ThenatureofthechangewhichtheioduretofsilverundergoesonDaguerreotypeplates，throughtheactionoflight，Mr。Huntconsiderstobeadecidedcaseofdecomposition，andcitesseveralcircumstancesinproofofhisposition。
ThesewithotherfactsgivenbyMr。HuntinhisgreatworkonthePhotographicart，buttovolumnioustoincludeinavolumeofthesizetowhichIamobligedtocofinemyself，shouldbethoroughlystudiedbyallDaguerreotypists。
PRISMATICANALYSIS。——Themostrefrangibleportionofthespectrum，（onaDaguerreotypeplate）appears，aftertheplatehasbeenexposedtothevaporofmercury，tohaveimpresseditscolors;
thelightanddelicatefilmofmercury，whichcoversthatportion，assumingafinebluetintaboutthecentralparts，whicharegraduallyshadedoffintoapalegrey;andthisisagainsurroundedbyaverydelicaterosehue，whichislostinabandofpurewhite。
Beyondthisaprotectinginfluenceispowerfullyexerted;
andnotwithstandingtheactionofthedispersedlight，whichisveryevidentovertheplate，alineisleft，perfectlyfreefrommercurialvapor，andwhich，consequently，whenviewedbyasidelight，appearsquitedark。
Thegreenraysarerepresentedbyalineofacorrespondingtint，considerablylessinsizethantheluminousgreenrays。
Theyellowraysappeartobewithoutaction，ortoactnegatively，thespaceuponwhichtheyfallbeingprotectedfromthemercurialvapor;anditconsequentlyisseenasadarkband。
Awhitelineofvapormarkstheplaceoftheorangerays。
Theredrayseffectthesensitivesurfaceinapeculiarmanner;
andwehavethemercurialvapor，assumingamoleculararrangementwhichgivestoitafinerosehue;thistintissurroundedbyalineofwhitevapor，shadedatthelowestextremitywithaverysoftgreen。Overthespaceoccupiedbytheextremeredrays，aprotectinginfluenceisagainexerted;thespaceisretainedfreefrommercurialvaporandthebandisfoundtosurroundthewholeoftheleastrefrangiblerays，andtouniteitselfwiththebandwhichsurroundstheraysofgreatestrefrangibility。
Thisbandisnotequallywelldefinedthroughoutitswholeextent。
Itismostevidentfromtheextremeredtothegreen;
itfadesinpassingthroughtheblue，andincreasesagain，asitleavestheindigo，untilbeyondtheinvisiblechemicalraysitisnearlyasstrongasitisatthecalorificendofthespectrum。
ImagesonDaguerreotypeplateswhichhavebeencompletelyobliteratedbyrubbingmayberestored，byplacingitinatolerablystrongsolutionofiodineinwater。
BROMIDEOFSILVER。——Thissalt，liketheiodide，doesnotappeartobereadilychangedbytheactionoflight;butwhencombinedwiththenitrateofsilveritformsaverysensitivephotographicpreparation。
Paperpreparedwiththissalt，blackensoveritswholeextentwithnearlyequalintensity，whensubmittedtotheprismaticspectrum。Themostcharacteristicpeculiarityofthespectrumisitsextravagantlength。
Insteadofterminatingatthemeanyellowray，thedarkenedportionextendsdowntotheveryextremityofthevisibleredrays。
Intintitisprettyuniformlyofagrey-blackoveritswholeextent，exceptthataslightfringeofrednessisperceptibleattheleastrefractedend。Beyondtheredray，anextendedspaceisprotectedfromtheagencyofthedispersedlight，anditswhitenessmaintained;
thusconfirmingtheevidenceofsomechemicalpowerinaction，overaspacebeyondtheluminousspectrum，whichcorrespondswiththeraysoftheleastrefrangibility。
Thissaltisextensivelyusedinphotographicdrawing。
PREPARATIONSOFGOLD。——ChlorideofGold，freedfromanexcessofacidisslowlychangedundertheactionoflight;
aregularlyincreasingdarknesstakingplaceuntilitbecomespurple，thefirstactionofthelightbeingtowhitenthepaper，which，ifremovedfromthelightatthisstage，willgraduallydarkenandeventuallydevelopethepicture。
Thisprocessmaybequickenedbyplacingthepaperincoldwater。
Chlorideofgoldwithnitrateofsilvergivesaprecipitateofayellowbrowncolor。Paperimpregnatedwiththeacetateoflead，whenwashedwithperfectlyneutralchlorideofgold，acquiresabrownish-yellowhue。
Thefirstimpressionoflightseemsrathertowhitenthandarkenthepaper，bydischargingtheoriginalcolor，andsubstitutingforitapalegreyishtint，whichbyslowdegreesincreasestoadarkslatecolor;
butifarrested，whileyet，notmorethanamoderateashgrey，andheldinacurrentofsteam，thecolorofthepartsacteduponbylight——
andofthatonly——darkensimmediatelytoadeeppurple。
HereImustleavethesubjectoftheactionoflightuponmetaliccompounds——
referringtoMr。Huntsworkforanyfurtherinformationthestudentmaydesireontheothermetals——asIfindmyselfgoingbeyondmylimits。
Icannot，however，entirelydismissthesubjectwithoutgivingafewexamplesoftheactionoflightonthejuicesofplants，someofwhichproduceverygoodphotographiceffect。
CORCHORUSJAPONICA——Thejuiceoftheflowersofthisplantimpartafineyellowcolortopaper，and，sofarasascertained，isthemostsensitiveofanyvegetablepreparation;
butowingtoitscontinuingtochangecoloreveninthedark，photographicimagestakenonpaperpreparedwithitsoonfadeout。
