ ( ! glass are requir$1 & ! furnace g5]ally consi/s simply ( an oblong *amb] or tank1 at "o end ( :i* ! raw mat]ials are f$ 91 :ile ! glass is )drawn by means ( ladles f "o or two suitable ap]tures at ! o!r end4 ,= economical work+1 h[ev]1 ! furnace mu/ be capable ( work+ at a high temp]ature1 because a *eap glass mixture is necess>ily some:at infusible1 at all ev5ts :]e col\r is consid]$4 ,?is w be obvi\s if we rememb] t ! fusibility ( a glass dep5ds ^u its alkali cont5ts1 & alkali is ! mo/ exp5sive con/itu5t ( su* glasses4 ,! actual raw mat]ials us$ 9 ! production ( roll$ plate-glass are s&1 lime/one & salt-cake1 ) ! requisite addition ( c>bon & ( flux+ & purify+ mat]ials4 ,! selection ( ^! mat]ials is made ) a view to ! greate/ purity & con/ancy ( composition :i* is available )9 ! /rictly-set limits ( price :i* ! l[ value ( ! f9i%$ product entails4 ,^! mat]ials are h&l$ 9 v l>ge quantities1 outputs ( f #fj to #aej tons ( f9i%$ glass p] week f a s+le furnace be+ by no means uncommon2 me*anical means ( h&l+ ! raw mat]ials & ( *>g+ !m into ! furnace are !re=e adopt$ :]ev] possible4 ,! glass is )drawn f ! furnace by means ( l>ge iron ladles4 ,^! ladles are us$ ( v>y+ sizes 9 su* a way z to conta9 ! prop] am\nt ( glass to roll to ! v>i\s sizes ( %eets requir$4 ,! sizes us$ are sometimes v l>ge1 & ladles hold+ z mu* z #ahj to #bjj lbs4 ( glass are us$4 ,^! ladles1 :5 fill$ ) glass1 are n c>ri$ by h&1 b are susp5d$ f sl+s atta*$ to trolleys t run on an ov]head rail4 ,! ladl]1 ^: body is protect$ by a felt apron & 8 face by a mask hav+ view-holes glaz$ ) gre5 glass1 takes ! empty ladle f a wat]-tr\gh1 9 :i* x has be5 cool$1 c>ries x to ! slightly incl9$ gangway t leads up to ! op5+ 9 ! front ( ! furnace1 & !re introduces ! ladle into ! molt5 glass1 giv+ x a half-turn s z to fill x ) a 8solid0 mass ( glass4 ,by giv+ ! ladle two or ?ree rapid upw>d j]ks1 ! op]ator !n deta*es ! glass 9 ! ladle z f> z possible f ! %eets & ?reads ( glass :i* w\ld o!rwise foll[ its )drawal2 !n ! "p ( ! h&le ( ! ladle ne> ! b[l is plac$ 9 ! hook atta*$ to ! ov]head trolley1 & by be>+ 8 weight on ! o!r end ( ! h&le1 ! workman draws ! :ole ladle up f ! molt5 ba? 9 ! furnace & out ?r\gh ! work+ ap]ture4 ,?is op]ation only takes a few seconds to p]=m1 b dur+ ?is "t ! ladl] is expos$ to great heat1 z a m or less int5se flame g5]ally issues f ! work+ ap]ture1 :5ce x is drawn upw>d "u ! hood ( ! furnace4 ,f ! furnace op5+1 ! ladl]1 g5]ally aid$ by a boy1 runs ! full ladle to ! roll+ table & !re empties ! ladle ^u ! table j 9 front ( ! roll]4 ,9 do+ ?is1 two di/9ctly diff]5t me?ods are employ$4 ,9 "o1 only ! p]fectly fluid portion ( ! glass is p\r$ out ( ! ladle by gradually tilt+ x1 ! *ill$ glass next to ! walls ( ! ladle be+ reta9$ !re & ultimately return$ to ! furnace :ile /ill hot4 ,9 ! o!r me?od1 ! *ill+ ( ! glass is m9imis$ z f> z possible1 & ! entire cont5ts ( ! ladle are empti$ ^u ! roll+ table by ! ladl]1 :o turns ! entire ladle ov] ) a rapid j]k :i* is s arrang$ z to ?r[ ! colde/ "p ( ! glass well away f ! re/4 ,:5 ! %eet is subsequ5tly roll$ ?is *ill$ portion is readily recognis$ by its d>k] col\r1 & s9ce x lies entirely at "o end ( ! %eet x is deta*$ be=e ! %eet goes any fur!r4 ,nei!r me?od appe>s to pres5t any prepond]at+ advantage4 ,illu/ration3 ,,fig4 #i4--,roll+ table = roll$ plate-glass4 ,! roll+ table us$ 9 ! manufacture ( roll$ plate is ess5tially a ca/-iron slab ( suffici5t size to accommodate ! l>ge/ %eet :i* is to be roll$2 ov] ?is slab moves a massive iron roll] :i* may be actuat$ ei!r by h& or by me*anical p[]--! latt]1 h[ev]1 be+ n[ almo/ univ]sal4 ,! ?ickness ( ! %eet to be roll$ is regulat$ by means ( slips ( iron plac$ at ! sides ( ! table 9 su* a way z to prev5t ! roll] f desc5d+ any fur!r t[>ds ! surface ( ! table3 s long z ! lay] ( glass is ?ick] ?an ^! slips1 ! entire weight ( ! roll] comes ^u ! s(t glass & presses x d[n1 b z soon z ! requir$ ?ickness is atta9$1 ! weight ( ! roll] is tak5 by ! iron slips & ! glass is n fur!r r$uc$ 9 ?ickness4 ,! wid? ( ! %eet is regulat$ by means ( a pair ( iron guides1 =m$ to fit ! =w>d face ( ! roll] & ! surface ( ! table1 9 ! mann] indicat$ 9 ,fig4 #i4 ,! roll]1 z x moves =w>d1 pu%es ^! guides be=e x1 & ! glass is conf9$ betwe5 !m4 ,:5 ! roll] has pass$ ov] ! glass1 ! %eet is left on ! iron table 9 a r$-hot1 s(t condition1 & x mu/ be all[$ to cool & h>d5 to a c]ta9 ext5t be=e x c be safely mov$4 ,9 ?is int]val1 ! *ill$ portion--if any--is p>tially sev]$ by an incision made 9 ! %eet by means ( a long iron implem5t some:at l a l>ge knife1 & !n ! %eet is loos5$ f ! b$ ( ! table by pass+ "u x1 ) a smoo? rapid /roke1 a flat-blad$ iron tool4 ,! %eet is next remov$ to ! anneal+ kiln or 8le>10 be+ fir/ drawn on to a /one slab & !nce pu%$ into ! m\? ( ! kiln4 ,at ?is /age ! *ill$ portion ( ! %eet is completely sev]$ by a bl[ :i* causes ! glass to break along ! incision previ\sly made4 ,! roll$-plate anneal+ kiln is ess5tially a long1 l[ tunnel1 kept hot at "o end1 :]e ! fre%ly-roll$ %eets are introduc$1 & cold at ! o!r end1 ! temp]ature decreas+ uni=mly d[n ! l5g? ( ! tunnel4 ,! %eets pass d[n ?is tunnel at a sl[ rate1 & are ?us gradually cool$ & anneal$ suffici5tly to und]go ! necess>y op]ations ( cutt+1 etc4 ,al?\gh ?us simple 9 pr9ciple1 ! prop] design & work+ ( ^! 8le>s0 is by no means simple or easy1 s9ce success dep5ds ^u ! correct adju/m5t ( temp]atures ?r\gh\t ! l5g? ( ! tunnel & a prop] rate ( movem5t ( ! %eets1 :ile ! mann] ( h&l+ & support+ ! %eets is vital to _! rema9+ flat & unbrok54 ,! actual movem5t ( ! %eets is effect$ by a sy/em ( mov+ grids :i* run longitud9ally d[n ! tunnel4 ,! %eets ord9>ily lie flat ^u ! /one slabs t =m ! floor ( ! tunnel1 & ! grids are l[]$ into recesses cut to receive !m4 ,at regul> int]vals ! iron grid b>s are rais$ j suffici5tly to lift ! %eets f ! b$ ( ! kiln1 & are !n mov$ longitud9ally a %ort di/ance1 c>ry+ ! %eets =w>d ) !m & imm$iately aft]w>ds aga9 deposit+ !m on ! /one b$4 ,! grids return to _! =m] position :ile l[]$ into _! recesses bel[ ! level ( ! kiln b$4 ,:5 !y em]ge f ! anneal+ kiln or 8le>0 ! %eets ( roll$ plate-glass are c>ri$ to ! cutt+ & sort+ room4 ,"h ! %eets are trimm$ & cut to size4 ,! edges ( ! %eets z !y leave ! roll+ table are some:at irregul>1 & sometimes a little 8bead$10 :ile ! ends are always v irregul>4 ,ends & edges are !re=e cut squ>e or 8trimm$0 by ! aid ( ! cutt+ diamond4 ,= ?is purpose ! %eet is laid ^u a flat table1 ! smoo!/ side ( ! %eet be+ plac$ upw>ds1 & long cuts are tak5 ) a diamond--good diamonds ( adequate size & skilful op]ators be+ necess>y to ensure good cutt+ on su* ?ick glass ov] long l5g?s4 ,/rips ( glass six or eight feet long & half an in* wide are frequ5tly deta*$ 9 ! c\rse ( ?is op]ation1 & ! f9al sep>ation is aid$ by slight tapp+ ( ! und]side ( ! glass j bel[ ! cut &--if necess>y--by break+ ! /rip (f by ! aid ( suitable tongs4 ,no v elaborate 8sort+0 ( roll$ plate glass is requir$1 except p]haps t ! %ade ( col\r 9 ! glass may v>y slightly f "t to "t1 & x is g5]ally pref]able to keep to "o %ade ( glass 9 fill+ any p>ticul> ord]4 ,ap>t f ?is1 ! roll$ plate cutt] has m]ely to cut out gross defects :i* w\ld int]f]e too s]i\sly ) ! usefulness ( ! glass4 ,z we h already indicat$1 air-bells & m9ute enclosures ( opaque matt] are n objectionable 9 ?is k9d ( glass1 b l>ge pieces ( opaque mat]ial mu/ g5]ally be cut out & reject$1 n only because !y are too unsightly to pass ev5 = r\gh glaz+ purposes1 b also because !y entail a consid]able risk ( spontane\s crack+ ( ! glass--9 fact1 visible cracks are ne>ly always se5 ar\nd l>ge 8/ones10 z ^! inclusions are call$4 ,^! may arise f v>i\s causes1 su* z incomplete melt+ ( ! raw mat]ials1 or ! contam9ation ( ! raw mat]ials ) infusible impurities1 b ! mo/ fruitful s\rce ( tr\ble 9 ?is direction lies 9 ! crumbl+ ( ! furnace l9+1 :i* introduces small lumps ( p>tially melt$ fire-clay into ! glass4 ,9 a roll$ plate tank furnace :i* is prop]ly con/ruct$ & work$1 ! p]c5tage ( %eets :i* h to be cut up on acc\nt ( su* enclosures %\ld be v small1 at all ev5ts until ! furnace is old1 :5 ! l9+s naturally %[ an increas+ t5d5cy to dis9tegrate4 ,return+ n[ to ! roll+ process1 x is readily se5 t a v slight modification w result 9 ! production ( roll$ plate-glass hav+ a patt]n impress$ ^u "o surface2 ?is modification consi/s 9 engrav+ ^u ! ca/-iron plate ( ! roll+ table 9 intaglio any patt]n t is to appe> ^u ! glass 9 relief4 ,z a matt] ( fact only v simple patt]ns are produc$ 9 ?is way1 su* z close p>allel longitud9al ribb+ & a loz5ge-patt]n1 ! reason probably be+ t ! co/ ( cutt+ an elaborate patt]n ov] ! l>ge area ( ! b$-plate ( "o ( ^! tables w\ld be v consid]able4 ,fur!r1 z ^! tables & _! b$-plates are s v heavy1 !y are n readily int]*ang$ or left /&+ idle1 s t only patt]ns requir$ 9 v great quantity c\ld be pr(itably produc$ 9 ?is way4 ,^! disadvantages are1 h[ev]1 l>gely ov]come by ! d\ble-roll+ ma*9e4 ,9 ?is ma*9e1 into ^: r elaborate details we _c ent] "h1 ! glass is roll$ out into a %eet ( ! desir$ size & ?ickness by be+ pass$ betwe5 two roll]s revolv+ ab\t /ation>y axes1 ! f9i%$ %eet em]g+ ov] ano!r roll]1 & pass+ on to a /one slab t moves =w>d at ! same rate z ! %eet is f$ d[n ^u x4 ,9 ?is ma*9e a patt]n c be readily impr9t$ ^u ! s(t %eet z x passes ov] ! la/ roll] by means ( a f\r? roll]1 ^u :i* ! patt]n is engrav$2 ?is is press$ d[n ^u ! %eet1 & leaves ^u x a cle>1 %>p & deep impress ( its patt]n4 ,! g5]al arrangem5t ( ! roll]s 9 ?is ma*9e is %[n 9 ! diagram ( ,fig4 #aj1 :i* repres5ts ! sectional elevation ( ! appliance4 ,aft] leav+ ! roll+ ma*9e1 ! c\rse ( ! 8figur$ roll$ plate0 produc$ 9 ?is mann] is exactly simil> to t ( ord9>y roll$ plate1 except t z a some:at s(t] k9d ( glass is g5]ally us$ = 8figur$10 ! temp]ature ( ! anneal+ kilns requires some:at diff]5t adju/m5t4 ,! cutt+ ( ! glass also requires r m c>e1 & x %\ld be not$ t su* glass c only be cut ) a diamond on ! smoo? side2 ! side ^u :i* ! patt]n has be5 impress$ 9 relief _c be mat]ially affect$ by a diamond4 ,?is is "o reason :y x is n feasible to produce su* glass ) a patt]n on bo? sides4 ,illu/ration3 ,,fig4 #aj4--,sectional diagram ( ma*9e = roll+ 8figur$ roll$0 plate-glass4 ,figur$ roll$ glass1 be+ ess5tially ( an ornam5tal or decorative nature1 is g5]ally produc$ 9 ei!r brilliantly :ite glass or 9 special t9ts & col\rs1 & ! mixtures us$ = atta9+ ^! are1 ( c\rse1 ! trade prop]ty ( ! v>i\s manufactur]s2 ! :it5ess ( ! glass1 h[ev]1 is only obta9able by ! use ( v pure &1 !re=e1 exp5sive mat]ials4 ,z reg>ds ! col\r$ plate-glasses1 a g5]al acc\nt ( ! pr9ciples und]ly+ ! production ( col\r$ glass w be f\nd 9 ,*apt] ,,xi4 ,! manufacture ( poli%$ plate-glass really /&s some:at by itself1 almo/ ! only feature :i* x has 9 common ) ! bran*es ( manufacture j describ$ be+ ! initial roll+ process4 ,! raw mat]ials = ! production ( plate-glass are *os5 ) ! greate/ possible c>e to ensure purity & regul>ity2 ow+ to ! v consid]able ?ickness ( glass :i* is sometimes employ$ 9 plate1 & also to ! l9e> dim5sions ( ! %eets :i* all[ ( num]\s int]nal reflections1 ! col\r ( ! glass w\ld become unpleasantly obtrusive if ! %ade 7 at all pron\nc$4 ,! actual raw mat]ials us$ v>y some:at f "o works to ano!r2 b1 z a rule1 !y consi/ ( s&1 lime/one1 & salt-cake1 ) "s soda-a% & ! usual additions ( flux+ & purify+ mat]ial su* z ars5ic1 manganese1 etc4 ,! glass is g5]ally melt$ 9 pots1 & extreme c>e is requir$ to ensure p]fect melt+ & f9+1 s9ce v m9ute defects are readily visible 9 ?is glass :5 f9i%$1 &1 ( c\rse1 detract mo/ s]i\sly f its value4 ,! me?od ( transf]r+ ! glass f ! melt+-pot to ! roll+ table diff]s some:at 9 diff]5t works4 ,9 _m cases ! melt+-pots !mselves are tak5 bodily f ! furnace & empti$ ^u ! b$-plate ( ! roll+ ma*9e1 :ile 9 o!r cases ! glass is fir/ transf]r$ to small] 8ca/+0 pots1 :]e x has to be heat$ aga9 until x has fre$ itself f ! bubbles enclos$ dur+ ! transf]5ce1 & !n ^! small] pots are us$ = p\r+ ! glass ^u ! roll+ slab4 ,! advantage ( ! latt] m complicat$ me?od lies1 no d\bt1 9 ! fact t ! l>ge melt+-pots1 :i* h to be> ! brunt ( ! heat & *emical action dur+ ! e>ly /ages ( melt+1 are n expos$ to ! great additional /ra9 ( be+ tak5 f ! hot furnace & expos$ = "s "t to ! cold outside air4 ,ap>t f ! me*anical risks ( fracture1 ?is treatm5t exposes ! pots to grave risks ( breakage f unequal expansion & contraction on acc\nt ( ! great diff]5ces ( temp]ature involv$4 ,:]e small] special ca/+-pots are us$1 ^! are n expos$ to su* prolong$ heat 9 ! furnace1 & are nev] expos$ to ! *emical action ( ! raw mat]ials1 s t ^! subsidi>y pots may p]haps be made ( a mat]ial bett] adapt$ to )/& sudd5 *anges ( temp]ature ?an ! high-class fire-clay :i* mu/ be us$ 9 ! con/ruction ( melt+ pots4 ,on ! o!r h&1 ! transf]5ce ( ! glass f ! melt+ to ! ca/+-pots involves a labori\s op]ation ( ladl+ & ! ref9+ ( ! glass1 ) its att5dant exp5diture ( "t & fuel4 ,f9ally1 ! production ( plate-glass 9 tank furnaces c\ld only be attempt$ by ! aid ( su* ca/+-pots 9 :i* ! glass w\ld h to und]go a second f9+ aft] be+ ladl$ f ! tank1 & ?is w\ld mat]ially less5 ! economy ( ! tank = ?is purpose1 :ile x is by no means an easy matt] to produce 9 tank furnaces qualities ( glass equal z reg>ds col\r & purity to ! be/ products ( ! pot furnace4 ,! )drawal ( ! pots conta9+ ! molt5 glass f ! furnace is n[ univ]sally c>ri$ out by p[]ful ma*9]y4 ,! pots are provid$ on _! out] surface ) projections by :i* !y c be held 9 suitably-%ap$ tongs or cradles4 ,a "p ( ! furnace wall1 :i* is con/ruct$ ea* "t 9 a tempor>y mann]1 is brok5 d[n2 ! pot is rais$ f ! b$ or 8siege0 ( ! furnace by ! aid ( lev]s1 & is !n bodily lift$ out by means ( a p[]ful =k4 ,! pot is !n lift$ & c>ri$ by means ( cranes until x is 9 position above ! roll+ table2 !re ! pot is tilt$ & ! glass p\r$ out 9 a /eady /ream ^u ! table1 c>e be+ tak5 to avoid ! inclusion ( air-bells 9 ! mass dur+ ! process ( p\r+4 ,:5 empty1 ! pot is return$ to ! furnace z rapidly z possible1 ! glass be+ mean:ile roll$ out into a slab by ! ma*9e4 ,except = ! great] size & weight ( bo? table & roll]1 ! plate-glass roll+ table is simil> to t already describ$ 9 connection ) roll$ plate4 ,( c\rse1 s9ce ! glass is p\r$ direct f ! pot1 !re is no *ill$ glass to be remov$4 ,fur!r1 ow+ to ! l>ge size ( %eets frequ5tly requir$1 ! b$ ( ! roll+ table _c be made ( a s+le slab ( ca/-iron1 a numb] ( c>efully jo9t$ plates be+1 9 fact1 pref]able1 z !y are less liable to w>p "u ! action ( ! hot glass4 ,9 arrang+ ! :ole ( ! roll+ plant1 ! *ief consid]ation to be kept 9 m9d is t x is necess>y to produce a flat %eet ( glass ( z ne>ly z possible equal ?ickness all ov]4 ,! f9al ?ickness ( ! :ole slab :5 gr\nd & poli%$ into a %eet ( plate-glass mu/ necess>ily be slightly less ?an t ( ! ?9ne/ "p ( ! r\gh roll$ %eet4 ,if1 !re=e1 !re are any consid]able v>iations ( ?ickness1 ! result w be t 9 "s p>ts ( ! %eet a consid]able ?ickness ( glass w h to be remov$ dur+ ! gr9d+ process4 ,?is w arise to a /ill m s]i\s ext5t if ! %eet z a :ole %\ld be b5t or w>p$ s z to dep>t mat]ially f flatness4 ,! two cases are illu/rat$ diagrammatically 9 ,fig4 #aa1 :i* %[s sectional views ( ! %eets be=e & aft] gr9d+ on an exagg]at$ scale4 ,illu/ration3 ,,fig4 #aa4--,sectional diagram illu/rat+ wa/e ( glass 9 gr9d+ curv$ or irregul> plate4 ,:ile x is evid5t t c>eful design ( ! roll+ table w avoid all t5d5cy to ! =mation ( %eets ( su* undesirable =m1 x is a mu* m difficult matt] to avoid all di/ortion ( ! %eet dur+ ! anneal+ process & :ile ! %eet is be+ mov$ f ! roll+ table to ! anneal+ kiln4 ,ow+ to ! great size ( ! slabs ( glass to be dealt )1 & /ill m to ! /r+5t requirem5t ( flatness1 ! cont9u\s anneal+ kiln1 9 :i* ! glass travels sl[ly d[n a tunnel f ! hot to ! cold end1 has n be5 adopt$ = ! anneal+ ( plate-glass1 & a =m ( anneal+ kiln is /ill us$ = t glass :i* is simil> 9 its mode ( op]ation to ! old-fa%ion$ kilns t 7 us$ = o!r k9ds ( glass be=e ! cont9u\s kiln 0 introduc$4 ,^! kilns simply consi/ ( *amb]s 9 :i* ! hot glass is seal$ up & all[$ to cool sl[ly & uni=mly dur+ a m or less protract$ p]iod4 ,9 ! case ( plate-glass1 ! slabs are laid flat on ! /one b$ ( ! kiln4 ,?is /one b$ is built up ( c>efully dress$ /one1 or blocks ( fire-brick b$d$ 9 s& 9 su* a way t !y c exp& freely lat]ally )\t caus+ any t5d5cy = ! floor to buckle upw>ds z x w\ld d if ! blocks 7 set firmly aga9/ "o ano!r4 ,! :ole *amb] is previ\sly heat$ to ! requisite temp]ature at :i* ! glass /ill %[s a v slight pla/icity4 ,! hot glass slabs f ! roll+ table are laid ^u ! b$ ( ?is kiln1 sev]al be+ usually plac$ side by side 9 ! "o *amb]1 & ! slabs 9 ! c\rse ( ! fir/ few h\rs settle d[n to ! cont\r ( ! b$ ( ! kiln1 f :i* %ape & position !y are nev] di/urb$ until !y are remov$ :5 q cold4 ,9 mod]n practice ! cool+ ( a kiln is all[$ to occupy f f\r to five days2 ev5 ?is rate ( cool+ is only p]missible if c>e is tak5 to provide = ! ev5 cool+ ( all p>ts ( ! kiln1 & = ?is purpose special air-passages are built into ! walls ( ! *amb] & b5ea? ! b$ ^u :i* ! glass re/s1 & air circulation is admitt$ to ^! 9 su* a way z to all[ ! :ole ( ! kiln to cool d[n at ! same rate2 9 ! abs5ce ( su* special arrangem5ts1 ! upp] p>ts ( ! kiln w\ld probably cool mu* m rapidly ?an ! base1 s t ! glass w\ld be mu* w>m] on its "u ?an on its upp] surface4 ,:5 ! slabs ( plate-glass are remov$ f ! anneal+ kilns !y v closely resemble %eets ( roll$ plate 9 appe>ance1 & !y are q suffici5tly transp>5t to all[ ( exam9ation & ! rejection ( ! m grossly defective portions2 ! m m9ute defects1 ( c\rse1 c only be detect$ aft] ! %eets h be5 poli%$1 b ?is prelim9>y exam9ation saves ! labori\s poli%+ ( mu* useless glass4 ,! process ( gr9d+ & poli%+ plate-glass consi/s ( ?ree pr9cipal /ages4 ,9 ! fir/ /age ! surfaces ( ! glass are gr\nd s z to be z p]fectly flat & p>allel z possible2 9 ord] to effect ?is object z rapidly z possible1 a co>se abrasive is us$ :i* leaves ! glass ) a r\gh grey surface4 ,9 ! second /age1 t ( smoo?+1 ^! r\gh grey surfaces are gr\nd d[n ) sev]al grades ( successively f9] abrasive until f9ally an exce$+ly smoo? grey surface is left4 ,9 ! ?ird & f9al /age1 ! smoo? grey surface is conv]t$ into ! brilliant poli%$ surface ) :i* we are famili> by ! action ( a poli%+ m$ium4 ,orig9ally ! v>i\s /ages ( ! gr9d+ & poli%+ processes 7 c>ri$ out by h&1 b a :ole s]ies ( +5i\s ma*9es has be5 produc$ = effect+ ! same purpose m rapidly & m p]fectly ?an h&-lab\r c\ld ev] d4 ,we _c hope to give any detail$ acc\nt ( ! v>i\s sy/ems ( gr9d+ & poli%+ ma*9es :i* are ev5 n[ 9 use1 b mu/ cont5t ourselves ) a survey ( "s ( ! m important consid]ations gov]n+ ! design & con/ruction ( su* ma*9]y4 ,9 ! fir/ place1 be=e vigor\s me*anical "w c be appli$ to ! surface ( a plate ( glass1 t plate mu/ be firmly fix$ 9 a def9ite position relatively to ! re/ ( ! ma*9]y1 & su* firm fix+ ( a plate ( glass is by no means readily atta9$1 s9ce ! plate mu/ be support$ ov] its :ole area if local fracture is to be avoid$4 ,:ile ! surface ( ! plate is 9 ! unev5 condition 9 :i* x leaves ! roll+ table1 su* a firm sett+ ( ! glass c only be atta9$ by b$d+ x 9 pla/]1 & ?is mu/ be done 9 su* a mann] z to avoid ! =mation ( air-bubbles betwe5 pla/] & glass2 if bubbles are all[$ to =m1 !y con/itute places :]e ! glass is unsupport$4 ,dur+ ! gr9d+ & poli%+ processes ^! unsupport$ places yield to ! heavy pressure t comes ^u !m1 & irregul>ities 9 ! f9i%$ poli%$ surfaces result4 ,! mo/ p]fect adhesion betwe5 glass & pla/] is atta9$ by spread+ ! pa/e ( pla/] on ! up-turn$ surface ( ! slab ( glass & l[]+ ! iron b$-plate ( ! gr9d+ table d[n ^u x1 ! b$-plate ) ! adh]+ slab ( glass be+ aft]w>ds turn$ ov] & br\ght into position 9 ! gr9d+ ma*9e4 ,:5 "o side ( ! glass has be5 poli%$1 x is g5]ally f\nd suffici5t to lay ! slab d[n on a b$ ( damp clo?1 to :i* x adh]es v firmly1 al?\gh slid+ is entirely prev5t$ by a few blocks fix$ to ! table 9 su* a way z to abut aga9/ ! edges ( ! %eet4 ,9 _m works1 h[ev]1 ! glass is set 9 pla/] = ! gr9d+ & poli%+ ( ! second side z well z ( ! fir/4 ,! process ( gr9d+ & poli%+ is /ill reg>d$ 9 _m plate-glass works z consi/+ ( ?ree di/9ct processes1 kn[n z r\gh gr9d+1 smoo?+ & poli%+ respectively4 ,=m]ly ^! ?ree /ages ( ! process 7 c>ri$ out sep>ately2 at fir/ by h&1 & lat] by ?ree diff]5t ma*9es4 ,9 ! mo/ mod]n practice1 h[ev]1 ! r\gh & smoo? gr9d+ are done on ! same ma*9e1 ! only *ange requir$ be+ ! sub/itution ( a f9] grade ( abrasive at ea* /ep = ! co>s] grade us$ 9 ! previ\s /age4 ,= ! poli%+ process1 h[ev]1 ! rubb+ implem5ts !mselves mu/ be ( a diff]5t k9d1 = :ile ! gr9d+ & smoo?+ is g5]ally done by means ( ca/-iron rubb]s mov+ ov] ! glass1 ! poli%+ is done ) felt pads4 ,! table ( ! ma*9e1 to :i* ! glass "u treatm5t is atta*$1 is !re=e made movable1 & :5 ! gr9d+ & smoo?+ processes are complete1 ! table ) its atta*$ glass is mov$ s z to come b5ea? a sup]/ructure c>ry+ ! poli%+ rubb]s1 & ! :ole is !n elevat$ s z to all[ ! rubb]s to be> on ! glass4 ,! e>lie/ =ms ( gr9d+ ma*9es gave a reciprocal motion to ! table :i* c>ries ! glass1 or ! gr9d+ rubb]s 7 mov$ backw>d & =w>d ov] ! /ation>y table4 ,rot>y ma*9es1 h[ev]1 7 introduc$ & rapidly ass]t$ _! sup]iority1 until1 at ! pres5t "t1 practically all plate-glass is gr\nd on rotat+ tables1 "s ( ^! atta9+ a diamet] ( ov] #cj ft4 ,! gr9d+ 8rubb]s0 consi/ ( heavy iron slabs1 or ( wood boxes %od ) iron1 b ( mu* small] diamet] ?an ! gr9d+ table4 ,! rubb]s !mselves are rot>y1 be+ caus$ to rotate ei!r by ! frictional drive ( ! rotat+ table bel[ !m1 or by ! action ( indep5d5t driv+ me*anism1 b ! design ( ! motions mu/ be s arrang$ t ! relative motion ( rubb] & glass %all be approximately ! same at all p>ts ( ! glass %eets1 o!rwise curv$ in/ead ( plane surfaces w\ld be =m$4 ,?is condition c be met by plac+ ! axes ( ! rubb]s at suitable po9ts on ! diamet] ( ! table4 ,! abrasive is f$ on to ! glass 9 ! =m ( a ?9 pa/e1 & :5 ea* grade or 8c\rse0 has done ! "w requir$ ( x1 ! :ole table is wa%$ d[n ?or\ghly ) wat] & !n ! next f9] grade is appli$4 ,! function ( ! fir/ or co>se/ grade is simply to remove ! surface irregul>ities & to =m a r\gh b plane surface4 ,! abrasive ord9>ily employ$ is %>p s&1 b only comp>atively light pressure c be appli$1 especially at ! beg9n+ ( ?is /age1 s9ce at t p]iod ! weight ( ! rubb] is at times borne by relatively small areas ( glass t project "h & !re above ! g5]al level ( ! slab4 ,z ^! are gr\nd away1 ! rubb]s take a l>g] & m uni=m be>+1 & great] pressure c be appli$4 ,! subsequ5t c\rses ( f9] abrasives are only requir$ to remove ! co>se pitt+s left 9 ! surface by ! action ( ! fir/ r\gh gr9d+ s&2 ! f9] abrasive replaces ! deep pits ( ! =m] grade by %all[] pits1 & ?is is c>ri$ on 9 a numb] ( /eps until a v smoo? 8grey0 surface is atta9$ & ! smoo?+ process is complete4 ,! revolv+ table or 8plat=m0 is n[ deta*$ f ! driv+ me*anism1 & mov$ along suitably plac$ rails on :eels provid$ = t purpose1 until x /&s bel[ ! poli%+ me*anism4 ,"h x is atta*$ to a fre% driv+ me*anism1 & x is !n ei!r rais$ s z to br+ ! glass into contact ) ! felt-cov]$ poli%+ rubb]s1 or ! latt] are l[]$ d[n ^u ! glass4 ,! poli%+ rubb]s are l>ge felt-cov]$ slabs ( wood or iron :i* are press$ aga9/ ! glass ) consid]able =ce2 _! movem5t is v simil> to t ( ! gr9d+ rubb]s1 b 9 place ( an abrasive !y are suppli$ ) a ?9 pa/e ( r\ge & wat]4 ,! "t requir$ = ! poli%+ process dep5ds ^u ! p]fection ( ! smoo?+ t has be5 atta9$2 9 fav\rable cases two or ?ree h\rs are suffici5t to conv]t ! 8grey0 surface into a p]fectly poli%$ "o2 :]e1 h[ev]1 some:at deep] pits h be5 left 9 ! glass1 ! "t requir$ = poli%+ may be mu* long]1 & ! poli% atta9$ w n be s p]fect4 ,! mode ( action ( a poli%+ m$ium su* z r\ge is n[ recognis$ to be totally diff]5t 9 "* f t ( ev5 ! f9e/ abrasive2 ! gra9s ( ! abrasive act by _! h>dness & ! %>pness ( _! edges1 *ipp+ away t9y p>ticles ( ! glass1 s t ! glass /eadily loses weight dur+ ! gr9d+ & smoo?