Theglasstubebeingrevolvedonitscentre，theindexissettothenumberofhalfsecondsrequired，andthesandrunningdown，therequiredtimeismarkedwithoutthepossibilityoferror。
Inpracticeitwillbefoundtobeafarmoreconvenientinstrumentforthepurposethaneitheraclockorasecondswatch，andisapplicablebothforthecameraandmercurybox。\"
Iftheartistfindsitdesirableornecessarytotaketheobjecttobecopiedinitsrightposition，thatisreversetheimageonthespectrum，hecandosobyattachingamirror（whichmaybehadofMr。Anthony，orMr。Roach）tothecameratube，atanangleofforty-fivedegrees。
If，aftertakingtheplatefromthecamera，itbeexamined，nopicturewillyetbevisible，butthisisbroughtaboutbytheFOURTHPROCESS。——BringingoutthePicture，orrenderingitVisible。——
Wenowcometotheuseofthemercurybath，Fig。11。Tothebathathermometerisattached，toindicatetheproperdegreeofbeatrequired，whichshouldneverberaisedabove170deg。Fahrenheit。Theplatemaybeputintooneoftheframes（seeFig。11，）overthemercury，facedownwards，andexaminedfromtimetotime，bysimplyraisingitwiththefingers，orapairofplyers。Thisoperation，aswellastheothers，shouldtakeplaceinthedarkcloset。
[hipho_26。gif]
Sometimes，topreventthenecessityofraisingtheplate，anadditionalcoverortopismadeuseof。Itconsistsofaboxfittedcloselytotheinnerrimofthebath，andhavinganinclinedtop（a，Fig。27。）Thetopiscutthroughandfittedwithframesforeachsizeofplate，likethosealreadydescribed，andinthebackisapieceofglass（b，）throughwhichtoviewtheprogressofmercurialization，andanadditionalpiece（c，）ononeside，coloredyellow，toadmitthelight。
Theoutlineonlyofthetopisheregiven，inordertoshoweveryportionofitatoneview。
Thepicture，beingfullydeveloped，isnowtakenoutandexamined;
itmustnot，however，beexposedtotoostrongalight。
Ifanyglaringdefectsbeperceived，itisbetternottoproceedwithit，butplaceitononesidetobere-polished;if，onthecontrary，itappearsperfect，youmayadvancetotheFIFTHOPERATION。——FixingtheImagesothatthelightcannolongeractuponit。——Thefollowingarticlesarerequiredforthispurpose：
Twoorthreeporcelainorglassdishes，inform，somethinglikefig。24。
Aplatesupport，fig。25。Few，Ibelieve，nowmakeuseofthis，althoughitisaveryconvenientarticle。
HyposulphiteofSoda，ApairofPlyers。
InEurope，theyalsouseadryingapparatus，Fig。27，butthis，liketheplatesupport，[hipho_27。gif]
isamatteroflittleconsequence，andmaybedispensedwith。
Iwill，however，describeit，forthebenefitofthosewhomaywishtouseit。
Avesselmadeofcopperorbrass，tinnedinside，andlargeenoughtotakeinthelargestplate，butnotmorethanhalfaninchwide，isthemostconvenient。Itmustbekeptperfectlyclean。
Hotdistilledwaterispouredintoit，andthetemperaturekeptupbyaspiritlamp。
HyposulphiteofSoda。——Havingmadeasolutionofhyposulphiteofsoda，andwellfilteredit——thestrengthisimmaterial;
abouthalfanounceofthesalttoapintofdistilledwaterissufficient——pouritintooneoftheporcelaindishes，putintoanotherplain，andintoathirddistilledwater。
Immersetheplatewithitsfacedownwardsintothehyposulphite，andthewholeofthesensitiveisremoved，andthelighthasnofartheractionuponit;itisthentoberemovedfromthehyposulphiteandplungedintotheplainwater，orplaceduponthesupport，fig。25，andthewaterpouredoverit。
Itisthenwashedinasimilarmannerwiththedistilledwaterandwellexamined，toseethatnottheslightestparticleofdustrestsonthesuface。Thenextstepistodryit。
Thismaybereadilyaccomplishedbyholdingtheplatewithyourplyers，andpouringdistilledwateroverit——ifitishot，somuchthebetter。
Applythespiritlamptotheback，atthecornerheldbytheplyers，atthesametimefacilitatingtheoperationwiththebreath;
passthelampgraduallydownwards，finishingattheextremecorner。
Thelastdropmaynowberemovedbyalittlebibulouspaper。
Asingledrop，even，ofdistilledwaterallowedtodryonanypartofthesurface，iscertaintoleaveastainwhichnoafterprocesscanremove。
Toillustratethenecessityforhavingperfectlycleanwater，andfreefromallforeignmatter——onlytobeavoidedbyusingthatwhichisdistilled——
intheseprocesses，Iwillrelatealittleanecdote。
Anoperatorinthiscity（NewYork）frequentlymadecomplainttome，thathisplateswereoccasionallyverybad;comingoutalloverinlittleblackandwhitespotsandspoilingmanyverygoodpictures，regrettingatthesametimethatperfectplateswerenotmade，forhehadlostmanycustomersinconsequenceofthesedefects。
Thesecomplaintsbeingsomewhatperiodical，Isuggestedthatthefaultmightbeinthehyposulphite，orchlorideofgoldsolutions，orparticlesofdustfloatingaboutintheroom，andnotintheplate。
Afewdaysafterhestated，thathisplateshavingservedhimagaininthesameway，heprocuredafreshsupplyofhyposulphiteofsodaandchlorideofgold，butafterapplyingthemtheresultwasnobetter。
Hethen，bymyadvice，thoroughlycleanedhiswashdishes，bottlesandwaterpail，madefreshsolutionsandhadnofurthertrouble，becomingsatisfiedthattheplatessufferedanundueshareofcensure。
SIXTHPROCESS。——GildingthePicture。——ThisisanimprovementthehonorofwhichisduetoM。Figeau，andmaytakeplaceeitherbeforethedryingprocess，oratanysubsequentperiod;butitimprovesthepicturesomateriallythatitshouldneverbeneglected。
Thearticlesnecessaryforgildingare——
APairofPlyars;oraGildingStand（seefig。19）andChlorideofGold;
orHyposulphiteofGold。
ThelatterisimportedbyMr。E。Anthony，205Broadway，NewYork，andisdecidedlythebestarticleforthepurpose。
Onebottlesimplydissolvedinaquartofwaterwillmakeaverystrongsolution，andgivesarichnesstothepictureimpossibletobeobtainedfromthechlorideofgold。
Theprocessispreciselysimilartothatdescribedbelowforchlorideofgold，takingcaretoceasethemomentthebubblesarewelldefinedoverthesurfaceoftheplate。
ManyDaguerreotypists，afterasuperficialtrial，discardthehyposulphiteofgoldasinferior;butIhavenohesitationinassertingthatthefaultlieswiththemselves;forineverycasewithinmyknowledge，whereitsusehasbeenpersistedinuntilthecorrectmethodhasbeenascertainedandthenatureofthegildinghasbecomefamiliar，itisalwayspreferred。
InillustrationofthisfactIwillrelateananecdote：