WALLFLOWER。——Thisfloweryieldsajuice，whenexpressedwithalcohol，fromwhichsubsides，onstanding，abrightyellowfinelydividedfaecula，leavingagreenish-yellowtransparentliquid，onlyslightlycoloredsupernatant。
Thefaeculaspreadswellonpaper，andisverysensitivetolight，butappearsatthesametimetoundergoasortofchromaticanalysis，andtocomportitselfasifcomposedoftwoverydistinctcoloringprinciples，verydifferentlyaffected。Theoneonwhichtheintensityandsub-orangetintofthecolordepends，isspeedilydestroyed，butthepaperisnottherebyfullywhitened。
Apaleryellowremainsasaresidualtint，andthisoncontinuedexposuretothelight，slowlydarkenstobrown。
Exposedtothespectrum，thepaperisfirstreducednearlytowhitenessintheregionoftheblueandvioletrays。
Moreslowly，aninsulatedsolarimageiswhitenedinthelessrefrangibleportionofthered。Continuetheexposure，andabrownimpressionbeginstobepercievedinthemidstofthewhitestreak，whichdarkensslowlyovertheregionbetweenthelowerblueandextremevioletrays。
THEREDPOPPYyieldsaverybeautifulredcolor，whichisentirelydestroyedbylight。Whenperfectlydriedonpaperthecolorbecomesblue。
Thisbluecolorisspeedilydischargedbyexposuretothesun’srays，andpaperspreparedwithitaffordveryinterestingphotographs。——
Futureexperimentswillundoubtedlymorefullydevelopethephotogenicpropertiesofflowers，andpracticallyapplythem。
Certainprecautionsarenecessaryinextractingthecoloringmatterofflowers。Thepetalsoffreshflowers，carefullyselected，arecrushedtoapulpinamortar，eitheraloneorwiththeadditionofalittealcohol，andthejuiceexpressedbysqueezingthepulpinacleanlinenorcottoncloth。Itisthentobespreaduponpaperwithaflatbrush，anddriedintheair。
Ifalcoholbenotadded，itmustbeappliedimmediately，astheairchangesordestroysthecolorinstantly。
Mostflowersgiveouttheircoloringmattertoalcoholorwater——
buttheformerisfoundtoweaken，andinsomecasestodischargealtogetherthesecolors;buttheyareinmostcasesrestoredindrying。
Papertingedwithvegetablecolorsmustbekeptperfectlydryandindarkness。
Tosecureanevenessoftintonpaperitshouldbefirstmoistenedonthebackbysponging，andblottingoffwithbibulouspaper。Itshouldthenbepinnedonaboard，themoistsidedownwards，sothattwoofitsedges——
therightandlowerones——projectalittleoverthoseoftheboard。
Inclinetheboardtwentyorthirtydegreestothehorizon，andapplythetincturewithabrushinstrokesfromrighttoleft，takingcarenottogoovertheedgeswhichrestsontheboard，buttopassclearlyoverthosethatproject;andalsoobservingtocarrythetintfrombelowupwardsbyquicksweepingstrokes，leavingnodryspacesbetweenthem。Crossthesewithotherstrokesfromabovedownwards，leavingnofloatingliquidonthepaper。
Dryasquicklyaspossible，avoiding，however，suchheatasmayinjurethetintCHAP。IV。
AFEWHINTSANDSUGGESTIONSTODAGUERREOTYPISTS。
ThereareveryfewwhomaynotbecapableofpractisingthePhotographicart，eitheronpaper，ormetalicplates——but，likeallotherprofessions，somearemorecleverinitsvariousprocessesthanothers。
Impatienceisagreatdrawbacktoperfectsuccess，andcombinedwithlazinessisadecidedenemy。Besidesthis，noonecanexcelinPhotographywhodoesnotpossessanaturaltasteforthefinearts，whoisnotquickindiscerninggraceandbeauty——isregardlessoftheprinciplesofperspective，foreshortingandotherrulesofdrawing，andwhosetsaboutitmerelyforthesakeofgain——withouttheleastambitiontorisetothefirstrank，bothinitspracticeandtheory。
Thereisnoprofessionortradeinwhichaslovenlymannerwillnotshowitself，andnonewhereitseffectswillbemoreapparentthanthis。
Inordertobegreatinanypursuit，wemustbeourselves，andkeepallthings，inorder。Inyourshowandreceptionrooms，letneatnessprevail;haveyourspecimenssoplaced——
leaningslightlyforward——astoobtainthestrongestlightuponthem，andatthesametimepreventthatglassinessofapearancewhichdetractssomateriallyfromtheeffecttheyareintendedtoproduce。Ifpossible，letthelightbeofanorth-westernaspect，mellowedbycurtainsofasemitransparenthue。
Yourshow-cases，atthedoor，shouldbekeptwellcleaned。
Ihaveoftenbeendisgustedwhileattemptingtoexamineportraitsinthecasesofourartists，atthegreasycoatingandmarksofdirtyfingersupontheglassandframeenclosingthem。
Believeit，manyagoodcustomerislostfornootherreason。
Inyouroperatingroom，dustshouldbecarefullyexcluded。
Itshouldbefurnishedwithnothingapttocollectandretaindust;
acarpetisthereforenotonlyauselessarticle，butveryimproper。
Abareflooristobeprefered;butifyoumustcoveritusematting。
Thereisnoplaceaboutyourestablishmentwheregreatercareshouldbetakentohaveorderandcleanliness;foritwillpreventmanyfailuresoftenattributedtoothercauses。
"Aplaceforeverything，andeverythinginitsplace，"shouldbeanabsolutemaximwithallartists。Donotobligetheladies，ongoingawayfromyourrooms，tosay——"ThatH。isaslovenlyman;