+ processes4 ,dur+ ! poli%+ process1 h[ev]1 !re is little or no fur!r loss ( weight1 ! glass =m+ ! hills or highe/ p>ts ( ! m9utely pitt$ surface be+ dragg$ or sme>$ ov] ! surface 9 su* a way z to gradually fill up ! pits & holl[s4 ,! "p play$ by ! poli%+ m$ium is probably p>tly *emical & p>tly physical1 b x results1 toge!r ) ! pressure ( ! rubb]1 9 giv+ to ! surface molecules ( ! glass a c]ta9 am\nt ( fre$om ( movem5t1 simil> to t ( ! molecules ( a viscid liquid2 ! surface lay]s ( glass are ?us enabl$ to 8fl[0 "u ! action ( ! poli%] & to smoo? out ! surface to ! beautiful level smoo?ness :i* is s *>act]i/ic ( ! surfaces ( liquids at re/4 ,?is explanation ( ! poli%+ process enables u to und]/& :y ! prop] consi/5cy ( ! poli%+ pa/e1 z well z ! prop] adju/m5t ( ! spe$ & pressure ( ! rubb]s1 plays su* an important "p 9 successful poli%+2 x also s]ves to expla9 ! well-kn[n fact t rapid poli%+ only takes place :5 ! glass surface has begun to be p]ceptibly heat$ by ! friction sp5t ^u x4 ,x has be5 e/imat$ t1 on ! av]age1 slabs ( plate-glass lose "o-?ird ( _! orig9al weight 9 ! gr9d+ & poli%+ processes1 & x is obvi\s t ! erosion ( ?is great weight ( glass mu/ absorb a great am\nt ( me*anical en]gy1 :ile ! co/ ( ! plant & upkeep is proportionately great4 ,e factor t t5ds to dim9i% ei!r ! total weight ( glass to be remov$ p] squ>e y>d ( f9i%$ plate1 or r$uces ! co/ ( removal1 mu/ be ( ! utmo/ importance 9 ?is manufacture4 ,! flatness ( ! plates z !y leave ! anneal+ kiln has already be5 ref]r$ to1 & ! reason :y ! processes ( gr9d+ & poli%+ h =m$ ! subject = innum]able pat5ts w n[ be app>5t4 ,! v l>ge expansion ( ! use ( plate-glass 9 mod]n build+ con/ruction1 toge!r ) ! /eady r$uction 9 ! prices ( plate1 are evid5ce ( ! success t has att5d$ ! ef=ts ( inv5tors & manufactur]s 9 ?is direction4 ,at ! pres5t "t1 plate-glass is manufactur$ 9 v l>ge %eets1 measur+ up to #bf ft4 9 l5g? by #ad ft4 9 wid?1 & 9 ?ickness v>y+ f #c_/af? ( an in* up to #a 941 or m1 = special purposes4 ,at ! same "t ! quality ( ! glass is f> high] to-day ?an x 0 at e>li] times4 ,?is high quality *iefly results f m c>eful *oice ( raw mat]ials & great] fre$om f ! defects aris+ dur+ ! melt+ & ref9+ processes1 :ile a rigid process ( inspection is appli$ to ! glass z x comes f ! poli%+ ma*9es4 ,= ?is purpose ! %eets are exam9$ 9 a d>k5$ room by ! aid ( a lamp plac$ 9 su* a way t its oblique rays reveal e m9ute imp]fection ( ! glass2 ^! imp]fections are m>k$ ) *alk1 & ! plate is subsequ5tly cut up s z to avoid ! defects t h ?us be5 detect$4 ,p]haps ! mo/ rem>kable fact ab\t ! quality ( mod]n plate-glass is its relatively high degree ( homog5eity4 ,glass1 z we h se5 9 ,*apt] ,i41 is n a *emically homog5e\s sub/ance1 b r a mixture ( a numb] ( sub/ances ( diff]5t d5sity & viscosity4 ,:]ev] ?is mixture is n suffici5tly intimate1 ! pres5ce ( div]se con/itu5ts becomes app>5t 9 ! =m ( /ri1 aris+ f ! refraction or b5d+ ( light-rays z !y pass f "o m$ium into ano!r ( diff]5t d5sity4 ,except 9 glass t has und]gone elaborate /irr+ processes1 su* /ri are nev] abs5t1 b ! skill ( ! glass-mak] consi/s 9 mak+ !m z few & z m9ute z possible1 & caus+ !m to assume directions & positions 9 :i* !y %all be z inconspicu\s z possible4 ,9 plate-glass ?is is g5]ally secur$ 9 a v p]fect mann]1 & to ord9>y obs]vation no /ri are visible :5 a piece ( plate-glass is look$ at 9 ! ord9>y way1 i4e41 ?r\gh its smalle/ ?ickness2 if ! same piece ( glass be look$ at transv]sely1 ! edges hav+ fir/ be5 poli%$ 9 su* a way z to r5d] ?is possible1 ! glass w be se5 to be full ( /ri1 g5]ally runn+ 9 f9e l9es p>allel ) ! poli%$ surfaces ( ! glass4 ,?is uni=m direction ( ! /ri is p>tly d]iv$ f ! fact t ! glass has be5 caus$ to fl[ 9 ?is direction by ! action ( ! roll] :5 fir/ =m$ into a slab1 b ?is process w\ld n oblit]ate any s]i\s inequalities ( d5sity :i* might exi/ 9 ! glass z x leaves ! pot1 s t successful results are only atta9able if great c>e is tak5 to secure ! greate/ possible homog5eity 9 ! glass dur+ ! melt+ process4 ,at ! pres5t "t probably ! great] bulk ( plate-glass is us$ = ! purpose ( glaz+ w9d[s ( v>i\s k9ds1 pr9cipally ! %[ w9d[s ( %ops1 etc4 ,z us$ = ?is purpose ! glass is f9i%$ :5 poli%$ & cut to size4 ,! only fur!r manipulation t is sometimes requir$ is t ( b5d+ ! glass to "s desir$ curvature1 examples ( b5t plate-glass w9d[-panes be+ v frequ5tly se54 ,?is b5d+ is c>ri$ out on ! f9i%$ glass1 i4e41 aft] x has be5 poli%$2 ! glass is c>efully heat$ 9 a special furnace until s(t5$1 & is !n g5tly made to lie aga9/ a /one or metal m\ld :i* has be5 provid$ ) ! desir$ curvature4 ,x is obvi\s t dur+ ?is op]ation !re are great risks ( spoil+ ! glass2 r\gh5+ ( ! surface by contact ) irregul> surfaces on ei!r ! m\ld1 ! floor ( ! kiln1 or ! implem5ts us$ 9 h&l+ ! glass1 c only be avoid$ by ! ex]cise ( mu* skill & c>e1 :ile all du/ mu/ also be exclud$ s9ce any p>ticles settl+ on ! surface ( ! hot glass w\ld be 8burnt 910 & c\ld n aft]w>ds be deta*$4 ,small defects c1 ( c\rse1 be subsequ5tly remov$ by local h&-poli%+1 & ?is op]ation is ne>ly always resort$ to :]e poli%$ glass has to und]go fire-treatm5t = ! purpose ( b5d+4 ,9 addition to its use = glaz+ 9 ! ord9>y s5se1 plate-glass is employ$ = a numb] ( purposes2 ! mo/ important & frequ5t ( ^! is 9 ! con/ruction ( ! bett] v>ieties ( mirrors4 ,= ?is purpose ! glass is frequ5tly bevell$ at ! edges1 & sometimes a c]ta9 am\nt ( cutt+ is also introduc$ on ! face ( ! mirror4 ,bevell+ is c>ri$ out on special gr9d+ & poli%+ ma*9es1 & a great v>iety ( ^! are 9 use at ! pres5t "t4 ,! process consi/s 9 gr9d+ (f ! corn]s ( ! %eet ( glass & replac+ ! r\gh p]p5dicul> edge left by ! cutt+ diamond by a smoo? poli%$ slope runn+ d[n f ! front surface to ! l[] edge at an angle ( f #de to #fj degrees4 ,s9ce only relatively small quantities ( glass h to be remov$1 small gr9d+ rubb]s only are us$1 & 9 "s ( ! late/ ma*9es ^! take ! =m ( rapidly-revolv+ em]y or c>borundum :eels4 ,^! gr9d+ :eels h prov$ s successful 9 gr9d+ ev5 ! h>de/ metals t x is surpris+ to f9d _! use 9 ! glass indu/ry almo/ entirely re/rict$ to ! 8cutt+0 ( ! bett] k9ds ( fl9t & 8cry/al0 glass = table w>e or o!r ornam5tal purposes4 ,! reason probably lies 9 ! fact t ! use ( su* gr9d+ :eels results 9 ! g5]ation ( a v consid]able am\nt ( local heat1 ?is effect be+ int5sifi$ on acc\nt ( ! l[ heat-conduct+ p[] ( glass4 ,if a piece ( glass be held ev5 lightly aga9/ a rapidly-revolv+ em]y :eel x w be se5 t ! "p 9 contact ) ! :eel is visibly r$-hot4 ,?is local heat+ is liable to lead to *ipp+ & crack+ ( ! glass1 & ^! tr\bles are ^? actually exp]i5c$ :5 em]y or c>borundum gr9d+ is attempt$ on l>g] pieces ( glass4 ,9 ! case ( at lea/ "o mod]n bevel-gr9d+ ma*9e1 h[ev]1 x is claim$ t ! injuri\s effects ( local heat+ are avoid$ by c>ry+ out ! entire op]ation "u wat]4 ,= ! purpose ( use 9 mirrors1 plate-glass is frequ5tly silv]$1 & ?is process is c>ri$ on s ext5sively t x has come to con/itute an entire indu/ry :i* has no ess5tial connection ) glass manufacture itself2 = t reason we d n propose to ent] on ! subject "h1 only add+ t ! nature & quality ( ! glass itself consid]ably affects ! ease & success ( ! v>i\s silv]+ processes4 ,ord9>y plate-glass1 ( c\rse1 takes ! v>i\s silv]+ coat+s v easily & uni=mly1 b !re are num]\s k9ds ( glass to :i* ?is does n apply1 al?\gh !re are probably few v>ieties ( glass :i* are suffici5tly /able = practical use1 & to :i* a silv]+ coat+ _c be satisfactorily appli$1 provid$ t ! mo/ suitable process be *os5 9 ea* case4 ,:ile !re is little if any use = col\r$ glass 9 ! =m ( poli%$ plate1 entirely opaque plate-glass1 col\r$ bo? black & :ite1 is us$ = c]ta9 purposes4 ,?us1 glass fascias ov] %op-fronts1 ! c\nt]s & %elves ( "s %ops1 & ev5 tomb/ones are sometimes made ( black or :ite poli%$ plate4 ,f ! po9t ( view ( glass manufacture1 h[ev]1 ^! v>ieties only diff] f ord9>y plate-glass 9 respect ( c]ta9 additions to ! raw mat]ials1 result+ 9 ! production ( ! :ite or black opacity4 ,! subsequ5t treatm5t ( ! glass is id5tical ) t ( ord9>y plate-glass1 except t ^! opaque v>ieties are r>ely requir$ to be poli%$ on bo? sides1 s t ! op]ations are simplifi$ to t ext5t4 ,c]ta9 limitations to ! use ( all k9ds ( plate-glass1 :e!r r\gh-roll$1 figur$ or poli%$1 7 =m]ly set by ! fact t "u ! influ5ce ( fire1 p>titions ( glass 7 liable to crack1 spl9t] & fall to pieces1 ?us caus+ damage beyond _! own de/ruction & leav+ a free passage = ! propagation ( ! fire4 ,to ov]come ^! disadvantages1 glass manufactur]s h be5 l$ to introduce a network or me%+ ( wire into ! body ( su* glass4 ,provid$ t ! glass & wire c be made s z to unite prop]ly1 !n ! prop]ties ( su* re9=c$ or 8wir$0 glass %\ld be extremely valuable4 ,9 ! ev5t ( breakage f any cause1 su* z fire or a viol5t bl[1 :ile ! glass w\ld /ill crack1 ! fragm5ts w\ld be held toge!r by ! wire network1 & ! plates ( glass z a :ole w\ld rema9 9 place1 nei!r caus+ de/ruction ?r\gh fly+ fragm5ts nor all[+ fire or1 = ! matt] ( t1 burgl> a free passage4 ,! utility ( su* a mat]ial has be5 readily recognis$1 b ! difficulty lies 9 its production4 ,^! difficulties arise f two causes4 ,! mo/ s]i\s ( ^! is ! consid]able diff]5ce betwe5 ! !rmal expansion ( ! glass & ( ! wire to be emb$d$ 9 x4 ,! wire is necess>ily introduc$ into r$-hot glass :ile ! latt] is be+ roll$ or ca/1 & !re=e glass & wire h to cool d[n f a r$ heat toge!r4 ,dur+ ?is cool+ process ! wire contracts mu* m ?an ! glass1 & breakage ei!r results imm$iately1 or ! glass is left 9 a condition ( sev]e /ra9 & is liable to crack spontane\sly aft]w>ds4 ,an attempt has be5 made to ov]come ?is difficulty by us+ wire made ( a nickel /eel alloy1 ^: !rmal expansion is v simil> to t ( glass2 b1 z a matt] ( fact1 ?is simil>ity ( !rmal expansion is only kn[n to hold = a %ort range ( mod]ate temp]atures1 & probably does n hold :5 ! /eel alloy is heat$ to r$ness4 ,9 ano!r direction1 great] success is to be atta9$ by ! use ( wire ( a v ductile metal :i* %\ld yield to ! /ress t comes ^u x dur+ cool+2 probably copp] wire w\ld answ] ! purpose1 b ! great co/ ( copp] is a det]r5t f its use4 ,a second difficulty is met ) 9 introduc+ wire nett+ into glass dur+ ! roll+ op]ation1 & ?is lies 9 effect+ a clean jo9 betwe5 glass & wire4 ,mo/ metals :5 heat$ give (f a consid]able quantity ( gas1 & :5 ?is gas is evolv$ aft] ! wire has be5 emb$d$ 9 glass1 num]\s bubbles are =m$1 & ^! n only r5d] ! glass v unsightly b also less5 ! adhesion betwe5 ! wire & ! glass4 ,?is difficulty1 h[ev]1 c be ov]come m readily ?an ! fir/1 s9ce ! surface ( ! metal c be kept clean & ! gas expell$ f ! int]ior ( ! wire by prelim9>y heat+4 ,on ! :ole1 h[ev]1 wir$ glass is p]haps /ill to be reg>d$ z a product ^: evolution is n yet complete1 & !re c be no d\bt t !re are great possibilities op5 to ! mat]ial :5 its manufacture has be5 m fully develop$4 ,,*apt] ,x4 ,,%eet ,,& ,,cr[n ,,glass4 ,9 ! prec$+ *apt] we h dealt ) ! processes ( manufacture employ$ 9 ! production ( bo? ! crude/ & ! mo/ p]fect =ms ( flat glass z us$ = su* purposes z ! glaz+ ( w9d[ op5+s4 ,! products n[ to be dealt ) are ( an int]m$iate "*1 %eet-glass possess+ _m ( ! prop]ties ( poli%$ plate1 b lack+ "s v important ones2 ?us %eet-glass is suffici5tly transp>5t to all[ an obs]v] to see ?r\gh x ) little or no di/urbance--9 ! be/ v>ieties ( %eet-glass ! optical di/ortion caus$ by its irregul>ities is s small t ! glass appe>s ne>ly z p]fect z poli%$ plate--b 9 ! *eap glass t is us$ = ! glaz+ ( ord9>y w9d[s1 %eets are (t5 employ$ :i* produce ! mo/ di/urb+1 & sometimes ! mo/ ludicr\s1 di/ortions ( objects se5 ?r\gh !m4 ,x is a curi\s fact t ev5 9 good h\ses ! use ( su* inf]ior glass is tol]at$ )\t comm5t1 ! g5]al public be+1 app>5tly1 rem>kably nonobs]vant 9 ?is respect4 ,9 ano!r direction %eet-glass has ! great advantage ov] plate-glass t x is v mu* light]1 or c at lea/ be produc$ ( mu* small] weight & ?ickness1 al?\gh ?is advantage entails ! consequ5t disadvantage t %eet-glass is usually mu* weak] ?an plate1 & c only be us$ 9 mu* small] sizes4 ,9 rec5t times ! production ( relatively ?9 plate-glass has1 h[ev]1 made su* /rides t x is n[ possible to obta9 poli%$ plate-glass ?9 en\gh & light en\gh = almo/ e ar*itectural purpose4 ,f9ally1 ! mo/ important advantage ( %eet-glass1 & ! "o :i* alone secures its use 9 a great numb] ( cases 9 pref]5ce to plate-glass1 is its *eapness1 ! price ( ord9>y %eet-glass be+ ab\t "o-f\r? t ( plate-glass ( ! same size4 ,! raw mat]ials = ! manufacture ( %eet-glass are s&1 lime/one1 salt-cake1 & a few accessory sub/ances1 su* z ars5ic1 oxide ( manganese1 an?racite coal or coke1 :i* diff] consid]ably accord+ to ! practice ( ea* p>ticul> works4 ,9 a g5]al way ^! mat]ials h already be5 dealt ) 9 ,*apt] ,,iii41 & we ne$ only add "h t ! %eet-glass manufactur] mu/ keep 9 view two decid$ly conflict+ consid]ations4 ,on ! "o h& ! requirem5ts made 9 ! case ( %eet-glass z reg>ds col\r & purity r5d] a rigor\s *oice ( raw mat]ial & ! exclusion ( any?+ at all d\btful v desirable2 b on ! o!r h& ! *ief comm]cial consid]ation 9 connection ) ?is product is its *eapness1 & 9 ord] to ma9ta9 a l[ sell+ price at a pr(it to himself ! manufactur] mu/ rigor\sly exclude all exp5sive raw mat]ials4 ,= ?is reason %eet-glass1 works su* z ^? ( ,belgium & "s p>ts ( ,g]many1 :i* h l>ge deposits ( pure s& close at h&1 possess a v consid]able advantage ov] ^? 9 less fav\r$ situations1 s9ce s& 9 p>ticul> =ms s l>ge a proportion ( ! glass1 & ! co/ ( c>riage frequ5tly exce$s1 & 9 _m cases v greatly exce$s1 ! actual price ( ! s& itself4 ,! same consid]ations w apply1 al?\gh 9 some:at less] degree1 to ! o!r bulky mat]ials1 su* z lime/one & salt-cake2 b bo? ^! are m g5]ally obta9able at mod]ate prices ?an are glass-mak+ s&s ( adequate quality = %eet manufacture4 ,ord9>y 8:ite0 %eet-glass is n[ almo/ univ]sally produc$ 9 tank furnaces1 & a v great v>iety ( ^! furnaces are us$ or advocat$ = ! purpose4 ,x w\ld be beyond ! scope ( ! pres5t book to ent] 9 detail into ! con/ruction ( ^! v>i\s types ( furnace or to discuss _! relative m]its at l5g?4 ,only a brief outl9e ( ! *ief *>act]i/ics ( ! mo/ important =ms ( %eet-tank furnaces w !re=e be giv5 "h4 ,%eet tanks diff] f ea* o!r 9 sev]al important respects2 ^! relate to ! sub-division ( ! tank into "o1 two1 or ev5 ?ree m or less sep>ate *amb]s1 to ! dep? ( ! ba? ( molt5 glass & ! height ( ! 8cr[n0 or vault ( ! furnace *amb]1 to ! %ape & position ( ! ap]tures by :i* ! gas & air are admitt$ into ! furnace1 & ! resultant %ape & disposition ( ! flame1 & f9ally to ! position & arrangem5t ( ! reg5]ative appliances by :i* "s ( ! heat ( ! wa/e gases is return$ into ! furnace4 ,tak+ ^! pr9cipal po9ts 9 ord]1 we f9d t 9 "s %eet tank furnaces ! :ole furnace con/itutes a s+le l>ge *amb]4 ,9 ?is type ( furnace ! :ole process ( fusion & f9+ ( ! glass goes on 9 ?is s+le *amb]1 & an endeav\r is made to graduate ! temp]ature ( ! furnace 9 a suitable mann] f ! hot end :]e ! raw mat]ials h to be melt$ d[n to ! cold] end :]e ! glass mu/ be suffici5tly visc\s to be ga!r$ on ! pipes4 ,x is obvi\s t ?is control ( ! temp]ature _c be s p]fect 9 a furnace ( ! s+le *amb] type z 9 "o t is sub-divid$4 ,su* sub-divid$ furnaces are1 z a matt] ( fact1 mu* m frequ5t 9 %eet-glass practice2 b ?is practice diff]s widely z to ! mann] & degree ( ! sub-division introduc$4 ,9 ! extreme =m ! glass practically passes ?r\gh ?ree indep5d5t furnaces m]ely connect$ ) "o ano!r by suitable op5+s ( relatively small area ?r\gh :i* ! glass fl[s f "o to ! o!r4 ,if x 7 possible to build furnaces ( mat]ials t c\ld resi/ ! action ( heat & ( molt5 glass to an indef9ite ext5t1 x is probable t ?is extreme type w\ld prove ! be/1 s9ce x gives ! op]ator ( ! furnace ! means ( controll+ ! fl[ ( glass 9 su* a way t no unmelt$ mat]ial c leave ! melt+ *amb] & ent] ! f9+ *amb]1 & t no insuffici5tly f9$ glass c leave ! f9+ *amb] & f9d its way into ! work+ *amb]4 ,b 9 practice ! fact t ?is extreme sub-division introduces a great deal ( extra furnace wall1 expos$ bo? to heat & to contact ) ! glass1 involves v s]i\s comp5sat+ disadvantages--! co/ ( con/ruction1 ma9t5ance & r5ewal ( ! furnace is greatly increas$1 :ile !re is also an increas$ s\rce ( contam9ation ( ! glass f ! erosion ( ! furnace walls4 ,x is1 !re=e1 9 accordance ) expectations to f9d t ! mo/ successful furnaces = ! production ( %eet-glass are int]m$iate 9 ?is respect betwe5 ! simple op5 furnace & ! completely sub-divid$ "o4 ,9 "s cases ! work+ *amb] is sep>at$ f ! melt+ & f9+ *amb] by a transv]se wall above ! level ( ! glass1 :ile fire-clay blocks float+ 9 ! glass j bel[ ?is cross wall s]ve to complete ! sep>ation & to reta9 any surface impurities t may float d[n ! furnace4 ,z reg>ds ! dep? ( glass 9 ! tank1 practice also v>ies v mu*4 ,! advantages claim$ = a deep ba? are t ! fire-clay bottom ( ! furnace is !reby kept cold] & is consequ5tly less attack$1 s t ?is portion ( ! furnace w la/ = _m ye>s4 ,on ! o!r h& ! exi/5ce ( a great mass ( glass at a mod]ate heat may easily prove ! s\rce ( contam9ation aris+ f cry/allisation or 8devitrification0 occurr+ !re & spread+ into ! hott] glass above4 ,also1 if = any reason x %\ld become necess>y to remove "p or all ( ! cont5ts ( ! tank1 ! great] mass ( glass 9 ^? ) deep ba?s becomes a =midable ob/acle4 ,on ! :ole1 h[ev]1 mod]n practice appe>s to fav\r ! use ( deep] ba?s1 dep?s ( #b ft4 #f 94 or ev5 #c ft4 be+ v usual1 :ile dep?s up to #d ft4 h be5 us$4 ,! "q ( ! prop] height ( ! 8cr[n0 or vault ( ! furnace is ( consid]able importance to ! prop] work+ ( ! tank4 ,= ! purpose ( produc+ ! mo/ p]fect combu/ion1 x is n[ cont5d$ t a l>ge free flame-space is requir$4 ,! e>li] glass-melt+ tanks1 l ! e>li] /eel furnaces1 7 built ) v l[ cr[ns1 =c+ ! flame into contact ) ! surface ( ! molt5 glass1 ! object be+ to promote direct heat+ by imm$iate contact ( flame & glass2 ! mod]n t5d5cy1 h[ev]1 is /rongly 9 ! direction ( high] cr[ns1 leav+ ! heat+ ( ! glass to be accompli%$ by radiation r ?an direct conduction ( heat4 ,!re c be little d\bt t up to a c]ta9 po9t ! enl>gem5t ( ! flame-space t5ds t[>ds great] cleanl9ess ( work+ & a c]ta9 economy ( fuel1 b if ! height ( a furnace cr[n be excessive !re is a decid$ loss ( economy4 ,flame-spaces z high z #f ft4 f ! level ( ! glass to ! highe/ "p ( ! cr[n h be5 us$1 b ! m usual heights range f #b ft4 to #e ft4 ,! 8ports0 or ap]tures by :i* pre-heat$ gas & air ent] ! furnace *amb] diff] v widely 9 v>i\s furnaces4 ,9 "s cases ! gas & air are all[$ to meet 9 a small combu/ion *amb] j be=e ent]+ ! furnace itself1 :ile 9 o!r cases ! gas & air ent] ! furnace by entirely sep>ate op5+s1 only meet+ 9 ! furnace *amb]4 ,! latt] arrangem5t t5ds to ! =mation ( a highly r$uc+ flame1 :i* is advantage\s = ! r$uction ( salt-cake1 b is by no means economical z reg>ds fuel consumption4 ,on ! o!r h&1 by produc+ a p]fect mix+ ( ! ent]+ gas & air 9 suitable proportions1 ! o!r type ( ports c be made to give almo/ any k9d ( flame desir$1 al?\gh _! t5d5cy is to =m a m oxidis+ atmosph]e )9 ! furnace4 ,! latt] type ( ports1 al?\gh widely v>i$ 9 detail1 are n[ almo/ univ]sally adopt$ 9 %eet tank furnaces4 ,all mod]n tank furnaces "w on ! pr9ciple ( ! recov]y ( heat f ! heat$ products ( combu/ion z !y leave ! furnace1 & ! return ( ?is heat to ! furnace by utilis+ x to pre-heat ! incom+ gas & air2 b ! means employ$ to effect ! application ( ?is 8reg5]ative0 pr9ciple diff] consid]ably 9 v>i\s types ( plant4 ,p]haps ! mo/ widely-us$ =m ( furnace is ! direct desc5dant ( ! orig9al ,siem5s reg5]ative furnace1 9 :i* f\r reg5]ator *amb]s are provid$ ) means = rev]s+ ! fl[ ( gas & air 9 su* a way t ea* pair ( *amb]s s]ves alt]nately to absorb ! heat ( ! outgo+ gases & subsequ5tly to return ?is heat to ! incom+ air t passes ?r\gh "o1 & ! incom+ gas t passes ?r\gh ! o!r ( ^! *amb]s4 ,9 ^! furnaces1 ! reg5]ator *amb]s !mselves are g5]ally plac$ und]nea? ! melt+ furnace1 & !y are built ( fire-brick & fill$ ) loosely-/ack$ fire-bricks1 ^: function x is to absorb or deliv] ! heat4 ,9 ! mo/ mod]n type ( furnaces ( ?is class1 ! gas-reg5]ators are omitt$ entirely1 ! air only be+ pre-heat$ by means ( reg5]ators1 :ile ! gas ent]s ! furnace direct f ! produc]1 ?us c>ry+ ) x ! heat g5]at$ 9 ! produc] dur+ ! gasification ( ! fuel4 ,:ile ?is arrangem5t is und\bt$ly economical1 x has ! s]i\s disadvantage1 especially 9 ! manufacture ( %eet-glass1 t ! gas1 ru%+ direct f ! produc] into ! furnace1 c>ries ) x a great deal ( du/ & a%1 :i* x has no opportunity ( deposit+1 z 9 ! old] types ( furnace1 9 long flues4 ,! mo/ s]i\s disadvantages ( ! ord9>y types ( reg5]ative furnaces are due to ! consid]able dim5sions ( ! reg5]ative app>atus1 necessitat+ a co/ly =m ( con/ruction & occupy+ a l>ge space1 :ile ! necessity ( p]iodically rev]s+ ! valves s z to secure ! alt]nation 9 ! fl[ ( outgo+ & incom+ gases requires special att5tion on ! "p ( ! m5 engag$ 9 op]at+ ! furnace1 z well z ! con/ruction & ma9t5ance ( valves "u conditions ( heat & dirt t are n fav\rable to ! life ( me*anical appliances4 ,x is claim$ t all ^! disadvantages are ov]come to a consid]able ext5t 9 "o or o!r ( ! v>i\s =ms ( furnace kn[n z 8recup]ative40 ,9 ^! furnaces !re is no alt]nation ( fl[1 & ! reg5]ator *amb]s are replac$ by ! 8recup]ators40 ,^! consi/ ( a l>ge numb] ( small flues or pipes pass+ ?r\gh a built-up mass ( fire-brick 9 two directions at "r-angles to "o ano!r2 ?r\gh ! pipes runn+ 9 "o direction ! wa/e gases pass out to ! *imney1 :ile ! incom+ gas & air pass ?r\gh ! o!r set ( pipes4 ,a transf]5ce ( heat betwe5 ! two curr5ts ( gas takes place by ! conductivity ( ! fire-brick1 & ?us ! outgo+ gases are cont9u\sly cool$ :ile ! +o+ gases are heat$--! transf]5ce ( heat be+ some:at simil> to t :i* takes place 9 ! surface cond5s] ( a /eam eng9e4 ,!oretically ?is is a mu* simpl] arrangem5t ?an t ( sep>ate reg5]ator *amb]s1 & to "s ext5t x is f\nd pref]able 9 practice1 b !re are c]ta9 disadvantages associat$ ) ! sy/em :i* arise pr9cipally f ! peculi> nature ( ! mat]ial--fire-brick--( :i* ! recup]ators mu/ be con/ruct$4 ,9 ! fir/ place1 ! heat-conductivity ( fire-brick is n v high1 s t1 9 ord] to secure effici5cy1 ! recup]ators mu/ be l>ge1 & :ile ! individual pipes mu/ be ( small diamet]1 _! area z a :ole mu/ be l>ge en\gh to all[ ! gases to pass ?r\gh some:at sl[ly4 ,next1 ow+ to ! t5d5cy ( fire-brick to w>p1 %r9k & crack "u ! prolong$ effects ( high temp]atures1 x becomes difficult to prev5t leakage ( gases f "o set ( pipes into ! o!r4 ,if ?is occurs to a mod]ate ext5t its only effect w be to all[ "s ( ! combu/ible gas to pass direct to ! *imney1 & at ! same "t a dilution ( ! gases ent]+ ! furnace by an addition ( products ( combu/ion f ! wa/e-gas flues4 ,?is1 ( c\rse1 w mat]ially r$uce ! effici5cy ( ! furnace & require a high] fuel consumption if ! temp]ature ( ! furnace is to be ma9ta9$ at its prop] level4 ,if1 h[ev]1 ! leakage %\ld become m s]i\s1 a disa/r\s explosion might easily result1 p>ticul>ly if ! nature ( ! leakage 7 su* z to all[ ! incom+ gas & air to mix 9 ! flues4 ,x foll[s f ^! consid]ations t1 al?\gh ! recup]ative furnace is some:at simpl] & *eap] to con/ruct1 x requires1 if any?+1 m c>eful ma9t5ance ?an ! old] =ms ( reg5]ative furnace4 ,tank furnaces = ! production ( %eet-glass 9 ?is c\ntry are g5]ally work$ f e>ly on ,monday morn+ until late on ,saturday night1 glass-bl[+ op]ations be+ susp5d$ dur+ ,sunday1 al?\gh ! heat ( ! furnace mu/ be ma9ta9$4 ,on ! ,cont95t1 & especially 9 ,belgium1 ! "w 9 connection ) ^! furnaces goes on )\t any int]mission on ,sunday--a diff]5ce :i*1 h[ev] desirable ! ,engli% practice may be1 has ! effect ( h&icapp+ ! output ( a ,briti% furnace ( equal capacity by ab\t #aj p] c5t4 )\t mat]ially less5+ ! work+ co/4 ,! process ( bl[+ %eet-glass 9 an ,engli% glassworks is g5]ally c>ri$ out by gr\ps ( ?ree workm51 viz41 a 8pipe-w>m]10 a 8ga!r]0 & a 8bl[]10 al?\gh ! precise division ( ! "w v>ies accord+ to circum/ances4 ,! pipe-w>m]'s "w consi/s 9 ! fir/ place 9 fet*+ ! bl[+-pipe f a small subsidi>y furnace 9 :i* he has previ\sly plac$ x = ! purpose ( w>m+ up ! ?ick 8nose0 end ^u :i* ! glass is subsequ5tly ga!r$4 ,! %eet-bl[]'s pipe itself is an iron tube ab\t #d ft4 #f 94 long1 provid$ at ! "o end ) a wood5 sleeve or h&le1 & a m\?piece1 :ile ! o!r end is ?ick5$ up into a sub/antial cone1 hav+ a r\nd end4 ,be=e introduc+ ! pipe into ! op5+ ( ! tank furnace1 ! pipe-w>m] mu/ see t ! hot end ( ! pipe is free f scale or dirt & mu/ te/1 by bl[+ ?r\gh x1 :e!r ! pipe is free f int]nal ob/ructions4 ,he !n places ! butt ( ! pipe 9 ! op5+ ( ! furnace & all[s x to acquire z ne>ly z possible ! temp]ature ( ! molt5 glass4 ,:5 ?is is ! case ! pipe is ei!r h&$ on to ! ga!r]1 or ! pipe-w>m]1 :o is usually only a y\?1 may take ! process "o /ep fur!r be=e h&+ x on to ! m highly skill$ workman4 ,?is next /ep consi/s 9 tak+ up ! fir/ ga!r+ ( glass on ! pipe4 ,= ?is purpose ! hot nose ( ! pipe is dipp$ into ! molt5 glass1 turn$ sl[ly r\nd once or twice & !n remov$1 ! ?read ( visc\s glass t comes up ) ! pipe be+ cut (f aga9/ ! fire-clay r+ t floats 9 ! glass 9 front ( ! work+ op5+4 ,a small quantity ( glass is ?us left adh]+ to ! nose ( ! pipe1 & ?is is n[ all[$ to cool d[n until x is fairly /iff1 ! :ole pipe be+ mean:ile rotat$ s z to keep ?is fir/ ga!r+ nicely r\nd$1 :ile a slight application ( air-pressure1 by bl[+ d[n ! pipe1 =ms a v small holl[ space 9 ! mass ( glass & secures ! fre$om ( ! op5+ ( ! pipe4 ,:5 ! glass =m+ ! fir/ ga!r+ has cool$ suffici5tly1 ! ga!r] proce$s to take up ! second ga!r+ ^u x4 ,! pipe is aga9 introduc$ into ! furnace & gradually dipp$ into ! molt5 glass1 b ?is mu/ be done ) great c>e s z to avoid ! inclusion ( air-bells betwe5 ! glass already on ! pipe & ! new lay] ( hott] glass t is n[ tak5 up4 ,?is fre$om f air-bells is secur$ by a skilful ga!r] by a gradual rotation ( ! pipe z x is l[]$ into ! glass1 ?us all[+ ! two lay]s ( glass to come into contact ) a sort ( roll+ motion t all[s ! air "t to escape4 ,:5 completely imm]s$1 ! pipe is rotat$ a few times & is !n )drawn & ! 