Agentlemantowhomithadbeenrecommended，purchasedabottle，andaftermakingoneortwotrialsofit，wrotetohiscorrespondent——\"Sendmetwobottlesofchlorideofgold，forIwantnomoreofthehyposulphite;itisgoodfornothing。\"
Afewweeksafterhesentforthreebottlesofthecondemnedarticle，confessingthatbehadfoundfaultunnecessarily;for，thatsincehehadbecomefamiliartoitsuse，hemustacknowledgeitssuperiority，andwouldusenoothergilding。
TheSolutionofChlorideofGoldispreparedbydissolvinginapintofdistilledwater，fifteengrainsofchrystalizedchlorideofgold。
Thissolutionwillbeofayellowtint。Inanotherpintofdistilledwaterdissolvefifty-fivegrainsofhyposulphiteofsoda;pourgradually，inverysmallquantities，thegoldintothehyposulphiteofsoda，stirringthesolutionatintervals;whenfinishedthemixtureshouldbenearlycolorless。
Placetheplateonitsstand，orholditintheplyers，inaperfectlyhorrizontalposition——silversurfaceupward——havingpreviouslyslightlyturneduptheedges，sothatitmayholdthesolution。
Wetthesurfacewithalcohol，lettinganysuperfluousquantitydrainoff。
Thealcoholisofnofartherusethantofacilitatetheflowingofthegoldmixtureoverthesurface。Nowpouron，carefully，asmuchofthepreparationofgoldaswillremainontheplate。
Theunderpartoftheplateisthentobeheatedasuniformlyaspossiblewiththespiritlamp;smallbubbleswillarrise，andtheappearanceoftheportraitorviewverysensiblyimproved。
Theprocessmustnotbecarriedtoofar，butassoonasthebubblesdisappearthelampshouldberemoved，andtheplateimmersedindistilledwater，anddriedasbeforedirected。
7th。COLORINGTHEPICTURE。——Iverymuchdoubttheproprietyofcoloringthedaguerreotypes，asIamofopinion，thattheyarelittle，ifany，improvedbytheoperation，atleastasitisnowgenerallypractised。
Thereareseveralthingsrequisiteinanartisttoenablehimtocolorahead，orevenalandscapeeffectively，andcorrectly，andImustsaythatveryfewofthesearepossessedbyouroperatorsasaclass。
Theserequirementsare，atalentfordrawing——taste——duediscriminationofeffect——strictobservanceofthecharacteristicpointsinthefeaturesofthesubject——quickperceptionofthebeautiful，andaknowledgeoftheartofmixingcolors，andblendingtints。
Themethodnowpursued，Idonothesitatetosay，andhavenofearsofbeingcontradictedbythosecapableofcritisizingisonthewholeruinoustoanydaguerreotype，andtoaperfectoneabsolutelydisgusting。
Thedaymaycomewhenaccuratecoloringmaybeobtainedinthecamera。
Untilthatday，ifwecannotleadtasteintotherightchannel，wewillendeavortogivesuchinstructionsthatDaguerreotypistsmayproceedwiththispartofhisworkwithabetterunderstandingoftheprinciplesinvolved。
ForthispurposeIhavepreparedashortchapterontheartofcoloring，whichmaybefoundinthelatterpartofthisvolume。
ToPreserveDaguerreotypestheymustbewellsealedandsecuredinacase，orframe。These，ofcourse，areselectedaccordingtothetasteofthecustomer，theprincipalrequisitebeinggoodglass。
MostDaguerreotypistspreferthewhiteFrenchplateglass——andmanythink，veryerroneously，thatnoneisgoodunlessitisthick——
butthegreatdesideratumisclearnessandfreedomfromblisters;
evenglassalittletingedwithgreenoryellowistobepreferredtotheFrenchplatewhencloudyorblisteredandthereisverylittleofitcomestothismarketthatisnotso。
Itistobehopedthatsomeofourglassfactorieswillmanagetomanufactureanarticleexpresslyfordaguerreotypes;
andIwouldrecommendthemtodoso，fortheywouldfinditquiteanitemofprofitannually。
Beforeenclosingthepictureinthecaseyoushouldbecarefultowipetheglassperfectlyclean，andblowfromthepictureanyparticlesofdustwhichmayhavefallenuponit。
Thentakestripsofstickingpaper，abouthalforthreequartersofaninchwide，andfirmlyandneatlysecureittotheglass，havingfirstplaceda\"mat\"betweenthemtopreventtheplatebeingscratchedbytheglass。
TOMAKESEALINGPAPER。——Dissolveoneounceofgumarabic，andaquarterofanounceofgumtragicanthinapintofwater;
thenaddateaspoonfulofbenzoin。Spreadthisevenlyononesideofgoodstouttissuepaper;letitdry，andthencutitupinstripes，abouthalforthreequartersofaninchwide，foruse。
Ifitbecomestoosoftforsummeruse，addgumarabic;
iftoohardandcracking，addbenzoinorgumtragicanth;
ifitgetstoothick，addwater。
COLOREDDAGUERREOTYPESONCOPPER。——Toeffectthis，takeapolishedplateofcopperandexposeittothevaporofiodine，orbromine，orthetwosubstancescombined;oreitherofthemincombinationwithchlorine。
Thisgivesasensitivecoatingtothesurfaceoftheplate，whichmaythenbesubmittedtotheactionoflightinthecamera。
Afterremainingasufficienttimeinthecamera，theplateistakenoutandexposedtothevaporofsulphurettedhydrogen。
Thisvaporproducesvariouscolorsontheplate，accordingtotheintensitywithwhichthelighthasactedonthedifferentparts;
consequentlyacoloredphotographicpictureisobtained。
Nofurtherprocessisnecessaryasexposuretolightdoesnoteffectthepicture。
Bythisprocesswehaveanadvantageoverthesilveredplate，bothineconomy，andintheproductionofthepictureincolors。
INSTANTANTANEOUSPICTURESBYMEANSOFGALVANISM。——Itwillbeseenbythefollowingvaluablecommunicationthatgalvanismcanbesuccessfullyappliedinproducingpicturesinstantly;aprocessofgreatimportanceinsecuringthelikenessofachild，orintakingviewsofanimatednature。
ColonelWhitneyinformsmethatheoncetookaviewofthesteepleoftheSt。LouisCourtHouseaftersundownbythismeans）andalsosecuredtheimageofamanintheactofsteppingintoastore，andbeforehehadtimetoplacehisfoot，raisedforthatpurpose，onthedoorstep。
Mr。WhitneyiswellknownasthetalentededitoroftheSundayMorningnews。
NewYork，January16，1849。
Mr。H。H。SNELLING。
DearSir，——AsyouareaboutpublishingahistoryoftheDaguerreotype，andrequestadescriptionofmymodeoftakingpicturesinstantaneouslybytheaidofgalvanism，Icomplywithgreatpleasure。
Intheyear1841，whilepracticingtheartinSt。Louis，Mo。，I
wasattimes，duringthesummer，muchtroubledwiththeelectricinfluenceoftheatmosphere，especiallyontheapproachofathunder-storm。AtsuchtimesIfoundthecoatingofmyplatesmuchmoresensitivethanwhentheatmospherewascomparativelyfreefromtheelectricfluid，andtheeffectwassoirregularthatnocalculationcouldcounteractthedifficulty。