seehowmydressisruinedbysittingdowninachairthatlookedasifithadjustcomeoutofaporterhousekitchenandhadnotbeencleanedforsixmonths。"
Inchoosingyouroperatingroom，obtainonewithanorth-westernaspect，ifpossible;andeitherwith，orcapableofhavingattached，alargeskylight。Goodpicturesmaybetakenwithoutthesky-light，butnotthemostpleasingoreffective。
Averyimportantpointtobeobserved，istokeepthecameraperfectlyfreefromdust。Theoperatorshouldbecarefultoseethattheslightestparticleberemoved，fortheactofinsertingtheplate-holderwillsetitinmotion，ifleft，andcausethoselittleblackspotsontheplate，bywhichanotherwisegoodpictureisspoiled。Thecamerashouldbesoplacedastopreventthesunshiningintothelenses。
Intakingportraits，theconformationofthesittershouldbeminutelystudiedtoenableyoutoplaceherorhiminapositionthemostgracefulandeasytobeobtained。Theeyesshouldbefixedonsomeobjectalittleabovethecamera，andtooneside——butneverinto，orontheinstrument，assomedirect;thelattergenerallygivesafixed，silly，staring，scowlingorpainfulexpressiontotheface。
Careshouldalsobetaken，thatthehandsandfeet，inwhateverposition，arenottooforwardorbackwardfromthefacewhenthatisingoodfocusIfanylargesurfaceofwhiteispresent，suchastheshirtfront，orlady’shandkerchief，apieceofdarkcloth（atemporarybosomofnankeenisbest，）maybeputoverit，butquicklywithdrawnwhentheprocessisabouttwothirdsfinished。
Averypleasingeffectisgiventoportraits，byintroducing，behindthesitter，anengravingorotherpicture——ifapainting，avoidthoseinwhichwarmandglowingtintspredominate。
Thesubjectofthesepicturesmaybeapplicabletothetasteoroccupationofthepersonwhoseportraityouaretaking。
Thisaddsmuchtotheinterestofthepicture，whichisotherwisefrequentlydull，coldandinanimate。
Mr。J。H。WhitehurstofRichmond，Va。，hasintroducedarevolvingbackground，whichissetinmotionduringtheoperation，andproducesadistinctnessandboldnessintheimagenototherwisetobeobtained。
Theeffectuponthebackgroundoftheplateisequallypleasing;
ithavingtheappearanceofabeautifullycloudedsky。
InpractisingPhotographicdrawingonpaper，thestudentmustbearinmindthatitispositivelyessential，tosecuresuccessinthevariousprocesses，tousetheutmostprecautioninspreadingthesolutions，andwashesfromthecombinationofwhichthesensitivesurfacesresult。Thesamebrushshouldalwaysbeusedforthesamesolution，andneverusedforanyother，andalwayswashedincleanwaterafterhavingbeenemployed。
Anymetalicmountingonthebrushesshouldbeavoided，asthemetalprecipitatesthesilverfromitssolution。
Thebrushesshouldbemadeofcamelsorbadger’shairandsufficientlybroadandlargetocoverthepaperintwoorthreesweeps;
forifsmallonesbeemployed，manystrokesmustbegiven，whichleavecorrespondingstreaksthatwillbecomevisiblewhensubmittedtolight，andspoilthepicture。
Thesefewpreliminaryhintsandsuggestions，will，Itrust，beofsomeservicetoallwhoadoptthispleasingartasaprofession;
andwill，withadueattentiontothedirectionsgiveninthepracticalworkingoftheDaguerreotype，Calotype，etc。，ensureacorrespondingmeasureofsuccess。
CHAP。V。
DAGUERREOTYPEAPPARATUS。
TheentireDaguerreotypeprocessiscomprisedinsevendistinctoperations;viz：
1。——Cleaningandpolishingtheplate。
2。——Applyingthesensitivecoating。
3——Submittingtheplatetotheactionoflightinthecamera。
4。——Bringingoutthepicture;inotherwordsrenderingitvisible。
5。——Fixingtheimage，ormakingitperminent——sothatthelightmaynolongeractuponit。
6。——Gilding：orcoveringthepicturewithathinfilmofgold——
whichnotonlyprotectsit，butgreatlyimprovesitsdistinctnessandtoneofcolor。
7。——Coloringthepicture。
Forthesevariousoperationsthefollowingarticles——
whichmakeuptheentireapparatusofaDaguerreanartist——
mustbeprocured1。——THECAMERA。——（Fig。5。）。TheCameraObscuraoftheItalianphilosophers，althoughhighlyappreciated，onaccountofthemagicalcharacterofthepicturesitproduced，remainedlittleotherthanascientifictoy，untilthediscoveryofM。Daguerre。
Thevalueofthisinstrumentisnowgreat，andtheinterestoftheprocesswhichitsoessentiallyaids，universallyadmitted。
Afulldescriptionofitwillthereforebeinteresting。
[hipho_5。gif]
Thecameraisadarkbox（a），havingatubewithlenses（b）placedinoneendofit，throughwhichtheradiationsfromexternalobjectspass，andformadiminishedpictureuponthegroundglass（g）placedattheproperdistanceintheboxtoreceiveit;
thecapccoveringthelensesatbuntiltheplateisreadytoreceivetheimageoftheobjecttobecopied。
Thusa（fig。6。）representingthelens，andbtheobjectdesiredtoberepresented，therays（c，c）proceedingfromitfalluponthelens，andaretransmittedtoapoint，whichvarieswiththecurvatureoftheglass，whereaninvertedimage（d）ofbisveryaccuratelyformed。