8?read0 aga9 cut (f4 ,! mass ( glass on ! end ( ! pipe is n[ consid]ably l>g] ?an be=e & requires m c>eful manipulation to cause x to reta9 ! prop]1 ne>ly sph]ical1 %ape4 ,dur+ ! cool+ process :i* n[ foll[s ! pipe is laid across an iron tr\gh1 kept brimful ( wat]2 ?is s]ves to cool ! pipe itself1 & also all[s ! pipe to be readily rotat$ backw>ds & =w>ds by roll+ x a little way along ! tr\gh4 ,:5 ! :ole mass ( glass has aga9 cool$ suffici5tly to be manipulat$ )\t risk ( rapid de=mation1 a ?ird ga!r+ ( glass is tak5 up1 9 precisely ! same mann] z t already describ$ = ! second ga!r+1 & if ! quantity ( glass requir$ is l>ge1 or ! glass itself is s hot & fluid t only a comp>atively small weight adh]es at ea* "t ( ga!r+1 ! process may be repeat$ a f\r? or ev5 a fif? "t1 b z ! weight ( pipe & adh]+ glass increases ) ea* ga!r+1 ea* /ep becomes m labori\s1 :ile ! hot glass1 be+ n[ held on a mu* l>g] sph]e1 t5ds to fl[ (f m readily1 s t great] skill is requir$ to avoid 8los+0 ! ga!r+4 ,! c>e & skill ) :i* ^! op]ations ( ga!r+ are c>ri$ out det]m9e1 to a l>ge ext5t1 ! quality ( ! result+ %eet ( glass2 any want ( regul>ity 9 ! %ape ( ! ga!r+ leads inevitably to v>iations ( ?ickness 9 diff]5t p>ts ( ! %eet1 :ile c>eless ga!r+ w introduce bubbles or 8bli/]s0 & o!r m>k+s4 ,dur+ ! int]m$iate cool+ /ages ! glass mu/ be protect$ f du/ & dirt ( all k9ds1 s9ce m9ute specks fall+ ^u ! hot glass give rise to an evolution ( m9ute gas bubbles :i* become pa9fully evid5t 9 ! sort+ room4 ,:5 ! la/ ga!r+ has be5 tak5 up & ! mass cool$ s f> z to all[ ( its be+ c>ri$ ab\t )\t fe> ( loss1 ! glass =ms an approximately sph]ical mass1 ) ! nose-end ( ! pipe at or ne> ! c5tre ( ! sph]e4 ,! next /ages ( ! process consi/ 9 ! prelim9>y %ap+ ( ?is mass 9 su* a way z to br+ ! bulk ( ! glass beyond ! end ( ! pipe1 & !n 9 =m+ j beyond ! end ( ! pipe a wid5$ %\ld] ( ?9n] & !re=e cold] glass1 ( ! diamet] requir$ = ! cyl9d] into :i* ! glass is to be bl[n4 ,?is is done by br++ ! glass into ! successive %apes %[n 9 ,fig4 #ab1 ! =m+ ( ! glass be+ effect$ by ! aid ( specially %ap$ blocks & o!r %ap+ in/rum5ts 9 :i* ! glass is turn$ & bl[n4 ,! f9al %ape atta9$ at ?is /age is a squat cyl9d] conta9+ ! bulk ( ! glass at its l[] end1 & connect$ to ! pipe by ! ?9n] & cold] neck & %\ld] already m5tion$4 ,illu/ration3 ,,fig4 #ab4--;,e>ly /ages 9 ! =mation ( cyl9d]s = %eet glass4 ,at ?is po9t ( ! process ! pipe ) its adh]5t glass is h&$ ov] to ! bl[] prop]4 ,?is op]ator works on a special /age erect$ 9 front ( small furnaces1 call$ 8bl[+ holes10 al?\gh 9 "s works ^! are disp5s$ )1 & ! /ages are erect$ 9 front ( ! melt+ furnace itself4 ,! %eet-bl[]'s /age is simply a plat=m plac$ ov] or at ! side ( a suitable excavation :i* gives ! bl[] ! necess>y space to sw+ ! pipe & cyl9d] freely at arm's l5g?4 ,! bl[+ process itself involves v little actual bl[+1 b dep5ds r ^u ! action ( gravitation & on c5trifugal effects = ! =mation ( ! l>ge1 elongat$ cyl9d] f ! squat cyl9d] ) :i* ! bl[] comm5ces4 ,! process consi/s 9 hold+ ! ?ick1 l[] end ( ! cyl9d] 9 ! heat+-furnace1 & :5 suffici5tly hot1 )draw+ x & sw++ ! pipe ) a p5dulum movem5t 9 ! bl[]'s pit4 ,! cyl9d] ?us elongates itself "u its own weight1 & any t5d5cy to collapse is c\nt]act$ by ! application ( air-pressure by ! m\?1 ! pipe be+ also1 at times1 rotat$ rapidly ab\t its own axis4 ,! re-heat+ ( ! l[] end ( ! cyl9d] is repeat$ sev]al times1 until f9ally ! glass has assum$ ! =m ( a cyl9d] ( equal ?ickness all ov]1 b clos$ ) a r\nd$ dome at ! l[] end 7,fig4 #ac74 ,?is r\nd$ end is n[ op5$4 ,9 ! case ( fairly ?9 & light cyl9d]s ?is is done by hold+ ! ?umb ov] ! m\?piece ( ! pipe 9 su* a way z to make an air-tight seal1 & !n heat+ ! end ( ! cyl9d] 9 ! bl[+-hole4 ,! heat bo? s(t5s ! glass at ! end & at ! same "t causes consid]able expansion ( ! air enclos$ 9 ! cyl9d]1 ) ! result t ! end ( ! cyl9d] is bur/ op54 ,aft] a little fur!r heat+1 dur+ :i* ! glass at ! end ( ! cyl9d] becomes v s(t1 & takes a wavy1 curly %ape1 ! bl[] )draws ! cyl9d] f ! furnace1 & hold+ x v]tically d[nw>ds 9 8 pit1 sp9s x rapidly ab\t its longitud9al axis4 ,! s(t glass at ! l[] end imm$iately op5s out "u ! c5trifugal action1 & ! bl[] increases ! spe$ ( rotation until ! s(t glass has op5$ out f> en\gh to =m a true cont9uation ( ! re/ ( ! cyl9d]1 & 9 ?is position x is all[$ to solidify4 ,) ?ick1 heavy cyl9d]s1 ! fir/ op5+ ( ! end is done 9 a diff]5t way4 ,a small quantity ( hot glass is tak5 up by an assi/ant on an iron rod1 & is laid ^u ! c5tre ( ! clos$ end ( ! cyl9d]4 ,! heat ( ?is mass ( hot glass s(t5s ! glass ( ! cyl9d]1 & ! op]ator1 ) ! aid ( a special pair ( %e>s1 cuts out a small circle ( ?is s(t5$ glass1 ?us op5+ ! end ( ! cyl9d]4 ,! f9al op]ation ( /raight5+ out ! op5$ end is c>ri$ out 9 ! same way z describ$ above = light] cyl9d]s4 ,illu/ration3 ,,fig4 #ac4--,lat] /age 9 %eet glass bl[+4 ,! complet$ cyl9d]1 /ill atta*$ to ! pipe1 is n[ c>ri$ away f ! bl[+-/age & laid ^u a wood5 rack2 !n ! bl[] takes up a piece ( cold iron1 & plac+ x aga9/ ! neck ( glass atta*+ ! cyl9d] to ! pipe1 produces a crack2 a %ort j]k !n s]ves to completely sev] ! pipe f ! cyl9d]4 ,a boy n[ takes ! pipe to a /& :]e x is all[$ to cool & :]e ! adh]+ glass cracks (f f x prior to pass+ x back to ! pipe-w>m] = fre% use4 ,on ! wood5 rack ! cyl9d] ( glass is all[$ to cool to a c]ta9 ext5t1 & !n ! rema9+ portion ( ! neck & %\ld] 7see ,fig4 #ac7 are remov$4 ,?is is done by a boy :o passes a ?read ( s(t1 hot glass ar\nd ! cyl9d] at ! po9t :]e x is to be cut (f2 ! ?read ( hot glass m]ely s]ves to produce int5se local heat+1 = z soon z x has become /iff1 ! ?read ( glass is pu%$ (f & a cold or moi/ iron is appli$ to ! cyl9d] at ! po9t :]e x _h be5 heat$ by ! ?read4 ,z a rule a crack imm$iately runs completely r\nd ! cyl9d] along ! l9e ( ! ?read1 & ! 8cap0 is ?us remov$4 ,! glass is n[ 9 ! =m ( a uni=m cyl9d] op5 at bo? ends1 b x mu/ be op5$ out into a flat %eet be=e x c assume ! famili> =m ( %eet-glass4 ,! fir/ /age 9 ! op5+-out process is t ( splitt+4 ,= ?is purpose ! cyl9d]s are c>ri$ to a special /&1 ^u :i* !y are laid 9 a horizontal position1 & "h a crack or cut is made along "o ( ! g5]at+-l9es ( ! cyl9d]4 ,?is may be done ei!r by ! application ( a hot iron1 foll[$1 if necess>y1 by slight moi/5+1 or by ! aid ( a cut f a heavy diamond drawn skilfully d[n ! inside ( ! cyl9d]4 ,x w be se5 f ! acc\nt ( ! process s f> giv51 t ! glass has z yet und]gone no real anneal+1 al?\gh ! bl[] is expect$ to 8anneal0 8 cyl9d] dur+ ! bl[+ process1 z f> z possible1 by nev] all[+ x to cool too sudd5ly1 & ?is degree ( anneal+ is usually suffici5t to save ! cyl9d] f break+ "u its int]nal /resses :5 left to cool on ! racks4 ,! surface ( ! glass1 h[ev]1 is left 9 a decid$ly h>d5$ condition1 especially on ! outside1 :i* has necess>ily be5 mo/ rapidly cool$4 ,= ?is reason--among o!rs--! splitt+ cut is always made on ! inside ( ! cyl9d]4 ,! diff]5ce betwe5 ! rates ( cool+ ( ! outside & inside ( ! cyl9d] has a fur!r effect1 :i* becomes evid5t z soon z ! cyl9d] is split4 ,! outside hav+ become h>d :ile ! inside 0 /ill relatively s(t1 ! out] lay]s ( glass are 9 a /ate ( compression & ! inn] lay]s 9 a /ate ( t5sion 9 ! cold cyl9d]4 ,z soon z ! cyl9d] is split1 h[ev]1 ^! /resses are to "s ext5t reliev$1 ! inn] lay]s be+ !n free to contract & ! out] lay]s to exp&2 ! result is an increase 9 ! curvature ( ! cyl9d]1 :i* slightly decreases 9 diamet]1 ! cut edges ov]lapp+4 ,if ! cyl9d] has be5 cool$ r too quickly1 or if ! glass itself has a high coeffici5t ( expansion1 ?is release ( int]nal /resses at ! mom5t ( splitt+ becomes v m>k$1 & ea* cyl9d] splits ) ! s\nd ( a small explosion1 :ile if ! int]nal /resses are /ill m sev]e1 ! cyl9d]s may ev5 fly to pieces z soon z !y are cut4 ,! next /age 9 ! manufacture ( a %eet ( glass is ! flatt5+ & anneal+ process4 ,= ?is purpose ! split cyl9d]s are tak5 to a special kiln1 g5]ally kn[n z a 8le>10 or 8lehr10 :]e !y are fir/ ( all rais$ to a dull r$-heat2 !y are !n lift$1 "o at a "t1 on to a smoo? /one or slab plac$ 9 a *amb] ( ! kiln :]e ! heat is great en\gh to s(t5 ! glass4 ,"h ! cyl9d] is laid d[n ) ! split edges upw>ds1 & by means ( a wood5 tool ! glass is sl[ly spread out1 be+ f9ally rubb$ d[n into p]fect contact ) ! slab or 8lagre40 ,f ! flatt5+ slab1 ! %eet z x n[ is passes into ! anneal+ kiln1 :i* communicates ) ! flatt5+ *amb]4 ,?is consi/s1 simil>ly to o!r cont9u\s anneal+ kilns already describ$ 9 connection ) o!r v>ieties ( glass1 ( a long tunnel1 heat$ to ! temp]ature ( ! flatt5+ kiln at "o end & ne>ly cold at ! o!r4 ,! %eets are mov$ d[n ?is tunnel at a uni=m sl[ rate by ! action ( a sy/em ( grids :i*1 at int]vals1 lift ! %eets f ! bottom ( ! kiln1 move !m =w>d by a %ort di/ance1 & aga9 deposit !m on ! bottom1 ! grids !mselves return+ to _! =m] position by a retrograde movem5t made bel[ ! level ( ! kiln-bottom1 & !re=e n affect+ ! glass4 ,on leav+ ! anneal+ kiln ! %eets ( glass are sometimes cov]$ ) a :ite deposit aris+ f ! products ( combu/ion 9 ! kiln & _! int]action ) ! glass itself4 ,?is deposit c be remov$ by simple me*anical rubb+1 b x is usual to dip ! glass into a weak acid ba?1 :i* dissolves ! :ite film & leaves ! glass cle> & bright1 ready = use4 ,f ! anneal+ kiln ! f9i%$ %eets ( glass are tak5 to ! sort+ room1 :]e !y are exam9$ 9 a good light aga9/ a black backgr\nd1 & are sort$ accord+ to _! quality = diff]5t purposes4 ,! defects :i* are f\nd 9 %eet-glass are ( a v v>i$ nature1 z w\ld be anticipat$ f ! long & complicat$ process ( manufacture :i* ! mat]ial und]goes 9 ! c\rse ( its trans=mation f ! raw mat]ials into ! f9i%$ %eet ( glass4 ,a full enum]ation ( all possible defects1 ) _! te*nical names1 ne$ n be giv5 "h1 b a description ( ! m important & frequ5t ones w be useful4 ,! defects may be conv5i5tly gr\p$ accord+ to ! /age ( ! process f :i* !y orig9ate4 ,! fir/ class ( defects accord+ly embraces ^? t arise f ! condition ( ! glass z x exi/s 9 ! work+-end ( ! furnace4 ,*ief ( ^! are :ite opaque enclosures1 kn[n z 8/ones40 ,^! may arise f a v>iety ( causes )9 ! furnace1 su* z an admixture ( infusible impurities ) ! raw mat]ials1 insuffici5t heat or duration ( melt+1 lead+ to a residue ( unmelt$ raw mat]ial 9 ! f9i%$ glass1 or f defective condition ( ! int]ior ( ! furnace1 lead+ to contam9ation ( ! glass ) small p>ticles ( fire-brick4 ,fur!r1 if any "p ( ! furnace has be5 all[$ to rema9 at too l[ a temp]ature1 or if ! composition ( ! glass is unsuitable1 cry/allisation may occur 9 ! glass1 & :ite pat*es ( cry/all9e mat]ial may f9d _! way into ! f9i%$ %eets4 ,ano!r defect t may arise f ! condition ( ! glass 9 ! furnace is ! pres5ce ( num]\s small bubbles1 kn[n z 8se$0 9 ! glass4 ,by ! bl[+ process ^! are drawn out into po9t$ ovals1 & !y are r>ely q abs5t f %eet-glass4 ,!y arise f ei!r incomplete f9+ ( ! glass 9 ! furnace or f all[+ ! glass to come into contact ) m9ute p>ticles ( du/ dur+ ! ga!r+ process4 ,ano!r possible defect to ! glass itself may be f\nd at times 9 too deep a col\r4 ,?is is only se5 readily :5 a %eet ( "s size is exam9$ edgewise1 z mo/ v>ieties ( ord9>y %eet-glass are too free f col\r to all[ ?is to be judg$ by look+ ?r\gh ! %eet 9 ! ord9>y way4 ,x foll[s f ?is fact t = practical purposes1 :]e ! light always trav]ses "o ?ickness ( ! glass only1 a slight diff]5ce ( col\r %\ld be reg>d$ z a v m9or consid]ation1 at all ev5ts z comp>$ ) fre$om f o!r defects4 ,! ga!r+ process 9 its turn is responsible = fur!r defects ( %eet-glass4 ,"s ( ^!1 su* z defects aris+ f ! use ( a dirty pipe1 are nev] all[$ to pass beyond ! sort+-room1 & are !re=e ( no int]e/ to ! us] ( glass4 ,( ^? ^: traces are se5 9 ! glass t passes into use1 8bli/]s0 & 8/r+0 are ! mo/ important4 8,bli/]s0 are some:at l>g]1 flat air-bells1 aris+ f ! inclusion ( air betwe5 successive lay]s ( ! ga!r+4 8,/r+0 is a v common defect 9 all %eet-glass4 ,to "s ext5t x may arise f want ( homog5eity 9 ! glass itself4 ,if ?is consi/s ( lay]s ( diff]5t d5sities & viscosities1 ! ga!r] w take ^! up on 8 ga!r+1 & ultimately !y w =m ?ick5$ ridges ( glass runn+ ar\nd ! cyl9d]s & across ! %eets4 ,su* /ri1 due to want ( homog5eity 9 ! glass1 are mu* m common 9 fl9t glass ?an 9 ! soda-lime glasses us$ = %eet manufacture1 b are n unkn[n 9 ! latt]4 ,on ! o!r h&1 ev5 if ! glass be z homog5e\s z possible1 ! ga!r] c produce ^! /ri if he takes up 8 glass f a place close to ! side ( ! fire-clay r+ t floats 9 ! furnace 9 front ( 8 work+ op5+4 ,glass always acts *emically ^u fire-clay1 gradually =m+ a lay] ( glass next to ! fire-clay t conta9s mu* m alum9a ?an ! re/ ( ! cont5ts ( ! furnace4 ,su* a lay] is =m$ on ! surface ( ea* r+ 9 a %eet tank1 b if ! ga!r+ is tak5 f ! c5tre ( ! r+1 ?is ?ick visc\s lay] ( alum9if]\s glass rema9s undi/urb$4 ,if1 h[ev]1 ! ga!r] br+s 8 pipe too ne> ! side ( ! r+1 ! glass w draw "s ( ?is diff]5t lay] on to ! ga!r+1 & ?is glass w =m ?ick ridges & /ri runn+ across ! %eet 9 all directions4 ,ano!r defect = :i* ! ga!r] is g5]ally responsible is t ( v>iation ( ?ickness )9 ! same %eet4 ,! bl[]1 h[ev]1 c also produce ?is defect4 ,dur+ ! bl[+ prop]1 a fur!r s]ies ( defects may be introduc$1 pr9cipally by all[+ p>ticles ( glass d]iv$ f c]ta9 /ages ( ! process to fall ^u ! hot glass ( ! cyl9d] & !re become atta*$ p]man5tly4 ,m s]i\s1 & also m frequ5t1 is ! great] or less mal=mation ( ! cyl9d]4 ,if ! glass z x leaves ! bl[] is ( any %ape o!r ?an t ( a true cyl9d]1 x becomes impossible to spread x into a truly flat %eet 9 ! flatt5+ kiln4 ,sometimes1 9 practice1 ! 8cyl9d]0 is wid] at "o end ?an at ! o!r1 or1 worse /ill1 x is ( unev5 diamet]1 %[+ exp&$ & contract$ areas alt]nately4 ,:5 su* a cyl9d] comes to be spread out on ! slab x _c be flatt5$ completely1 & v>i\s holl[s & hillocks are left1 :i* m> ! flatness ( ! %eet & int]f]e ) ! regul> passage ( light ?r\gh x :5 9 use4 ,f9ally1 ! process ( flatt5+ is apt to introduce defects ( its own4 ,! mo/ common ( ^! are scrat*es aris+ f m>ks left by ! flatt5+ tool2 inde$1 9 all %eet glass x is q possible to see1 by c>eful exam9ation ( ! surfaces1 ^u :i* side ! flatt5+ tool 0 us$4 ,%eet-glass ?us has "o side decid$ly bright] & bett] 9 surface ?an ! o!r1 ! bett] side be+ t :i* re/$ ^u ! 8lagre0 dur+ ! flatt5+ process4 ,on ! o!r h&1 if ! slab itself be n q p]fect1 or if any =eign body be all[$ to re/ ^u x1 t side ( ! glass w be m>k$ 9 a correspond+ mann]4 ,9 ! acc\nt ( ! manufacture ( %eet-glass giv5 above1 we h outl9$ "o typical =m ( ! process1 b ne>ly e /age is subject to modifications accord+ to ! practice & p>ticul> circum/ances ( ea* works4 ,we w n[ describe "o or two special modifications t are ( m g5]al importance4 ,fir/1 z reg>ds ! melt+ process1 al?\gh ! tank-furnace has almo/ entirely sup]s$$ ! pot furnace = ! production ( ord9>y %eet-glass1 !re are /ill "s special circum/ances "u :i* ! pot furnace is capable ( hold+ its own4 ,?us1 :]e = special purposes x is desir$ to produce a v>iety ( %eet-glass :i*1 z reg>ds all defects aris+ out ( ! glass itself1 & especially z reg>ds col\r1 is requir$ to be z p]fect z possible1 melt+ 9 pots is f\nd advantage\s1 & = "s v special purposes ev5 cov]$ 7hood$7 pots are us$4 ,= su* special purposes1 too1 sulphate ( soda is elim9at$ f ! raw mat]ials & c>bonate ( soda 7soda a%7 sub/itut$4 ,= ! production ( t9t$ glasses also1 :e!r !y are t9t$ ?r\gh\t _! mass1 or m]ely cov]$ ) a ?9 lay] ( t9t$ glass 78fla%$071 manufacture 9 pot r ?an tank furnaces is g5]ally adopt$1 ! exact nature & composition ( ! glass be+ f> bett] "u control 9 ! case ( pots4 ,! bl[+ process is also subject to wide v>iations ( practice4 ,! mo/ important ( ^! v>iations conc]ns ! %ape & dim5sions ( ! cyl9d]s4 ,9 ,engli% & ,belgian works ! dim5sions ( ! cyl9d]s are s *os5 t ! l5g? ( ! cyl9d] con/itutes ! longe/ dim5sion ( ! f9i%$ %eet1 ! diamet] ( ! cyl9d] =m+ ! %ort] dim5sion4 ,9 "s p>ts ( ,g]many1 h[ev]1 ! practice is ! rev]se ( ?is1 ! cyl9d]s be+ bl[n %ort] & mu* wid]1 s t ! circumf]5ce ( ! cyl9d] con/itutes ! longe/ dim5sion ( ! f9i%$ %eet4 ,x is1 h[ev]1 pretty g5]ally recognis$ t ! latt] me?od has v s]i\s disadvantages1 al?\gh x is claim$ t some:at m p]fect glass c be obta9$ by its means4 ,= ! production ( a special v>iety ( glass1 kn[n z 8bl[n plate glass10 ?is me?od ( bl[+ %ort wide cyl9d]s is /ill adh]$ to4 ,?is is a v pure =m ( %eet-glass1 bl[n into ?ick1 small %eets :i* are subsequ5tly gr\nd & poli%$ 9 ! same mann] z plate-glass4 ,"h ! great ?ickness ( glass requir$ seems to r5d] ! bl[+ ( long cyl9d]s v difficult1 & ! o!r =m is !re=e adopt$4 ,on ! o!r h&1 ,engli% pat5t plate-glass1 :i* is made by gr9d+ & poli%+ ! be/ quality ( ord9>y %eet-glass1 is made f glass bl[n into long n>r[ cyl9d]s 9 ! mann] describ$ 9 detail above4 ,! process ( bl[+ describ$ above is capable1 ) slight modifications1 ( yield+ glass ) surfaces o!r ?an ! pla9 smoo? face ( ord9>y %eet-glass4 ,?us flut$ & 8muffl$0 glass are produc$ 9 a v simil> mann] to t describ$ above = ord9>y %eet1 except t ! flut+ or ! irregul> surface m>k+s :i* con/itute ! peculi>ities ( ^! two v>ieties ( glass1 are impress$ ^u ! surface ( ! cyl9d] at an e>ly /age 9 ! process4 ,f ! outl9e description giv5 above ( ! usual me?od ( manufacture ( %eet-glass1 x w readily be se5 t ?is is a long1 complicat$1 & labori\s process1 involv+ ! employm5t ( mu* skill$ lab\r1 & involv+ ! production ( a relatively complicat$ =m1 viz41 ! clos$ cyl9d]1 z a prelim9>y to ! production ( a v simple =m1 viz41 ! flat %eet4 ,x is !re=e by no means surpris+ to f9d t a great _m inv5tors h work$ & are /ill work+ at ! problem ( a direct me*anical me?od ( produc+ flat glass possess+ a natural 8fire poli%0 at lea/ equal to t ( ord9>y %eet-glass4 ,! e>li] inv5tors h almo/ uni=mly endeav\r$ to atta9 ?is object by attempt+ to improve ! process ( roll+ glass1 ) a view to obta9+ roll$ %eets hav+ a satisfactory surface4 ,we h already indicat$ :y ^! ef=ts h nev] met ) success & :at reasons !re are = believ+ t !y are nev] likely to atta9 _! object4 ,a totally diff]5t l9e is t tak5 by ,siev]t1 to ^: inv5tions we h already ref]r$ 9 connection ) ! me*anical production ( bl[n articles4 ,?is inv5tor has endeav\r$ to utilise 8 process = bl[+ l>ge articles ( glass = ! direct production ( %eets ( flat glass4 ,8 me?od is to bl[1 by ! /eam process describ$ 9 ano!r *apt]1 a l>ge cubical vessel1 hav+ flat sides1 ! flatness ( ^! sides be+ ensur$ by bl[+ ! vessel into or aga9/ a m\ld hav+ flat sides4 ,?is flat-sid$ vessel is ultimately to be cut up into five l>ge %eets4 ,?is process also appe>s to involve "s ( ! ma9 difficulties ( roll+ z reg>ds ! means ( transf]r+ ! glass f ! furnace to ! plate ( ! bl[+ ma*9e1 & 9 practice ! inv5tor has n yet succe$$ 9 produc+ glass ( suffici5tly good surface = ! purposes ( %eet glass4 ,ano!r class ( processes entirely avoid all means ( transf]r+ molt5 glass f ! furnace to any ma*9e1 by work+ on glass direct f ! molt5 ba? itself4 ,"s ( ^! processes are 9 actual use 9 ,am]ica1 & o!rs are be+ exp]im5t$ ) 9 ,europe1 b _! complete te*nical & comm]cial success has yet to be prov$2 !re c1 h[ev]1 be little d\bt t !y h ov]come ! greate/ ( ! _m difficulties t /ood 9 ! way ( ! me*anical production ( %eet-glass1 & t !y are !re=e de/9$ v %ortly to solve ! problem completely1 9 :i* case !y w\ld1 ( c\rse1 rapidly sup]s$e ! h& process4 ,"o ( ! e>lie/ ( ^! direct processes propos$ to all[ ! molt5 glass to fl[ out f ! furnace1 d[nw>d1 ?r\gh a n>r[ slit =m$ 9 ! side or bottom ( ! tank4 ,! impossibility ( keep+ su* a n>r[ orifice op5 & at ! same "t regulat+ ! fl[ ( glass made ?is proposal impracticable1 al?\gh ! use ( draw+ orifices has be5 reviv$ 9 "o ( ! late/ processes4 ,! ,am]ican process1 :i* is said to be at "w "u comm]cial conditions1 is n entirely satisfactory 9 ?is respect--t x is a me*anical process = ! production ( cyl9d]s & n ( flat %eets1 s t ! subsidi>y processes ( splitt+ & flatt5+ /ill rema9 to be c>ri$ out z be=e4 ,9 ?is process an iron r+ is l[]$ into ! ba? ( molt5 glass ?r\gh an ap]ture f above2 ! glass is all[$ to adh]e to ! r+ :i* is !n sl[ly rais$ by me*anical means1 draw+ a cyl9d] ( glass ) x4 ,if left to itself1 su* a cyl9d]1 ow+ to ! effects ( surface t5sion 9 ! glass1 w\ld soon contract & break (f1 b ! ,am]ican inv5tion avoids ?is action by *ill+ ea* bit ( ! cyl9d] z soon z x is =m$4 ,?is is done by ! aid ( air bla/s deliv]$ ^u bo? sides ( ! glass z x em]ges f ! ba?1 & x is claim$ t by ?is means cyl9d]s ( any desir$ l5g? & diamet] may be drawn direct f ! ba?4 ,! obvi\sly great me*anical difficulties connect$ ) ^! op]ations h probably be5 ov]come1 b n )\t sacrific+ mu* ( ! simplicity ( ! arrangem5t1 & ! relative economy ( ?is process z a :ole1 comp>$ ) ! h& process1 has yet to ass]t itself4 ,! inv5tions ( ,f\rcault1 :i* are at pres5t be+ develop$ on ! ,cont95t by a syndicate ( glass manufactur]s1 aim at a mu* m direct process4 ,"h also ! glass is drawn direct f ! molt5 ba? by ! aid ( a draw+-iron t is imm]s$ 9 ! glass & !n sl[ly rais$1 b 9 ?is case ! piece imm]s$ is simply a /raight b>1 & ! aim is to draw out a flat %eet4 ,9 ?is case ! t5d5cy1 "u surface t5sion1 is to contract ! %eet into a ?read1 & app>5tly ! simple device ( *ill+ ! em]g+ glass is n adequate to prev5t ?is 9 a satisfactory mann]1 & subsidi>y devices h be5 add$4 ,^? t h be5 pat5t$ include a me*anism ( l9k$ metal rods s arrang$ z to be imm]s$ & drawn out ( ! glass cont9u\sly ) ! em]g+ %eet1 9 su* a mann] z to support ! v]tical edges ( ! glass & s aid 9 resi/+ ! t5d5cy ( ! glass to contract lat]ally4 ,ano!r device consi/s 9 ! use ( a slit or orifice =m$ 9 a l>ge fire-brick t floats on ! surface ( ! glass4 ,?r\gh ?is orifice ! glass is drawn1 ( ! desir$ ?ickness & wid?4 ,! use ( ?is orifice1 h[ev]1 int]f]es m>k$ly ) ! p]fection ( ! product1 & 9 fact all ! glass produc$ 9 ?is way %[s q pla9ly a set ( longitud9al /riations due to ! inevitable irregul>ities 9 ! lips ( ! draw+ slot4 ,fur!r1 x appe>s to be impracticable to draw ?9 glass 9 ?is way1 a ?ickness ( f #b to #c millimetres 7ab\t #a_/h in*7 be+ ! lea/ t is practicable1 on acc\nt ( ! l>ge am\nt ( breakage t occurs ) weak] %eets4 ,?is process1 9 its pres5t /age ( developm5t1 h[ev] promis+1 does n appe> to h solv$ ! problem ( me*anical manufacture ( %eet-glass1 s9ce x is j 9 ! ?9n]1 light] k9ds ( glass t ! advantages ( %eet are mo/ pron\nc$4 ,on ! o!r h&1 x is q possible t ?is draw+ process1 or "s developm5t aris+ f x1 may %ortly supplant ! ca/+ process 9 ! production ( poli%$ plate-glass1 al?\gh = ! l>ge/ sizes ( ?is product also1 ! difficulty & dang] ( h&l+ ! weights involv$ may prove a s]i\s ob/acle4 ,cr[n ,glass4--,al?\gh ?is is a bran* ( manufacture t is ne>ly obsolete1 x des]ves brief notice "h1 p>tly because x is /ill us$ = ! production ( special articles1 & also because x illu/rates "s int]e/+ possibilities 9 ! use & manipulation ( glass4 ,! process ( bl[+ cr[n glass may be briefly describ$ z t ( fir/ bl[+ an approximately sph]ical holl[ ball1 !n op5+ ?is at "o side & exp&+ ! glass into a flat disc by ! action ( c5trifugal =ces produc$ by a rapid rotation ( ! glass 9 front ( a l>ge op5+ 9 a special heat+ furnace4 ,! actual process involves1 ( c\rse1 ! prelim9>y ( ga!r+ ! prop] quantity ( glass1 mu* 9 ! mann] already describ$ 9 connection ) %eet-glass manufacture4 ,?is ga!r+ is !n bl[n out into a holl[ sph]ical vessel4 ,?is vessel is n[ atta*$ to a subsidi>y iron rod by means ( a small ga!r+ ( hot glass1 appli$ at ! po9t opposite ! pipe itself1 ! glass be+ ?us1 = a mom5t1 atta*$ to bo? ! pipe & ! 8pontil0 or 8punty0 7z ! rod is call$74 ,! pipe is1 h[ev]1 deta*$ by crack+ (f ! neck ( ! orig9al glass1 :i* n[ rema9s atta*$ to ! pontil 9 ! %ape ( an op5 b[l4 ,?is b[l is n[ re-heat$ v /rongly 9 front ( a special furnace1 ! op5 side ( ! b[l be+ pres5t$ to ! fire4 ,! pontil is mean:ile held 9 a horizontal position & rotat$4 ,z ! glass s(t5s ! rotation spreads x out1 until f9ally ! entire mass ( glass is =m$ into a simple flat disc sp9n+ rapidly be=e ! m\? ( ! furnace4 ,?is flat disc or 8table0 ( cr[n glass is all[$ to cool some:at1 is deta*$ f ! pontil by a %>p j]k1 & is !n anneal$ 9 a simple kiln 9 :i* ! glass is /ack$1 seal$ up1 & all[$ to cool naturally4 ,x is obvi\s t by ?is process no v l>ge %eets ( glass c be produc$2 tables #d ft4 9 diamet] are already on ! l>ge side1 & ^! c only be cut up into mu* small] %eets on acc\nt ( ! lump ( glass by :i* ! table 0 orig9ally atta*$ to ! pontil1 & :i* rema9s fix$ 9 ! c5tre ( ! f9i%$ disc4 ,= c]ta9 ornam5tal purposes1 :]e an 8antique0 appe>ance is desir$1 ^! bullions are valu$1 b = practical purposes !y int]f]e v s]i\sly ) ! use ( ! glass4 ,z a matt] ( fact1 ev5 sev]al in*es away f ! c5tral bullion itself1 cr[n glass is g5]ally m>k$ ) circul> wav+s1 :i* r5d] x readily recognisable 9 ! w9d[s ( old] build+s1 b :i* decid$ly detract f ! p]fection ( ! glass4 ,on ! o!r h&1 cr[n glass is /ill valu$ = c]ta9 purposes1 su* z microscope slides & cov] glasses1 :]e entire fre$om f surface m>k+s1 su* z ^? f\nd 9 %eet glass z a result ( ! flatt5+ op]ations1 is desirable4 ,:ile1 !re=e1 ! process has m]ely an hi/orical int]e/ s f> z ord9>y %eet-glass purposes are conc]n$1 x is /ill us$ 9 special cases4 ,,*apt] ,,xi4 ,,col\r$ ,,glasses4 ,9 v>i\s *apt]s ?r\gh\t ! =ego+ portions ( ?is book we h _h occasion to ref] to ! col\r ( glass & ! causes affect+ x1 b ^! ref]5ces h *iefly be5 made f ! po9t ( view ( ! production ( glasses z ne>ly col\rless z possible "u ! circum/ances4 ,:ile x is obvi\s t = ! great majority ( ! purposes = :i* x is us$ ! abs5ce ( all visible coloration is desirable or ev5 ess5tial 9 ! glass employ$1 !re are num]\s o!r uses :]e a def9ite coloration is requir$4 ,?us we h1 z indu/rial & te*nical uses ( col\r$ glass1 ! employm5t ( ruby1 gre5 & purple glasses = signall+ purposes1 z 9 ! signal lamps ( our railways1 ! r$ tail-lights ( motor-c>s1 or ev5 ! r$ or gre5 sectors ( c]ta9 h>b\r lights & ligh?