Thissatisfiedmethatelectricitywasinsomemeasureanimportantagentinthechemicalprocess，anditoccurredtomethattheelementmightbeturnedtoadvantage。
Idetermined，therefore，toenteronaseriesofexperimentstotestmytheory。Findingitimpossibletoobtainanelectricmachine，andunwillingtoabandontheexamination，itoccurredtome，thatthegalvanicinfluencemightanswerthesamepurpose。
Ithereforeproceededtomakeagalvanicbatteryinthefollowingsimplemanner。Iobtainedapieceofzincabouttwoincheslong，oneinchwide，andaneighthofaninchthick。
OnthisIsolderedanarrowstripofcopper，aboutsixincheslong，thesolderedendlaidononesideofthezinc，andextendingitswholelength。Thebatterywascompletedbyplacingthezincinaglasstumbler，two-thirdsfullofdilutesulphuricacid，strongenoughtoproduceafreeactionofthemetals。
Theupperendofthecopperslipextendingabovethetumblerwassharpenedtoapoint，andbentalittleovertheglass。
Themethodofusing，wasthus：——Afterpreparingtheplateintheusualmannerandplacingitinthecamera，insuchmannerastoexposethebackoftheplatetoview，thebatterywaspreparedbyplacingthezincintheacid，andassoonasthegalvanicfluidbegantotraverse（ascouldbeknownbytheeffervessenceoftheacid，operatingonthezincandcopper）thecapofthecamerawasremoved，andtheplateexposedtothesitter;atthesameinstantthepointofthebatterywasbroughtquicklyagainstthebackoftheplate，andthecapreplacedinstantly。Iftheplateisexposedmorethananinstantafterthecontactthepicturewillgenerallybefoundsolarized。
BythisprocessIhavetakenpicturesofpersonsintheactofwalking，andintakingthepicturesofinfantsandyoungchildrenIfounditveryuseful。
Veryrespectfullyyours，THOMASR。WHITNEY。
CHAP。VII
PAPERDAGUERREOTYPES。——ETCHINGDAGUERREOTYPES。
Mr。Huntdescribesaprocess，discoveredbyhimselfbywhichtheDaguerreanartmaybeappliedtopaper。
Hisdescriptionisasfollows：——
\"Placingthepaperonsomehardbody，washitoverononeside——
bymeansofaverysoftcamel’shairpencil——withasolutionofsixtygrainsofbromideofpotassium，intwofluidouncesofdistilledwater，andthendryitquicklybythefire。
Beingdry，itisagainwashedoverwiththesamesolution，anddriedasbefore。Asolutionofnitrateofsilver——
onehundredgrainstoanounceofdistilledwater——istobeappliedoverthesamesurface，andthepaperquicklydriedinthedark。
Inthisstatethepapersmaybekeptforuse。
\"Whentheyarerequired，theabovesolutionofsilveristobeplentifullyapplied，andthepaperplacedwetinthecamera，thegreatestcarebeingtakenthatnodaylight——
noteventhefaintestgleam——fallsuponituntilthemomentwhenyouareprepared，byremovingthedarkslide，topermitthelight，radiatingfromtheobjectyouwishtocopy，toactinproducingthepicture。Afterafewsecondsthelightmustbeagainshutoff，andthecameraremovedintoadarkroom。\"
Thenecessityofremovingthecameraisnowavoidedbytheuseofthedarkslide，alreadydescribed，coveringthepictureintheholder，whichalonemayberemoved。——Amer。Aut。
\"Itwillbefoundbytakingthepaperfromtheholder，thatthereisbutaveryfaintoutline——ifany——yetvisible。Placeitaside，inperfectdarknessuntilquitedry;thenplaceitinthemercurialvaporbox（meaningbath）andapplyaverygentleheattothebottom。
Themomentthemercuryvaporizes，thepicturewillbegintodevelopeitself。
Thespiritlampmustnowberemovedforashorttime，andwhentheactionofthemercuryappearstocease，itistobeverycarefullyappliedagain，untilawelldefinedpictureisvisible。Thevaporizationmustthenbesuddenlystopped，andthephotographremovedfromthebox。
Thedrawingwillthenbeverybeautifulanddistinct;butmuchdetailisstillclouded，forthedevelopementofwhichitisonlynecessarytoplaceitinthedarkandsufferittoremainundisturbedforsomehours。Thereisnowaninexpressiblecharmaboutthepictures，equalingthedelicatebeautyofthedaguerreotype;butbeingverysusceptibleofchange，itmustbeviewedbythelightofataperonly。
Thenitrateofsilvermustnowberemovedfromthepaper，bywellwashingitinsoftwater，towhichasmallquantityofsalthasbeenadded，anditshouldafterwardsbesoakedinwateronly。Whenthepicturehasbeendried，washitquicklyoverwithasoftbrushdippedinawarmsolutionofhyposulphiteofsoda，andthenwashitforsometimeindistilledwater，inorderthatallthehyposulphitemayberemoved。
Thedrawingisnowfixedandwemayuseittoprocurepositivecopies，（theoriginalbeingtermedanegative，）manyofwhichmaybetakenfromoneoriginal。\"
\"Theactionoflightonthispreparation，doesindeedappeartobeinstantaneous。Theexquisitedelicacyofthispreparationmaybeimagined，whenIstatethatinfivesecondsinthecamera，Ihave，duringsunshine，obtainedperfectpictures，andthatwhentheskyisovercast，oneminuteisquitesufficienttoproduceamostdecidedeffect。\"
\"Thisverybeautifulprocessisnotwithoutitsdifficulties;
andtheauthorcannotpromisethat，evenwiththeclosestattentiontotheabovedirections，annoyingfailureswillnotoccur。
Itoftenhappensthatsomeaccidentalcircumstance——generallyaprojectingfilmoralittledust——willoccasionthemercurialvaportoactwithgreatenergyononepartofthepaper，andblackenitbeforetheotherportionsareatalleffected。Again，themercurywillsometimesaccumulatealongthelinesmadebythebrush，andgiveastreakyappearancetothepicture，althoughtheselinesarenotatallevidentbeforethemercurialvaporwasapplied。
（Abrushsufficientlylarge——andtheymaybeeasilyobtained——
will，inameasure，preventthisdifficulty。——AmerAu。）
Ihavestatedthatthepapershouldbeplacedwetinthecamera;
thesamepapermaybeuseddry，whichoftenisagreatconvenience。
Wheninthedrystatealittlelongerexposureisrequired;
andinsteadoftakingapictureinfourorfiveseconds，twoorthreeminutesarenecessary。\"
Thedurabilityofdaguerreotypeshasbeen，andisstill，doubtedbymany，butexperimenthasprovedthattheyaremorepermanentthanoilpaintingsorengravings。
ETCHINGDAGUERREOTYPES。——Thereareseveralmethodsofaccomplishingthisobject;discoveredandappliedbydifferentindividuals。
ThefirstprocesswaspublishedatViennabyDr。Berres，andconsistedincoveringtheplatewiththemucilageofgumarabic，andthenimmersingtheplateinnitricacidofdifferentstrengths。