Atthispoint，termedthefocus，thesensitivephotographicmaterialisplacedforthepurposeofobtainingtherequiredpicture。
Thegreatdisideratuminaphotographiccameraisperfectlenses。
Theyshouldbeachromatic，andtheutmost[hipho_6。gif]
transparencyshouldbeobtained;andundertheclosestinspectionoftheglassnottheslightestwavyappearance，ordarkspotshouldbedetected;andacurvaturewhichasmuchaspossiblepreventssphericalaberrationshouldbesecured。
Theeffectproducedbythislastdefectisaconvergenceofperpendiculars，asforinstance;twotowersofanybuilding，wouldberepresentedasleaningtowardseachother;andinaportraitthefeatureswouldseemcontracted，distortedandmingledtogether，soastothrowthepictureoutofdrawingandmakeitlookmorelikeacaricaturethanalikeness。
Ifthelensbenotachromatic，achromaticaberrationtakesplace，whichproducesanindistinct，hazyappearancearoundtheedgesofthepicture，arisingfromtheblendingoftherays。
Thediameterandfocallengthofalensmustdependinagreatmeasureonthedistanceoftheobject，andalsoonthesuperficiesoftheplateorpapertobecovered。Forportraitsoneof11/2inchesdiameter，andfrom41/2to51/2inchesfocusmaybeused;butfordistantviews，onefrom2inchesto3inchesdiameter，andfrom8to12inchesfocallengthwillanswermuchbetter。Forsinglelenses，theapertureinfrontshouldbeplacedatadistancefromit，correspondingtothediameter，andofasizenotmorethanonethirdofthesame。
Avarietyofmovablediaphramsorcaps，tocovertheapertureinfront，areveryuseful，astheintensityofthelightmaybemodifiedbythemandmoreorlessdistinctnessandclearnessofdelineationobtained。
ThesecapsalwaycomewithVoitlanderinstrumentsandshouldbesecuredbythepurchaser。
Thoughthesingleacromaticlensanswersverywellforcopyingengravings;
takingviewsfromnatureorart，forportraitsthedoubleshouldalwaysbeused。Theextensivemanufactureofthemostapprovedcameras，bothinEuropeandinthiscountry，obviatesallnecessityforanyoneattemptingtoconstructonefortheirownuse。Lensesarenowmadesoperfectbysomeartisansthat，whatiscalledthe"quickworkingcamera"
willtakeapictureinonesecond，whiletheordinarycamerasrequirefromeighttosixty。
ThecamerainmostgeneraluseisthatmanufacturedbyVoitlanderandSonofGermany。Theirsmallsizeconsistsoftwoseperateacromaticlenses;
thefirst，orexternalone，hasafreeapertureof11/2inches;thesecond，orinternal，15/8inches;andbothhavethesamefocus，viz：53/4inches。
Thelargersizediffersfromthesmaller。Theinnerlensisanachromatic31/4inchesdiameter，itsfocallengthbeing30inches。Theouterlensisameniscus——thatisboundedbyaconcaveandconvexsphericalsurfacewhichmeet——havingafocallengthof18inches。Foreverydistantview，theapertureinfrontiscontractedbyadiaphramto1/8ofaninch。
Bythismeansthelightisreflectedwithconsiderableintensityandtheclearnessandcorrectnessofthepicturesaretrulysurprising。
THEAMERICAinstrumentsareconstructedonthesameprincipleandmanyofthemareequallyperfect。Mr。EdwardAnthonyof205Broadway，NewYorkcity，hasconstructed，andsoldcamerasfullyequaltotheGermanandforwhichVoitlanderinstrumentshavebeenrefusedinexchangebythepurchaser。
Theordinarycamerabox（seefig。5，a）variesinsizetosuitthetube，andistermedmedium，half，orwhole。
Withintheboxisaslidetoassistinregulatingthefocus，andinenlargingordiminishingthepicture。Inoneendofthisslideisaspringedgrooveintowhichtheground-glassspectrum（gfig。5）isslid，forthepurposeofmoreconvenientlyarrangingthefocus。Aftertheplateisprepareditisplacedintheholder——
partlyseenate，fig。5，andcoveredwiththedarkslidef，fig。5;
thespectrumisthenwithdrawnandtheholdertakesitsplace，andthelidsd，d，areclosedafterremovingthedarkslidef。
Theplateisnowreadytoreceivetheimage，andthecapcmayberemovedtoadmitthelightintothebox。
AcameraconstructedbyVoitlanderisthusdescribedbyMr。Fisher。
"Itismadeentirelyofbrass，sothatvariationsofclimatehasnoeffectuponit。Itisveryportableandwhenpackedinitsbox，withallthenecessaryapparatusandmaterialsforpractisingtheDaguerreotypeart，occupiesbutverylittlespace。
Itisnot，however，welladaptedfortheCalotypeprocess。"
"ThebrassfootA（fig。7。），isplacedonatable，orotherfirmsupport，andthepillarB。screwedintoit;thebodyofthecamera，C，CislaidintothedoubleforkedbearingD。D。Theinstrumentisnowproperlyadjustedbymeansofthesetscrews，e，e，e，inthebrassfoot，oritmayberaised，lowered，ormoved，bythetelescopestand，andwhencorrect，fixedbythescrewb。Thelandscapetobedelineatedisviewedeitherthroughthe[hipho_7。gif]
smalllens，g，orwiththenakedeyeonthegroundglassplateH，thefocusbeingadjustedbythescrewI。Theopticalpartoftheinstrumentconsistofthesmallsetofachromaticlensesalreadydescribed。
Whentheportraitorviewisdeleniatedonthegroundglasstotheentiresatisfactionoftheoperator，thebrasscapLisplacedoverthelens，andtheentirebodyisremovedawayintothedark，takingcarenottodisturbthepositionofthestand。