\ses2 aga91 col\r$ glasses1 ruby1 gre51 & yell[1 are ext5sively employ$ 9 connection ) photography4 ,r less exact+ 9 _! dem&s ^u ! correctness ( ! col\r employ$ are ! ar*itectural & ornam5tal uses to :i* col\r$ glass is s ext5sively put 9 bo? public & dome/ic build+s1 :ile1 f9ally1 col\r$ glass is l>gely ! f\ndation ^u :i* ! /a9$-glass work] builds up 8 arti/ic a*ievem5ts2 9 ano!r direction1 col\r$ glass is also utilis$ 9 ! production ( ornam5tal articles & ( "s table-w>e4 ,:ile x mu/ be admitt$ t 9 a great _m cases ! col\r-res\rces ( ! glass mak] are hopelessly misappli$1 yet 9 really arti/ic h&s few o!r mat]ials are capable ( yield+ results ( equal beauty4 ,by ! 8col\r0 ( a glass is g5]ally und]/ood ! t9t or col\r :i* is obs]v$ :5 x is view$1 9 comp>atively ?9 slices1 by transmitt$ light2 ! actual col\r is ?us a prop]ty1 n s mu* ( ! k9d or v>iety ( glass z ( ea* individual piece1 s9ce ?ick pieces out ( ! same melt+ w %[ a diff]5t t9t f t se5 9 ?9n] pieces4 ,z we h already po9t$ out1 su* glasses z %eet or plate1 :i* appe> practically col\rless :5 view$ 9 ! ord9>y way1 %[ a v decid$ gre5 col\r :5 view$ ?r\gh a consid]able ?ickness4 ,9 ! same way1 a v ?9 lay] ( ! glass kn[n z 8fla%+ ruby0 %[s a brilliant r$ t9t1 b a ?ickness ( "o-sixte5? ( an in* is suffici5t to r5d] ! glass practically opaque1 giv+ x a black appe>ance by bo? transmitt$ & reflect$ light4 ,aga91 cobalt blue glass1 :5 exam9$ ) a spectroscope 9 ?9 lay]s1 is f\nd to transmit a notable proportion ( r$ rays1 b ?ick] pieces entirely suppress ^! rays4 ,^! ph5om5a w be readily und]/ood :5 we recollect t col\r 9 a transp>5t m$ium arises f ! fact t ! m$ium has diff]5t absorb+ p[]s = light ( diff]5t col\rs4 ,all transp>5t sub/ances1 & c]ta9ly glass1 are only p>tially transp>5t3 all light waves pass+ ?r\gh su* a sub/ance are gradually absorb$1 & ! ext5t to :i* !y are absorb$ diff]s accord+ to ! l5g? ( ^! waves4 ,x always happ5s t = "s special wave-l5g?s ! sub/ance has ! p[] ( absorb+ ! en]gy ( ! ent]+ waves & conv]t+ x into heat-vibrations ( its own molecules or atoms4 ,9 ! mo/ transp>5t & col\rless glasses ?is process1 s f> z ! waves ( ord9>y light are conc]n$1 only goes on to a negligibly slight ext5t2 if1 h[ev]1 we ext5d our view beyond ! range ( ord9>y visible light1 & consid] ! region ( %ort] waves t lies 9 ! spectrum beyond ! violet1 we f9d t ord9>y col\rless glass becomes /rongly absorb5t2 ?us to waves ( ab\t half ! l5g? ( ^? :i* produce ^u our eyes ! impression ( yell[ light1 ord9>y glass is z opaque z is a piece ( metal to :ite light4 ,9 ?is wid] s5se1 !n1 we may fairly say t all glasses are col\r$--i4e41 all h a p[] ( selective absorption2 b 9 ! case ( ^? :i* are ne>ly col\rless 9 ! ord9>y s5se1 ?is absorption takes place only = waves :i* are ei!r decid$ly %ort] or decid$ly long] ?an ^? to :i* our eyes are s5sitive4 ,^? glasses :i* appe> col\r$ 9 ! ord9>y s5se1 on ! o!r h&1 owe ?is prop]ty to ! fact t ! p[] ( absorption = light-waves ext5ds into ! region ( ! visible spectrum2 ?us a blue or violet glass is practically opaque to r$ rays1 :ile a r$ glass is opaque to blue1 gre5 or violet rays4 ,?is /atem5t may be v]ifi$ 9 a /rik+ mann] by hold+ ov] "o ano!r a piece ( deep blue or gre5 glass & a simil> piece ( ruby glass--! comb9ation w be f\nd to be v ne>ly opaque ev5 :5 ea* glass by itself is practically transp>5t4 ,! "q :i* n[ naturally pres5ts itself to u is1 :at is ! ess5tial diff]5ce betwe51 = in/ance1 a piece ( r$ glass & a piece ( 8:ite0 glass t conf]s ^u ! =m] ! p[] ( absorb+ blue light8 ,a p]fectly complete & satisfactory answ] to ?is "q is n1 9 ! writ]'s op9ion1 available 9 ! pres5t /ate ( our k1 b to a c]ta9 ext5t ! diff]5ce betwe5 ! two k9ds ( glass c be expla9$4 ,! diff]5ce is produc$1 9 ! fir/ in/ance by introduc+ into ! col\rless glass "s additional *emical elem5t or elem5ts1 ! sub/ances 9 "q be+ g5]ally kn[n z 8col\r+ oxides10 al?\gh !y are by no means always introduc$ 9 ! =m ( oxides1 & are frequ5tly pres5t 9 ! glass 9 entirely diff]5t =ms4 ,to a c]ta9 ext5t ! col\r ( ! glass may be ascrib$ to a def9ite 8col\r+0 prop]ty ( ! *emical elem5ts conc]n$2 ?us mo/ ( ! *emical comp\nds ( su* elem5ts z nickel1 cobalt1 iron1 manganese & copp] are m or less deeply col\r$ sub/ances1 & x w\ld seem z if ! atoms or 8ions0 ( ^! elem5ts _h ! specific p[] ( absorb+ c]ta9 v>ieties ( light-waves :ile n mat]ially affect+ o!rs4 ,b ?is specific 8col\r+0 prop]ty is n s easily expla9$ :5 we recollect t ! col\rs ( iron comp\nds1 = example1 may be gre5 or r$ accord+ to ! /ate ( comb9ation 9 :i* t elem5t is pres5t1 & t iron has also ! p[] ( imp>t+ ei!r a gre5 or a yell[ col\r to glass accord+ to circum/ances4 ,! detail$ discussion ( ^! que/ions1 h[ev]1 lies outside our pres5t scope1 & we mu/ conf9e ourselves to ! broad /atem5t t col\r+ sub/ance 9 glass may be r\ghly divid$ into two k9ds or gr\ps2 ! fir/ & probably ! l>ge/ gr\p are ^? bodies :i* occur 9 glass 9 true solution1 ! elem5t itself be+ pres5t 9 ! comb9$ /ate z a silicate or o!r su* comp\nd 7borate1 phosphate1 etc47 :i* is soluble 9 ! glass4 ,9 ?is class1 ! col\r+ effect ^u ! glass is specifically t ( ! elem5t introduc$1 & is br\ght ab\t 9 ! same way z ! col\r+ ( wat] :5 a col\r$ salt--su* z copp] sulphate--is dissolv$ 9 x4 ,! second class ( col\r+ sub/ances1 h[ev]1 behave 9 a diff]5t mann]2 !y are probably pres5t 9 ! glass 9 a /ate ( extremely f9e division1 & held n 9 true solution1 b really 9 a sort ( me*anical susp5sion t approximates to ! condition ( :at is kn[n z a 8colloidal solution40 ,! po9t :i* is kn[n beyond d\bt1 ?anks to ! rese>*es ( ,si$5topf & ,szigmondi on ultra-microscopical p>ticles1 is t 9 c]ta9 col\r$ glasses1 ( :i* ruby glass is ! be/ example1 ! col\r+ sub/ance1 be x gold or cupr\s oxide1 is pres5t 9 ! =m ( m9ute b by no means atomic or molecul> p>ticles susp5d$ 9 ! glass4 ,! pres5ce ( ^! p>ticles has be5 made optically evid5t1 al?\gh x c h>dly be said t !y h be5 r5d]$ visible1 & x is at all ev5ts probable t ^! susp5d$ p>ticles act ea* z a :ole 9 absorb+ ! light-waves *>act]i/ic ( ! col\r :i* !y produce 9 glass4 ,?is be+ ! case1 x is easy to und]/& h[ readily ! col\r ( su* glasses is alt]$ or spoilt by manipulations :i* involve heat+ & cool+ at diff]5t rates--too rapid a rate ( cool+ produc+ a diff]5t gr\p+ ( ! m9ute p>ticles1 alt]+ _! size or %ape1 or ev5 oblit]at+ !m entirely by all[+ ! elem5t 9 "q to g into or to rema9 9 solution 9 ! glass4 ,:ile x w\ld be entirely =eign to ! purpose ( ?is volume to give 9 ?is place a s]ies ( recipes = ! production ( v>i\s k9ds ( col\r$ glass1 x w be desirable to /ate 9 g5]al t]ms ! col\rs or range ( col\rs :i* c be produc$ 9 v>i\s k9ds ( glass by ! introduction ( ^? *emical elem5ts :i* are ord9>ily us$ 9 ?is way4 ,9 g5]al t]ms x may be said t ! light] elem5ts d n z a rule t5d to ! production ( col\r$ glasses1 :ile ! heavi] elem5ts1 s f> z !y c be reta9$ 9 ! glass 9 ei!r solution or susp5sion1 t5d to produce an int5se col\r+ effect4 ,! elem5t lead appe>s to =m a /rik+ exception to ?is rule1 b ?is is due to ! fact t :ile ! silicates ( mo/ ( ! o!r heavy elem5ts are m or less un/able1 ! silicate ( lead is v /able1 & c only be decompos$ by ! action ( r$uc+ ag5ts4 ,:5 lead silicates are decompos$ 9 ?is way1 h[ev]1 ! result+ glass imm$iately receives an exce$+ly deep col\r1 be+ turn$ a deep opaque black1 al?\gh 9 v ?9 lay]s ! col\r is decid$ly br[n4 ,on ! o!r h&1 glasses v ri* 9 lead are always decid$ly yell[ 9 col\r1 & x has be5 %[n t ?is coloration is due to ! natural col\r ( lead silicates & n to ! pres5ce ( impurities4 ,:at has j be5 said ( lead applies1 ) only v slight modification1 also to ! r>e metal ?allium & its comp\nds1 :i* h be5 introduc$ into glass = special purposes4 ,leav+ ^! two exceptional bodies on "o side1 we n[ pass to a consid]ation ( ! elem5ts 9 ! ord] ( _! *emical gr\p+4 ,! r>e elem5ts w n be consid]$ except 9 c]ta9 cases :]e _! pres5ce 9 traces is liable to affect results atta9$ 9 practice4 ,! ,alkali ,metals1 sodium1 potassium1 li?ium1 etc41 & _! comp\nds1 h no specific col\r+ effect1 al?\gh ! pres5ce ( soda or ( pota% 9 a glass affects ! col\rs produc$ by su* sub/ances z manganese1 nickel1 sel5ium1 etc4 ,copp]1 z w\ld be anticipat$ f ! deep col\r ( mo/ ( its comp\nds1 produces p[]ful col\r+ effects on glass4 ,cupric silicates produce int5se gre51 to gre5i%-blue t9ts4 ,copp]1 ei!r z metal or oxide1 add$ to glass 9 ! ord9>y way1 always produces ! gre5 col\r2 b :5 ! full oxidation ( ! copp] is prev5t$ by ! pres5ce ( a r$uc+ body1 & ! glass is cool$ sl[ly1 or is expos$ to repeat$ heat+ foll[$ by sl[ cool+1 an int5se ruby coloration is produc$4 ,9 practice ?is col\r is produc$ by introduc+ t9 z well z copp] into ! mixture1 & s regulat+ ! conditions ( melt+ z to fav\r r$uction r ?an oxidation ( ! copp]4 ,"u ^! circum/ances ! copp] is left 9 ! glass 9 a f9ely divid$ & ev5ly susp5d$ /ate2 if exactly ! "r /ate ( division & susp5sion is arriv$ at1 a beautiful r$ t9t is ! result1 al?\gh ! coloration ( ! glass is s int5se t x c only be employ$ 9 v ?9 %eets1 be+ 8fla%$0 ^u ! surface ( col\rless glass to give x ! necess>y /r5g? & ?ickness = practical use4 ,x is fur!r v easy to slightly alt] ! arrangem5t ( ! copp] 9 ! glass1 ) ! result ( produc+ an opaque1 /reaky sub/ance resembl+ seal+-wax 9 col\r & appe>ance1 ?is product be+1 ( c\rse1 useless f ! glass-mak]'s po9t ( view4 ,f9ally1 by exce$+ly sl[ cool+1 & "u o!r fav\r+ conditions :i* are n really und]/ood1 ! p>ticles ( susp5d$ col\r+-mat]ial--be x metallic copp] or cupr\s oxide--gr[ 9 size & atta9 visible dim5sions1 appe>+ z m9ute %imm]+ flakes1 ?us produc+ ! beautiful sub/ance kn[n z 8av5tur9e40 ,silv] is nev] introduc$ into glass mixtures1 ! reason be+ t x is s readily r$uc$ to ! metallic /ate f all its comp\nds t x _c be reta9$ 9 ! glass except 9 a f9ely-divid$ =m1 caus+ ! glass to assume a black1 metallic appe>ance resembl+ ! /a9s produc$ by ! r$uction ( lead 9 fl9t glasses4 ,on ! o!r h&1 silv] yields a beautiful yell[ col\r :5 appli$ to glass z a surface /a91 & x is widely us$ = t purpose4 ,gold is introduc$ into glass = ! production ( brilliant ruby t9ts2 its behavi\r is v simil> to t ( copp]1 except t ! noble metal has a great t5d5cy to return to ! metallic /ate )\t ! aid ( r$uc+ ag5ts4 ,no addition ( t9 is !re=e requir$1 b ! rate ( cool+1 etc41 mu/ be prop]ly regulat$1 s9ce rapidly cool$ glass conta9+ gold %[s no special col\r1 ! ri* ruby t9t be+ only develop$ :5 ! glass is re-heat$ & cool$ sl[ly4 ,! col\r+ effect ( gold is und\bt$ly m regul> & uni=m ?an t ( copp]1 & x is accord+ly possible to obta9 mu* light] %ades ( r$ ) ! aid ( ! noble metal4 8,gold ruby0 c !re=e be obta9$ ( a t9t light en\gh to be us$ 9 %eets ( ord9>y ?ickness1 & ! process ( 8fla%+0 is n ess5tial4 ,! elem5ts ( ! second gr\p1 su* z magnesium1 calcium1 /rontium1 b>ium1 z9c & cadmium1 ex]t no /rong specific col\r+ action on glass1 ) p]haps ! exception ( cadmium1 & t elem5t only does s to any consid]able ext5t 9 comb9ation ) sulphur1 sulphide ( cadmium hav+ ! p[] ( produc+ ri* yell[ col\rs 9 glass4 ,! sulphur comp\nds ( b>ium also readily produce deep gre5 & yell[ col\rs1 & ! =mation ( ^! t9ts is1 inde$1 v difficult to avoid 9 ! case ( glasses conta9+ mu* b>ium4 ,a col\r+ effect has sometimes be5 ascrib$ to z9c1 b ?is is n 9 accordance ) facts4 ,( ! elem5ts ( ! ?ird gr\p1 only boron & alum9ium are ev] f\nd 9 glass 9 any notable quantity4 ,boron is pres5t 9 ! =m ( boric acid or borates1 & z su* produces no col\r+ effect1 nor does !re seem to be any t5d5cy = ! sep>ation ( free boron4 ,! comp\nds ( alum9ium also possess no col\r+ effect1 al?\gh c]ta9 comp\nds ( ?is elem5t are utilis$ = imp>t+ a :ite opacity to glass = c]ta9 purposes--su* glass be+ kn[n z 8opal40 ,! elem5ts ( ! f\r? gr\p are ( great] importance 9 connection ) glass4 ,c>bon is capable ( ex]t+ p[]ful col\r+ effects :5 introduc$ into glass4 ,^! effects are ( two k9ds1 viz41 indirect 9 consequ5ce ( ! r$uc+ action ( c>bon on o!r sub/ances pres5t1 & direct f ! pres5ce ( f9ely-divid$ c>bon or c>bides 9 ! glass4 ,! latt] are simil> 9 k9d to ^? produc$ by ! pres5ce ( o!r f9ely-divid$ elem5t>y bodies 7copp]1 gold1 lead1 etc47 except t ! lightness ( ! c>bon p>ticles t5ds to ! production ( yell[ & br[n col\rs r ?an ( r$ & black1 :ile ! *emical nature ( c>bon r5d]s ! glass 9 :i* x is susp5d$ indiff]5t to rapid cool+1 s f> z ! c>bon t9t is conc]n$4 ,! indirect effects ( c>bon1 9 r$uc+ o!r sub/ances t may be pres5t 9 ! glass1 become evid5t ) mu* small] proportions ( c>bon ?an are requir$ to produce visible direct effects4 ,z we h se5 above1 c>bon1 9 ! =m ( coke1 *>coal or an?racite coal1 is regul>ly introduc$1 z a r$uc+ m$ium1 into glass mixtures conta9+ sulphate ( soda4 ,if ev5 a slight excess ( c>bon be us$ = ?is purpose1 ! =mation ( sulphides & poly-sulphides ( sodium & ( calcium results1 & ^! bodies1 l all sulphides1 imp>t a gre5i%-yell[ t9t to ! glass1 at ! same "t br++ o!r undesirable results 9 _! tra94 ,silicon1 9 ! =m ( silicic acid & its comp\nds1 is a fundam5tal con/itu5t ( all v>ieties ( glass1 & 9 ?is =m is 9 no s5se a col\r+ sub/ance2 on ! o!r h&1 !re is no d\bt t "u "s conditions silicon may be r$uc$ to ! metallic /ate at temp]atures :i* normally occur 9 glass-furnaces1 & x is practically c]ta91 t if pres5t 9 glass 9 ?is condition1 silicon w\ld col\r ! glass4 ,x is j possible t "s ( ! col\r+ effects produc$ 9 ord9>y glass by p[]ful r$uc+ ag5ts1 su* z c>bon1 ei!r 9 ! solid =m or z a con/itu5t ( furnace gases1 may be due to ! r$uction ( silicon 9 ! glass4 ,t9 by itself does n appe> to h any col\r+ effect ^u glass1 except t its oxide1 9 a f9ely susp5d$ /ate1 produces opalesc5ce &1 9 l>ge quantities1 :ite opacity4 ,t91 h[ev]1 is us$ 9 conjunction ) copp] 9 ! production ( copp]-ruby1 to :i* ref]5ce has already be5 made4 ,lead & ,?allium h already be5 dealt )1 & x only rema9s to add t _! pres5ce 9 ! glass1 al?\gh n 9 itself produc+ any int5se col\r+ action1 increases ! col\r+ effects ( o!r sub/ances4 ,?is is probably m]ely a p>ticul> case ( ! fact t d5se glasses1 ( high refractive index1 are m s5sitive to col\r+ ag5cies ?an ! light] glasses ( l[ refractive index2 ?is applies to b>ium z well z to lead & ?allium glasses4 ,phosphorus occurs 9 "s few glasses 9 ! =m ( phosphoric acid1 & ?is sub/ance1 z su*1 has no col\r+ effect4 ,calcium phosphate1 h[ev]1 is sometimes add$ to glasses = ! purpose ( produc+ opalesc5ce4 ,its action 9 ?is respect is probably simil> to t ( t9 oxide & alum9ium fluoride1 ^! sub/ances all rema9+ undissolv$ 9 ! glass 9 ! =m ( m9ute p>ticles 9 a f9ely divid$ & susp5d$ /ate4 ,ars5ic does n ex]t a col\r+ effect on glass1 & ow+ to its volatile nature x c only be reta9$ 9 glass 9 small quantities & "u special conditions4 ,a 8decol\ris+0 action is sometimes ascrib$ to ars5ic1 b if ?is action really exi/s x c only be ascrib$ to ! fact t ars5ic comp\nds are capable ( act+ z c>ri]s ( oxyg51 & _! pres5ce ?us t5ds to facilitate ! oxidation ( impurities conta9$ 9 ! glass4 ,a fur!r ref]5ce to ?is subject w be f\nd bel[ 9 ref]5ce to ! comp\nds ( manganese4 ,antimony1 al?\gh frequ5tly add$ to special glass mixtures1 does n appe> to produce any v p[]ful effects1 except possibly 9 ! direction ( produc+ :ite opacity if pres5t 9 l>ge proportions4 ,! sulphide ( antimony1 h[ev]1 ex]ts a col\r+ influ5ce1 al?\gh its volatile & un/able "* r5d]s ! effects unc]ta94 ,vanadium1 ow+ to its r>ity1 is probably nev] add$ to glass mixtures = col\r+ purposes1 al?\gh x is capable ( produc+ vivid yell[ & gre5i% t9ts :5 pres5t ev5 9 m9ute proportions4 ,on ! o!r h&1 vanadium occurs 9 small proportions 9 a numb] ( fire-clays1 includ+ "s ( ^? ( ! ,/\rbridge di/rict1 & glass melt$ 9 pots conta9+ ?is elem5t is liable to h its col\r spoilt by tak+ up ! vanadium f ! clay4 ,sulphur is an elem5t ^: pres5ce 9 v>i\s =ms is liable to affect ! col\r ( glass 9 a v>iety ( ways4 ,! col\r+ effects ( sodium-1 calcium-1 cadmium-1 & antimony-sulphides h already be5 ref]r$ to4 ,sulphur probably nev] exi/s 9 glass 9 ! uncomb9$ /ate at all1 b sulphur & its oxides1 :i* are (t5 conta9$ 9 furnace gases1 sometimes ex]t a v m>k$ action ^u hot glass4 ,! pres5ce ( sulphur gases 9 ! atmosph]es ( bl[+-holes & anneal+ kilns is liable to produce 9 ! glass a peculi> yell[i% milk9ess :i* p5etrates = a consid]able dep? into ! mass ( ! glass & _c be remov$ by subsequ5t treatm5t4 ,glass vessels1 p>ticul>ly if made ( glass produc$ f raw mat]ials among :i* salt-cake has figur$1 are also affect$ by contact ) fus$ sulphur or its vap\r1 ! effect be+ a gradual dis9tegration ( ! glass4 ,! precise me*anism ( ^! actions is n kn[n at pres5t1 b !y probably consi/ 9 ! =mation ( sulphur comp\nds )9 ! glass1 possibly giv+ rise to an evolution ( m9ute bubbles ( gas4 ,sel5ium1 :i* is *emically s closely relat$ to sulphur1 is a relatively r>e elem5t1 :i* is1 h[ev]1 f9d+ "s use 9 glass-manufacture z a col\r+ & a decol\r+ ag5t4 ,! introduction ( sel5ium or ( its comp\nds "u suitable conditions into a glass mixture produces or t5ds to produce a peculi> yell[i%-p9k coloration1 ! int5sity ( ! col\r produc$ be+ dep5d5t ^u ! *emical nature ( ! glass z a :ole &1 ( c\rse1 ^u ! am\nt ( sel5ium left 9 ! glass at ! end ( ! melt+ process1 ?is latt] 9 turn dep5d+ ^u ! duration & temp]ature ( ! process 9 "q4 ,! p9k col\r ( sel5ium glass is be/ develop$ 9 ^? conta9+ b>ium z a base1 b x is also develop$ 9 lead glasses1 :ile soda-lime glasses d n %[ ! col\r s well4 ,z a 8decol\ris]0 ! action ( sel5ium is entirely t ( produc+ a complem5t>y col\r :i* is int5d$ to 8cov]0 ! gre5 or blue t9t ( ! glass2 :]e ! dep? ( ! t9t to be 8cov]$0 is small1 sel5ium c be us$ v successfully 9 ?is way1 al?\gh x is a relatively co/ly sub/ance = su* a purpose4 ,no oxidis+ or 8cleans+0 action c be ascrib$ to sel5ium or its comp\nds4 ,*romium is "o ( ! mo/ int5sely active col\r+ sub/ances t are available = ! glass-mak]1 & x is accord+ly us$ v ext5sively4 ,x has ! advantage ( relative *eapness1 & c be conv5i5tly obta9$ & introduc$ into glass 9 ! =m ( pure comp\nds ^: col\r+ effect c be accurately anticipat$2 ! col\rs produc$ by ! aid ( *romium h ! fur!r advantage ( be+ v con/ant 9 "*1 be+ little affect$ by oxidis+ or r$uc+ conditions1 & only v slightly by ! l5g? or temp]ature ( ! melt+ process4 ,! rate ( cool+1 9 fact1 appe>s to be ! only factor t mat]ially affects ! col\rs produc$ by comp\nds ( *romium4 ,! col\rs produc$ by *romium alone are v>i\s dep?s ( a bright gre51 ! dep? v>y+1 ( c\rse1 ) ! proportion ( *romium t is pres5t 9 ! glass & ) ! purity ( ! glass itself4 ,v frequ5tly1 *romium is us$ 9 conjunction ) ei!r iron or copp] to produce v>i\s t9ts ( 8cold blue0 & 8celadon gre50 respectively4 ,?is elem5t is mo/ usually introduc$ into ! glass mixture 9 ! =m ( potassium bi*romate2 al?\gh o!r comp\nds might be employ$1 ?is sub/ance pres5ts sev]al advantages to ! glass mak]4 ,9 ! fir/ place1 s9ce ! col\r+ effect ( *romium is v int5se1 x mu/ be us$ 9 v small quantities1 & if *romic oxide itself 7 us$1 ! weigh+ w\ld h to be c>ri$ out ) extreme c>e2 potassium bi*romate1 h[ev]1 conta9s a mu* small] proportion ( ! effective col\r+ sub/ance1 s t mu* l>g] weights c be employ$1 & ! accuracy ( weigh+ requir$ is proportionately r$uc$4 ,a fur!r consid]ation arises f ! fact t *romic oxide is itself an extremely refractory body1 & is !re=e comp>atively difficult to incorporate ) glass1 :ile its pres5ce t5ds to make ! glass itself m viscid & refractory2 ! simultane\s introduction ( ! alkali1 z provid$ by ! use ( ! bi*romate1 is ?us an advantage 9 re/or+ ! fluidity & s(tness ( ! glass :5 f9i%$1 :ile also facilitat+ ! solution ( ! *romium 9 ! glass dur+ ! fusion process2 ?is process ( solution1 h[ev]1 takes "s "t1 *romium glasses be+ liable to appe> pat*y if insuffici5t "t is giv5 to ! 8f\nd+40 ,uranium is "o ( ! r>] & m co/ly elem5ts1 b is nev]!less us$ 9 glass-mak+ = special purposes on acc\nt ( ! v beautiful fluoresc5t yell[ col\r :i* x imp>ts :5 add$ 9 small proportions4 ,?is yell[ is q *>act]i/ic & unmi/akable1 s t none ( ! o!r v>ieties ( yell[ glass c ev] be us$ z a sub/itute = uranium glass1 b ! great co/ ( ! latt] prev5ts its ext5d$ use4 ,uranium is usually introduc$ into glass mixtures 9 ! =m ( a *emical comp\nd1 su* z uranyl-acetate or uranyl-nitrate1 bo? ^! sub/ances be+ obta9able 9 ! =m ( small1 int5sely bright yell[ cry/als4 ,fluor9e occurs 9 a numb] ( glasses 9 ! =m ( dissolv$ or susp5d$ fluorides1 pr9cipally fluoride ( alum9ium4 ,! elem5t is n ess5tially a col\r+ sub/ance1 & is only m5tion$ "h because ! fluoride nam$ is ! mo/ frequ5tly us$ means ( produc+ 8opal0 glass4 ,! fluoride is mo/ frequ5tly introduc$ into ! glass mixtures z calcium fluoride1 us$ 9 conjunction ) felsp>1 or z cryolite1 a natural m9]al :i* consi/s ( a d\ble fluoride ( sodium & alum9ium4 ,manganese is "o ( ! mo/ important col\r+ elem5ts us$ by ! glass-mak]4 ,:5 introduc$ into glass 9 ! abs5ce ( o!r col\r+ +r$i5ts1 comp\nds ( manganese produce a range ( col\rs ly+ 9 ! region ( p9ki%-purple to violet1 accord+ to ! *emical nature ( ! glass4 ,! exact col\r produc$ v>ies accord+ z ! glass has lead1 lime or b>ium z its base1 & x also dep5ds ^u ! pres5ce ( soda or pota% z ! alkal9e con/itu5t4 ,! nature & int5sity ( ! col\r1 h[ev]1 :i* ! addition ( a giv5 p]c5tage ( manganese w produce dep5ds ^u o!r factors besides ! *emical composition ( ! bases us$ 9 ! mixture4 ,! heat & duration ( ! 8f\nd0 & ! r$uc+ or oxidis+ conditions ( ! furnace 9 :i* x has be5 c>ri$ on v mat]ially affect ! result4 ,?us1 a glass hav+ a slight t+e ( p9k or purple d]iv$ f manganese c be r5d]$ entirely col\rless by ! action ( r$uc+ gases or by introduc+ into ! glass a r$uc+ sub/ance1 su* z a piece ( wood4 ,x w ?us be se5 t :ile manganese is a mo/ useful elem5t = ! glass-mak]1 its employm5t requires mu* skill & c>e1 & g5]ally involves "s tr\blesome manipulations be=e ! desir$ result is atta9$4 ,9 practice1 manganese is mo/ frequ5tly us$ ) o!r col\r+ +r$i5ts = ! production ( :at may be call$ 8comp\nd0 col\rs1 ! function ( ! manganese be+ to provide ! 8w>m0 elem5t1 i4e41 ! p9k or purple compon5t1 requir$4 ,"o ( ! mo/ important uses ( manganese com+ "u ?is head is its use z a 8decol\ris]40 ,by a 8decol\ris]0 ! glass-mak] und]/&s a sub/ance :i* c be us$ to improve ! col\r ( a glass :i*1 f ! nature ( its raw mat]ials & conditions ( melt+1 w\ld h a gre5] col\r ?an is ?\ght desirable = ! product 9 "q4 ,x may be said at once t ! mo/ p]fect & satisfactory me?od ( obta9+ ! bett] col\r requir$ is to adopt ! use ( pur] raw mat]ials & me?ods ( melt+ less liable to lead to contam9ation ( ! glass4 ,on ! o!r h&1 ?is radical c\rse is (t5 impossible on ! gr\nd ( exp5se1 & ! less satisfactory c\rse mu/ be adopt$ ( cov]+ "o undesirable col\r by ano!r complem5t>y col\r :i* w\ld1 9 itself1 be equally undesirable4 ,! rationale ( ?is proc$ure dep5ds ^u ! fact t a slight am\nt ( absorption ( light is n readily detect$ by ! human eye if x be uni=mly or ne>ly uni=mly di/ribut$ ov] ! :ole range ( ! visible spectrum1 i4e41 if ! col\r ( ! result+ light is ne>ly neutral1 :ile an equally slight absorption 9 "o region ( ! spectrum1 :ile actually all[+ m light to pass ?r\gh ! glass1 is at once detect$ by ! eye ow+ to ! col\r ( ! transmitt$ light4 ,n[ x has be5 f\nd t ! col\r produc$ 9 glass by ! addition ( v small proportions ( manganese is approximately complem5t>y to ! gre5i%-blue t+e ( ! less pure v>ieties ( ord9>y glass2 ! addition ( manganese 9 suitable proportions to su* glass !re=e results 9 ! production ( a glass :i* transmits light ( approximately neutral1 usually slightly yell[1 col\r1 ! increas$ total absorption only becom+ noticeable 9 l>ge pieces4 ,?is 8cov]+0 ( ! gre5i% t+e is g5]ally mo/ completely successful 9 ! case ( soda-fl9t glasses1 b ! me?od is also us$ to a c]ta9 ext5t 9 ! case ( ! soda-lime glasses us$ = %eet & plate-glass manufacture4 ,manganese add$ to glass = ?is purpose is g5]ally introduc$ into ! mixture 9 ! =m ( ! p[d]$ black oxide 7manganese dioxide71 :i* is available z a natural ore 9 a condition ( suffici5t purity4 ,add$ 9 ?is =m1 ! manganese comp\nd ex]ts a d\ble action1 ! decomposition ( ! dioxide result+ 9 ! lib]ation ( oxyg5 )9 ! mass ( melt+ glass1 & ?is oxyg5 itself ex]ts a fav\rable influ5ce on ! result+ col\r ( ! glass1 s9ce x removes organic mat]ials ^: subsequ5t r$uc+ action w\ld be delet]i\s1 & x also conv]ts all iron comp\nds pres5t into ! m highly-oxidis$ 7f]ric7 /ate 9 :i* _! col\r+ effects are less int5se4 ,! actual col\r+ effect ( ! manganese itself is1 ( c\rse1 aft]w>ds develop$1 & produces ! effects discuss$ above4 ,! 