Mr。Figeau，ofwhomIhavealreadyspoken，likewisediscoveredaprocessfortheengravingofDaguerreotypes;andfoundedonthebeliefthatthelightsofaDaguerreotypeplateconsistsofunalteredsilver，whilethedarkorshadowsconsistsofmercuryoranamalgamofmercurywithsilver。
Hefindsthatacompoundacid，consistingofamixtureofnitric，nitrous，andmuriaticacids，orofnitricmixedwithnitrateofpotassandcommonsalt，hasthepropertyofattachingthesilverinpresenceofthemercurywithoutactinguponthelatter。Bi-chlorideofcopperanswersthepurposealso，butlesscompletely。
\"WhenthecleansurfaceofaDaguerreotypeplateisexposedtotheactionofthismenstruum，particularlyifwarm，thewhiteparts，orlightsarenotaltered，butthedarkpartsareattacked，andchlorideofsilverisformed，ofwhichaninsoluablecoatingissoondeposited，andtheactionoftheacidsoonceases。
Thiscoatofchlorideofsilverisremovedbyasolutionofammonia，andthentheacidappliedagain，andsoon，untilthedepthofbitinginissufficient。However，itisnotpossible，byrepeatingthisprocess，togetasufficientforceofimpression;
asecondoperationisrequired，inordertoobtainsuchadepthaswillholdtheink，togiveadarkimpression;forthispurposethewholeplateiscoveredwithdryingoil;thisisclearedoffwiththehand，exactlyinthewayacopperplateprintercleanshisplate。
Theoilisthusleftinthesinkings，ordarkbitteninpartsonly。
Thewholeplateisnowplacedinasuitableapparatus，andthelightsorprominentpartsofthefacearegiltbytheelectrotypeprocess。
ThewholesurfaceisnowtouchedwithwhattheFrenchengraverscallthe\"ResinGrain，\"（grainderesine），aspeciesofpartialstoppingout，anditisatoncebittenintoasufficientdepthwithnitricacid，thegildingpreservingthelightsfromallactionoftheacid。
Theresingraingivesasurfacetothecorrodedpartssuitableforholdingtheink，andtheplateisnowfinishedandfittogiveimpressionsresemblingaquatint。Butassilverissosoftametalthatthesurfaceoftheplatemightbeexpectedtowearrapidly，thediscovererproposestoshielditbydepositingoveritswholesurfaceaverythincoatofcopperbytheelectrotypeprocess;
whichwhenwornmayberemovedatpleasuredowntothesurfaceofthenoblemetalbeneath，andagainafreshcoatofcopperdeposited;
andsoanunlimitednumberofimpressionsobtainedwithoutinjuringtheplateitself。\"
If，ashasbeenasserted，steelmayberenderedsufficientlysensitive，totakephotographicimpressions，towhatarevolutionwilltheartofengravingbesubjectbythediscoveryofthisprocess。
CHAP。VIII。
PHOTOGENICDRAWINGONPAPER。
WeshallnowproceedtodescribethevariousprocessesforPhotogenicdrawingonpaper;first，however，impressingonthemindoftheexperimenter，thenecessitywhichexistsforextremecareineverystageofthemanipulation。
InthisportionofmyworkIamentirelyindebtedtotheworksofProfessorsHunt，Fisherandothers。
I。APPARATUSANDMATERIALS。——Paper。——Theprincipaldifficultytobecontendedwithinusingpaper，isthedifferentpowerofimbibitionwhichweoftenfindpossessedinthesamesheet，owingtotriflinginequalitiesinitstexture。Thisis，toacertainextent，tobeovercomebyacarefulexaminationofeachsheet，bythelightofacandleorlampatnight，orinthedark。
Byextendingeachsheetbetweenthelightandtheeye，andslowlymovingitupanddown，andfromlefttoright，thevariationsinitstexturewillbeseenbythedifferentquantitiesoflightwhichpassthroughitindifferentparts;
anditisalwaysthesafestcoursetorejecteverysheetinwhichinequalitiesexist。Papersometimescontainsminuteportionsofthread，blackorbrownspecks，andotherimperfections，allofwhichmateriallyinterferewiththeprocess。Somepaperhasanartificialsubstancegiventoitbysulphateoflime（PlasterofParis）;thisdefectonlyexists，however，inthecheapersortsofdemy，andthereforecanbeeasilyavoided。
Inallcasessuchpapershouldberejected，asnoreallysensitivematerialcanbeobtainedwithit。Paper-makers，asiswellknown，oftenaffixtheirnametoonehalfthesheet;
thismoietyshouldalsobeplacedaside，asthelettersmustfrequentlycomeoutwithannoyingdistinctness。
Wellsizedpaperisbynomeansobjectionable，indeed，israthertobepreferred，sincethesizetendstoexaltthesensitivepowersofthesilver。Theprincipalthingtobeavoided，istheabsorptionofthesensitivesolutionintothepores;
anditmustbeevidentthatthisdesideratumcannotbeobtainedbyunsizedpaper。Takingallthingsintoconsideration，thepaperknownassatinpostwouldappeartobepreferable，althoughtheprecautionsalreadyrecommendedshouldbetakeninitsselection。
Brushes。——Thenecessarysolutionsaretobelaiduponthepaperbybrushes。
Somepersonspassthepaperoverthesurfaceofthesolutions，thuslickingup，asitwere，aportionofthefluid;butthismethodisapttogiveanunevensurface;italsorapidlyspoilsthesolutions。
Atallevents，thebrushisthemostreadyandthemosteffectualmeans。
DistilledWater。——Allthewaterused，bothformixingthesolutions，washingthepaper，orcleaningthebrushes，mustbedistilled，toobtaingoodresults，forreasonsbeforespecified。
BlottingPaper。——Inmanyinstances，thepreparedpaperrequirestobelightlydriedwithbibulouspaper。Thebestdescriptionisthewhitesort。
Ineachstageofthepreparationdistinctportionsofbibulouspapermustbeused。Ifthesebekeptseperateandmarked，theycanbeagainemployedforthesamestage;butitwouldnotdo，forexample，todrythefinishedpictureinthesamefoldsinwhichthesensitivepaperhadbeenpressed。
Averyconvenientmethodistohavetwoorthreequartosizebooksofbibulouspaper，oneforeachseperateprocess。
NitrateofSilver。——Inthepracticeofthephotographicart，muchdependsonthenitrateofsilver。Careshouldbetakentoprocurethebest;thecrystalizedsaltismostsuitableforthepurpose。Whileintheformofcrystalitisnotinjuredbyexposuretolight，butthebottlescontainingthesolutionsofthissaltshouldatalltimesbekeptwrappedindarkpaper，andexcludedfromdaylight。
II。DIFFERENTMETHODSOFPREPARINGTHEPAPER。——PreparationofthePaper。——
Dipthepapertobepreparedintoaweaksolutionofcommonsalt。