ThebodyisnowdetachedatthepartH，andthepreparedpaperorplateenclosedinthebrassframeworkintroducedinitsplace;
thewholeisagainplaceduponthepedestal，thebrasscapLisremoved，bywhichthepaperorplateisexposedtothefullinfluenceofthelight，afterwhichthecapisagainreplaced。
Mr。Woodbridge，ofthiscity，hasconstructedaninstrumentfortakingfulllengthportraitsonplates10by13inches，whichisworthyofsomenotice。
Itisadoublecamera，consistingoftwoboxes，placedinaframe，oneabovetheother，andsoarrangedastoslideeasilyupanddown。
Afterthefocushasbeenadjusted，ontheobject，inbothcameras，theplateisputintotheupperbox，inthemanneralreadydescribed，untilthesuperiorportionofthefigureiscomplete;itisthenplacedinthesecondboxandthelowerextremitiesobtained。
Theadjustmentoftheinstrumentissocompletethat[hipho_8。gif]
aperfectunionofthepartsiseffectedinthepicturewithouttheleastpossiblelineofdemarkationbeingvisible。Fig。8givesafrontviewofthisinstrument。
Fig。9representsTalbot’sCalotypeCamera，——averybeautifulinstrument。
Thecopyingcameraboxhasanextraslideinthebackend，bywhichitmaybeconsiderablylengthenedatpleasure。
II。——CAMERASTAND。——Thebestconstructedstandsaremadeofmapleorblackwallnutwood，havingacastironsocket（a，fig。12，）throughwhichtheslidingrodbpasses，andintowhichthelegsc，c，withironscrewferulesareinserted。
Theplatformdismadeoftwopieces，hingedtogether，asate，andhavingathumbscrewforthepurposeofelevatingordepressingtheinstrument。
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III。MERCURYBATH。——Fig。13givesafrontviewofthemercurybathnowingeneraluseinthiscountryformercurializingandbringingoutthepicture。Itisquiteanimprovementonthosefirstused。
Tomakeitmoreportableitisinthreepieces，abandc;
havingagrooveeononesidetoreceivethethermometretubeandscalebywhichtheproperdegreeofheatingthemercuryisascertained。
Intothetoparenicelyfittedtwoorthreeironframes，withshoulders，fortheplatetorestin，suitableforthedifferentsizesofplates。
Thebathisheatedbymeansofaspiritlampplacedunderit。
Fromtwotofourouncesofhighlypurifiedmercuryareputintothebathatatime。
IV。PLATEBLOCKSANDVICES。——Thereareseveralkindsofthisarticleinuse;
Ishalldescribethetwobestonly。
Fig。10givesanideaoftheimprovementontheEnglishhandblock。
Thetopaisperfectlyflat[hipho_10。gif]
andsmooth——alittlesmallerthantheplate，soastopermitthelattertoprojectaverylittleallaround——havingatoppositeanglescctwoclasps，onefixedtheothermoveable，butcapableofbeingfastenedbythethumbscrewd，soastosecuretheplatetightlyupontheblock。
Thisblockturnsuponaswivle，b，whichisattachedtothetablebythescrewc，Thisblockisonlyusedforholdingtheplatewhileundergoingthefirstoperationincleaning。
[hipho_11。gif]
Fig。11，showstheformofLewis’newlypatentedplatevice，whichfordurability，simplicityandutilityispreferabletoallothers。
Itconsistsofasimpleplatformandarmofcastiron，theformer，a，havingagroove，d，inthecentreforfixingthedifferentsizesofplatebeds，e——andthelattersupportingtheleaves，ef。
Onthisvicewhichissecuredtoatable，orbench，theplatereceivesitsfinishingpolishwithrouge，orpreparedlampblack。
Mr。Lewisgivesthefollowingdirectionsforitsuse。"Asthecamwearstightenitwiththeadjustingscrew（g）soastoallowthelever（f）tofallbackintoahorizontalposition;theplatebeinginitsplaceatthetime。Oilthewearingpartsoccasionally。"
SomeDaguerreotypists，however，useafootlathewithbuffwheelsofvariousforms;butthisviceissufficientforallordinarypurposes。
V。COATINGBOXES。——Theusualformforiodineand[hipho_12。gif]
[hipho_13。gif]
bromineboxesissee，atfigs。14and15。TheyarefarsuperiortothoseinusewiththeEnglishoperators。
Eachconsistsofawoodenbox（a，）havingfirmlyembededwithinitastoutglassjar（c），theedgesofwhichareground。
Overthisisplacedtheslidingcoverb，doublethelengthofthebox，onehalfoccupiedbyapieceofgroundglass（e），tightlypressedupontheglasspotbyaspring（i）beneaththecrossbarg，andfitsthepotsoaccuratelythatiteffectuallypreventstheescapeofthevaporoftheiodine，bromineorotheracceleratingliquidcontainedtherein。
Theotherhalfofthelidiscutthrough，shouldersbeingleftatthefouranglesforthedifferentsizesofframes，designedtorecievetheplatewhileundergoingthecoatingprocess。
Whentheplateisputintotheframe，thecoverbisshovedunderthesecondlidhandwhencoatedtotheproperdegree，itresumesitsformerpositionandtheplateisplacedintheholderofthecamerabox。Totestthetightnessofthebox，lightapieceofpaper，putitintothepotandcoveritwiththeslidinglid。
Theburningpaperexpelstheairfromthepot，andifitbeperfectlytightyoumayraisethewholeboxbythelid。
VI。GLASSFUNNELS。——AreanecessaryarticletotheDaguerreotypist，forfilteringwater，solutions，&c。