8cov]+0 ( ! gre5i% t9ts due to iron & o!r comp\nds is only possible :5 ^! are pres5t 9 v small proportions4 ,:5 l>g] quantities ( ^! sub/ances h be5 introduc$ into ! glass ! addition ( manganese modifies ! result+ col\r1 b is no long] able to neutralise x4 ,a v l>ge range ( col\rs c be obta9$ by us+ v>i\s proportions ( iron & manganese1 ! be/-kn[n ( ^! be+ ! w>m br[n t9t kn[n z 8hock-bottle10 :ile all %ades betwe5 ?is & ! bright gre5 ( iron & ! purple ( manganese c be obta9$ by suitable mixtures4 ,:at has be5 said above z to ! s5sitiv5ess ( manganese col\rs applies ) ev5 great] =ce to ^! mix$ t9ts1 s9ce "h bo? ! iron & ! manganese comp\nds are liable to und]go *anges ( oxidation4 ,copp]-manganese & *romium-manganese col\rs are also us$1 z inde$ almo/ any numb] ( col\r+ +r$i5ts may be simultane\sly introduc$ into a glass mixture1 ! result+ col\r be+1 z a rule1 purely additive4 ,iron is s widely di/ribut$ among ! mat]ials ( ! e>?'s cru/ t x is exce$+ly difficult to exclude x entirely f any k9d ( glass1 al?\gh ! pure/ v>ieties ( glass conta9 ! m]e/ traces ( ?is elem5t4 ,*eap] v>ieties ( glass1 h[ev]1 always conta9 iron 9 measurable quantity1 :ile ! *eape/ k9ds ( glass conta9 consid]able proportions ( ?is elem5t4 ,! col\r+ effects ( iron h already be5 allud$ to at v>i\s po9ts 9 ! e>li] *apt]s z well z 9 ! section on manganese j prec$+4 ,little fur!r rema9s to be said "h4 ,j z ! less highly oxidis$ comp\nds ( iron--i4e41 ! 8f]r\s0 comp\nds--always %[ a decid$ gre5 t9t1 s glasses conta9+ iron :5 melt$ "u ! usually preval5t r$uc+ conditions ( a glass-mak+ furnace1 %[ a decid$ gre5 t9t ^: dep? dep5ds ^u ! am\nt ( iron pres5t1 provid$ no manganese or o!r 8decol\ris]0 has be5 introduc$4 8,f]r\s0 comp\nds are1 h[ev]1 readily conv]t$ into ! m highly oxidis$ or 8f]ric0 /ate by ! action ( oxidis+ ag5ts1 & ?is *ange c also be br\ght ab\t 9 molt5 glass by ! action ( su* sub/ances z nitrates or o!r s\rces ( oxyg54 ,! f]ric comp\nds1 h[ev]1 %[ *>act]i/ic yell[ t9ts :i* are mu* less int5se & vivid ?an ! correspond+ gre5 col\rs ( ! 8f]r\s0 s]ies1 & a simil> result is br\ght ab\t by ! oxidation ( iron comp\nds conta9$ 9 glass2 h5ce ! 8wa%+0 or cleans+ effects ascrib$ to oxidis+ ag5ts introduc$ 9 ! fusion ( glass4 ,x %\ld1 h[ev]1 be borne 9 m9d t ! oxidation ( o!r sub/ances besides iron comp\nds1 viz41 organic matt]1 c>bon & sulphur comp\nds1 may1 & probably does1 play a mo/ important "p 9 ?is process 9 ! case ( mo/ v>ieties ( glass4 ,nickel ex]ts a p[]ful col\r+ influ5ce on glass1 9 accordance ) ! fact t mo/ ( ! o!r comp\nds ( ?is elem5t are also deeply col\r$4 ,! exact col\r produc$ 9 glass dep5ds ^u ! nature ( ! glass & on ! condition ( oxidation 9 :i* ! nickel is pres5t4 ,! col\rs1 h[ev]1 are usually ( a gre5i%-br[n t9t1 al?\gh bright] col\rs c be produc$ by nickel "u special conditions4 ,?is elem5t is n1 h[ev]1 mu* us$ z a col\r+ ag5t 9 practice1 al?\gh x has be5 advocat$ z a 8decol\ris]40 ,! writ] is n1 h[ev]1 aw>e t x has ev] be5 successfully us$ = ?is purpose1 &1 9 fact1 ! col\rs to :i* x gives rise d n appe> to be ev5 approximately complem5t>y to ! ord9>y gre5 & blue t9ts :i* 8decol\ris]s0 are int5d$ to cov]4 ,cobalt is "o ( ! mo/ p[]ful col\r+ ag5ts 9 glass1 & is v l>gely us$ 9 ! production ( all v>ieties ( blue glass4 ,! blue col\r produc$ by cobalt is1 9 fact1 probably ! mo/ 8c]ta90 ( ! col\rs available to ! glass-mak]1 ?is t9t be+ lea/ affect$ by all ^? circum/ances t lead to v>iations 9 o!r t9ts4 ,almo/ ! only difficulty involv$ 9 ! use ( cobalt is ! great col\r+ p[] ( ?is elem5t1 :i* requires t = mo/ purposes only v small quantities may be add$ to ! glass mixture4 ,=m]ly cobalt 0 add$ to glass mixtures 9 ! =m ( 8zaffre10 :i* 0 a v impure =m ( cobalt oxide4 ,at ! pres5t "t1 h[ev]1 ! m exp5sive b mu* m satisfactory pure oxide ( cobalt is 9 almo/ univ]sal use4 ,?is sub/ance %[s a p]fectly con/ant composition &1 by means ( accurate weigh+1 enables ! glass-mak] to introduce precisely ! "r am\nt ( cobalt into 8 bat*4 ,! range ( col\rs :i* are available to ! mod]n glass manufactur] are1 z w be se5 f a consid]ation ( ! li/ ( col\r+ elem5ts giv5 above1 practically unlimit$1 p>ticul>ly z ^! sub/ances c be us$ 9 almo/ any comb9ation to produce mix$ or int]m$iate t9ts4 ,?is practically inf9ite v>iety ( possible t9ts1 inde$1 involves ! pr9cipal difficulty enc\nt]$ by ! manufactur] ( col\r$ glass1 i4e41 t ( mat*+ 8 t9ts1 or ( keep+ ! col\r ( any p>ticul> v>iety ( glass s con/ant t pieces produc$ at v>i\s times c be us$ indiscrim9ately toge!r4 ,?is ideal is1 p]haps1 nev] entirely realis$1 b 9 ! case ( glasses int5d$ = special te*nical uses ! ideal degree ( con/ancy is v closely approa*$4 ,9 addition to be+ call$ ^u to produce a l>ge v>iety ( diff]5t t9ts1 ! glass-mak] is also call$ ^u to produce v>i\s dep?s ( ! same t9t4 ,9 _m cases ?is c be readily done by ! simple means ( v>y+ ! am\nt ( col\r+ mat]ial add$ to ! glass4 ,:]e ! col\r+ effect ( small quantities ( ^! sub/ances is n excessively p[]ful !re is no v great difficulty 9 do+ ?is1 b 9 c]ta9 cases ?is mode ( regulat+ ! int5sity ( ! col\r is n available4 ,?us copp]-ruby glass _c readily be made ( s light a t9t z to appe> ( reasonable dep? :5 us$ 9 %eets ( ! ?ickness ( ord9>y %eet-glass4 ,z has already be5 indicat$1 ! desir$ t9t is obta9$ by ! process ( 8fla%+10 i4e41 ( plac+ a v ?9 lay] ( deep ruby-col\r$ glass ^u ! surface ( a %eet ( ord9>y m or less col\rless glass ( ! usual ?ickness4 ,?is is g5]ally accompli%$ by hav+ a pot ( molt5 ruby glass available close to a pot f :i* col\rless glass is be+ ga!r$4 ,a small ga!r+ ( ruby glass is fir/ tak5 up on ! pipe1 & ! rema9+ ga!r+s requir$ = ! production ( ! %eet are tak5 f ! pot ( col\rless glass4 ,:5 su* a composite ga!r+ is bl[n into a cyl9d] 9 ! mann] describ$ 9 ! previ\s *apt]1 ! ruby glass lies z a ?9 lay] ov] ! inn] face ( ! cyl9d]1 b special c>e & skill on ! "p ( ! ga!r] & bl[] is requir$ to ensure t ?is lay] %all be ev5ly di/ribut$ & ( ! "r ?ickness to produce j ! t9t ( ruby requir$4 ,s9ce ! :ole lay] ( r$ glass is s ?91 a v slight want ( uni=mity 9 its di/ribution leads to wide v>iations ( t9t1 & 9 practice ^! are (t5 se5 9 ! less successful cyl9d]s ( su* glass4 ,! *emical composition ( ! ruby & ! col\rless glass :i* are to be employ$ = ?is purpose mu/ also be prop]ly adapt$ to "o ano!r 9 ord] to produce two glasses :i* %all h z ne>ly ! same coeffici5t ( !rmal expansion z possible4 ,if ?is requirem5t is n met1 ! result+ glass is subject$ to int]nal /ra9s :i* may lead to fracture1 :ile1 if ! ruby glass has ! high] coeffici5t ( expansion1 ! %eet aft] flatt5+ t5ds to draw itself up on ! 8fla%$0 side & _c be pass$ out ( ! anneal+ kiln 9 a prop]ly flat condition4 ,al?\gh mo/ usually appli$ to copp]-ruby glass1 ! fla%+ process is (t5 us$ ) o!r col\rs also4 ,col\r$ glass ( ?is k9d is at once recognis$ :5 look$ at ?r\gh ! edges4 ,?us exam9$ ! glass simply %[s ! gre5i% t9t ( ord9>y %eet-glass :i* con/itutes practically ! entire ?ickness ( ! %eet4 ,9 ! same way1 if su* 8fla%$0 glass be cut or et*$ 9 su* a way t ! lay] ( col\r$ glass is remov$ 9 places1 ! result+ patt]n appe>s 9 :ite on ! col\r$ gr\nd--a feature :i* is utilis$ = c]ta9 decorative purposes4 ,! fla%+ process j describ$1 x %\ld be not$1 is applicable to any =m ( glass-w>e :i* is bl[n f a ga!r+1 & ! col\r$ lay] c be appli$ ei!r ^u ! inside or outside ( any object ?us produc$4 ,9 addition to ! palette ( col\rs :i* ! glass-mak] is able to supply1 ! arti/ 9 /a9$ glass has a fur!r range ( col\rs at 8 disposal 9 ! =m ( /a9s & transp>5t col\rs :i* c be appli$ to ! surface ( glass & develop$ & r5d]$ m or less p]man5t by be+ prop]ly 8fir$40 ,! col\rs produc$ 9 ?is way are also1 9 "o s5se1 col\r$ glasses1 or r glazes1 ^: raw mat]ials are put ^u ! glass by ! bru% ( ! pa9t]1 & only subsequ5tly caus$ to comb9e & melt by suitable heat+4 ,! degree ( heat applicable "u ^! circum/ances is1 h[ev]1 v limit$ by ! necessity ( avoid+ any great s(t5+ ( ! sub/ratum ( glass1 :ile _m ( ! col\rs !mselves are compos$ ( mat]ials :i* c\ld n resi/ v high temp]atures4 ,! fluxes us$ 9 ! composition ( ^! col\rs mu/ = ?is reason be ( a v fusible k9d1 ) ! inevitable result ( a greatly r$uc$ *emical /ability z comp>$ ) ! glass itself4 ,! :ole subject ( pa9t+ on glass1 ev5 f ! purely te*nical z ap>t f ! /hetic po9t ( view1 is a v wide "o1 & lies outside ! scope ( ! pres5t volume4 ,only "o fur!r te*nical po9t 9 connection ) glass-pa9t+ & /a9$ glass "w w !re=e be t\*$ ^u "h4 ,?is is an example ( ! fact t ! m te*nically 8p]fect0 mod]n product is n always pref]able = special purposes :i* h be5 well s]v$ by old] & f> less 8p]fect0 products4 ,! production ( te*nically excell5t col\r$ glass 9 mod]n times 01 some:at surpris+ly at fir/1 accompani$ by a v m>k$ decl9e 9 ! arti/ic beauty ( /a9$ glass w9d[s produc$ ) ?is mod]n mat]ial2 ! anci5t art ( /a9$ glass 01 !re=e1 = a "t reg>d$ z a 8lo/ art10 & glass-mak]s 7 blam$ = be+ unable to produce ! brilliant & beautiful t9ts :i* _h be5 =m]ly available4 ,m c>eful /udy1 h[ev]1 reveal$ ! fact t :ile ! actual col\r ( mod]n glass 0 at lea/ z brilliant & v>i$ z t ( anci5t glass1 ! diff]5ce lay 9 ! fact t ! mod]n glass 0 practically entirely free f su* imp]fections z air-bubbles1 /ri1 & o!r defects :i* improv$ appliances & me?ods _h enabl$ ! glass-mak] to elim9ate f 8 products4 ,f9d+ ! beauty ( 8 w>es greatly improv$ by ?is increas$ purity ( ! glass 9 ! case ( w9d[ glass & table w>e1 x 0 natural = ! glass-mak] to endeav\r to produce ! same 8improvem5t0 9 ! col\r$ glasses int5d$ = arti/ic purposes &1 inde$1 x is m ?an likely t ! /a9$-glass work]s !mselves press$ ?is l9e ( improvem5t ^u him by a dem& = 8bett]0 glass4 ,x turn$ out1 h[ev]1 on close exam9ation1 t ?is v p]fection ( mod]n glass r5d]$ x less adapt$ = ^! arti/ic purposes4 ,a p]fect piece ( glass1 hav+ smoo? surfaces & no int]nal regul>ities1 all[s ! rays ( light fall+ ^u x to pass ?r\gh undeflect$ 9 direction1 & m]ely *ang$ 9 col\r1 accord+ to ! t9t ( ! glass 9 "q4 ,on look+ at ! glass1 ext]nal objects c be q cle>ly se51 & mu* ( ! int]e/ & my/]y ( ! glass itself is lo/4 ,on ! o!r h&1 :5 fall+ ^u a piece ( glass hav+ an irregul> surface1 & conta9+ all mann] ( irregul>ities su* z /ri1 air-bells1 & ev5 pieces ( enclos$ solid matt]1 ! light is scatt]$1 refract$1 & deflect$ into all mann] ( directions until x almo/ appe>s to emanate f ! body ( ! glass itself1 :i* ?us appe>s almo/ to %9e ) an int]nal light ( its own2 ! eye c h>dly p]ceive ! pres5ce ( ext]nal objects1 & ! :ole w9d[ appe>s z a brilliant self-lum9\s object4 ,once _! att5tion _h be5 drawn to ^! facts1 mod]n glass-mak]s endeav\r$1 & ) mu* success1 to reproduce ! desirable qualities ( ! anci5t glass1 :ile /ill avail+ !mselves ( mod]n me?ods to produce m /able glasses & a wid] range ( col\rs4 ,! irregul> surface ( ! old glass is imitat$ by us+ roll$ or 8muff$0 in/ead ( ord9>y bl[n glass1 :ile ! int]nal texture is r5d]$ non-homog5e\s by ! delib]ate introduction ( solid & gase\s impurities & by manipulations s arrang$ z to leave ! glass 9 lay]s ( diff]5t d5sity1 :i* appe> 9 ! f9i%$ glass z 8/ri40 ,z a consequ5ce1 x is probably n too mu* to claim t ! mod]n work]s 9 col\r$ glass h mat]ials at _! disposal :i* are at lea/ z suitable = ! purpose z ^? t 7 available 9 ! be/ days ( ! anci5t art4 ,"s ref]5ce has already be5 made to ! te*nical uses ( col\r$ glass1 b "o or two fur!r po9ts 9 t connection rema9 to be discuss$4 ,= su* te*nical purposes z railway & m>9e signals1 ! cons5sus ( practical exp]i5ce has decid$ 9 fav\r ( c]ta9 col\rs ( glass1 su* z r$ & gre5 ( p>ticul> t9ts4 ,on ! o!r h&1 = v>i\s purposes 9 connection ) photography1 ! glass-mak] does n appe> to h be5 able to meet ! new requirem5ts1 ) ! result t flimsy & o!rwise unsatisfactory scre5s made ( gelat9e or celluloid /a9$ ) organic dyes are employ$ 9 place ( col\r$ glass 9 su* cases1 = example1 z ! cov]+ ( lamps = use 9 photograph]s' 8d>k0 rooms1 & = ! light-filt]s us$ = or?o*romatic & tri-*romatic photography4 ,9 all ^! cases x is necess>y to use a transp>5t col\r$ m$ium :i* transmits only light ( a c]ta9 v def9ite range ( wave-l5g?s1 & !re is no d\bt t = ! glass-mak]1 :o is conf9$ to ! use ( a numb] ( elem5t>y bodies = 8 col\r+ m$ia1 x is by no means easy to comply ) ^! requirem5ts ( exact transmission & absorption4 ,on ! o!r h&1 ! field ( available col\r$ glasses has n be5 fully explor$ f ?is po9t ( view1 ! only ext5sive "w on ! subject hav+ be5 done 9 connection ) ! ,j5a firm ( ,s*ott1 :o h put ^u ! m>ket a s]ies ( col\r$ glasses ( accurately-kn[n absorb+ p[]4 ,!re is1 h[ev]1 little d\bt t a mu* great] ext5sion ( ?is field is possible1 & t x w be op5$ up by a glass-mak] :o und]takes ! exhau/ive /udy ( col\r$ glasses f ?is po9t ( view1 al?\gh x mu/ be admitt$ t !re is consid]able d\bt :e!r ! results obta9able by ! aid ( anil9e & o!r dyes z appli$ to gelat9e c ev] be equall$ by col\r$ glasses4 ,,*apt] ,,xii4 ,,optical ,,glass4 ,optical glass diff]s s widely f all o!r v>ieties ( glass t its manufacture may almo/ be reg>d$ z a sep>ate indu/ry1 to :i*1 inde$1 a sep>ate volume c\ld well be devot$4 ,9 ! pres5t *apt] we propose to give an outl9e ( ! mo/ important prop]ties ( optical glass1 & 9 ! next *apt] to describe ! m important features ( ! processes us$ 9 its production4 ,! prop]ties :i* affect ! value ( optical glass may r\ghly be divid$ into two gr\ps4 ,! fir/ gr\p comprises ! specifically 8optical0 prop]ties--i4e41 ^? directly influ5c+ ! behavi\r ( light 9 its passage ?r\gh ! glass1 :ile ! second gr\p cov]s ^? prop]ties ( a m g5]al nature1 :i* are ( special importance 9 glass t is to be us$ = optical purposes4 ,optical ,prop]ties ( ,glass4--,! mo/ ess5tial prop]ty ( glass 9 ?is respect is homog5eity4 ,we h already indicat$ t glass c nev] be reg>d$ z a def9ite *emical sub/ance or comp\nd1 b t x usually consi/s ( mutual solutions ( v>i\s complex silicates1 borates1 etc4 ,solutions be+ ( ! v nature ( mixtures ( two or m diff]5t sub/ances1 x foll[s t !y c only become homog5e\s :5 complete mix+ has tak5 place4 ,we h a famili> example ( ! =mation ( su* a solution :5 sug> is dissolv$ 9 wat]4 ,! wat] ne> ! sug> becomes saturat$ ) sug> & ( diff]5t d5sity f ! rema9+ wat]2 if ! liquid is slightly /irr$ a v *>act]i/ic ph5om5on makes its appe>ance--! pure wat] & ! d5se sug> solution d n at once mix completely1 ! d5s] liquid rema9+ = a "t dissem9at$ ?r\gh\t ! :ole fluid mass 9 ! =m ( m or less f9e l9es1 %eets1 or eddies1 & ^! are visible because ! imp]fectly mix$ liquids h diff]5t effects on ! light pass+ ?r\gh !m4 ,9 ! case ( sug>-wat] we are1 h[ev]1 deal+ ) a v mobile liquid1 & a few turns ( a tea-spoon suffice to r5d] ! mixture complete1 & ! liquid1 :i* = a few mom5ts _h appe>$ turbid1 becomes homog5e\s & transp>5t4 ,9 ! case ( glass1 :5 ! raw mat]ials are melt$ toge!r1 a mixture is =m$ ( liquids ( diff]+ d5sities simil> to t :i* 0 tempor>ily =m$ 9 ! sug>-wat] solution4 ,molt5 glass1 h[ev]1 is nev] s mobile a liquid z ord9>y wat]1 nor is x 9 ! ord9>y c\rse ( manufacture subject$ to any su* ?or\gh mix+ action z t :i* is produc$ by a spoon 9 a glass ( wat]4 ,9 glass z ord9>ily manufactur$1 !re=e1 x is n surpris+ to f9d t ! lack ( homog5eity :i* orig9ates dur+ ! melt+ p]si/s to ! end4 ,its effects c be trac$ :5ev] a ?ick piece ( ord9>y glass is c>efully exam9$1 :5 ! ?reads or lay]s ( diff]+ d5sities c be recognis$ 9 ! =m ( m9ute int]nal irregul>ities 9 ! glass4 ,^! defects are kn[n z /ri or ve9s1 & _! pres5ce 9 glass int5d$ = ! bett] k9d ( optical "w r5d]s ! glass useless4 ,z w be se5 bel[ 9 ! production ( optical glass1 special means are adopt$ = ! purpose ( r5d]+ x z homog5e\s z possible2 9 fact1 ! e>ly hi/ory ( optical glass manufacture is simply ! hi/ory ( attempts to ov]come ?is v defect4 ,! problem is1 h[ev]1 beset by *emical & physical difficulties ( no mean ord]1 & ev5 9 ! be/ mod]n practice only a small proportion ( ea* melt+ or crucible full ( glass is entirely free f ve9s or /ri4 ,9 _m cases ^! defects are v m9ute1 & sometimes escape obs]vation until ! /age ( ! f9i%$ l5s is rea*$4 ,at t /age1 h[ev]1 _! pres5ce becomes pa9fully evid5t f ! fact t !y int]f]e s]i\sly ) ! %>p def9ition ( ! images =m$ by ! l5s 9 "q4 ,x w be se5 t 9 su* a case "t & money has be5 wa/$ by gr9d+ & poli%+ :at turns out to be a useless piece ( glass4 ,me?ods are1 !re=e1 us$ = exam9+ ! glass be=e x is work$1 :]eby ! exi/5ce ( ! smalle/ /ri c sc>cely escape detection4 ,^! me?ods dep5d ^u ! pr9ciple t a beam ( p>allel light pass+ ?r\gh a plate ( glass w meet ) no di/urbance s long z ! glass is homog5e\s1 b if /ri are pres5t1 !y w cause ! light to deviate f p>allelism :]ev] x falls ^u !m4 ,"u su* illum9ation1 !re=e1 ! /ri w appe> z ei!r d>k or bright l9es1 :5 !y c be readily detect$4 ,"o =m ( app>atus us$ = ?is purpose is illu/rat$ 9 ,fig4 #ad4 ,illu/ration3 ,,fig4 #ad4--;,diagram ( /ri-te/+ app>atus4 ,l1 s\rce ( light2 ,s1 slit2 ,a & ,b1 simple convex l5ses2 ,g1 glass "u te/2 ,e1 eye ( obs]v]4 ,! arr[s indicate ! pa?s ( light-rays4 ,transp>5cy & col\r are obvi\sly fundam5tally important prop]ties ( glass4 ,9 "o s5se homog5eity is ess5tial to transp>5cy1 b ! aspect ( ! subject :i* we are n[ consid]+ is t ( ! absorption ( light 9 ! c\rse ( regul> transmission ?r\gh glass4 ,x may be said at once t no glass is ei!r p]fectly transp>5t or1 :at comes to ne>ly ! same ?+1 p]fectly free f col\r4 ,9 ! case ( ! be/ optical glasses x is true t ! absorption ( light is v slight1 b ev5 ^!1 :5 consid]able ?icknesses are view$1 %[ a gre5i%-yell[ or blui% col\r+4 ,on ! o!r h&1 c]ta9 optical glasses :i* are us$ at ! pres5t "t = _m ( our be/ l5ses absorb light s /rongly or are s deeply col\r$ t a ?ickness ( a few in*es is suffici5t to reveal ?is defect4 ,to "s ext5t public ta/e or op9ion :i* objects to ! use ( ev5 a slightly gre5i% glass 9 optical in/rum5ts ( good quality is to blame = ! t9t ( ^! glasses4 ,9 _m cases glass-mak]s c\ld produce a v slightly gre5i% glass1 b 9 ord] to ov]come ?is col\r !y delib]ately add to ! glass a col\r+ oxide imp>t+ to ! glass a col\r m or less complem5t>y to ! natural gre5 t9t4 ,! result is a m or less neutral-t9t$ glass :i*1 h[ev]1 absorbs mu* m light ?an ! naturally gre5 glass w\ld h done4 ,s9ce su* glass is frequ5tly us$ = photographic l5ses1 x is int]e/+ to note t ! light rays ^: transmission is sacrific$ 9 ord] to avoid ! gre5 t9t are ^? ly+ at or ne> ! blue end ( ! spectrum1 s t ! photographic rapidity ( ! result+ l5ses is decid$ly r$uc$ by ! use ( su* glass4 ,refraction & ,disp]sion4--,! quantitative prop]ties ( glass1 gov]n+ its effect ^u incid5t & transmitt$ light1 are1 ( c\rse1 ( fundam5tal importance 9 all its optical uses4 ,! fundam5tal optical con/ant ( ea* v>iety ( optical glass is kn[n z its refractive index2 ?is numb] really repres5ts ! ratio ( ! velocity ) :i* light waves are propagat$ ?r\gh ! glass to ! velocity ) :i* !y travel ?r\gh free space4 ,n only does ?is ratio v>y ) e *ange 9 ! *emical composition & physical condition ( ! glass1 b x also v>ies accord+ to ! l5g? ( ! light waves !mselves4 ,9 o!r words1 ! %ort waves ( blue light are transmitt$ ?r\gh glass ) a diff]5t velocity f t ) :i* ! long] waves ( r$ light are transmitt$4 ,! consequ5ce is t :5 a beam ( :ite light is pass$ ?r\gh a prism x is split up & spread out into a numb] ( beams repres5t+ all ! col\rs ( ! spectrum 9 _! prop] ord]1 ! blue light suff]+ ! greate/ deflection f its orig9al pa?1 :ile ! r$ light suff]s lea/ deflection4 ,bo? ! actual & relative am\nt by :i* light rays ( v>i\s col\rs are deflect$ "u su* circum/ances dep5ds ^u ! nature ( ! glass 9 "q2 !re=e1 to fully *>act]ise ! optical prop]ties ( a giv5 k9d ( glass x is necess>y to /ate n only its refractive index b to specify ! refractive indices = a suffici5t numb] ( diff]5t wave-l5g?s ( light1 suitably di/ribut$ ?r\gh ! spectrum4 ,= ?is purpose a numb] ( well-m>k$ spectrum l9es h be5 *os51 ! sy/ematic use ( ! p>ticul> set ( l9es :i* is n[ usually employ$ be+ due to ! initiative ( ,abb & ,s*ott at ,j5a1 :o initiat$ ! sy/em ( specify+ ! optical prop]ties ( glass 9 ?is way4 ,! actual l9es *os5 are ! l9e kn[n z ,a1 correspond+ to a wave-l5g? ( #jgfgg micro-millimetres1 & ! l9es kn[n z ,c1 ,d1 ,f1 & ,g1 ^: wave-l5g?s1 9 ! same units1 are #jfefc1 #jehic1 #jdhfb1 & #jdcda respectively4 ,! ,a l9e1 h[ev]1 lies s ne> ! extreme r$ end ( ! spectrum t ! data conc]n+ x are seldom requir$4 ,z a matt] ( fact1 ! actual refractive index is only /at$ 9 mo/ tables ( optical glasses = sodium light 7,d l9e71 ! disp]sive prop]ties ( ! glass be+ indicat$ by tabulat+ ! diff]5ces betwe5 ! refractive indices = ! v>i\s l9es1 ! table ?us conta9+ columns m>k$ ,c-,d1 ,d-,f1 ,f-,g4 ,^! figures are usually describ$ z ! 8disp]sion0 ( ! glass f ,c to ,d1 ,d to ,f1 etc4 ,9 addition to ^! figures x is usual to tabulate :at is call$ ! 8mean disp]sion0 ( ! glass1 :i* is simply ! diff]5ce betwe5 ! refractive indices = ,c & ,f l9es2 ?is int]val is usually tak5 z repres5t+ t "p ( ! spectrum :i* is ( ! greate/ importance = visual purposes4 ,a fur!r con/ant :i* is ( great importance 9 ! calculations = a*romatic l5ses is obta9$ by divid+ ! mean disp]sion into ! refractive index = ! ,d l9e m9us "o 7usually writt5 7,c-,f7_/7n,d-#a774 ,?is t]m1 = :i* no satisfactory "n has yet be5 sugge/$1 *>act]ises ! ratio ( ! disp]sive p[] ( ! glass to its total refract+ p[]4 ,x is usually d5ot$ by ! ,greek lett] 4 ,! foll[+ table 7tak5 f ! ,catalogue ( ! ,optical ,conv5tion1 #aije7 gives a li/ ( optical glasses produc$ by ,messrs4 ,*ance1 ( ,birm+ham4 ,?is li/1 al?\gh x is n ne>ly s long z t issu$ by ! ,fr5* & ,g]man firms :o manufacture optical glass1 conta9s examples ( ! mo/ important types ( optical glass :i* are available at ! pres5t "t4 ,^?1 h[ev]1 :o wi% to use ! data = ! purpose ( l5s calculation are advis$ to consult ! late/ issues ( ! optical glass-mak]s' catalogues1 s9ce ! range ( types available1 & ev5 ! actual figures = "s ( ! glasses1 are liable to v>iation f "t to "t4 ,,table ,,( ,,optical ,,prop]ties4 ---------------------------------------- ------------------------- ,p>tial & ,m$ium ,relative ,p>tial ,disp]sions4 ,dis- ------------------------------ ,"n4 n,d4 4 p]- ,c-,d ,d-,f ,f-,g sion4 ,c-,d4 --- ,d-,f4 --- ,f-,g4 --- ,c-,f4 ,c-,f4 ,c-,f4 ,c-,f4 ---------------------------------------- -------------------- ,extra ,h>d ,cr[n #adieifddjjggjjjbbhbifjjedbgjdjjdcaefj ,boro-silicate ,cr[n #aejiffccjjhjcjjbcfbidjjefbgjjjjddfeee ,h>d ,cr[n #aeagefjejjhefjjbebbidjjfjdgjfjjdhdeed 99,m$ium ,b>ium ,cr[n #aegchegijjiijjjbicbifjjfiggjdjjeebeeg 99,d5se/ ,b>ium ,cr[n #afjfeegijajdfjjcjhbidjjgchgjejjehiefc ,s(t ,cr[n #aeaebefijjijfjjbfdbiajjfdbgjhjjeagegj 99,m$ium ,b>ium ,cr[n #aeffjefcjajjfjjbigbiejjgjigjdjjegfegb ,b>ium ,light ,fl9t #aedebecejajbjjjbihbibjjgbbgjajjehbegj ,extra ,light ,fl9t #aecafdijjajhejjcacbhhjjggbgaajjfcjehj ,extra ,light ,fl9t #aecccdhejajiijjcbbbicjjggggjgjjfdjehb ,boro-silicate ,fl9t #aefbcdgdjaahgjjcdcbhijjhddgaajjficehd 99,b>ium ,light ,fl9t #aehccdffjabeajjcfbbhhjjhhigaajjgbaegf ,soda ,fl9t #aedhbdehjaaiejjcdcbhgjjhebgacjjfijegg ,light ,fl9t #aedgbdehjaaifjjcdhbiajjhdhgjijjgjgeia ,light ,fl9t #aefajdcbjabiijjcgbbhgjjibggacjjggjeic ,light ,fl9t #aegfjdajjadjdjjdjbbhfjajjbgacjjhdjeih ,light ,fl9t #aeghgdjgjadbjjjdjdbhdjajafgaejjhdjeia ,d5se ,fl9t #afaahcfijafegjjdgjbhdjaahggafjajjdfjf ,d5se ,fl9t #afbadcfajagbbjjdiabhejabcagaejajdffjh ,d5se ,fl9t #afbbecfjjagbijjdicbhfjabcfgaejajedfji ,extra ,d5se ,fl9t #afdficcgjaiagjjedabhejacgfgbjjaagjfee ,d5se/ ,fl9t #agabibiijbchdjjfgjbhajagadghijaffafgh ---------------------------------------- -------------------- ,9 ! table on p4 #bab ! fir/ column conta9s ! ord9>y trade names by :i* ! v>i\s types ( glass are kn[n4 ,^! names1 :ile some:at arbitr>y1 indicate 9 a r\gh way ! *emical nature ( ! glass conc]n$4 ,?us ! ^w 8fl9t0 always implies a glass conta9+ lead & !re=e hav+ a comp>atively high refractive index & l[ value ( 1 :ile ! ^w 8cr[n10 orig9ally appli$ only to lime-silicate glasses1 is n[ us$ = all glass hav+ a high value ( 4 ,9 ! next column ( ! table are giv5 ! refractive indices ( ! glasses1 :ile ! ?ird column conta9s ! values ( 4 ,x w be se5 t ! glasses are arrang$ 9 desc5d+ ord] ( magnitude 9 respect ( ?is con/ant4 ,an inspection ( ! figures 9 ^! two columns w reveal ! fact t = ! majority ( ! glasses conta9$ 9 ?is table ! value ( decreases z ! refractive index increases4 ,! glasses :i* are an exception to ?is rule are indicat$ by an 994 ,z a matt] ( fact ?is rule appli$ to all glasses t 7 kn[n or 7 at all ev5ts comm]cially available prior to ! mod]n advances 9 optical glass manufacture :i* 7 initiat$ by ,abb & ,s*ott ( ,j5a4 ,x 0 ,abb's insight into ! requirem5ts ( optical in/rum5t design t l$ him to realise ! importance ( ov]com+ ?is limitation 9 ! ratio betwe5 ! disp]sive & refractive p[]s ( glass4 ,) ! collaboration ( ,s*ott he succe$$ 9 produc+ a :ole s]ies ( previ\sly unkn[n v>ieties ( optical glass 9 :i* ! relation betwe5 n,d & is n t ( approximately simple inv]se proportionality :i* holds = ! old] cr[n & fl9t-glasses4 ,mo/ valuable & 9 _m ways mo/ typical ( ^! new glasses are ^? kn[n z ! 