Thesolutionshouldnotbesaturated，butsixoreighttimesdilutedwithwater。Whenperfectlymoistened，wipeitdrywithatowel，orpressitbetweenbibulouspaper，bywhichoperationthesaltisuniformlydispersedthroughitssubstance。Thenbrushoverit，ononesideonly，asolutionofnitrateofsilver。Thestrengthofthissolutionmustvaryaccordingtothecolorandsensitivenessrequired。
Mr。Talbotrecommendsaboutfiftygrainsofthesalttoanounceofdistilledwater。Someadvisetwentygrainsonly，whileotherssayeightygrainstotheounce。Whendriedinadarkroom，thepaperisfitforuse。Torenderthispaperstillmoresensitive，itmustagainbewashedwithsaltandwater，andafterwardswiththesamesolutionofnitrateofsilver，dryingitbetweentimes。Thispaper，ifcarefullymade，isveryusefulforallordinaryphotographicpurposes。
Forexample，nothingcanbemoreperfectthantheimagesitgivesofleavesandflowers，especiallywithasummer’ssun;thelight，passingthroughtheleaves，delineateseveryramificationoftheirfibres。
Inconductingthisoperation，however，itwillbefoundthattheresultsaresometimesmoreandsometimeslesssatisfactory，inconsequenceofsmallandaccidentalvariationsintheproportionsemployed。
Ithappenssometimesthatthechlorideofsilverformedonthesurfaceofthepaperisdisposedtoblackenofitself，withoutanyexposuretolight。
Thisshowsthattheattempttogiveitsensibilityhasbeencarriedtoofar。
Theobjectis，toapproachasnearlytothisconditionaspossiblewithoutreachingit;sothatthepreparationmaybeinastatereadytoyieldtotheslightestextraneousforce，suchasthefeeblesteffectoflight。
Cooper’sMethod。——Soakthepaperinaboilinghotsolutionofchlorateofpotash（thestrengthmattersnot）forafewminutes;
thentakeitout，dryit，andwetitwithabrush，ononesideonly，dippedinasolutionofnitrateofsilver，sixtygrainstoanounceofdistilledwater，or，ifnotrequiredtobesosensitive，thirtygrainstotheouncewilldo。Thispaperpossessesagreatadvantageoveranyother，fortheimagecanbefixedbymerewashing。
Itis，however，veryapttobecomediscoloredeveninthewashing，orshortlyafterwards，andis，besides，notsosensitive，nordoesitbecomesodarkasthatmadeaccordingtoMr。Talbot’smethod。
Daguerre’sMethod。——Immersethepaperinhydrochloric（orasitismorecommonlycalled，muriatic）ether，whichhasbeenkeptsufficientlylongtobecomeacid;thepaperisthencarefullyandcompletelydried，asthisisessentialtoitsproperpreparation。
Itisthendippedintoasolutionofnitrateofsilver，anddriedwithoutartificialheatinaroomfromwhicheveryrayoflightiscarefullyexcluded。Bythisprocessitacquiresaveryremarkablefacilityinbeingblackenedonaveryslightexposuretolight，evenwhenthelatterisbynomeansintense。
Thepaper，however，rapidlylosesitsextremesensitivenesstolight，andfinallybecomesnomoreimpressionablebythesolarbeamsthancommonnitratepaper。
BromidePaper。——Ofallcommonphotographicpaper，thebest，becausetheleasttroublesomeinmaking，andthemostsatisfactoryinresult，isthatwhichistermedbrominepaper，andwhichisthusprepared：——Dissolveonehundredgrainsofbromideofpotassiuminoneounceofdistilledwater，andsoakthepaperinthissolution。
Takeoffthesuperfluousmoisture，bymeansofyourbibulouspaper，andwhennearlydry，brushitoverononesideonly，withasolutionofonehundredgrainsofnitrateofsilvertoanounceofdistilledwater。
Thepapershouldthenbedriedinadarkroom，and，ifrequiredtobeverysensitive，shouldasecondtimebebrushedoverwiththenitrateofsilversolution。
Inpreparingthepapersmentionedabove，therearetwocircumstanceswhichrequireparticularattention。Inthefirstplace，itisnecessarytomarkthepaperonthesidespreadwiththesolutionsofnitrateofsilver，nearoneoftheextremecorners。
Thisanswerstwopurposes：inthefirstplaceitservestoinformtheexperimemtalistofthesensitivesurface;andsecondly，itwillbeaguideastowhichportionofthepapershasbeenhandledduringtheapplicationofthesolution，astheimpressofthefingerswillprobablycomeoutuponthephotograph。
Thesecondcautionis，thattheapplicationofthesensitivesolution（nitrateofsilver，）andthesubsequentdryingofthepaper，mustbealwaysconductedinaperfectlydarkroom，thelightofacandlealonebeingused。
III。PHOTOGENICPROCESSONPAPER。——Method。——Thesimplestmodeistoprocureaflatboardandasquareofglass，largerinsizethantheobjectintendedtobecopied。
Ontheboardplacethephotographicpaper[hipho_29。gif]
withthepreparedsideupwards，anduponittheobjecttobecopied;
overbothlaytheglassandsecurethemsothattheyareincloseconnectionbymeansofbindingscrewsorclamps，similartog。g。fig。29。Shouldtheobjecttobecopiedbeofunequalthickness，suchasaleaf，grass，&c。，itwillbenecessarytoplaceontheboard，first，asoftcushion，whichmaybemadeofapieceoffineflannelandcottonwool。
Bythismeanstheobjectisbroughtintoclosercontactwiththepaper，whichisofgreatconsequence，andaddsmateriallytotheclearnessofthecopy。
Thepaperisnowexposedtodiffuseddaylight，or，stillbetter，tothedirectraysofthesun，whenthatpartofthepapernotcoveredbytheobjectwillbecometingedwithavioletcolor，andifthepaperbewellprepared，itwillinashorttimepasstoadeepbrownorbronzecolor。Itmustthenberemoved，asnoadvantagewillbeobtainedbykeepingitlongerexposed;
onthecontrary，thedelicatepartsyetuncoloredwillbecomeinsomedegreeaffected。Thephotogenicpaperwillnowshowamoreorlesswhiteanddistinctrepresentationoftheobject。
Theapparatusfiguredat29consistsofawoodenframesimilartoapictureframe;apieceofplateglassisfixedinfront;
anditisprovidedwithaslidingcoverofwood，c。，whichisremovedwhenthepaperisreadytobeexposedtotheactionofthelight。
Theback，d。，whichisfurnishedwithacushion，asjustdescribed，ismadetoremoveforthepurposeofintroducingtheobjecttobecopied，anduponitthepreparedpaper;thebackisthenreplaced，and，byaidofthecrosspieceandscrew，e。，thewholeisbroughtintoclosecontactwiththeglass。
Theobjectsbestdelineatedonthesephotographicpapers，arelace，feathers，driedplants，particularlytheferns，sea-weedsandthelightgrasses，impressionsofcopperplateandwoodengravings，particularlyiftheyhaveconsiderablecontrastoflightandshade——（theseshouldbeplacedwiththefacedownwards，havingbeenpreviouslypreparedashereafterdirected）——
paintingsonglass，etchings，&c。