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VII。GILDINGSTAND。——Fornervouspersonsthegildingstandisausefularticle。Itisadjustedtoaperfectlevelbythumbscrewsplacedinitsbase。
VIII。SPIRITLAMPS。——ThemostusefulandeconomicalofthosemadearetheBritania，astheyarelessliabletobreak;
andthetubeforthewickbeingfastenedtothebodybyascrewrendersitlessliabletogetoutoforderorexplode。
Glassisthecheapest，andforanamateurwilldoverywell，butforaprofessedartisttheBritaniashouldalwaysbeobtained。
IX。COLORBOX。——Thesearegenerallyfoundonsaleattheshops，andusuallycontaineightcolors，fourbrushesandagoldcup。
Theartistwould，however，dowelltoobtain，allthecolorsmentionedinthelastchapterofthiswork，andbesuretogettheverybest，astherearevariousqualitiesofthesamecolor，particularlycarmine，whichisveryexpensive，andthecupidityofsomemayinducethemtosellapoorarticleforthesakeoflargerprofits。
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STILL。——Daguerreotypistsshouldalwaysusedistilledwaterforsolutions，andwashingtheplate，ascommonwaterholdsvarioussubstancesinsolutionwhichdetractverymateriallyfromtheexcellenceofaphotograph，andoftengivesmuchtrouble，quiteunaccountabletomany。
ForthepurposeofdistillingwatertheapparatusrepresentedatFig。16
isbothconvenientandeconomical。
Itmaybeeitherwhollyofgoodstouttin，orofsheetirontinnedontheinside，andmaybeusedoveracommonfire，oronastove。
Aisthebody，whichmaybemadetoholdfromonetofourgallonsofwater，whichisintroducedattheopeningb，whichisthenstoppedbyacork。
Thetubedconnectstheneckaofthestillwiththewormtub，orrefrigeratorB，ate，whichiskeptfilledwithcoldwaterbymeansofthefunnelc，anddrawnoffasfastasitbecomeswarmbythecockf。
Thedistilledwateriscondensedintheworm——andpassesoffatthecockb，underwhichabottle，orothervessel，shouldbeplacedtoreceiveit。
Thedifferentjointsarerenderedtightbylute，orinitsabsence，somestiffpastespreaduponapieceoflinenandwrappedaroundthemwillanswerverywell;anadditionofsealingwaxoverallwillmakethemdoublysecure。
[hipho_16。gif]
HYGROMETER。——Thisisaninstrumentnevertobefound，Ibelieve，intheroomsofouroperators，althoughitwouldbeofmuchusetothem，forascertainingthequantityofmoisturefloatingabouttheroom;
andasitisnecessarytohavetheatmosphereasdryaspossibletopreventanundueabsorptionofthiswateryvaporbytheiodine&c。，andtoprocuregoodpictures，——itsdetectionbecomesamatterofimportance。
Mason’shygrometer，manufacturedbyMr。RoachandsoldbyMr。Anthony，205Broadway，NewYorkisthebestinuse。
Itconsistsoftwothermometretubesplaced，sidebyside，onametalicscale，whichisgraduatedequallytobothtubes。
Thebulbofoneofthesetubescommunicates，bymeansofanet-workofcotton，withaglassreservoirofwaterattachedtothebackofthescale。Fig。17and18representafrontandbackviewofthisinstrument。
Fig。17isthefrontview，showingthetubeswiththeirrespectivescales;
thebulbbbeingcoveredwiththenetworkofcottoncommunicatingwiththereservoircfig。18，atd。
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Theevaporationofthewaterfromthisbulbdecreasesthetemperatureofthemercuryinthetubebinproportiontothedrynessoftheatmosphere，andthenumberofdegreesthetubebindicatesbelowthatoftheother，showstherealstateoftheatmosphereintheroom;forinstance，ifbstandsatfortyandaatsixty-onetheroomisinastateofextremedryness，thedifferenceoftwenty-onedegreesbetweenthethermometers——letastandatanyonepoint——givesthisresult。
Iftheydonotdiffer，orthereisonlyfourorfivedegreesvariation，theatmosphereoftheroomisverymoistandmeansshouldbetakentoexpelthesuperfluousquantity。
HEADRESTS。——Thebuttonheadrestwithchairbackclip，Afig。
19——ismuchthebestfortravellingartists，asitcanbetakenapart，intoseveralpiecesandcloselypacked;iseasilyandfirmlyfixedtothebackofachairbytheclampandscrewaandb，andisreadilyadjustedtothehead，asthebuttonsc，candarmsd，daremovable。
Sometimesthebuttonrestisfixedtoapole，whichisscrewedtothechair;
butthismethodisnotsosecureandsolidastheclipandoccupiesmoreroominpacking。Boththepoleandclip，arefurnishedinsomecaseswithbrassbandrestsinsteadofthebutton;buttheonlyrecommendationthesecanpossiblypossessintheeyesofanyartist，istheircheapness。
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ForaDaguerreotypistpermanentlylocatedtheindependentironhead-rest，Bfig。19，isthemostpreferable，principallyonaccountofitssolidity。
Itisentirelyofiron，issupportedbyatripoda）ofthesamemetalandcanbeelevatedbymeansofarod（b）passingthroughthebodyofthetripod，toaheightsufficientforaperson，standing，torestagainst。
GALVANICBATTERY。——Thisarticleisusedforthepurposeofgivingtoimperfectlycoatedplatesathickercoveringofsilver。
Theformofbatterynowmostuniversallyemployedforelectrotype，andothergalvanicpurposes，isSmee’s——Fig。20。Itconsists[hipho_20。gif]