8b>ium cr[n0 glasses1 :i* comb9e ! high refractive index ( a light fl9t or ev5 a d5se fl9t-glass ) ! high value ( an ord9>y cr[n glass4 ,x w\ld lead too f> into ! subject ( l5s con/ruction to expla9 9 detail ! possibility op5$ up to ! optician by ! use ( ^! new] v>ieties ( glass4 ,we mu/ cont5t ourselves ) po9t+ out t ! great =w>d /rides m>k$ by ! production ( apo*romatic microscope objectives1 ( ana/igmatic photographic l5ses1 & ! mod]n telescope objectives are all bas$ ^u ! employm5t ( ^! new optical m$ia2 & al?\gh optical glasses ( ^! new] types are at ! pres5t "t produc$ 9 ! optical glass manufactories ( ,france & ,engl&1 9 quality & quantity at lea/ equal to ! output ( ! ,j5a works !mselves1 ^! great optical a*ievem5ts /& z a la/+ monum5t to ! pione] "w ( ,abb & ,s*ott 9 ?is field4 ,! la/ six columns ( ! table ( optical glasses giv5 above conta9 figures :i* def9e ! mann] 9 :i* ea* ( ! glasses nam$ di/ributes ! v>i\s sections ( ! spectrum4 ,! columns ,c-,d1 ,d-,f1 & ,f to ,g give z already indicat$ ! diff]5ces betwe5 ! refractive indices = ! ,c1 ,d1 ,f & ,g l9es respectively2 ! small] figures 9 ! int]m$iate columns indicate ! ratio ( ea* ( ^! diff]5ces to ! mean disp]sion ( ! glass4 ,if all k9ds ( glass di/ribut$ ! v>i\s portions ( ! spectrum 9 ! same proportionate mann]1 m]ely diff]+ 9 ! total am\nt ( disp]sion produc$1 ^! figures w\ld be id5tically ! same = all glasses4 ,9 actual fact x w be se5 t ! figures diff] v widely f "o type ( glass to ano!r4 ,a mom5t's consid]ation w %[ t :5 two glasses are us$ 9 a l5s = ! purpose ( a*romatis+ "o ano!r1 i4e41 :5 "o is us$ to neutralise ! disp]sion ( ! o!r1 su* a*romatisation c only be p]fect if ^! ratios 7! relative p>tial disp]sions7 are ! same = bo? glasses4 ,to put ! same /atem5t 9 m concrete t]ms1 if ! spectrum produc$ by "o glass is comp>atively long-drawn out at ! r$ end1 relatively compress$ at ! blue end1 :ile 9 ! o!r glass ! opposite relation holds betwe5 ! two ends ( ! disp]sion spectrum1 x is evid5t t ! two spectra c nev] be sup]pos$ 9 su* a way z to entirely neutralise "o ano!r--! spectrum produc$ by ! "o glass w pr$om9ate & leave a residual col\r at ! blue end1 :ile ! o!r w pr$om9ate at ! o!r end4 ,9 ! case ( l5ses a*romatis$ by ! use ( su* glasses1 !re w always be a slight fr+e ( col\r ar\nd ! bord]s ( ! images :i* !y produce4 ,"o ( ! aims :i* ,abb & ,s*ott set !mselves 9 ! production ( new v>ieties ( optical glass 0 to obta9 "o or m pairs ( glasses 9 :i* ! relative p>tial disp]sions %\ld be z ne>ly alike z possible :ile ! actual values ( %\ld diff] z widely z possible4 ,"s success 9 ?is direction 0 at fir/ claim$ by ! ,j5a work]s1 b un=tunately "s ( ! mo/ promis+ glasses 9 ?is respect 7 f\nd to be too un/able = practical use & _h ultimately to be ab&on$4 ,at ! pres5t "t ! only pair ( really p]fectly a*romatic glasses (f]$ by ! ,j5a firm is t tabulat$ bel[1 & x w be se5 t al?\gh ! relative p>tial disp]sions are v closely alike1 ! values ( ! two glasses only diff] by #aj1 & at lea/ "o ( ^! glasses is n readily obta9able 9 really satisfactory optical quality4 ,on ! o!r h&1 practically p]fectly a*romatis$ l5ses 7g5]ally kn[n z 8apo*romatic07 h be5 produc$1 especially by ,zeiss ( ,j5a1 = microscopic purposes1 by ! c>eful selection ( glasses suit$ to ea* o!r 9 ?is respect4 ,su* a solution ( ! problem is fur!r facilitat$ by ! fact t 9 ^! l5ses m ?an two v>ieties ( glass c be us$ to neutralise "o ano!r1 :ile a natural m9]al 7fluorite7 is also employ$4 ,f ! glass-mak]'s po9t ( view1 h[ev]1 ! problem ( produc+ a satisfactory pair ( glasses capable ( entirely a*romatis+ "o ano!r has yet to be solv$4 ---------------------------------------- --------------------- c-d d-f f-g ,"n4 n,d ,c-,f4 ,c-,d4 --- ,d-,f4 --- ,f-,g4 --- c-f4 c-f4 c-f4 ---------------------------------------- --------------------- ,telescope ,cr[n #aebedfagjjheb #jjbej #bib #jjfjb #gjg #jjdhd #efh ,telescope ,fl9t #aebaaeahjjajjgjjbig #bid #jjgaj #gje #jjegg #egc ---------------------------------------- --------------------- ,! table ( optical glasses giv5 above1 al?\gh brief z comp>$ ) ! li/s issu$ by ,fr5* & ,g]man optical glass-mak]s1 fairly cov]s ! range ( practically available glasses1 & a rapid inspection w at once %[ h[ extremely limit$ ?is range really is4 ,?us ! refractive index v>ies only betwe5 ! limits #adi & #aga1 & ev5 if we admit z practical glasses su* extreme types--(f]$ by "s mak]s--z w\ld ext5d ?is range to #adj 9 "o direction & to #ahj 9 ! o!r1 ?is does n affect ! pres5t argum5t4 ,( c\rse1 a glass ( a refractive index z l[ z #aj1 or ev5 #aaj1 is n !oretically possible1 s9ce ! m]e d5sity ( any sub/ance ent]s into ! factors t affect its refractive index1 & a glass hav+ a d5sity l[] ?an t ( wat] 7^: refractive index is ab\t #ac7 is sc>cely conceivable4 ,9 ! o!r direction1 h[ev]1 ! limits met ) 9 ! case ( glass are consid]ably exce$$ by c]ta9 natural m9]al sub/ances4 ,?us ! diamond has a refractive index ( #bdb1 :ile ! g>nets %[ refractive indices f #age to #aha4 ,! values ( f\nd 9 ! table ( optical glasses are /ill m n>r[ly re/rict$1 ly+ betwe5 #fg & #bi1 :ile su* a m9]al z fluorite %[s a value ( #ied4 ,^! facts %[ t x is physically possible to obta9 transp>5t sub/ances hav+ optical prop]ties ly+ f> beyond ! limit$ range cov]$ by our pres5t optical glasses1 & x sc>cely ne$s %[+ t if su* an ext5d$ range ( mat]ials 7 available greatly increas$ possibilities w\ld be op5$ up to ! design] ( optical in/rum5ts4 ,x is consequ5tly int]e/+ to inquire z to ! actual causes :i* limit ! range ( optical glasses at pres5t available4 ,x w be f\nd t ^! limits are set by ! prop]ties ( glass itself4 ,:ile ! m ord9>y k9ds ( glass1 hav+ av]age optical prop]ties & %[+ disp]sive p[]s r\ghly con=m+ to ! law ( inv]se proportionality ) refractive index :i* gov]ns ! old] v>ieties ( optical glass1 are *emically /able sub/ances1 %[+ little t5d5cy to und]go ei!r *emical *anges or to cry/allise dur+ cool+1 ! m extreme glasses exhibit ^! undesirable features to an increas+ ext5t ! m ne>ly ! limit ( our pres5t range is approa*$4 ,z ! *emical composition ( a glass is 8=c$0 by ! addition ( special sub/ances int5d$ to affect its optical prop]ties 9 an abnormal direction1 s ! *emical & physical /ability ( ! glass is rapidly less5$4 ,! m extreme glasses1 9 fact1 behave z active *emical ag5ts readily ent]+ into reaction or comb9ation ev5 ) relatively in]t sub/ances 9 _! environm5t--!y act vigor\sly ^u ! fire-clay vessels 9 :i* !y are melt$1 & !y are readily attack$ by acids1 moi/ure or ev5 w>m air1 :5 9 ! f9i%$ condition1 :ile _m ( !m c only be prev5t$ f assum+ ! condition ( a cry/all9e 7& opaque7 agglom]ate by be+ rapidly cool$ ?r\gh c]ta9 critical ranges ( temp]ature4 ,a limit to ! possibility ( production is set by ^! t5d5cies :5 !y exce$ a c]ta9 am\nt--a po9t be+ rea*$ :]e x ceases to be practicable to ov]come ! t5d5cy ( ! glass to self-de/ruction4 ,on ! l9es ( our pres5t glasses1 !re=e1 x does n appe> hopeful to look = any consid]able ext5sion ( ! range ( our optical m$ia4 ,on ! o!r h&1 z ! kn[n optical prop]ties ( transp>5t cry/all9e m9]als %[1 a mu* great] range ( optical con/ants w\ld become available if x 7 possible to manufacture artificial m9]al cry/als ( suffici5t size & purity = optical purposes1 & ! au?or believes t 9 ?is direction progress 9 optical mat]ials is ultimately b\nd to lie#a4 #a ,see a ,pap] by ! pres5t au?or on 8,possible ,directions ( ,progress 9 ,optical ,glass0--,proce$+s ( ! ,optical ,conv5tion1 ,london1 #aije4 ,9 addition to possess+ ! requisite optical con/ants1 a good col\r & p]fect homog5eity1 c]ta9 o!r prop]ties are ess5tial 9 good optical glass4 ,^! are ! g5]al physical & *emical qualities :i* are ess5tial 9 all good glass1 b especially emphasis$ by ! fact t ! requirem5ts = optical glass are m /r+5t ?an = any o!r v>iety ( ! mat]ial4 ,?us *emical /ability is ( ! greate/ importance1 = ! be/ l5ses w\ld soon become useless if ! action ( atmosph]ic moi/ure 7 to affect !m appreciably--! poli%$ surfaces w\ld rapidly become dull & ! :ole l5s w\ld soon be r5d]$ useless4 ,! conditions gov]n+ ! *emical /ability ( glass & ! me?ods ( te/+ ?is quality h already be5 indicat$ 7,*apt]s ,i4 & ,,ii474 ,! h>d] v>ieties ( optical glass1 su* z ! glasses quot$ 9 ! above table "u ! names ( 8,h>d ,cr[n0 & ,boro-,silicate ,cr[n1 are probably among ! mo/ durable & *emically resi/ant ( all v>ieties ( glass1 b z we h already indicat$1 :5 extreme optical prop]ties are requir$1 ! necess>y *emical composition ( ! glass always entails a sacrifice ( ?is great *emical /ability1 until a limit is rea*$ :]e valuable optical prop]ties no long] c\nt]balance ! s]i\s disadvantage ( a *emical composition :i* r5d]s ! glass liable to rapid dis9tegration4 ,9 c]ta9 special cases x is1 p]haps1 possible to protect l5ses made ( su* un/able glass by cov]+ !m ) cem5t$-on l5ses ( /able glass1 b ?is device entails concomitant limitations 9 ! design ( ! optical sy/em & is1 !re=e1 r>ely us$4 ,9 any case1 h[ev]1 x is well = ! l5s-design] to consid] ! relative /ability ( ! glasses employ$ :5 arrang+ ! ord] 9 :i* !y are to be us$1 s9ce x is obvi\sly pref]able to put a h>d1 durable glass on ! outside ( 8 sy/em1 :]e x is mo/ directly expos$ to atmosph]ic moi/ure1 & is also subject to h&l+ & 8clean+0 by inexp]t h&s4 ,?is latt] factor is a v important "o = ! life ( any l5s4 ,9 ! fir/ place1 a glass surface is v s]i\sly affect$ by ! m9ute film ( organic matt] :i* is left ^u x :5 x has be5 t\*$ ) ev5 a clean f+]2 unless ! glass is ( ! be/ quality 9 ?is respect1 su* f+]m>ks readily develop into iridesc5t spots & may ev5 turn into black /a9s4 ,p>ticles ( du/ all[$ to settle on ! surface ( ! glass w affect x 9 ! same way1 s t ! protection af=d$ by m]e me*anical enclosure 9 ! tube ( an in/rum5t is ( decid$ value 9 pres]v+ a glass surface4 ,x %\ld1 h[ev]1 be not$ t 9 "s in/ances ! int]ior metal surfaces ( optical in/rum5ts are v>ni%$ ) sub/ances t give (f vap\rs = a long "t aft] ! in/rum5t is complet$1 & 9 t case ! inside l5ses are apt to be t>ni%$ 9 consequ5ce4 ,on ! o!r h&1 outside l5ses are also expos$ to direct me*anical injury f h&l+ & 8clean+40 ,z f> z ! latt] op]ation is conc]n$1 x frequ5tly happ5s1 p>ticul>ly 9 glasses conta9+ soda1 t a slight surface dimm+ is =m$ on ! glass :5 x has be5 left 9 a m or less damp place = a long "t4 ,?is dimm+ is *iefly due to ! =mation on ! surface ( a great numb] ( v m9ute cry/als ( c>bonate ( soda1 :i* are h>d & %>p en\gh to scrat* ! glass itself if rubb$ ab\t ov] x4 ,if su* a l5s be wip$ ) a dry clo?1 h[ev] clean & s(t1 ! effect is a p]man5t injury to ! poli%$ surface1 :i* c\ld readily be avoid$ by fir/ wa%+ ! l5s ) clean wat]1 or ev5 by us+ a wet clo? in/ead ( a dry "o = ! fir/ wip+4 ,! me*anical h>dness ( ! glass is an important factor 9 det]m9+ its resi/ance to su* injuri\s treatm5t or to ! effects ( accid5tal contact ) h>d1 %>p bodies4 ,! subject ( ! h>dness ( glass has already be5 discuss$ 9 a g5]al way 9 ,*apt] ,,ii41 & little rema9s to be add$ "h4 ,broadly speak+1 a high degree ( h>dness & a l[ refractive index are f\nd toge!r4 ,?is /atem5t is c]ta9ly true :]e any consid]able diff]5ce ( h>dness is consid]$1 z1 = example1 9 comp>+ a h>d cr[n glass ) a d5se fl9t2 b :]e ! diff]5ce ( refractive index or ( d5sity is small1 x is n at all c]ta9 t ! light] glass w also be ! h>d]4 ,! prop]ties involv$ 9 ! quality kn[n z 8h>dness0 also affect 9 a v m>k$ mann] ! behavi\r ( glass :5 subject$ to ! gr9d+ & poli%+ processes4 ,! ease ) :i* a good poli% c be obta9$ v>ies v mu* 9 diff]5t k9ds ( glass1 bo? ! h>de/ & ! s(te/ glasses %[+ !mselves difficult 9 ?is respect4 ,! h>d] glasses are c]ta9ly less liable to accid5tal scrat*+ dur+ ! poli%+ op]ations1 & g5]ally "w 9 a clean] mann]2 b ! "t requir$ to produce a satisfactory poli% is mu* great] ow+ to ! resi/ance to displacem5t (f]$ by ! molecules4 ,bo? ! spe$ ( work+ & ! pressure ex]t$ dur+ ! poli%+ op]ation h1 9 fact1 to be c>efully adapt$ to ! quality ( ! glass 9 ?is respect if ! be/ possible results are to be obta9$4 ,ano!r prop]ty :i* is ess5tial 9 optical glass ( ! highe/ quality is t ( fre$om f int]nal /ra9s4 ,?is subject w be aga9 ref]r$ to lat] 9 connection ) ! anneal+ processes us$ 9 ! manufacture ( optical glass1 & x ne$ only be m5tion$ "h t ! pres5ce ( int]nal /ra9 is readily recognis$ 9 glass1 by ! aid ( ! pol>iscope4 ,p]fectly anneal$ glass1 entirely free f int]nal /ra9s1 produces no effect ^u a beam ( pol>is$ light pass+ ?r\gh x1 :ile ev5 slightly /ra9$ glass becomes m>k$ly d\bly-refract+4 ,= _m purposes ( optics ?is d\ble refraction becomes undesirable or ev5 inadmissible1 especially z x is accompani$ by small v>iations 9 ! effective index ( refraction ( v>i\s portions ( ! mass ( glass4 ,fur!r1 if ! am\nt ( d\ble refraction obs]v$ is at all s]i\s x indicates a /ate ( /ra9 :i* may easily lead to ! fracture ( ! :ole piece1 p>ticul>ly :5 und]go+ ! e>li] /ages ( ! gr9d+ process or if expos$ to %ocks ( any sort4 ,z w be se5 bel[1 p]fectly anneal$ glass is obta9able1 b v special means are requir$ = its production1 & ! optician %\ld = t reason avoid mak+ unnecess>ily extreme dem&s 9 ?is direction4 ,! v small am\nt ( d\ble refraction frequ5tly f\nd 9 ! bett] class ( optical glass is entirely h>mless = mo/ purposes4 ,,*apt] ,,xiii4 ,,optical ,,glass4 ,! process ( manufactur+ ! be/ qualities ( optical glass may be briefly describ$ z consi/+ 9 obta9+ a crucible full ( ! pure/ & mo/ homog5e\s glass1 & !n all[+ x to cool sl[ly & to solidify 9 situ4 ,f ! result+ mass ( glass ! be/ pieces are pick$ & m\ld$ into ! desir$ %ape = optical use4 ,x w be se5 at once t 9 ?is process !re is an ess5tial diff]5ce f all o!rs t h be5 describ$ 9 ?is book--viz41 t ! glass is nev] remov$ f ! melt+-pot :ile molt51 & t none ( ! op]ations ( ga!r+1 p\r+1 roll+1 press+1 or bl[+ are appli$ to x4 ,! reason = ?is app>5tly irrational mode ( proc$ure lies 9 ! fact t ! p]fect homog5eity ess5tial = optical purposes c only be atta9$ by labori\s means1 & c !n only be reta9$ if ! glass is left to solidify undi/urb$2 any movem5t by ! introduction ( pipes or ladles w\ld result 9 ! contam9ation ( ! glass by /ri & o!r objectionable defects4 ,! *oice & proportion ( raw mat]ials us$ 9 ! production ( any giv5 quality ( optical glass is gov]n$ by ! *emical composition :i* exp]im5t has %[n to be necess>y to yield ! desir$ optical prop]ties4 ,! composition ( optical glass mixtures _c !re=e be v>i$ to suit ! conditions ( ! furnace or to facilitate ready melt+ & f9+1 s t _m ( ! usual res\rces ( ! glass-mak] cease to be available 9 ! v case :]e _! aid w\ld be mo/ welcome to facilitate ! production ( te*nically p]fect glass4 ,on ! o!r h&1 ! manufactur] has a c]ta9 am\nt ( *oice z to ! precise =m 9 :i* ! v>i\s *emical +r$i5ts are to be introduc$ into ! mixture1 & he makes 8 *oice among oxides1 c>bonates1 nitrates1 & hydrates1 accord+ to ! behavi\r t x is desir$ to imp>t to ! mass dur+ ! e>li] /ages ( fusion4 ,! /ate ( purity 9 :i* ! v>i\s sub/ances are comm]cially obta9able also ent]s l>gely into ! "q1 s9ce ! greate/ possible degree ( purity 9 ! raw mat]ials is ess5tial to ! production ( glass ( good col\r1 or r fre$om f col\r4 ,s9ce homog5eity is s ess5tial 9 ! f9i%$ product1 v ?or\gh mix+ ( ! raw mat]ials is necess>y 9 ! case ( optical glass1 & ! +r$i5ts are = ?is purpose g5]ally us$ 9 a /ate ( f9] division ?an is necess>y ) o!r v>ieties ( glass4 ,z a rule ! quantities ( mixture ( any "o k9d t are requir$ are n l>ge en\gh to ju/ify ! use ( me*anical appliances1 & v c>eful h&-mix+ is c>ri$ out4 ,al?\gh x is q possible to obta9 successful melt+s f raw mat]ials alone1 x is pref]able to mix ) ^! a c]ta9 proportion ( 8cullet0 or brok5 glass d]iv$ f a previ\s melt+ ( ! same sort4 ,! brok5 glass us$ = ?is purpose is fir/ c>efully pick$ ov] = ! purpose ( reject+ pieces t conta9 visible impurities1 al?\gh pieces %[+ /ri are n usually reject$4 ,! great] "p ( ?is cullet is g5]ally mix$ z ev5ly z possible ) ! raw mat]ials1 b a c]ta9 proportion is res]v$ = ano!r purpose1 z expla9$ bel[4 ,! furnaces us$ = ! production ( optical glass v>y v mu* 9 type 9 diff]5t works4 ,9 "s ! old-fa%ion$ conical coal furnaces are /ill us$1 ! disadvantages atta*$ to _! employm5t be+ outweigh$--9 ! op9ion ( ! manufactur]s--by _! simplicity & ease ( regulation4 ,9 o!r works gas-fir$ reg5]ative furnaces ( ! mo/ rec5t type are in/all$1 & 9 ^! also optical glass ( ! highe/ quality c be produc$4 ,z a rule1 h[ev]1 optical glass furnaces diff] f o!r pot-furnaces f\nd 9 glass-works 9 ?is respect--t ! =m] are usually con/ruct$ to receive "o pot or crucible only1 :ile 9 o!r glass furnaces f f\r to twelve or ev5 tw5ty pots are heat$ at ! same "t4 ,! reason = ?is re/riction 9 ! capacity ( ! furnaces lies 9 ! fact t s9ce ! mixtures us$ = optical glass _c be adju/$ to suit ! furnace1 ! latt] mu/ be work$ z f> z possible 9 su* a way z to suit ! mixture to be melt$ 9 x1 & ?is implies t e pot w require its own adju/m5t ( times & temp]atures1 & ?is x w\ld be difficult1 if n impossible1 to secure if m ?an "o pot 7 heat$ 9 ! same furnace4 ,x is fur!r to be rememb]$ t ! am\nt ( c>e & att5tion requir$ dur+ ! melt+ ( a pot ( optical glass is out ( all proportion to t ne$$ ) o!r v>ieties1 s t little w\ld be ga9$ by hav+ a numb] ( pots 9 "o furnace1 s9ce sev]al sets ( m5 w\ld be requir$ to t5d !m4 ,9 addition to ! s+le-pot melt+ furnace1 a v important "p ( ! equipm5t ( ! optical glass works is =m$ by a numb] ( kilns or ov5s :i* are us$ = ! prelim9>y heat+1 & sometimes = ! f9al cool+ ( ! v>i\s crucibles or pots4 ,simil> kilns are us$ 9 o!r bran*es ( ! indu/ry1 b 9 ^? cases ! pots1 once introduc$ into ! furnace1 are expect$ to la/ = a numb] ( weeks1 or ev5 mon?s4 ,9 optical glass manufacture1 on ! o!r h&1 a pot is us$ once only1 s t fre% pots are requir$ = e new melt+4 ,! kilns 9 :i* ^! pots are heat$ up be=e be+ plac$ 9 ! melt+ furnace are ?us 9 v frequ5t use4 ,z a rule !y are simply fire-brick *amb]s provid$ ) suffici5t grate-room & flue-space to be gradually rais$ to a r$ heat 9 ! c\rse ( f\r or five days1 :ile = ! purpose ( gradual cool+ !y c be seal$ up l ! anneal+ kilns us$ = poli%$ plate-glass4 ,! pots or crucibles 9 :i* optical glass is melt$ are usually ( ! same %ape z ! cov]$ pots us$ = fl9t-glass z illu/rat$ 9 ,fig4 #b4 ,! optical glass pots1 h[ev]1 are made consid]ably ?9n] 9 ! wall1 s9ce !y are n requir$ to )/& ! prolong$ action ( molt5 glass 9 ! same way z pots us$ = fl9t-glass manufacture4 ,on ! o!r h&1 ! fire-clays us$ = ?is purpose mu/ be *os5 ) special c>e s z to avoid any contam9ation ( ! glass by iron or o!r impurities :i* might rea* ! glass f ! pot4 ,= ! production ( c]ta9 special glasses1 9 fact1 pots made ( special mat]ials are requir$1 s9ce ^! glasses1 :5 molt51 produce a rapid *emical attack ^u ord9>y fire-clays4 ,a c]ta9 am\nt ( ! alum9if]\s mat]ial ( ! pot is1 9 fact1 always introduc$ into ! glass by ! gradual dissolv+ action ( glass on fire-clay :i* we h already describ$4 ,! glass contam9at$ ) ^! alum9if]\s sub/ances is g5]ally m visc\s ?an ! re/ ( ! cont5ts ( ! pot1 & !re=e ord9>ily rema9s m or less adh]5t to ! walls ( ! crucible1 b ! inevitable di/urbances :i* accompany ! processes ( melt+ & f9+ lead to ! dissem9ation ( "s ( ?is visc\s glass ?r\gh ! entire pot 9 ! =m ( ve9s or /ri1 :i* are only remov$ dur+ ! /irr+ process4 ,on ! o!r h&1 m ( ?is visc\s glass is con/antly be+ =m$ s long z ! glass rema9s molt51 & if di/urbances are n suffici5tly avoid$ dur+ ! lat] /ages ( ! process fre% ve9s may easily be =m$4 ,! actual op]ations ( produc+ a melt+ ( optical glass beg9 by ! gradual heat+-up ( ! pot 9 ! kiln j describ$4 ,:5 ! pot has rea*$ a full r$ heat ! doors ( ! kiln are op5$ & ! pot drawn out by means ( a long heavy iron =k runn+ on :eels2 ?is implem5t is run into ! m\? ( ! kiln & ! t9es ( ! =k are pu%$ "u ! pot1 & ! latt] is !n readily lift$ up & )drawn f ! kiln4 ,mean:ile ! temp]ature ( ! furnace has be5 regulat$ 9 su* a mann] z to be approximately equal to t atta9$ by ! heat+ kiln1 s t ! pot1 :5 transf]r$ z rapidly z possible f ! kiln to ! furnace1 is n subject$ to any v sudd5 heat+2 7 x attempt$ to place ! new pot 9 a furnace at full melt+ heat ! fire-clay w\ld %r9k rapidly & ! entire vessel w\ld fall to pieces4 ,ev5 "u ! be/ conditions x is n possible to avoid ! occasional failure ( a pot by crack+ ei!r at ?is or a slightly lat] /age ( ! process4 ,! latt] occurr5ce is apt to be p>ticul>ly disa/r\s1 z ! pot may !n be full ( molt5 glass1 :i* runs out & is lo/4 ,z soon z ! empty pot has be5 put into place1 ! melt+ furnace is c>efully seal$ up by means ( tempor>y "w built ( l>ge fire-bricks1 ! :ole be+ s arrang$ t ! m\? ( ! hood ( ! pot is left accessible by means ( an ap]ture 9 ! tempor>y furnace wall4 ,?is ap]ture c be clos$ by "o or m slabs ( fire-clay1 & :5 ^! are remov$ an op5+ is left by :i* ! raw mat]ials are introduc$1 & ?r\gh :i* ! o!r manipulations are c>ri$ out4 ,:5 ?is /age ( ! process is rea*$1 ! wagons conta9+ ! mix$ raw mat]ials are usually :eel$ into place 9 front ( ! furnace1 b ! introduction ( ! mat]ials !mselves into ! pot is n begun until sev]al h\rs lat]1 :5 ! furnace has be5 vigor\sly heat$ & an approa* to ! melt+ heat has be5 atta9$4 ,:5 ! furnace & pot h atta9$ ! necess>y temp]ature1 b be=e ! raw mat]ials are introduc$1 a small quantity ( ! cullet1 :i* has be5 res]v$ = ?is purpose1 is ?r[n into ! pot & all[$ "t to melt1 & !n only is ! fir/ *>ge ( mixture put into ! pot4 ,! object ( ?is proce$+ is to coat ! bottom & "p ( ! walls ( ! pot ) a lay] ( molt5 glass :i* s]ves to protect x f ! *emical & physical attack ( ! raw mat]ials dur+ ! viol5t action :i* takes place :5 !y are fir/ expos$ to ! furnace heat4 ,! gradual fill+ ( ! pot ) molt5 glass is n[ c>ri$ out by ! introduction ( successive *>ges ( raw mat]ial2 z ! mixture n only occupies m space ?an ! glass x =ms1 b also fro?s up a good deal dur+ melt+1 ! quantities introduc$ ea* "t mu/ be c>efully adju/$ s z to avoid an ov]fl[ ( half-melt$ glass ?r\gh ! m\? ( ! pot4 ,z ! pot is m & m ne>ly fill$1 ! space left = ! raw mat]ials is proportionately dim9i%$1 & ! lat] *>ges are !re=e mu* small] ?an ! fir/ few4 ,:51 f9ally1 suffici5t mat]ial has be5 introduc$ to fill ! pot completely1 ! next /age ( ! process comm5ces4 ,:5 ! la/ *>ge ( raw mat]ials has melt$1 ! glass 9 ! pot is left 9 ! /ate ( a m or less visc\s liquid full ( bubbles ( all sizes2 x is ess5tial t ^! bubbles %\ld escape & leave ! glass pure & 8f9e10 & ?is result c only be a*iev$ by rais+ ! temp]ature ( ! furnace & all[+ ! glass to become m fluid1 :ile ! rise ( temp]ature also causes ! bubbles to exp& ow+ to ! expansion ( ! gas conta9$ 9 !m4 ,9 bo? ways1 rise ( temp]ature facilitates ! escape ( ! bubbles1 & ! furnace is !re=e heat$ to ! full1 & ?is extreme heat is ma9ta9$ until ! glass is free f bubbles4 ,9 ! case ( ! m fusible glasses ! temp]ature requir$ = ?is purpose is n excessively high1 &1 inde$1 9 ! case ( ^! glasses c>e is tak5 to avoid too high a temp]ature1 z x entails o!r disadvantages4 ,9 ! case ( ! h>d] cr[n glasses1 h[ev]1 ! difficulty lies 9 produc+ an adequately high temp]ature )\t at ! same "t endang]+ ! life ( furnace & crucible4 ,! difficulty ( free+ ! molt5 glass f bubbles con/itutes "o ( ! causes t limit ! range ( our optical glasses 9 "o direction--/ill h>d] glasses c\ld be melt$1 b x w\ld n be feasible to ma9ta9 a temp]ature high en\gh to r5d] !m fluid en\gh to 8f9e40 ,9 ! case ( o!r k9ds ( glass1 aga91 x becomes impossible to entirely remove ! bubbles f ! molt5 mass ev5 :5 v hot & v fluid4 ,! exact cause is n kn[n1 b 9 "s k9ds ( glass ! bubbles =m$ are s m9ute t ev5 :5 ! glass is p]fectly mobile ! bubbles %[ no t5d5cy to escape1 :ile 9 o!r k9ds ( glass !re appe>s to be a /eady evolution ( m9ute bubbles z soon z ! temp]ature is rais$ ) a view to remov+ ^? already 9 ! glass4 ,z ?is prop]ty atta*es to "s ( ! mo/ valuable ( ! new] v>ieties ( optical glass1 opticians & ! public h le>nt to put up ) ! pres5ce ( m9ute bubbles 9 ! l5ses & prisms made ( ^! glasses4 ,^! bubbles are1 h[ev]1 v m9ute & d n int]f]e ) ! optical p]=mance ( ! l5ses1 c41 except to ! ext5t ( arre/+ & scatt]+ ! v small proportion ( light t falls ^u !m2 _! pres5ce is !re=e to be reg>d$ z a small b unavoidable drawback to ! use ( glasses :i* (f] advantages t completely outweigh ?is defect4 ,return+ to ! melt+ process1 we f9d t ! extreme heat+ requir$ = ! purpose ( 8f9+0 ! glass is cont9u$ = a consid]able p]iod ( "t1 z long z ?irty h\rs 9 "s cases1 ! glass be+ exam9$ f "t to "t to te/ its condition z reg>ds fre$om f bubbles4 ,?is is done by tak+ a small sample ( glass out ( ! pot & exam9+ x to see if x /ill conta9s bubbles4 ,9 "s works ?is te/ is made by tak+ up a v small ga!r+ ( glass on ! end ( a small pipe & bl[+ x into a sph]ical flask2 on look+ at su* a flask 9 a suitable light ! pres5ce ( ev5 m9ute bubbles is readily detect$4 ,9 o!r works a simpl] process is adopt$1 a small quantity ( glass be+ ladl$ out ( ! pot on ! surface ( a flat iron rod4 ,x is all[$ to cool on ! rod1 & :5 pu%$ (f =ms a small b> ( glass "s eight or t5 in*es long & ab\t an in* wide2 9 ?is also ! pres5ce ( bubbles is easily detect$4 ,^! te/ pieces are kn[n among glass-mak]s z 8pro(s40 ,:5 pro(s1 tak5 z j describ$1 h %[n t ! glass is free f bubbles1 ! extreme heat ( ! furnace is all[$ to abate1 & ! fire-clay slabs 9 front ( ! m\? ( ! pot are remov$4 ,! next /ep is t ( skimm+ ! surface ( ! glass4 ,s9ce mo/ ( ! mat]ials liable to contam9ate ! cont5ts ( a pot are specifically light] ?an ! molt5 glass1 !y w be f\nd float+ on ! surface1 & ! surface glass is !re=e remov$ ) a view to ridd+ ! glass ( any?