TofixtheDrawings。——Mr。Talbotrecommendsthatthedrawingsshouldbedippedinsaltandwater，andinmanyinstancesthismethodwillsucceed，butattimesitisequallyunsuccessful。
Iodideofpotassium，or，asitisfrequentlycalled，hydriodateofpotash，dissolvedinwater，andverymuchdiluted，（twenty-fivegrainstooneounceofwater，）isamoreusefulpreparationtowashthedrawingswith;itmustbeusedveryweakoritwillnotdissolvetheunchangedmuriateonly，asisintendedbuttheblackoxidealso，andthedrawingbetherebyspoiled。
Butthemostcertainmaterialtobeusedisthehyposulphiteofsoda。
Oneounceofthissaltshouldbedissolvedinaboutapintofdistilledwater。Havingpreviouslywashedthedrawinginalittlelukewarmwater，whichofitselfremovesalargeportionofthemuriateofsilverwhichistobegotridof，itshouldbedippedonceortwiceinthehyposulphitesolution。
Bythisoperationthemuriatewhichliesuponthelighterpartswillbecomesoalteredinitsnatureastobeunchangedbylight，whiletherestremainsdarkasbefore。
Itwillbeevidentfromthenatureoftheprocess，thatthelightsandshadowsofanobjectarereversed。Thatwhichisoriginallyopaquewillinterceptthelight，andconsequentlythosepartsofthephotogenicpaperwillbeleastinfluencedbylight，whileanypartoftheobjectwhichistransparent，byadmittingthelightthroughit，willsuffertheeffecttobegreaterorlessinexactproportiontoitsdegreeoftransparency。
Theobjectwhollyinterceptingthelightwillshowawhiteimpression;
inselecting，forexample，abutterflyforanobject，theinsect，beingmoreorlesstransparent，leavesaproportionategradationoflightandshade，themostopaquepartsshowingthewhitest。
Itmaybesaid，therefore，thatthisisnotnatural，andinordertoobtainatruepicture——or，asitistermed，apositivepicture——
wemustplaceourfirstacquiredphotographuponasecondpieceofphotogenicpaper。Beforewedothis，however，wemustrenderourphotographtransparent，otherwisetheopacityofthepaperwillmarourefforts。
Toaccomplishthisobject，thebackofthepapercontainingthenegative，orfirstacquiredphotograph，shouldbecoveredwithwhiteorvirginwax。
Thismaybedonebyscrapingthewaxuponthepaper，andthen，afterplacingitbetweentwootherpiecesofpaper，passingaheatedironoverit。
Thepicture，beingthusrenderedtransparent，shouldnowbeappliedtoasecondpieceofphotogenicpaper，andexposed，inthemannerbeforedirected，eithertodiffusedday-lightortothedirectraysofthesun。
Thelightwillnowpenetratethewhiteparts，andthesecondphotographbethereverseofthefirst，oratruepictureoftheoriginal。
Insteadofwax，boiledlinseedoil——itmustbethebestandmosttransparentkind——maybeused。Thebackofthenegativephotographshouldbesmearedwiththeoil，andthenplacedbetweensheetsofbibulouspaper。
Whendrythepaperishighlytransparent。
IV。APPLICATIONOFPHOTOGENICDRAWING。——Thismethodofphotogenicdrawingmaybeappliedtousefulpurposes，suchasthecopyingofpaintingsonglassbythelightthrownthroughthemonthepreparedpaper——
Imitationsofetchings，whichmaybeaccomplishedbycoveringapieceofglasswithathickcoatofwhiteoilpaint;whendry，withthepointofaneedle，linesorscratchesaretobemadethroughthewhiteleadground，soastolaytheglassbare;
thenplacetheglassuponapieceofpreparedpaper，andexposeittothelight。Ofcourseeverylinewillberepresentedbeneathofablackcolor，andthusanimitationetchingwillbeproduced。
Itisalsoapplicabletothedelineationofmicroscopicobjects，architecture，seulpture，landscapesandexternalnature。
Anovelapplicationofthisarthasbeenrecentlysuggested，whichwoulddoubtlessproveusefulinverymanyinstances。
Byrenderingthewoodusedforengravingssensitivetolight，impressionsmaybeatoncemadethereon，withouttheaidoftheartist’spencil。Thepreparationofthewoodissimplyasfollows：——Placeitsfaceorsmoothsidedownwards，inaplatecontainingtwentygrainsofcommonsaltdissolvedinanounceofwater;hereletitremainforfiveminutes，takeitoutanddryit;thenplaceitagainfacedownwardsinanotherplatecontainingsixtygrainsofnitrateofsilvertoanounceofwater;hereletitrestoneminute，whentakenoutanddriedinthedarkitwillbefitforuse，andwillbecome，onexposuretothelight，ofafinebrowncolor。
Shoulditberequiredmoresensitive，itmustbeimmersedineachsolutionasecondtime，forafewsecondsonly。
Itwillnowbeverysooneffectedbyaverydiffusedlight。
Thisprocessmaybeusefultocarversandwoodengraversnotonlytothosewhocutthefineobjectsofartisticaldesign，butstillmoretothosewhocutpatternsandblocksforlace，muslin，calico-printing，paperhangings，etc。，asbythismeanstheerrors，expenseandtimeofthedraughtsmanmaybewhollysaved，andinaminuteortwothemostelaboratepictureordesign，orthemostcomplicatedmachinery，bedelineatedwiththeutmosttruthandclearness。
CHAP。IX。
CALOTYPEANDCHRYSOTYPE。
ThematerialsandapparatusnecessaryfortheCalotypeprocessare——
TwoorThreeShallowDishes，forholdingdistilledwater，iodide，potassium，&c。——thesamewaterneverbeingusedfortwodifferentoperations。
WhiteBibulousPaper。
PhotogenicCamera——Fig。9。
PressureFrame——Fig29。
Paper，oftheverybestquality——directionsforthechoiceofwhichhavebeenalreadygiven。
AScreenofYellowGlass。
Camels’orBadgers’hairBrushes：——Aseperateonebeingkeptforeachwashandsolution，andwhichshouldbethoroughlycleansedimmediatelyafterusingindistilledwater。
Thatusedforthegallo-nitrateissoondestroyed，owingtotherapiddecompositionofthatpreparation。
AGraduatedMeasure。
ThreeorFourFlatBoards，towhichthepapermaybefixedwithdrawingpins。
AHotWaterDryingApparatus，fordryingthepaperwillalsobefounduseful。
InpreparingtheCalotypepaper，itisnecessarytobeextremelycareful，notonlytopreventthedaylightfromimpringinguponit，butalsotoexclude，ifpossible，thestrongglareofthecandleorlamp。
Thismaybeeffectedbyusingashadeofyellowglassorgauze，whichmustbeplacedaroundthelight。Lightpassingthroughsuchamediumwillscarcelyaffectthesensitivecompounds，theyellowglassinterceptingthechemicalrays。
PreparationoftheIodizedPaper。——Dissolveonehundredgrainsofcrystalizednitrateofsilverinsixouncesofdistilledwater，andhavingfixedthepapertooneoftheboards，brushitoverwithasoftbrushononesideonlywiththissolution，amarkbeingplacedonthatsidewherebyitmaybeknown。