ofapieceofplatinizedsilver，A，onthetopofwhichisfixedabeamofwood，B，topreventcontactwiththesilver。
AbindingscrewCissolderedontothesilverplatetoconnectitwithanydesiredobject，bymeansofthecopperwire，e。
Aplateofamalgamatedzinc，D，varyingwiththefancyoftheoperatorfromonehalftotheentirewidthofthesilverisplacedoneachsideofthewood。Thisissetintoaglassvessel，P，——theextremeendsofthewoodrestinguponitsedge——onwhichtheacidwithwhichitischargedhasnoeffect。Thejarischargedwithsulphuridacid，（commonoilofvitriol）dilutedineightpartsitsbulkofwater。
Thezincplatesofthebatteryhavebeenamalgamatedwithquicksilver，andwhenthebatteryissetintothejarofacidthereshouldbenoactionpercieveduponthemwhenthepolesF，G，arenotincontact。
Shouldanyactionbepercieved，itindicatesimperfectamalgamation;
thiscanbeeasilyremediedbypouringalittlemercuryuponthemimmediatelyafterremovingthemfromtheacid，takingcaretogetnoneuponthecentreplateA。
Directionsforuse。——AsheetofsilvermustbeattachedtothewireconnectedwiththecentreplateAofthebattery，andplacedinthesilversolution——preparedasdirectedbelow。
Theplatetobesilveredisfirstcleanedwithdilutedsulphuricacid，andthenattachedtothewire，G，proceedingfromthezincplatesD，D，andplacedinthesilversolution，oppositethesilverplateattachedtothepoleF，andabouthalfaninchfromit。
Aslighteffervescencewillnowbepercievedfromthebattery，andthesilverwillbedepositedupontheDaguerreotypeplate，whileatthesametimeaportionofthesilverplateisdissolved。
Topreparethesolutionofsilver。——Dissolveoneounceofchlorideofsilverinasolutionoftwoouncesofcyanideofpotassium，previouslydissolvedinonequartofwater。
Theoxideofsilvermaybeusedinsteadofthechloride。
Thissolutionisputintoatumbler，orothervessel。
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ThisbatterywiththenecessaryarticlesforusingitmaybeobtainedofE。Anthony，205Broadway，NewYorkcity。
Theotherarticlesrequiredbyeveryoperatormaybesimplyenumerated，viz：
Stickng，orsealingpaper。
Apairofpliers，orforceps。
Porcelainpansordishes，forapplyingthehyposulphiteofsodaandwashingaftertheimagineisfixed，somethinginformlikefig。23。
Asupportforholdingtheplatewhilebeingwashed，likefig。24
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BUFFSTICKS。——Fig。25。——Theseareusuallyfromonetothreefeetinlength，andaboutthreeincheswide——somethinktwoandahalfsufficient。
Theunderside，whichisconvex，iscoveredwithastripoffinelypreparedbuckskin，orvelvet，wellpaddedwithcottonortow。
Allthearticlesenumeratedinthischaptermaybeobtained，oftheverybestqualityandatthemostreasonablerates，ofMr。E。Anthony，205，Broadway，NewYork。
CHAP。VI。
THEDAGUERREOTYPEPROCESS。
TheprocessoftakingDaguerreotypepicturesdiffersverymateriallyfromallothersofthephotographicart，inasmuchastheproductionoftheimageiseffecteduponplatesofcoppercoatedwithsilver。
Thesilveremployedshouldbeaspureaspossible;thethicknessoftheplateisoflittleconsequence，providedtherebesufficientsilvertobearthecleaningandpolishing——isfreefromcopperspots，issusceptibleofahighpolish，anexquisitelysensitivecoatingandapleasingtone。
ThesequalitiesarepossessedtoaneminentdegreebytheFrenchplates。
Havingalreadyenumeratedthevariousprocesses——andtheapparatusnecessaryforthemanipulation，Iwillheregivealistofthechemicalstobeused，andthenproceedtoexplainthemmorefully。
Therequisitechemicalsare——
NITRICACID，ROUGE，DRYIODINE，MERCURY，DRYINGPOWDER，HYPOSULPHITEOFSODA，CYANIDEOFPOTASSIUM，CHLORIDEOFGOLD;OR
ROTTENSTONE，HYPOSULPHITEOFGOLD。
TRIPOLI，CHLORIDEOFSILVER。
CHLORIDEOFIODINE，}theircompounds，orotherBROMINE}acceleratingmixtures。
FIRSTOPERATION。——Cleaningandpolishingtheplate。——
Forthispurposetheoperatorwillrequirethe——
PlateBlocks，PlateViceSpiritLamp，PolishingBuffs，NitricAcid，dilutedinfifteentimesitsbulkofwaterGalvanicBattery，togalvanizetheplate，ifitistooimperfecttobeusedwithout，previouscleaningit，asdirectedinthelastchapter。
Rottenstone，Tripoli，whichistoooftendispensedwith。
Rouge，orlampblack——thefirstbeingmostpreferable。
TheEnglishoperatorsmixthetwotogether。
PreparedcottonWool，orCantonflannel。Ifthefirstisused，itshouldbeexcludedfromthedust，asitisnotsoeasilycleansedasthelatter。
Theplateissecured，withitssilversideupward，totheblock，bythemeansdescribedonpage58——havingpreviouslyturnedtheedgesbackwardallaround。Theamountofcleaningaplaterequires，dependsuponthestateitisin。Wewillsupposeoneintheworstcondition;dirty，scratched，andfullofmercuryspots，allofwhichimperfectionsaremoreorlesstobeencountered。
Themercuryspotsaretoberemovedbyburningtheplate。