+ t may h be5 accid5tally introduc$ & t has n melt$ & become incorporat$ ) ! molt5 mass4 ,! next /eps 9 ! process are ^? ( /irr+ ! molt5 glass ) a view to r5d]+ x homog5e\s & free f /ri4 ,! /irr] us$ = ?is purpose is usually a cyl9d] ( fire-clay1 previ\sly burnt & heat$4 ,?is is provid$ ) a deep squ>e hole 9 "o end1 & x is held at fir/ by means ( a small iron b> pass$ into ?is hole4 ,by ?is means ! r$-hot cyl9d] ( fire-clay is introduc$ into ! op5 m\? ( ! pot1 & :5 x has atta9$ approximately ! temp]ature ( ! molt5 glass x is dipp$ into ! glass itself1 9 :i* x ultimately floats4 ,:5 /irr+ is to beg91 ! squ>e1 d[n-turn$ end ( a long iron b> is introduc$ into ! correspond+ squ>e hole 9 ! upp] end ( ! /irr]1 & by ?is means ! fire-clay cyl9d] is held 9 a v]tical position 9 ! glass & giv5 ! /eady rotatory movem5t :i* con/itutes ! /irr+ process4 ,= ?is purpose ! long iron b> j m5tion$ is made to pass ov] a swivel-:eel1 :ile a workman moves x /eadily by ! aid ( a l>ge wood5 h&le4 ,?is op]ation is always labori\s & try+2 ! workman is necess>ily expos$ to ! int5se heat radiat$ f ! op5 m\? ( ! crucible1 s t m5 h to relieve ea* o!r at frequ5t int]vals4 ,dur+ ! e>li] /ages ( ! /irr+ process ! glass is v hot & mobile1 b ! /irr+ is cont9u$1 ) %ort int]vals1 until ! glass is s cold & /iff t ! /irr] c sc>cely be mov$ 9 x at all1 s t ! "w ( mov+ ! /irr] becomes heavy t[>ds ! end ( ! op]ation4 ,! actual am\nt ( /irr+ requir$ v>ies accord+ to ! nature ( ! glass1 & ! size ( ! pot or crucible 9 "q4 ,"s melt+s are f\nd to be satisfactory aft] z little z f\r h\rs' /irr+1 :ile = o!rs z mu* z #bj h\rs are requir$4 ,:5 ! glass has /iff5$ to su* an ext5t t x is no long] possible to cont9ue ! /irr+1 prep>ations are made = ! f9al cool+-d[n ( ! pot ( glass4 ,! fire-clay /irr] is sometimes )drawn f ! glass1 b ?is is labori\s1 & entails dragg+ a consid]able quantity ( glass out ( ! pot ) ! clay cyl9d]2 m usually1 !re=e1 ! /irr] is simply left emb$d$ 9 ! glass4 ,! next object to be accompli%$ is t ( cool+ ! glass z rapidly z safety w p]mit until x has become def9itely 8set0--! purpose be+ to prev5t ! recrudesc5ce ( /ri z a result ( convection curr5ts or o!r causes :i* might di/urb ! homog5eity ( ! glass4 ,?is rapid cool+ is obta9$ 9 v>i\s ways2 9 "o mode ( proc$ure ! furnace is s arrang$ t by op5+ a numb] ( ap]tures provid$ = ! purpose cold air is drawn 9 & ! pot & its cont5ts *ill$ !reby )\t be+ mov$4 ,?is me?od has ! advantage t ! pot conta9+ ! visc\s glass is nev] mov$ or di/urb$ 9 any way1 b on ! o!r h& ! cool+ :i* c be effect$ )9 ! furnace itself is nev] v rapid1 & ! furnace z well z ! pot is *ill$4 ,fur!r :5 ! glass has be5 *ill$ d[n to a c]ta9 po9t ?is rapid rate ( cool+ mu/ be arre/$1 z o!rwise ! :ole cont5ts ( ! pot w\ld crack & spl9t] into m9ute fragm5ts4 ,:]e ! pot has be5 left 9 ! furnace ?is c only be done by seal+ up ! :ole furnace ) tempor>y brickwork & lut+s ( fire-clay1 leav+ x to act z an anneal+ kiln until ! glass has cool$ d[n approximately to ! ord9>y temp]ature1 a process t occupies a p]iod ( f "o to two weeks accord+ to ! size ( ! melt+4 ,su* en=c$ idl5ess ( a melt+ furnace is ( c\rse v undesirable f an economical po9t ( view1 & x is g5]ally avoid$ by adopt+ ! alt]native me?od ( draw+ ! pot bodily out ( ! furnace z soon z ! /irr+ op]ation is end$4 ,= ?is purpose ! tempor>y brickwork =m+ ! front ( ! furnace is brok5 d[n1 & ) ! aid ( a long cr[-b> ! bottom ( ! pot is lev]$ up f ! b$ or siege ( ! furnace to :i* x adh]es /rongly1 be+ b\nd d[n by ! /icky visc\s mass ( molt5 glass & half-molt5 fire-clay :i* always accumulates on ! b$ ( ! furnace4 ,! pot be+ tempor>ily held up by ! ins]tion ( a piece ( fire-brick1 ! t9es ( a long & heavy iron =k runn+ on a massive iron truck are introduc$ b5ea? ! pot2 an iron b& provid$ ) long h&les is !n pass$ ar\nd ! pot1 & ! latt] is !n drawn =w>d by ! aid ( suitable pulley blocks4 ,! t9es ( ! =k are !n rais$1 & ! pot is :eel$ out ( ! furnace & deposit$ ^u a suitable support4 ,"h x is all[$ to cool to ! requisite ext5t1 :5 x is aga9 pick$ up on ! t9es ( ! =k & deposit$ 9 an anneal+ kiln :i* has be5 previ\sly w>m$ to a suitable temp]ature4 ,x w be se5 t ?is h&l+ ( a heavy mass ( int5sely hot mat]ial involves mu* lab\r1 :ile !re is also a risk ( los+ ! glass if ! pot %\ld break be=e ! glass has set suffici5tly4 ,e c>e is tak5 to prev5t su* an accid5t1 ! pot be+ wrapp$ r\nd ) *a9s or o!rwise support$ 9 su* a way t a small crack c\ld n readily develop into a l>ge gap4 ,:5 su* a melt+ ( glass has cool$ suffici5tly1 ei!r 9 ! furnace or 9 ! anneal+ kiln1 to be safely h&l$1 ! :ole pot is drawn out1 & ! fire-clay %ell1 :i* is g5]ally f\nd crack$ into _m pieces1 is brok5 away by ! aid ( a hamm]4 ,"u fav\rable circum/ances ! :ole ( ! glass may h cool$ intact z "o solid lump sometimes weigh+ ov] half a ton4 ,unless special c>e is tak51 h[ev]1 x is m usual to f9d ! glass m or less fissur$1 a numb] ( l>ge lumps be+ accompani$ by a great mass ( small fragm5ts4 ,^! are n[ pick$ ov]1 & all ^? :i* are free f visible imp]fections or :i* c be readily deta*$ f su* imp]fections by ! aid ( a *ipp+ hamm] are put ^u "o side = fur!r treatm5t4 ,! next /ep ( ?is treatm5t consi/s 9 m\ld+ ! r\gh brok5 lump into ! %ape ( plates1 blocks1 or discs accord+ to ! purpose = :i* ! glass may be requir$ by ! optician4 ,! plant us$ = ! m\ld+ process v>ies widely1 b 9 all cases ! op]ation consi/s 9 gradually heat+ ! glass 9 a suitable kiln until x is s(t en\gh to adapt itself to ! %ape ( ! m\ld provid$ = ! purpose4 ,9 "s cases ^! m\lds are made ( fire-clay1 & ! glass is simply all[$ to settle into !m by its own weight2 9 o!r cases iron m\lds are us$1 & ! glass is work$ into !m by ! aid ( g5tle pressure f wood or metal m\ld+ tools4 ,9 yet o!r cases1 p>ticul>ly :]e ! glass is requir$ 9 ! =m ( small ?9 discs or :]e x is to be =m$ into ! approximate %ape ( concave or convex l5ses1 ! aid ( a press is sometimes invok$4 ,9 all cases ! m\ld+ process is foll[$ by ! f9al anneal+1 :i* consi/s 9 cool+ ! glass v gradually f ! r$ heat at :i* x has be5 m\ld$1 d[n to ! ord9>y temp]ature4 ,! l5g? ( "t occupi$ by su* cool+ dep5ds v mu* ^u ! size ( ! object & also ^u ! degree ( ref9em5t to :i* x is necess>y to c>ry ! removal ( small int]nal /ra9s 9 ! glass4 ,= _m purposes x is suffici5t to all[ x to cool d[n naturally 9 a l>ge kiln 9 ! c\rse ( six or eight days4 ,= special purposes1 h[ev]1 :]e p]fect fre$om f d\ble refraction is dem&$1 mu* great] ref9em5ts are requir$1 & special anneal+ kilns1 ^: temp]ature c be accurately regulat$ & ma9ta9$1 are employ$4 ,9 ^! ! anneal+ op]ation c be c>ri$ out s gradually t a rate ( cool+ 9 :i* a fall ( #a ,c4 occupies sev]al h\rs c be ma9ta9$1 s t v p]fectly anneal$ glass c be produc$ ev5 9 discs or blocks ( l>ge size4 ,:5 remov$ f ! anneal+ kiln ! plates or discs ( optical glass are tak5 to a gr9d+ or poli%+ work%op1 :]e c]ta9 ( _! faces or edges are gr\nd & poli%$ 9 su* a way z to p]mit ( ! exam9ation ( ! glass = bubbles1 /ri & o!r defects 9 ! mann] indicat$ 9 ! previ\s *apt]4 ,z ! am\nt ( sort+ t c be done :ile ! glass is /ill 9 r\gh fragm5ts is necess>ily v limit$1 x foll[s t a consid]able proportion ( ! glass :i* has be5 m\ld$ & anneal$ mu/ be reject$ z useless :5 ?us f9ally exam9$4 ,a yield ( p]fect optical glass1 am\nt+ to #aj or at mo/ #bj p] c5t4 ( ! total cont5ts ( ea* pot1 is !re=e all t c be expect$1 & small] yields are by no means infrequ5t--a consid]ation t w s]ve to expla9 ! relatively high price ( optical z comp>$ ) o!r v>ieties ( glass4 ,a consid]ation ( ! v>i\s factors t are involv$ 9 ! production ( a piece ( p]fect optical glass w make x app>5t t ! co/ & difficulty ( its production increases rapidly ) ! weight ( ! piece to be produc$1 s t x is n surpris+ to f9d t ! price ( v l>ge discs ( p]fect optical glass su* z ^? requir$ = l>ge a/ronomical telescopes1 rea*es figures :i* become prohibitive :5 v l>ge sizes are consid]$4 ,?us1 :ile x is q possible to obta9 say #ajj p\nds ( good glass f a s+le melt+ if ! glass is to be us$ 9 ! =m ( pieces n weigh+ m ?an five or six p\nds ea*1 x is only r>ely t a s+le block ( p]fect glass c be f\nd weigh+ #ajj p\nds4 ,9 ! =m] case ! be/ pieces c be pick$1 ! wor/ defects c be elim9at$ by *ipp+ ! r\gh fragm5ts1 & at a lat] /age o!r defective pieces c be cut (f or gr\nd away2 n s :]e a l>ge s+le block is requir$4 ,a s+le f9e ve91 p]haps too small to be visible to ! unaid$ eye1 may be f\nd to run ?r\gh a :ole block 9 su* a way t x _c be remov$ )\t break+ or cutt+ up ! :ole piece1 & x w be se5 t ! frequ5cy ) :i* ?is is liable to occur increases ) ! volume ( ! piece requir$4 ,! difficulties ( re-heat+ & m\ld+ are also increas$ enorm\sly ) ! size ( ! individual pieces ( glass t h to be dealt )1 & :]e v l>ge pieces h to be heat$ & cool$ accid5tal breakage becomes a s]i\s risk4 ,9 view ( ^! difficulties x is n surpris+ to f9d t ! dim5sions ( our a/ronomical refractors appe> to h approa*$ _! limit1 b r are we l$ to admiration ( ! skill & ent]prise t has pu%$ ?is limit s f> z to produce discs ( optical glass measur+ z mu* z "o metre 9 diamet]4 ,,*apt] ,,xiv4 ,,miscellane\s ,,products4 ,! field ( glass-manufacture is s wide & ! numb] & v>iety ( its products s great1 t 9 ! limit$ compass ( ?is volume x is impossible to fully enum]ate !m all2 !re are1 h[ev]1 a c]ta9 numb] ( ^! products :i*1 :ile ( consid]able importance 9 !mselves1 yet d n fall readily "u any ( ! head+s ( ! prec$+ *apt]s4 ,a %ort space w !re=e be devot$ to "s ( ^! 9 ?is place4 ,glass ,tub+4--,a widely-useful =m ( glass is t ( tubes ( all sizes & %apes1 rang+ f ! f9e capill>y tubes us$ 9 ! con/ruction ( !rmomet]s to ! heavy drawn or press$ pipes t h be5 employ$ = dra9age & o!r purposes4 ,! process ( manufacture employ$ v>ies accord+ to ! size & nature ( ! tube t is requir$4 ,?us lamp-*imneys are really a v>iety ( tube1 us$ 9 %ort l5g?s & made ( relatively wide diamet] & ?9 walls4 ,^! are n1 h[ev]1 ord9>ily made 9 ! =m ( long tubes cut into %ort sections1 b--z has already be5 m5tion$--!y are bl[n into m\lds 9 ! =m ( a ?9-wall$ cyl9drical bottle1 ^: neck & bottom are subsequ5tly remov$4 ,by ?is process ! v>i\s =ms ( *imneys = oil-lamps1 hav+ contractions at c]ta9 p>ts ( _! l5g?1 c be readily produc$4 ,! articles m /rictly describ$ z glass tubes are1 h[ev]1 produc$ by a process 9 :i* actual bl[+ plays only a v m9or "p4 ,a ga!r+ ( suitable size is tak5 up on a pipe1 a v small int]ior holl[ space is produc$ by bl[+ into ! pipe1 & !n ! ga!r+ is elongat$ by sw++ ! pipe 9 a suitable mann]4 ,! end ( ! elongat$ ga!r+ fur!/ f ! pipe is !n atta*$ to a rod or 8pontil0 held by a second workman1 & ! two m5 !n proce$ to move ap>t1 draw+ out ! ga!r+ ( glass betwe5 !m4 ,accord+ to ! bore & ?ickness ( wall requir$ 9 ! tube1 ! m5 regulate ! spe$ at :i* !y move ap>t2 ! ?9n] ! tube is to be ! m rapidly !y move1 9 ord] to draw ! glass out to a suffici5t ext5t be=e x h>d5s too mu*4 ,! rate ( draw+ mu/1 ( c\rse1 also be adapt$ to ! nature ( ! glass 9 "q1 & ?is w v>y v widely4 ,= ! production ( ! small] bor$ tubes ! m5 f9d x necess>y to sep>ate at a sm>t trot1 :ile heavy tubes su* z are us$ = gauge-glasses1 are drawn ( h>d glass by a v gradual movem5t4 ,9 "s cases1 ! sett+ ( ! glass1 :5 ! tube has atta9$ ! desir$ ?ickness1 is ha/5$ by ! aid ( an air-bla/1 or--9 m primitive fa%ion--by boys wav+ fans ov] ! hot glass4 ,9 any case1 suitable tr\ghs are provid$ = receiv+ ! tube :5 drawn1 & f ^! ! tube is tak5 to an anneal+ kiln to und]go ?is necess>y op]ation4 ,! glass us$ = ! production ( tub+ v>ies v widely accord+ to ! purpose = :i* ! product is int5d$4 ,almo/ any ( ! m usual v>ieties ( glass c be readily drawn out into tubes1 & ! *oice ( ! k9d ( glass to be employ$ is !re=e left to o!r consid]ations4 ,tub+ requir$ = ! use ( ! lamp-work]1 i4e41 = ! production ( in/rum5ts or o!r articles by ! aid ( ! glass-bl[]'s bl[-pipe1 mu/ h ! capacity ( und]go+ repeat$ cool+ & heat+ )\t %[+ signs ( cry/allisation 7devitrification71 :ile reasonable s(tness 9 ! flame is also requir$4 ,= ?is purpose1 also1 glass conta9+ lead is n admissible1 s9ce ?is w\ld black5 "u ! influ5ce ( ! bl[-pipe flame4 ,soda-lime glasses r ri* 9 alkali are mo/ frequ5tly us$ = ^! purposes2 "o consequ5ce ( _! *emical composition1 h[ev]1 is t su* glass t5ds to und]go decomposition :5 /or$ = any l5g? ( "t1 m especially 9 damp places4 ,frequ5tly ?is decomposition only manife/s itself on heat+ ! glass 9 a flame1 :5 x ei!r flies to pieces or turns dull & r\gh on ! surface4 ,su* glass is sometimes said to h 8devitrifi$10 b ?is is n really ! case2 :at has actually happ5$ is t ! atmosph]ic moi/ure has p5etrat$ = "s little di/ance into ! ?ickness ( ! glass1 probably hydrat+ "s ( ! silica2 on heat+1 ?is moi/ure is driv5 (f1 ) ! result t ei!r a few l>ge cracks1 or innum]able f9e ones1 are =m$4 ,9 ! latt] case ^! d n readily disappe> :5 ! glass is s(t5$ & ! dull1 r\gh surface is left at ! end ( ! op]ation4 ,= purposes :]e ! glass is to be expos$ to high temp]atures1 tub+ made ( s-call$ 8h>d glass0 is employ$4 ,?is is practically a =m ( ,bohemian cry/al glass1 ! *emical composition be+ t ( a pota%-lime glass r ri* 9 lime4 ,to "s ext5t ?is ,bohemian h>d glass has be5 sup]s$$ by ! special 8combu/ion tube0 glass manufactur$ by ,s*ott1 ( ,j5a4 ,?is is a v refractory borosilicate glass conta9+ "s magnesia2 x c]ta9ly )/&s high] temp]atures ?an h>d ,bohemian glass1 & is r less s5sitive to *anges ( temp]ature2 on ! o!r h&1 x has ! inconv5i5t prop]ty ( %[+ a :ite opalesc5ce :5 x has once be5 heat$1 & ?is1 aft] a "t1 r5d]s ! glass completely opaque4 ,= _m purposes1 :]e heat-resi/+ qualities are *iefly requir$1 ord9>y glass has n[ a =midable rival 9 ! %ape ( vitrifi$ silica1 :i* is n[ available z a satisfactory comm]cial product4 ,?is sub/ance (f]s ! great advantage t = mo/ ord9>y purposes x may be reg>d$ z entirely infusible1 s9ce ! int5se heat ( an oxyg5-f$ flame is requir$ to s(t5 or melt ! silica4 ,fur!r1 vitre\s silica has an extremely l[ coeffici5t ( expansion1 & appe>s also to h a r high coeffici5t ( !rmal conductivity4 ,! result is t tubes & o!r articles made ( ?is mat]ial possess an a/oni%+ am\nt ( !rmal endurance 7see ,*apt] ,,ii474 ,a :ite-hot tube or rod ( ?is mat]ial c be plung$ into cold wat] ) impunity1 & no special c>e ne$ be ex]cis$ 9 heat+ or cool+ articles made ( ?is sub/ance1 unless articles ( great size & ?ickness are involv$1 & ev5 ) ^! only little caution is ne$$4 ,! only disadvantages :i* mu/ be balanc$ aga9/ ! great advantages j nam$ lie 9 ! relatively high co/ ( ! articles & 9 _! some:at s5sitive behavi\r to c]ta9 *emical influ5ces4 ,z reg>ds co/1 vitre\s silica is at pres5t available 9 two diff]5t =ms2 9 ! fir/ =m x resembles ord9>y glass v closely 9 appe>ance1 ! %ape & f9i% ( ! tubes & vessels ( ?is k9d hav+ und]gone v great improvem5ts q rec5tly4 ,?is silica glass has1 9 fact1 be5 work$ f molt5 silica 9 a way m or less analog\s to t 9 :i* ord9>y glass is work$1 ! great extra co/ ( ! silica w>e be+ due1 9 "p1 at all ev5ts1 to ! extremely high temp]ature requir$ = melt+ & work+ ?is mat]ial2 ord9>ily1 9 ! production ( ! class ( silica w>e n[ ref]r$ to1 ?is heat is g5]at$ by ! lib]al--& !re=e exp5sive--use ( oxyg5 gas4 ,9 great contra/ to ?is glass-l1 transp>5t silica w>e is ! o!r =m 9 :i* ?is mat]ial is available4 ,?is is a s]ies ( products obta9$ f ! fusion ( silica 9 special =ms ( electric furnace2 9 ?is w>e ! m9ute bubbles s readily =m$ 9 ! fusion ( all =ms ( qu>tz are n ev5 p>tially elim9at$1 & by _! pres5ce--(t5 9 ! =m ( long-drawn-out1 capill>y holl[s--!y imp>t to ?is w>e its v *>act]i/ic milky appe>ance4 ,! price ( ?is product1 :i* is mo/ly us$ 9 ! =m ( tubes1 al?\gh su* articles z bas9s1 crucibles1 & ev5 muffles ( consid]able size are available1 is mu* l[] ?an t ( ! transp>5t v>iety1 be+ 9 fact decid$ly l[] ?an t ( ! be/ porcela92 on ! o!r h&1 ev5 ?is price is consid]ably above t ( ! be/ glass tub+4 ,ap>t f ! "q ( co/1 ! use ( silica w>e is fur!r limit$ by its s5sitiv5ess to all =ms ( basic mat]ials4 ,?us alkal9e solutions _c be all[$ to come into contact ) ?is sub/ance1 s9ce !y attack x vigor\sly1 especially :5 w>m4 ,at high temp]atures all basic mat]ials produce a rapid attack on silica w>e1 ! silica1 9 fact1 behav+ z a /rongly acid body at & above a r$ heat4 ,! attack :i* occurs :5 su* a sub/ance z iron or copp] oxide is all[$ to come into contact ) heat$ vitrifi$ silica is1 9 fact1 s rapid t a tube is completely de/roy$ 9 a few m9utes1 ! =mation ( silicates result+ 9 ! crack+ & dis9tegration ( ! :ole piece4 ,:ile1 !re=e1 silica w>e1 especially 9 its *eap] =ms1 und\bt$ly possesses great advantages & possibilities1 its use mu/ be c>ri$ on ) c>eful ref]5ce to its *emical nature4 ,vitre\s silica1 9 addition to ! uses & advantages j nam$1 has also an int]e/ f ! optical po9t ( view2 ?is arises f ! fact t x is transp>5t to %ort 7ultra-violet7 light waves to :i* all ord9>y v>ieties ( glass are completely opaque4 ,q rec5tly1 ! ,j5a works h produc$ special glasses :i* are m transp>5t to ^! ultra-violet rays ?an ord9>y glass1 b ev5 ^! fall f> %ort ( silica 9 ?is respect4 ,?is prop]ty ( transp>5ce to ultra-violet light is utilis$ 9 two widely diff]5t directions4 ,"o ( ^! is 9 ! production ( ultra-violet light :5 requir$ = m$ical or o!r special purposes2 a mo/ en]getic s\rce ( su* rays is available by ! use ( tubes ( vitrifi$ silica )9 :i* ! m]cury-vap\r arc is produc$4 ,9 ano!r direction ! employm5t ( qu>tz l5ses makes x possible to take advantage ( ! optical prop]ties ( ultra-violet light 9 connection ) microscopy2 = ! purpose ( con/ruct+ a p]fect optical sy/em1 cry/all9e qu>tz w\ld be useless1 s9ce its prop]ty ( d\ble refraction w\ld int]f]e hopelessly ) ! p]=mance ( ! l5ses4 ,?is is n[ ov]come by ! use ( vitre\s silica l5ses1 9 ! case ( ! 8ultra-violet microscope10 z made by ,c>l ,zeiss1 ( ,j5a4 ,s f>1 h[ev]1 x has only be5 possible to produce q small pieces ( vitre\s silica suffici5tly free f bubbles to be us$ = optical purposes4 ,! great difficulty lies n s mu* 9 m]ely melt+ ! qu>tz d[n z 9 free+ x f ! air-bubbles enclos$ )9 x2 ! c\rse usually adopt$ ) glass1 ( rais+ ! temp]ature & all[+ ! bubbles to rise to ! surface1 becomes impossible 9 ?is case1 because ! silica itself beg9s to vap\rise & ev5 to boil vigor\sly at temp]atures n v f> above its melt+ po9t4 ,q rec5tly1 h[ev]1 two ,am]ican work]s h claim$ to be able to ov]come ?is difficulty by ! use ( bo? vacuum & high pressure appli$ at ! e>li] & lat] /ages ( ! fusion process respectively1 s t x may %ortly be possible to produce vitre\s silica 9 l>ge & p]fectly cle> blocks4 ,we h already indicat$ t glass tub+ & rod =m ! basis ^u :i* ! glass-work]1 ) ! aid ( ! bl[-pipe or 8lamp10 fa%ions 8 productions1 :i*1 ( c\rse1 include a great numb] ( sci5tific in/rum5ts & appliances us$ m especially 9 ! field ( *emi/ry4 ,9 ano!r direction also glass tub+ s]ves z a basis = a bran* ( ! glass indu/ry2 ?is is ! manufacture ( c]ta9 classes ( glass beads1 :i* are =m$ by cutt+ up a heat$ glass tube ( suitable diamet] & col\r into %ort1 m or less sph]ical sections4 ,9 "s cases ! col\r ( ! beads is secur$ by us+ glass ( ! desir$ t9t1 b 9 o!r cases ! beads are made ( col\rless glass1 & a col\r+ sub/ance is plac$ 9 ! int]ior ( ! bead4 ,solid glass rods are also employ$ = a v>iety ( purposes2 _! mode ( manufacture is exactly analog\s to t ( tub+1 except t ! ga!r+ is drawn out )\t hav+ fir/ _h a holl[ space produc$ at its c5tre by ! bl[]4 ,9 its mo/ att5uat$ =m glass rod becomes glass ?read or fibre2 ?is is produc$ by draw+ hot glass v rapidly1 ! result+ ?read be+ w\nd on a l>ge :eel4 ,at "o "t ?is mat]ial f\nd consid]able use1 s9ce x 0 f\nd possible to sp9 & weave ! ?9ne/ glass fibres into fabrics :i* c\ld be us$ = dress purposes4 ,x is n1 h[ev]1 to be regrett$ t ?is fa%ion has nei!r ext5d$ nor surviv$1 s9ce x 0 c]ta9ly liable to produce s]i\s injury to heal?4 ,x is a well-kn[n fact t !re are few m injuri\s or ev5 dang]\s sub/ances to be inhal$ into ! human ?roat & lungs ?an f9ely-divid$ glass2 glass fibre1 moreov]1 :5 subject$ to con/ant b5d+ & we>1 is b\nd to und]go frequ5t fracture1 & ! atmosph]e ( a ball-room1 = example1 9 :i* sev]al su* dresses 7 worn w\ld soon be contam9at$ ) innum]able f9e1 %>p p>ticles ( glass :i* w\ld produce an injuri\s effect on ^? inhal+ !m4 ,at ! pres5t "t glass fibre is us$ = little else ?an ! 8glass wool0 requir$ = c]ta9 special purposes 9 *emical laboratories4 ,fus$ qu>tz or silica fibres1 ( extreme t5uity1 b ( relatively v great /r5g?1 are employ$ 9 _m sci5tific in/rum5ts1 :]e _! extreme lightness & p]fect ela/icity & fre$om f :at is kn[n z 8ela/ic fatigue0 r5d]s !m ( v great value4 ,^! fibres are n drawn f a mass ( molt5 silica1 z is done ) glass1 b are produc$ by atta*+ a nail or bolt to a small bead ( fus$ silica produc$ by ! aid ( an oxyg5-f$ bl[pipe2 ! nail or bolt is !n sudd5ly %ot away d[n a long passage or simil> space by means ( a cross-b[1 draw+ a v f9e fibre ( silica ) x2 ! mo/ difficult "p ( ?is op]ation1 h[ev]1 consi/s 9 f9d+ & h&l+ ! fibres ?us produc$4 ,artificial ,gems4--,! fact t pieces ( suitably-col\r$ glass c be made to %[ a sup]ficial1 b sometimes m or less deceptive1 resemblance to preci\s /ones1 has l$ to ! manufacture ( imitation jewels ( all descriptions4 ,! glass us$ = ?is purpose is usually a v d5se fl9t-glass ^: high refractive index facilitates ! imitation :i* is aim$ at4 ,! ext]nal %apes ( gems are1 ( c\rse1 readily imitat$ by cutt+ & gr9d+ ! glass1 :ile ! requisite col\rs are atta9able by means ( ! col\r+ mat]ials describ$ 9 ,*apt] ,,xi4 ,to a casual obs]v] ! diff]5ce 9 sp>kle & brilliance :i* arises f ! diff]5ce betwe5 ! refractive index ( ! heavy fl9t-glass 7ab\t #ah7 & t ( m9]als 7:i* ranges f #ag to #bb7 is n readily app>5t1 b clos] exam9ation w at once reveal ! diff]5ce4 ,! det]m9ation ( ! optical con/ants by means ( a refractomet] w\ld at once reveal ! true "* ( ! imitation1 b an ev5 readi] te/ is t ( h>dness4 ,! d5se fl9t-glass is naturally s(t1 & is readily scrat*$ by mo/ ( ! h>d] m9]als1 :ile ! preci\s /ones1 m p>ticul>ly g>nets1 rubies & diamonds1 are v h>d4 ,if an attempt is made to scrat* an ord9>y %eet ( w9d[-glass1 x w be f\nd t mo/ real preci\s /ones w d s readily1 :ile fl9t-glass imitations w fail to make m ?an a slight m>k1 :i* is m sme> ?an scrat*4 ,! te/ by det]m9+ ! specific gravity is also obvi\sly applicable1 s9ce ! fl9t-glass w readily betray its pres5ce by its high d5sity 7ov] #d74 ,9 q a diff]5t class f ! imitation gems made ( cut fl9t-glass are ! artificial gems1 :i* 9 nature & composition are exact reproductions ( natural gems1 b :i* h be5 produc$ by artificial processes4 ,z f> z ! writ] is aw>e ^! are only f\nd 9 any l>ge numb]s 9 ! case ( ! ruby1 b 9 t case1 at all ev5ts1 x is said t ! production ( ! artificial cry/als is at lea/ z co/ly z ! pur*ase ( ! natural /ones4 ,!re c1 h[ev]1 be v little d\bt t z ! processes ( fusion & cry/allisation become bett] kn[n & und]/ood1 & ! *emi/ry ( silicate m9]als is develop$1 ! artificial production ( m9]al cry/als 91 at all ev5ts1 mod]ate sizes w become increas+ly possible2 x is ev5 to be hop$ t _! production w be s f> p]fect$ z to place _! really valuable prop]ties at ! s]vice ( man4 ,*ill$ ,glass4--,9 all ! processes ( glass manufacture describ$ 9 ! pres5t book1 anneal+ has always play$ an important "p4 ,! glass1 aft] x has und]gone its la/ treatm5t "u ! influ5ce ( heat1 is subject$ to a gradual cool+ process ) ! object ( free+ x f ! int]nal /ra9s :i* x w\ld o!rwise reta91 & :i* w\ld1 ord9>ily1 endang] its exi/5ce & int]f]e ) its use4 ,x is1 h[ev]1 well kn[n t surfaces ( glass subject$ to su* int]nal /ra9s z result 9 a compressive /ress on ! glass ne> ! surface1 are less liable to injury1 & are app>5tly /rong] ?an :5 ! glass is anneal$ & ! /resses are remov$4 ,on ! o!r h&1 glass surfaces "u t5sion are extremely delicate & fragile4 ,9 "s respects1 !re=e1 glass :i* has n be5 anneal$ may appe> to be /rong] ?an ! anneal$ product4 ,! well-kn[n case ( ! ,rup]t's drop is an example ( ?is k9d4 ,rup]t's drops are produc$ by dropp+ molt5 glass into wat]2 !y g5]ally take ! =m ( a m or less sph]ical body hav+ a long tail1 tap]+ (f into a ?read1 atta*$ to x4 ,su* a ,rup]t's drop may be /ruck ) a heavy hamm]1 & w safely resi/ a bl[ t w\ld spl9t] a simil> body made ( anneal$ glass4 ,if1 h[ev]1 ! surface be scrat*$1 or ! tip ( ! tail be brok5 (f1 ! entire 8drop0 breaks up1 sometimes ) a viol5t explosion1 into m9ute fragm5ts4 ,num]\s inv5tors1 among :om ,de la ,ba/ie & ,siem5s figure mo/ conspicu\sly1 h endeav\r$ to utilise ^! prop]ties ( *ill$ glass1 n exactly by endeav\r+ to produce t extreme degree ( int]nal /ra9 :i* is *>act]i/ic ( ! ,rup]t's drop1 b by produc+ :at !y describe z 8temp]$0 glass1 9 :i* ! int]nal /ra9s h be5 r$uc$ by less viol5t cool+ to su* an ext5t z to reta9 "s ( ! advantages ( ! h>d5$1 int]nally /ra9$ condition :ile approximat+ m or less to ! saf] /ate ( anneal$ glass4 ,at "o "t articles ( ?is k9d 7 frequ5tly se5 z curiosities1 su* z tumbl]s t c\ld be dropp$ on ! floor )\t break+1 etc41 b ^! articles g5]ally end$ by receiv+ a slight scrat* or *ip & promptly fall+ into fragm5ts4 ,z a matt] ( fact1 h[ev]1 "s temp]$ glass is actually manufactur$ by ! firm ( ,siem5s at ! pres5t "t = special purposes4 ,de la ,ba/ie's process 0 tri$ 9 ,engl&1 & "s success 0 claim$ = x2 b x is n 9 comm]cial op]ation at ! pres5t "t1 & nev] appe>s to h atta9$ any great importance4 ,massive ,glass4--,en?usia/s = ! ext5sion ( ! use ( glass h endeav\r$ to apply x to a great v>iety ( purposes1 includ+ ! con/ruction ( build+s & ! pav+ ( /reets4 ,9 ! =m] case1 :i* 0 exemplifi$ at ! ,p>is ,exhibition ( #aijj1 advantage 0 tak5 ( ! light-transmitt+ p[] ( ! mat]ial1 b al?