Whennearlydrydipitintoasolutionofiodideofpotassium，containingfivehundredgrainsofthatsaltdissolvedinapintofwater。
Whenperfectlysaturatedwiththissolution，itshouldbewashedindistilledwater，drainedandallowedtodry。Thisisthefirstpartoftheprocess，andthepapersopreparediscallediodizedpaper。
Itshouldbekeptinaport-folioordraweruntilrequired：
withthiscareitmaybepreservedforanylengthoftimewithoutspoilingorundergoinganychange。
Mr。Cundellfindsastrongersolutionofnitrateofsilverpreferable，andemploysthirtygrainstotheounceofdistilledwater：
healsoaddsfiftygrainsofcommonsalttotheiodideofpotassium，whichheappliestothemarkedsideofthepaperonly。
Thisisthefirstprocess。
PreparationofthepaperfortheCamera。——ThesecondprocessconsistsinapplyingtotheaboveasolutionwhichhasbeennamedbyMr。Talbotthe\"Gallo-NitrateofSilver;\"itispreparedinthefollowingmanner：
Dissolveonehundredgrainsofcrystalizednitrateofsilverintwoouncesofdistilledwater，towhichisaddedtwoandtwo-thirddrachmsofstrongaceticacid。Thissolutionshouldbekeptinabottlecarefullyexcludedfromthelight。Now，makeasolutionofgallicacidincolddistilledwater：thequantitydissolvedisverysmall。
Whenitisrequiredtotakeapicture，thetwoliquidsabovedescribedshouldbemixedtogetherinequalquantities;butasitspeedilyundergoedecomposition，andwillnotkeepgoodformanyminutes，onlyjustsufficientforthetimeshouldbeprepared，andthatusedwithoutdelay。
Itisalsowellnottomakemuchofthegallicacidsolution，asitwillnotkeepformorethanafewdayswithoutspoiling。
Asheetoftheiodizedpapershouldbewashedoverwithabrushwiththismixedsolution，carebeingtakenthatitbeappliedtothemarkedside。
Thisoperationmustbeperformedbycandlelight。Letthepaperresthalfaminute，thendipitintooneofthedishesofwater，passingitbeneaththesurfaceseveraltimes;itisnowallowedtodrain，anddriedbyplacingitsmarkedsideupwards，onthedryingapparatus。
Itisbetternottotouchthesurfacewithbibulouspaper。
Itisnowhighlysensitive，andreadytoreceivetheimpression。
Inpracticeitisfoundbetterandmoreeconomicalnottomixthenitrateofsilverandgallicacid，butonlytobrushthepaperwiththesolutionofthenitrate。
Mr。Talbothasrecentlyproposedsomemodificationsinhismethodofpreparingthecalotypepaper。Thepaperisfirstiodizedintheusualway;
itisthenwashedoverwithasaturatedsolutionofgallicacidindistilledwateranddried。Thuspreparedhecallsittheio-gallicpaper：
itwillremaingoodforaconsiderabletimeifkeptinapressorportfolio。
Whenrequiredforuse，itiswashedwithasolutionofnitrateofsilver（fiftygrainstotheounceofdistilledwater），anditisthenfitforthecamera。
ExposureintheCamera。——Thecalotypepaperthuspreparedpossessesaveryhighdegreeofsensibilitywhenexposedtolight，andwearethusprovidedwithamediumbywhich，withtheaidofthephotogeniccamera，wemayeffectuallycopyviewsfromnature，figures，buildings，andeventakeportraitsfromtheshadowsthrownonthepaperbythelivingface。
Thepapermaybeusedsomewhatdamp。Thebestplanforfixingitinthecameraistoplaceitbetweenapieceofplateglassandsomeothermaterialwithaflatsurface，asapieceofsmoothslateoranironplate，whichlatter，ifmadewarm，rendersthepapermoresensitive，andconsequentlythepictureisobtainedmorerapidly。
TimeofExposure。——Withregardtothetimewhichshouldbeallowedforthepapertoremaininthecamera，nodirectrulescanbelaiddown;thiswilldependaltogetheruponthenatureoftheobjecttobecopied，andthelightwhichprevails。
Allthatcanbesaidis，thatthetimenecessaryforformingagoodpicturevariesfromthirtysecondstofiveminutes，anditwillbenaturallythefirstobjectoftheoperatortogainbyexperiencethisimportantknowledge。
BringingOutthePicture。——Thepaperwhentakenfromthecamera，whichshouldbedonesoastoexcludeeveryrayoflight——andherethedarkslideofthecameraplateholderbecomesofgreatuse——
bearsnoresemblancetothepicturewhichinrealityisformed。
Theimpressionislatentandinvisible，anditsexistencewouldnotbesuspectedbyanyonenotacquaintedwiththeprocessbypreviousexperiment。Themethodofbringingouttheimageisverysimple。
Itconsistsinwashingthepaperwiththegallo-nitrateofsilver，preparedinthewayalreadydescribed，andthenwarmingitgently，beingcarefulatthesametimenottoletanyportionbecomeperfectlydry。Inafewsecondsthepartofthepaperuponwhichthelighthasactedwillbegintodarken，andfinallygrowentirelyblack，whiletheotherpartsretaintheiroriginalcolor。
Evenaweakimpressionmaybebroughtoutbyagainwashingthepaperinthegallo-nitrate，andoncemoregentlywarmingit。
Whenthepaperisquiteblack，asisgenerallythecase，itisahighlycuriousandbeautifulphenomenontowitnessthecommencementofthepicture，firsttracingoutthestrongeroutlines，andthengraduallyfillingupallthenumerousandcomplicateddetails。
Theartistshouldwatchthepictureasitdevelopesitself，andwheninhisjudgmentithasattainedthegreatestdegreeofstrengthandclearness，heshallstopfurtherproceedingsbywashingitwiththefixingliquid。
Hereagainthemixedsolutionneednotbeused，butthepicturesimplybrushedoverwiththegallicacid。
TheFixingProcess。——Inordertofixthepicturethusobtained，firstdipitintowater;thenpartlydryitwithbibulouspaper，andwashitwithasolutionofbromideofpotassium——containingonehundredgrainsofthatsaltdissolvedineightortenouncesofdistilledwater。
Thepictureisagainwashedwithdistilledwater，andthenfinallydried。
Insteadofbromideofpotassium，asolutionofhyposulphiteofsoda，asbeforedirected，maybeusedwithequaladvantage。
Theoriginalcalotypepicture，likethephotographiconedescribedinthelastchapter，isnegative，thatistosay，ithasitslightsandshadesreversed，givingthewholeanappearancenotconformabletonature。Butitiseasyfromthispicturetoobtainanotherwhichshallbeconformabletonature;viz。，inwhichthelightsshallberepresentedbylights，andtheshadesbyshades。
Itisonlynecessarytotakeasheetofphotographicpaper（thebromidepaperisthebest），andplaceitincontactwithacalotypepicturepreviouslyrenderedtransparentbywaxoroilasbeforedirected。
Fixitintheframe，Fig。29，exposeitinthesunshineforashorttime，andanimageorcopywillbeformedonthephotogenicpaper。
Thecalotypepaperitselfmaybeusedtotakethesecond，orpositive，picture，butthisMr。Talbotdoesnotrecommend，foralthoughittakesamuchlongertimetotakeacopyonthephotogenicpaper，yetthetintsofsuchcopyaregenerallymoreharmoniousandagreeable。
Afteracalotypepicturehasfurnishedanumberofcopiesitsometimesgrowsfaint，andthesubsequentcopiesareinferior。
Thismaybepreventedbymeansofaprocesswhichrevivesthestrengthofthecalotypepictures。Inordertodothis，itisonlynesessarytowashthembycandlelightwithgallo-nitrateofsilver，andthenwarmthem。Thiscausesalltheshadesofthepicturetodarkenconsiderably，whilethewhitepartsareunaffected。
Afterthisthepictureisofcoursetobefixedasecondtime。
Itwillthenyieldasecondseriesofcopies，and，inthisway，agreatnumbermayfrequentlybemade。
Thecalotypepictureswhenpreparedaswehavestated，possessayellowishtint，whichimpedestheprocessoftakingcopiesfromthem。
Inordertoremedythisdefect，Mr。Talbothasdevisedthefollowingmethod。Thecalotypepictureisplungedintoasolutionconsistingofhyposulphiteofsodadissolvedinabouttentimesitsweightofwater，andheatednearlytotheboilingpoint。
Thepictureshouldremaininabouttenminutes;itmustthenberemoved，washedanddried。Bythisprocessthepictureisrenderedmoretransparent，anditslightsbecomewhiter。
Itisalsorenderedexceedinglypermanent。Afterthisprocessthepicturemaybewaxed，andthusitstransparencyincreased。
Thisprocessisapplicabletoallphotographicpaperspreparedwithsolutionsofsilver。
Havingthusfully，anditishopedclearly，consideredtheprocess，itmaybenecessarybeforedismissingthecalotypefromnotice，toaddoneortworemarksfromtheobservationsandlaborsofsomewhohaveexperimentedinthisart。Dr。RyaninhislecturesbeforetheRoyalPolytechnicInstitution，hasobserved，thatintheiodizingprocessthesensitivenessofthepaperismateriallyinjuredbykeepingittoolonginthesolutionofiodideofpotassium，owingtothenewlyformediodideofsilverbeingsoexceedinglysolvableinexcessofiodideofpotassiumasinafewminutestobecompletelyremoved。
Thepapershouldhedippedinthesolutionandinstantlyremoved。
Thereisanotherpoint，too，inthepreparationoftheiodizedpaperinwhichsuggestionsforaslightdeviationfromMr。Talbot’splanhavebeenmade。Inthefirstinstance，itisrecommendedthatthepaperbebrushedoverwiththeiodideofpotassium，insteadofthenitrateofsilver，transposing，infact，theapplicationofthefirsttwosolutions。
Thepaper，havingbeenbrushedoverwiththeiodideofpotassiuminsolution，iswashedindistilledwateranddried。
Itisthenbrushedoverwithnitrateofsilver，andafterdryingisdippedfor，amomentinafreshsolutionofiodideofpotassiumofonlyone-fourththestrengthofthefirst，thatistosay，onehundredandtwenty-fivegrainsofthesalttoapintofwater。Afterthisitisagainwashedanddried。
Theadvantagederivedfromthismethod，isamoresensitivepaper，andamoreevendistributionofthecompoundsoverthesurface。
AnotherdeviationfromMr。Talbot’smethodhasbeensuggested，asfollows：
Brushthepaperoverwithasolutionofonehundredgrainsofnitrateofsilvertoanounceofwater。Whennearly，butnotquite，dry，dipitintoasolutionoftwenty-fivegrainsofiodideofpotassiumtooneounceofdistilledwater，drainit，washitindistilledwaterandagaindrainit。
Nowbrushitoverwithaceto-nitrateofsilver，madebydissolvingfiftygrainsofnitrateofsilverinoneounceofdistilledwater，towhichisaddedonesixthofitsvolumeofstrongaceticacid。
Dryitwithbibulouspaper，anditisreadyforreceivingtheimage。
Whentheimpressionhasbeenreceived，whichwillrequirefromonetofiveminutesaccordingtothestateoftheweather，itmustbewashedwithasaturatedsolutionofgallicacidtowhichafewdropsoftheaceto-nitrateofsilver，madeasabove，havebeenadded。
Theimagewillthusbegraduallybroughtout，andmaybefixedwithhyposulphiteofsoda。Toobtainthepositivepicture，papermustbeusedbrushedoverwithanammonio-nitrateofsilver，madethus：
fortygrainsofnitrateofsilveristobedissolvedinoneounceofdistilledwater，andliquidammoniacautiouslyaddedtillitre-dissolvestheprecipitate。
Apleasingeffectmaybegiventocalotype，orindeedtoallphotographicpictures，bywaxingthemattheback，andmountingthemonwhitepaper，orifcoloredpaperbeused，variousbeautifultonesofcolorareproduced。
POSITIVECALOTYPE。
AtameetingoftheBritishAssociation，ProfessorGrovedescribedaprocessbywhichpositivecalotypepicturescouldbedirectlyobtained;andthusthenecessitytotransferbywhichtheimperfectionsofthepaperareshown，andwhichismoreoveratroublesomeandtediousprocess，isavoided。
Aslightfavorsmostchemicalactions，Mr。Grovewasledtobelievethatapaperdarkenedbythesun（whichdarkeningissupposedtoresultfromtheprecipitationofsilver）
mightbebleachedbyusingasolventwhichwouldnotattackthesilverinthedark，butwoulddosointhelight。
Theplanfoundtobethemostsuccessfulisasfollows：
ordinarycalotypepaperisdarkenedtillitassumesadeepbrowncolor，almostamountingtoblack;itisthenredippedintotheordinarysolutionofiodideofpotassium，anddried。
Whenrequiredforuseitisdrawnoverdilutenitricacid——
onepartacidtotwoandahalfpartswater。Inthisstate，thosepartsexposedtothelightarerapidlybleached，whilethepartsnotexposedremainunchanged。Itisfixedbywashinginwater，andsubsequentlyinhyposulphiteofsoda，orbromideofpotassium。
Mr。Grovealsodescribesaprocessforconvertinganegativecalotypeintoapositiveone，whichpromises，whencarriedout，tobeofgreatutility。
Letanordinarycalotypeimageorportraitbetakeninthecamera，anddevelopedbygallicacid;thendrawnoveriodideofpotassiumanddilutenitricacidandexposedtofullsunshine;whilebleachingthedarkparts，thelightisredarkeningthenewlyprecipitatediodideinthelighterportionsandthusthenegativepictureisconvertedintoapositiveone。
Thecalotypeprocesshasbeenappliedtotheartofprinting，inEngland，butitpossessesnoadvantageswhateveroverthemethod，withtype，nowsogloriouslybroughttoperfection;
andIcanhardlythinkitwilleverbemadeofanyutility。
Forthebenefitofthecurious，however，IwillgiveMr。Talbot’smethod。