\gh ! build+s erect$ ) l>ge blocks ( ca/ glass 7 n displeas+ 9 effect1 ?is use has n f\nd any consid]able ext5sion4 ,= pav+ purposes1 ! h>dness & durability ( glass are ! only useful qualities1 & "h also--al?\gh sev]al trials h be5 made 9 ,france--no signs ( any consid]able application ( ! new products are z yet visible4 ,:at has be5 said above ) ref]5ce to ! injuri\s "* ( glass du/ applies1 fur!r1 to glass pavem5ts1 s9ce _! natural we> w\ld result 9 ! =mation ( consid]able quantities ( ?is du/4 ,! advocates ( glass pav+1 h[ev]1 sugge/ t ! h>dness ( glass w\ld greatly r$uce ! actual am\nt ( we>1 & t consequ5tly ! du/ w\ld be r$uc$ consid]ably4 ,?is is a matt] :i* prolong$ exp]i5ce alone c decide1 b x does n seem obvi\s t glass blocks %\ld we> m sl[ly ?an /one setts made ( good granite1 = example4 ,on ! o!r h&1 ! glass blocks c\ld probably be produc$ m *eaply1 s9ce ! lab\r ( cutt+ to size w\ld be obviat$ by ca/+ ! blocks to ! desir$ dim5sions4 ,wat]-glass1 or silicate ( soda or pota% is p]haps sc>cely to be class$ "u ! head+ ( 8,glass ,manufacture0 at all1 b x be>s a c]ta9 relation%ip to glass 9 sev]al ways4 ,?us "o ( ! modes ( manufactur+ wat]-glass is by ! fusion ( s& & alkali 9 tank furnaces some:at resembl+ ^? us$ = glass production2 ! fus$ silicate1 moreov]1 solidifies z a vitre\s mass1 9 :i* respect x also resembles su* sub/ances z borax1 etc4 ,! uses ( silicate ( soda & pota% are1 h[ev]1 s f> remov$ f ! field ( glass-manufacture t we _c ent] into !m "h4 ,9 conclud+ ?is *apt]1 we wi% to describe "o m product ( ! glassworks1 & ?is includes "s ( ! mo/ impressive & spl5did examples ( ! glass-mak]'s art4 ,^! are ! great mirrors & l5ses by ^: aid our ligh?\ses & se>*lights s5d =? _! p[]ful beams ( light4 ,al?\gh ^! objects are call$ 8mirrors0 & 8l5ses10 s9ce !y fulfil ! functions ( su* optical organs1 yet 9 _! nature & mode ( manufacture !y are s f> remov$ f ! glass us$ = ! production ( o!r k9ds ( l5ses t !y c\ld n be includ$ "u ! head+ ( 8optical glass40 ,! *>act]i/ic feature 9 ! manufacture ( optical glass is ! mann] 9 :i* ea* sep>ate pot or melt+ is all[$ to cool d[n & to break up into irregul> fragm5ts :i* are subsequ5tly m\ld$ to ! desir$ %ape4 ,7 x attempt$ to manufacture ! l>ge glass bodies requir$ = ligh?\se purposes 9 ?is mann]1 ! co/ w\ld approximate to t ( ! l>ge discs us$ = telescope objectives1 & ?is w\ld ( c\rse be entirely prohibitive4 ,! requirem5ts z reg>ds col\r1 homog5eity & fre$om f o!r defects1 :i* mu/ be met 9 ligh?\se l5ses1 are fur!r n ne>ly s /r+5t z ^? :i* are ess5tial 9 ord9>y optical "w ( good quality4 ,! reason = ?is diff]5ce arises f ! fact t ligh?\se l5ses & se>*light mirrors are us$ m]ely to imp>t a desir$ direction to a beam ( light1 & n = ! purpose ( produc+ %>ply-def9$ images2 slight irregul>ities 9 ! glass are !re=e n ( su* s]i\s importance4 ,ligh?\se glass c !re=e be produc$ by r less elaborate means2 al?\gh e c>e is tak5 to make ! glass z p]fect z possible1 x is br\ght into approximately ! desir$ =m by ca/+ ! molt5 glass 9 iron m\lds ( ! prop] %ape4 ,:5 remov$ f ^! m\lds & anneal$1 ! glass is fix$ on l>ge revolv+ tables & gr\nd & poli%$ to ! f9al %ape ( l5ses & annul> l5s-segm5ts z requir$ = ! v>i\s types ( ,fresnel ligh?\se l5ses4 ,9 ?is way complete r+s1 =m+ annul> l5ses1 are produc$ up to #dh in*es diamet]4 ,r+s ( l>g] size are usually built up ( a numb] ( segm5ts1 & ^! built-up r+s sometimes h a radius z l>ge z #g feet4 ,= ! majority ( ligh?\se l5ses1 x %\ld be add$1 a h>d soda-lime glass hav+ a refractive index ( #aej to #aeb is us$1 b = special purposes a d5se fl9t-glass hav+ a refractive index ( #afc is employ$4 ,mirrors = se>*light purposes are ( v v>i$ =ms & sizes1 ! %ape dep5d+ l>gely ^u ! p>ticul> =m ( beam :i* !y are design$ to project4 ,= _m purposes a p>abolic =m is requir$1 :ile 9 o!rs1 :]e a flat1 fan-%ap$ beam is to be produc$1 a =m hav+ an elliptical section 9 a horizontal plane & a p>abolic section 9 ! v]tical plane is requir$4 ,9 mo/ cases ^! mirrors are produc$ by b5d+ plates ( glass1 previ\sly rais$ to ! necess>y degree ( heat1 ov] suitably %ap$ m\lds1 ! surface be+ subsequ5tly re-poli%$ to remove any r\ghness result+ f ! b5d+ process4 ,ano!r type ( mirrors is t kn[n z 8,mang910 :i* has two sph]ical surfaces plac$ ecc5trically 9 su* a way t ! c5tre ( ! mirror is consid]ably ?9n] ?an ! p]iph]y2 9 ?is type ( mirror ! reflect+ action ( ! back surface is modifi$ by ! refract+ action ( ! front surface1 b bo? are sph]ical1 & c !re=e be accurately gr\nd & poli%$ by ! usual me*anical means4 ,su* mirrors are manufactur$ ( s+le pieces ( glass up to #f feet 9 diamet]4 ,,app5dix ,,bibliography4 ,! exi/+ lit]ature ( glass manufacture is s limit$ t a complete bibliography c\ld almo/ be giv5 on a s+le page2 9 ! ,engli% language1 9 p>ticul>1 !re are exce$+ly few books & pap]s on ! subject4 ,! ,fr5* & ,g]man lit]ature ( ! subject is a little m ext5sive4 ,9 giv+ a li/ ( ! works1 & m p>ticul>ly 9 ref]r+ to ^? :i* he has consult$ 9 ! prep>ation ( ! pres5t volume1 ! au?or ?9ks x w be an advantage to indicate _! scope1 &1 to "s ext5t1 :at he believes to be _! value1 9 ord] to save ! /ud5t ! tr\ble ( seek+ out comp>atively inaccessible works only to f9d t !y conta9 little t is ( value = 8 purpose4 ,engli% ,books & ,pap]s on ,glass ,manufacture4 ,! ,pr9ciples ( ,glass ,mak+ 7,george ,bell ,sons74 ,by ,p[ell ,*ance4 ,an elem5t>y book giv+ a cle> & concise acc\nt ( ! old] processes1 m especially 9 connection ) fl9t & plate-glass4 ,glass4 ,articles 9 #i? ,edition ( ,encyclopdia ,britannica4 ,a detail$ acc\nt ( processes1 m or less cov]+ ! entire subject1 b ! processes describ$ are mo/ly obsolete at ! pres5t "t4 ,glass4 ,article 9 ,supplem5t to #i? ,edition ( ,encyclopdia ,britannica4 ,by ,h>ry ,j4 ,p[ell4 ,a brief summ>y ( m rec5t developm5ts4 ,p>ticul>ly valuable 9 ref]5ce to arti/ic ,engli% fl9t-glass4 ,j5a ,glass4 ,by ,hove/adt1 translat$ by ,j4 ,d4 & ,a4 ,ev]ett4 ,conta9s a full acc\nt ( ! sci5tific "w on glass & its practical application1 done 9 connection ) ! ,j5a ,works ( ,s*ott4 ,p>ticul>ly int]e/+ 9 connection ) ! subjects ( ,*apt]s ,i41 ,,ii41 ,,xii41 & ,,xiii4 ,z ! title indicates1 ! book is writt5 f ! ,j5a po9t ( view1 & sc>cely does ju/ice to "w done else:]e4 ,! book has ga9$ consid]ably at ! h&s ( ! translators4 ,"s ,prop]ties ( ,glass4 ,by ,w4 ,ros5ha94 7,transactions ( ! ,optical ,society ( ,london1 #aijc47 ,gives a brief acc\nt ( ! prop]ties ( glass z affect+ its optical uses4 ,possible ,directions ( ,progress 9 ,optical ,glass4 ,by ,w4 ,ros5ha94 7,proce$+s ( ! ,optical ,conv5tion1 ,london1 #aije47 ,has be5 ref]r$ to 9 ! text ( ?is book 7,*apt] ,,xii474 ,catalogue ( ! ,optical ,conv5tion ,exhibition1 ,london1 #aije4 ,conta9s hi/orical & g5]al notices ( optical & ligh?\se glass1 glass-work+ ma*9]y1 etc4 ,glass = ,optical ,in/rum5ts4 ,by ,r4 ,t4 ,glazebrook4 7,cantor ,lectures to ! ,society ( ,arts47 ,gives an acc\nt ( mod]n optical glass manufacture4 ,old ,engli% ,glasses4 ,by ,alb]t ,h>t%orne4 ,gives an acc\nt ( ! hi/ory ( glass-mak+ 9 ,engl&4 ,! ,me?ods ( ,glass ,bl[+4 ,by ,w4 ,%5/one4 ,describes ! manipulation ( glass-bl[+ = exp]im5tal purposes1 i4e41 lamp "w4 ,fr5* ,books on ,glass ,manufacture4 ,guide du ,v]ri]4 ,by ,g4 ,bontemps4 ,a classical "w by "o ( ! greate/ exp]ts ( 8 day4 ,mu* ( ! cont5ts ( ! book is1 h[ev]1 entirely out ( date at ! pres5t "t4 ,! book is int]e/+ z be+ ! "w ( ! man :o introduc$ optical glass manufacture into ,engl&4 ,v]res et ,emaux4 ,by ,l4 ,c(fignal4 ,*iefly ( int]e/ 9 connection ) ! subjects ( ,*apt] ,,viii4 ,le ,v]re et le ,cry/al4 ,by ,j4 ,h5rivaux4 7,p4 ,vicq ,dunod et ,cie41 ,p>is47 ,a l5g?y book pr(usely illu/rat$ & giv+ a great weal? ( detail$ in=mation4 ,! writ] 0 = "s "t ! g5]al manag] ( "o ( ! l>ge/ plate-glass manufactories 9 ,europe2 8 acc\nt ( plate-glass manufacture is1 !re=e1 especially valuable4 ,mu* space 9 ?is book is devot$ to hi/orical & /hetical matt]4 ,la ,v]r]ie au ,,xxieme ,sicle4 ,by ,j4 ,h5rivaux4 7,p>is1 ,r4 ,b]n>d et ,cie41 #aijc47 ,practically a supplem5t to ! prec$+2 "s ( ! processes & products describ$ are1 h[ev]1 n ( a practical nature4 ,*iefly valuable = rec5t developm5ts 9 plate-glass & bottle-glass manufacture4 ,g]man ,books on ,glass ,manufacture4 ,die ,glasfabrikation4 ,by ,r4 ,g]n]4 7,a4 ,h>tleb5's ,v]lag1 ,vi5na & ,leipzig1 #ahig47 ,a concise & cle> acc\nt ( mo/ ( ! m important processes ( glass manufacture4 ,v practical 9 "*4 ,! in=mation giv5 appe>s to be reliable1 al?\gh f> f complete4 ,die ,h]/ellung ,gross] ,glasko]p] & ,die ,be>beitung ,gross] ,glasko]p]4 ,by ,c4 ,wetzel4 7,h>tleb5's ,v]lag1 ,vi5na & ,leipzig1 #aijj & #aija respectively47 ,describes num]\s special processes & appliances devis$ = use 9 connection ) l>ge glass objects4 ,"s ( ^! descriptions1 h[ev]1 appe> to be little m ?an transcripts f pat5t specifications4 ,glasfabrik5 und ,hohlglasfabrikation4 ,by ,r4 ,dralle4 7,leipzig1 ,baumga]tn]1 #ahhf47 ,look$ ^u z a classic 9 ,g]many4 ,gives detail$ plans & draw+s ( entire bottle-works1 includ+ furnaces & all accessories4 ,deals pr9cipally ) bottle manufacture4 ,die ,glasfabrikation4 ,by ,dr4 ,e4 ,ts*eus*n]4 7,weim>1 ,b4 ,h4 ,voigt1 #ahhh47 ,a full detail$ acc\nt ( all processes kn[n at ! "t4 ,! rapid progress ( mod]n practice has1 h[ev]1 already r5d]$ ?is book to "s ext5t obsolete4 ,j5a] ,glas4 ,by ,hove/adt4 ,already ref]r$ to 9 respect ( ! ,engli% translation4 ,d] ,spre*saal4 7,s*midt1 ,weim>47 ,a trade j\rnal devot$ to ! discussion ( te*nical matt]s relat+ to ! glass & c]amic indu/ries4 ,occasionally conta9s articles & ab/racts ( te*nical or sci5tific int]e/ 9 connection ) glass manufacture4 99 99 99 99 99 ,9 addition to ! books & pap]s nam$ 9 ! above li/1 a great numb] ( sci5tific pap]s1 notes1 etc41 are to be f\nd scatt]$ ?r\gh\t ! te*nical & sci5tific publications ( ! _w2 ^? t h prov$ ( real int]e/ & importance h1 h[ev]1 left _! m>k on ! indu/ry1 & w be f\nd describ$ or ref]r$ to 9 connection ) ! v>i\s bran*es ( manufacture describ$ 9 ! pres5t volume or 9 ! books nam$ above4 ,,index ,a4 ,abb1 #h1 #aj1 #baj1 #bah ,absorption ( light 9 glass1 #cb1 #agi ,acid1 action (1 on glass1 #aa boric1 action (1 on glass1 #aa1 #ahf c>bonic1 action (1 on glass1 #ab hydr(luoric1 action (1 on glass1 #ab phosphoric1 action (1 on glass1 #aa ,air1 compress$1 #ia1 #aje1 #aag ,alkali *lorides1 use (1 9 glass manufacture1 #da cont5t ( hygroscopic glass1 #f metals1 #ahd nitrates1 #dd1 #gh s\rces (1 #dj ,alkal9e liquids1 action (1 on glass1 #aa ,alum9ium1 #ea1 #ahf ,ammonia soda1 #da ,ana/igmatic photographic l5ses1 #bac ,anci5t w9d[s1 col\rs (1 #af1 #bjb ,anneal+ bottles1 #ajc kiln1 #ajc = optical glass1 #bce = plate glass1 #ace = roll$ plate glass1 #abg ,an?racite coal1 #db1 #ec1 #gi ,antimony1 #ahh ,apo*romatic objectives1 #bac ,ars5ic1 #eb1 #gh1 #aje1 #aag1 #ahh ,artificial gems1 #bdf ,au]ba*1 #bb ,av5tur9e1 #ahe ,b4 ,bact]ia1 action (1 on glass1 #ac ,b>ium comp\nds1 #dg1 #ahf cr[n glass1 #bab glass1 #g ,b>ytes1 #dh ,bases o!r ?an alkalies1 s\rces (1 #de ,beads1 #bdd ,behavi\r1 *emical1 ( glass1 #f ,b5d+ plate glass1 #add ,bevell+1 #ade ,black a%1 #da ,bli/]s 9 %eet glass1 #afj1 #afh ,blocks1 fire-clay1 #eh tank1 #ei ,bl[]1 %eet glass1 #aeh ,bl[]'s *air1 #aaa ,bl[+ glass1 #hi holes1 #ia1 #afa1 #ahi %eet glass1 #afa ,bl[n glass1 decoration (1 #aad plate glass1 #aga ,bohemian glass1 #aji1 #bdj ,boil+ up1 #ha ,bottles1 anneal+ (1 #ajc bl[+1 improvem5ts 91 #ii ma*9es1 #ajj col\r (1 #if manufacture1 furnace =1 #ig m\lds = bl[+1 #ih production (1 by h&1 #ih raw mat]ials =1 #ie /r5g? (1 #ah ,boric acid1 #aa ,boron1 #ahf ,boro-silicate cr[n1 #bab ,b\*]'s bottle-bl[+ ma*9e1 #aja ,bricks1 fire-clay1 #eh silica1 #fj ,bubbles 9 optical glass1 #bcj removal (1 #ha ,burn+1 pots1 #eh ,c4 ,cadmium1 #ahf ,calcium c>bonate1 #df oxide1 #de1 #ahf sulphate1 #dg ,c>bon1 #ec1 #gi1 #ahf ,c>bonate ( soda1 #da ,c>bonic acid1 action (1 on glass1 #ab ,c>boys1 bl[+ (1 #ajd ,ca/+ plate glass1 #acb ,*air1 glass-bl[]'s1 #aaa ,*alk1 #df ,*amotte1 #eg ,*ance1 #baa ,*>coal1 #db1 #eh1 #gi ,*>g+ furnaces1 #ge ,*emical behavi\r ( glass1 #f composition ( glass1 #e ( optical glass1 #bag reactions dur+ fusion1 #gf ,*ill$ glass1 #bdg ,*imneys1 gaslight1 #bc lamp1 #bch ,*romium1 col\r+ effect (1 #aij ,clean+ ( l5ses1 #bbj ,coal1 an?racite1 #db1 #ec1 #gi ,cobalt1 col\r+ effect (1 #aig ,coke1 #db1 #ec1 #gi ,col\r ( anci5t w9d[s1 #af glass1 #cb !ory (1 #aha optical glass1 #bjh %eet glass1 #afg ,col\r$ bl[n glass1 #aac glass1 #agh te*nical uses (1 #bjc ,combu/ion tub+1 #g1 #bda ,compress$ air = glass bl[+1 #ia1 #aje1 #aag ,conductivity1 electrical1 ( glass1 #cj !rmal1 ( glass1 #bd1 #bi ,copp]1 col\r+ effect (1 #ahd ruby1 #ahd1 #ahh1 #aih ,corrosion ( glass1 #aa ,cov]$ pots1 #ef1 #aji ,cr[n1 boro-silicate1 #bai glass1 #age1 #baa h>d1 #bab1 #bai s(t1 #bab telescope1 #bae ,cr[ns1 furnace1 #fj ,crucibles1 manufacture (1 #ef = glass melt+1 #ed ,cru%+ /r5g? ( glass1 #ai ,cryolite1 #eb ,cry/allisation ( glass1 #c ,cry/als1 m9]al1 #bah ,cullet1 #gd = optical glass1 #bbd ,cutt+ roll$ plate glass1 #abh ,cyl9d]s1 %eet glass1 #afa1 #aga ,d4 ,decol\risation ( glass1 #eb1 #ahh1 #aij1 #aic1 #aig ,decoration ( bl[n glass1 #aad ,defects 9 roll$ plate glass1 #abi %eet glass1 #aff ,def9ition ( glass1 #a ,de la ,ba/ie1 #bdh ,devitrification1 #c1 #aa ,diamond1 refractive index (1 #baf ,dimm+ ( glass surfaces1 #ab ,d9as bricks1 #fa ,dipp+ ( %eet glass1 #aff ,disp]sion ( optical glass1 #bji p>tial1 #bad ,d\ble refraction 9 optical glass1 #bba roll+ ma*9e1 #acj ,draw+ tubes1 #bci ,ductility ( glass1 #bj ,durability ( glass1 te/s =1 #ad ,du/1 action (1 on l5ses1 #bbj glass1 #bde ,e4 ,ela/icity ( glass1 #bj1 #bd ,electrical prop]ties ( glass1 #bi ,ep9al1 #ci ,et*+ ( glass1 #ab ,expansion1 coeffici5t ( !rmal1 #bd1 #be ,f4 ,felsp>1 #dj1 #dd ,fibres1 glass1 #bde silica1 #bde ,figur$ roll$ plate glass1 #hg1 #acj cutt+ (1 #aca ,f+]-m>ks on l5ses1 #bai ,f9+ ( glass1 #ha optical glass1 #bbi ,fire-clay1 action (1 on glass1 #f = pots1 #ee wett+ up1 #eg ,fire-poli%1 #aag ,fla%$ glass1 #be1 #aii ,fl9t1 #dj boro-silicate1 #bab d5se1 #bab1 #bdf d5se/1 #bab extra d5se1 #bab glass1 #g1 #di1 #gh1 #ajh1 #baa light1 #bab soda1 #bab telescope1 #bae ,fluorite1 refractive index (1 #baf ,fonta9ebleau1 #ch ,f\nd+ ( optical glass1 #bbg ,f\rcault process1 #agd ,fresnel1 #bea ,furnace cr[ns1 #fj gas1 #fc ,furnaces = bottle manufacture1 #ig glass melt+1 #ed1 #fb optical glass1 #bbe plate glass1 #acc roll$ plate glass1 #abb %eet glass1 #aea1 #agj ports1 #fg recup]ative1 #ff1 #aef reg5]ative1 #ff1 #aee tank1 #ei1 #fi economy (1 #gb ,fusion1 process (1 #gc temp]ature ( glass1 #e ,freez+ ( glass1 #b ,g4 ,gaslight1 *imneys =1 #bc ,gas produc]s1 #fb1 #fd ,ga!r]1 #aeh ,ga!r+ ( glass1 #he1 #hh1 #aeh ,gauge tubes1 #aj1 #ah1 #bc1 #bf ,gems1 artificial1 #bdf ,gho/s1 photographic1 #af ,glaub]'s salt1 #dc ,gold1 col\r+ effect (1 #ahe ,gr9d+ plate glass1 #acg ,gypsum1 #dg ,h4 ,h>d5$ glass1 #bj ,h>dness ( glass1 #ba te/s =1 #bb ,heavy sp>1 #dh ,h5rivaux1 #ai ,h]tz1 #bb ,hock-bottle col\r1 #aie ,hoh5bocka1 #ch ,holl[ glass-w>e1 #ajh ,horse-%oe flame1 #fi ,hydr(luoric acid1 action (1 on glass1 #ab ,hygroscopic glass1 alkali cont5t (1 #f ,i4 ,ind5tation modulus1 #bb ,index1 refractive1 #baf ,insulat+ prop]ties ( glass1 #bi ,iron1 #if col\r+ effect (1 #aif oxidation (1 9 glass1 #aie ,irregul>ities caus$ by roll+1 #hf ,j4 ,j5a1 #g1 #aj1 #ad1 #bf1 #bi1 #bjc1 #baj1 #bac1 #bda ,k4 ,kelp1 #dj ,k[alski1 #ai ,l4 ,laboratory w>e1 #aj1 #bc ,ladl+ glass1 #he roll$ plate glass1 #abd ,lagre1 #aff ,lamp-*imneys1 #aaj1 #bch ,lamp-"w1 #bdj1 #bdd ,l>ge vessels1 production (1 #aje ,lead1 #di1 #ahc1 #ahh ,le> = roll$ plate glass1 #abg %eet glass1 #afe ,leighton1 #ci ,l5ses1 clean+ (1 #bbj f+]-m>ks on1 #bbj press+ small1 #id ,light1 action (1 on glass1 #ae ,ligh?\se glass1 #agh1 #bej ,lime1 slak$1 #de ,lime-/one1 #df ,limit$ range ( vitre\s bodies1 #d ,lippe1 #ch ,lynn1 #ci ,m4 ,ma*9es1 bevell+1 #ade d\ble roll+1 #acj gr9d+1 #aci poli%+1 #ada ,magnesia1 #dh1 #ahf ,manganese1 #ae1 #eb1 #hj ,mang9 mirrors1 #beb ,m>v]1 #aaa ,massive glass1 #bdi ,me*anical prop]ties ( glass1 #ah ,metal1 atta*m5t (1 to glass1 #bf ,m9]als1 cry/all9e1 #bag ,mirrors1 #ade se>*light1 #bea ,mix+ ( mat]ials1 #gc ,m\lds = glass-bl[+1 #ij1 #aaj1 #aaf press$ glass1 #aai ,muffl$ glass1 #agb ,muranese glass1 #abc ,n4 ,nickel1 #if col\r+ effect (1 #aig /eel1 #bg1 #adh ,nitrates1 alkali1 #dd1 #gh ,o4 ,objectives1 apo*romatic1 #bac telescope1 #bah ,opal glass1 #de1 #eb1 #ahf ,opaque plate glass1 #adf ,op5 pots1 #ef ,optical glass1 anneal+1 #bce *emical composition (1 #bag cool+ (1 #bcc co/ (1 #bcg f9+1 #bbi f\nd+1 #bbg furnaces =1 #bbe h>dness (1 #bbj m\ld+1 #bce press+1 #ic range (1 #baf raw mat]ials =1 #bbc sort+1 #bce /ability (1 #bai /ra9 91 #bba /irr+1 #bca yield (1 #bcf prop]ties ( glass1 #bje ,p4 ,pa9t+ on glass1 #bja ,p>ason1 #ajb ,pat5t plate glass1 #aga ,pav+ /ones1 glass1 #bdi ,pe>l a%1 #dc ,phosphoric acid1 #aa ,phosphorus1 #ahh ,photographic gho/s1 #af l5ses1 ana/igmatic1 #bac col\r (1 #bji ,pipe1 glass-mak]'s1 #hi %eet-bl[]'s1 #aeh w>m]1 #aeh ,plate glass1 anneal+ kiln =1 #ace b5d+ (1 #add bl[n1 #aga ca/+1 #acb col\r (1 #cc figur$ roll$1 #hg flatness (1 #acd furnaces =1 #acc gr9d+ ma*9es1 #aci (1 #acg mirrors1 #ade opaque1 #adf poli%+ ma*9es1 #ada poli%+ (1 #acg raw mat]ials =1 #acb roll$1 #hf1 #abc silv]+1 #adf sizes (1 #adc /r5g? (1 #ae /ri 91 #adc wir$1 #bg1 #adg ,plat9um1 #bg ,poli%+1 !ory (1 #ada ,pontil1 #ih1 #agf1 #bci ,pota%1 #dc ,potato1 use (1 9 glass melt+1 #ha ,ports1 furnace1 #fg ,pots1 burn+ (1 #eh cov]$1 #ef dry+ (1 #eh = fl9t glass1 #aji optical glass1 #bbf manufacture (1 #ef op51 #ef ,p\r+ ( glass1 #he1 #hg ,press$ glass1 #ib1 #aah composition (1 #abj ,presses = glass1 #aai ,pro(s1 #hb1 #bca ,purity ( mat]ials1 #cf ,q4 ,qu>tz1 #dj ,r4 ,range1 limit$1 ( vitre\s bodies1 #d ,recup]ative furnaces1 #ff1 #aef ,r$ lead1 #di ,refraction1 d\ble1 9 optical glass1 #bba ( light 9 optical glass1 #bji ,refractive index1 #baf ,reg5]ative furnace1 #ff1 #aee ,rei*san/alt1 #aj ,resi/ance to cry/allisation ( glass1 #d ,r+s = ligh?\se l5ses1 #bea ,rod1 glass1 #bde ,roll$ plate glass1 #hf1 #abc anneal+1 #abg cutt+1 #abh defects (1 #abi figur$1 #acj furnaces1 #abc ladl+1 #abd raw mat]ials =1 #abd roll+1 #abf sort+1 #abi surface (1 #abb ,roll+ ( glass1 #hf ,rubies1 artificial1 #bdg ,ruby1 copp]1 #ahd1 #ahh1 #aih fla%$1 #ahd gold1 #ahe ,rup]t's drops1 #bdh ,s4 ,salt-cake1 #cg1 #db1 #gi1 #ahi ,s&1 #ch ,s&/one1 #ci ,s*ott1 #h1 #ai1 #bjc1 #bac1 #bda ,scrat*es on %eet glass1 #afi ,se>*lights1 #bej ,se$ 9 %eet glass1 #afg ,sel5ium1 col\r+ effect (1 #aij ,%eet glass1 #gj bli/]s 91 #afj1 #afh bl[+1 #afa col\r (1 #cc1 #afg comp>$ ) plate1 #adi cyl9d]s1 #afa1 #aga defects (1 #aff dipp+1 #aff flatt5+1 #afe furnaces1 #aea1 #agj le>1 #afe me*anical production (1 #agc raw mat]ials =1 #aej sort+1 #aff splitt+1 #afd /r5g? (1 #ah ,si$5topf1 #ahb ,siege blocks1 #ei ,siem5s1 #bdh ,siev]t1 #ib1 #aje1 #aag1 #agb processes1 #aje1 #aag ,signal glasses1 #bjc ,silica bricks1 #fa glass1 #e1 #bf1 #bda s\rces (1 #cg ,silicon1 col\r+ effect (1 #ahg ,silv]1 col\r+ effect (1 #ahe ,silv]+ plate glass1 #adf ,sizes ( plate glass1 #adb ,soda a%1 #da c>bonate1 #da sulphate1 #cg1 #db1 #gi sulphide1 #hj sulphite1 #gi ,solidification ( glass1 #a ,solutions1 analogy (1 ) glass1 #bjf ,sort+ roll$ plate glass1 #abi ,specific heat ( glass1 #be1 #bi inductive capacity ( glass1 #bi ,/a9s1 col\r$1 #bjj ,/assfur?1 #dd ,/ones 9 roll$ plate glass1 #abi %eet glass1 #afg ,/orage ( mat]ials1 #cg ,/ra9 9 optical glass1 #bba ,/r5g? ( glass1 #ai ,/ri 9 col\r$ glass1 #bjc optical glass1 #bjf1 #bbg plate glass1 #adc te/+ app>atus1 #bjg ,/r+ 9 %eet glass1 #afh ,/rontium1 #hf ,/ructure ( glass1 #a ,sulphur1 col\r+ effect (1 #ahi ,surfaces1 *emical behavi\r ( glass1 #h1 #aj ,szigmondi1 #ahb ,t4 ,table1 roll+1 #abf ,tank blocks1 #ei furnaces1 #ei1 #fi economy (1 #gb = %eet glass1 #aeb ,telescope objectives1 #bac ,temp]ature ( fusion ( glass1 #e ,temp]$ glass1 #bj1 #bdh ,t5sile /r5g? ( glass1 #ai ,?allium1 #ahc1 #ahh ,!ory ( col\rs 9 glass1 #aha poli%+1 #ada ,!rmal endurance ( glass1 #bc prop]ties ( glass1 #bc ,!rmomet] glass1 #g1 #h1 #bh ,t91 col\r+ effect (1 #ahg ,tonnelot1 #g ,transp>5cy ( glass1 #ca optical glass1 #bjh ,trautw9e1 #ai ,tub+1 #bch combu/ion1 #g draw+ (1 #bci ,tumbl]s1 #aaa ,u4 ,ultra-violet microscope1 #bdc ,v4 ,vanadium1 col\r+ effect (1 #ahi ,ve9s 9 optical glass1 #bjf1 #bbg ,w4 ,wat]1 action (1 on glass1 #aj glass1 #bej ,wett+ up clay1 #eg ,w9kelmann1 #ai ,wir$ plate glass1 #bg1 #adg ,)]ite1 #dh ,wool1 glass1 #bde ,y4 ,"y's modulus1 #bj ,z4 ,zaffre1 #aig ,zeiss1 #bac1 #bdd ,z9c1 col\r+ effect (1 #di1 #ahf ,zs*imm]1 #ad ,,bradbury1 ,,agnew1 ,,co4 ,,ld41 ,,pr9t]s1 ,,london ,,& ,,tonbridge4 ,d4 ,,van ,,no/r& ,,company ,publi% ! foll[+ ,catalogues :i* w be s5t gratis on ,application4444 ,,*emical4 #add ,page ,alphabetical & ,classifi$ ,li/ ( ,books on ,*emi/ry1 ,*emical ,te*nology & ,physics4 ,arrang$ by subjects & au?ors4 ,,electrical4 #aab ,page ,classifi$ ,catalogue ( ,electrical ,books4 ,index$4 #h page li/ ( ,electrical ,books issu$ 9 #aijg4 ,,te*nical4 #abb ,page ,li/ arrang$ by ,au?ors4 #dh ,page ,li/ ( ,sci5tific ,books rec5tly issu$ & 9 prep>ation4 #h ,page ,supplem5tal ,li/ ( ,books on ,manufactures & ,indu/ries4 #h ,page ,li/ ( ,books j issu$4 ,,mon?ly ,,record4 #af ,page ,mon?ly ,record ( ,sci5tific ,lit]ature ,s5t regul>ly to any address1 on reque/4 #bc ,murray & #bg ,w>r5 ,/reets1 ,new ,york4 ,d4 ,van ,no/r& ,company ,ann\nce ! e>ly issue ( ! ,,we/m9/] ,,s]ies4 #hvo1 clo?1 fully illu/rat$1 ,ea*1 #b4jj net4 ,mu* ( ! in=mation =?com+ 9 ^! volumes is ei!r n available to ! g5]al public1 or if available1 is widely scatt]$4 ,^! volumes w be issu$ at %ort int]vals4 ,,n[ ,,ready4 ,,india-,,rubb] ,,& ,,its ,,manufacture1 ) ,*apt]s on ,gutta-,p]*a & ,balata4 ,by ,h4 ,l4 ,t]ry1 ,f4,i4,c41 ,assoc4 ,in/4 ,m4,m4 ,,electric ,,p[] ,,& ,,traction4 ,by ,f4 ,h4 ,davies1 ,a4,m4,i4,e4,e4 ,,liquid ,,& ,,gase\s ,,fuels1 ,,& ,,! ,,"p ,,!y play 9 ,mod]n ,p[] ,production4 ,by ,pr(essor ,vivian ,b4 ,lewes1 ,f4,i4,c41 ,f4,c4,s4 ,,coal4 ,by ,james ,tonge1 ,m4,i4,m4,e41 ,f4,g4,s41 etc4 7,lectur] on ,m9+ at ,victoria ,univ]sity1 ,man*e/]74 ,,! ,,book3 ,its ,hi/ory & ,developm5t4 ,by ,cyril ,dav5port1 ,v4,d41 ,f4,s4,a4 ,,iron ,,& ,,/eel4 ,by ,j4 ,h4 ,/ansbie1 ,b4,sc41 ,f4,i4,c4 ,,t[n ,,gas ,,= ,,light+ ,,& ,,heat+4 ,by ,w4 ,h4 ,y4 ,webb]1 ,c4 ,e4 ,,glass4 ,by ,walt] ,ros5ha91 ,sup]9t5d5t ( ! ,dep>tm5t ( ,metallurgy 9 ! ,national ,physical ,laboratory1 late ,sci5tific ,advis] 9 ! ,glass ,works ( ,messrs4 ,*ance ,bros4 ,co4 ,,9 ,,prep>ation4 ,,pat5ts4 ,trade ,m>ks & ,designs4 ,by ,k5ne? ,r4 ,swan 7,oxon471 ( ! ,inn] ,temple1 ,b>ri/]-at-,law4 ,,! ,,manufacture ,,( ,,pap]4 ,by ,r4 ,w4 ,s9dall1 ,f4,c4,s4 ,,wood ,,pulp ,,& ,,its ,,applications4 ,by ,c4 ,f4 ,cross1 ,e4 ,j4 ,bevan1 & ,r4 ,w4 ,s9dall4 ,,/eam ,,eng9es4 ,by ,j4 ,t4 ,rossit]1 ,m4,i4,e4,e41 ,a4,m4,i4,m4,e4 ,,preci\s ,,/ones4 ,) a ,*apt] on ,artificial ,/ones4 ,by ,w4 ,good*ild1 ,m4,b41 ,b4,*4 ,,electric ,,lamps4 ,by ,maurice ,solomon1 ,a4,c4,g4,i41 ,a4,m4,i4,e4,e4 ,,/eam ,,locomotives4 ,by ,vaughan ,p5dr$1 ,m4,i4,me*4,e4 ,,gold ,,& ,,preci\s ,,metals4 ,by ,?omas ,k4 ,rose1 ,d4,sc41 ( ! ,royal ,m9t4 ,,electro-,,metallurgy4 ,by ,j4 ,b4 ,c4 ,k]%aw1 ,f4,i4,c4 ,,photography4 ,by ,alfr$ ,watk9s1 ,presid5t-,elect ( ! ,photographic ,conv5tion1 #aijg4 ,,comm]cial ,,pa9ts ,,& ,,pa9t+4 ,by ,a ,s4 ,j5n+s1 ,hon4 ,consult+ ,exam9]1 ,city & ,guilds ( ,london ,in/itute4 ,,brew+ ,,& ,,di/ill+4 ,by ,james ,grant1 ,f4,s4,c4 ,publi%]s & ,booksell]s1 #bc ,murray & #bg ,w>r5 ,/reets1 ,,new ,,york4 ,transcrib]'s ,notes ,punctuation1 hyph5ation1 & spell+ 7 made consi/5t :5 a pr$om9ant pref]5ce 0 f\nd 9 ?is book2 o!rwise !y 7 n *ang$4 ,simple typographical errors 7 correct$2 occasional unbalanc$ quotation m>ks reta9$4 ,ambigu\s hyph5s at ! ends ( l9es 7 reta9$4 ,! appe>ance ( ! ,table ( ,cont5ts has be5 alt]$ slightly4 ,index n *eck$ = prop] alphabetization or correct page ref]5ces4 ,9 ! ,index1 x 0 uncle> to ! ,transcrib] :e!r "s ( ! ind5tations indicat$ sub-entries or impli$ ditto m>ks1 s ! ind5tations h be5 treat$ "h z multiple levels ( sub-entries4