Todothisholdtheplateovertheflameofaspiritlamp，moreparticularlyunderthemercuryspots，untilthey，assumeadullappearance，whenthelampistoberemoved，andtheplateallowedtocool，afterwhichitisattachedtotheblock。
Placetheblockupontheswivle，andholditfirmlywiththelefthand;
takeasmallknotorpelletofcotton，or，ifyoulikeitbetter，asmallpieceofcantonflannel——wetitwithalittledilutednitricacid;
thensiftsomefinelypreparedrottenstone——Davie’s，*ifyoucangetit——
uponit，andrubitovertheplatewithacontinualcircularmotion，tillalltracesofthedirtandscratchesareremoved;thenwipeofftherottenstonewithacleanpieceofcotton，adopting，asbefore，aslightcircularmotion，atthesametimewipingtheedgesoftheplate。
Eventhebackshouldnotbeneglected，butthroughlycleansedfromanydirtorgreasyfilmitmayhavereceivedfromhandling。
*SoldbyE。Anthony。
Whenthisisthoroughlyaccomplished，mixaportionofyourtripoliwiththedilutenitricacid，totheconsistenceofthickcream。
Thentakeapelletofcottonandwellpolishtheplatewiththismixture，inthesamemanneraswiththerottenstone。Continuetheprocesstill，onremovingthetripoliwithacleanpellet，theplateexhibitsaclear，smooth，brightsurface，freefromallspots，orscratches。
AnyremainsoftheacidontheplatemaybeentirelyremovedBysiftingonitalittleDryingpowder，andthenwipingitcarefullyoffwithafinecamelshairbrush，orduster。Thefinishingpolishisnowtobegiven。
Forthispurposetherouge——oramixtureofrougeandlamp-black，intheproportionofonepartoftheformertosevenofthelatter——isused。
Itshouldbekepteitherinamuslinbag，orwidemouthbottle，overwhichapieceofmuslinistied——infact，boththerottenstoneandtripolishouldbepreservedfromthedustinthesamemanner。
Withalittleofthispowderspreadoverthebuff——describedonpage53——
theplaterecievesitsfinalpolish;thecircularmotionischangedforastraightoneacrosstheplate，which，ifintendedforaportrait，shouldbebuffedthenarrowway;butif，foralandscapeorviewofahouse，thelengthwayoftheplate。
Theoperationofcleaningtheplateatfirstappearsdifficultandtedious，andmanyhavebeendeterredfromattemptingthisinterestingartonthataccount;but，inreality，itismoresimpleinpracticethanindescription，andwithalittlepatienceandobservation，alldifficultiesareeasilyovercome。
Greatcaremustbetakentokeepthebufffreefromallextraneousmatter，andperfectlydry，andwhennotinuseitshouldbewrappedupintissuepaper，orplacedinatightbox。
Theplateshouldbebuffedimmediatelybeforethesensitivecoatingisgiven;particlesofdustarethuseffectuallyremoved;
thetemperatureoftheplateisalsoincreasedbythefriction，andtherequiredtintmorereadilyobtained。
SECONDOPERATION。——Applyingthesensativecoating。——Theapparatusandchemicalsrequired，areanIodinebox——seefig。14page53。
Brominebox——similartotheiodineboxbutatrifledeeper。
DryIodine。
Bromine，oracompoundofBromineandChlorideofIodine，orothersensitivemixture。
MostofourbestoperatorsusethecompoundBromineandChlorideofIodine。IntheearlydaysoftheDaguerreotype，Iodinealonewasusedinpreparingtheplate，andalthoughitstillplaysaveryimportantpart，otherpreparations，calledacceleratingliquids，quickstuff，&c。，areused，andthediscoveryofwhichhasaloneensuredtheapplicationoftheDaguerreotypesuccessfullytoportraittaking——forwhenfirstintroducedamongusittookfromfivetotenminutestoproduceatolerablegoodview，whilenowbutthefractionofaminuteisrequiredtoobtainanaccuratelikeness。
Toiodizetheplateperfectlyitmustbeplacedovertheiodinevaporimmediatelyafterbuffing。Scatterfromasixteenthtotheeighthofanounceofdryiodineoverthebottomofyourcoatingbox，andslightlycoveritwithcottonwool。Theplateisthendroppedintotheframeb，fig。12，withitssilveredsurfacedownward，andthrustunderthelidh。Thebrightsurfaceoftheplateissooncoatedwithafilmofiodineofafineyellowcolor;
itisthenremovedandplacedovertheacceleratingsolution。
Itisnotabsolutelynecessarytoperformthisoperationinthedark，althoughabrightlightshouldbeavoided。
Notsothenextpartoftheprocess，viz;givingtheplateitsextremesensitiveness，orcoatingwiththeacceleratingliquids。
Inthisgreatcautionshouldbeusedtopreventtheslightestrayoflightimpringingdirectlyontheplate，andinexaminingthecolorreflectedlightshouldalwaysbeused。
Aconvientmethodofexaminingtheplate，istomakeasmallholeinthepartitionoftheclosetinwhichyoucoat，andcoveritwithapieceoftissuepaper;byquicklyturningtheplatesothatthepaperisreflecteduponitthecolorisverydistinctlyshown。
Mostofouroperatorsarenotsoparticularinthisrespectastheyshouldbe。
ACCELERATINGLIQUID。——Ofthesethereareseveralkinds，whichdifferbothincompositionandaction——someactingveryquickly，othersgivingafinertonetothepicturealthoughtheyarenotsoexpeditiousinthereoperations;orinotherwords，notsosensitvetotheactionoflight。TheseareadoptedbyDaguerreotypistsaccordingtotheirtastesandpredjudices。
Theyareallappliedinthesamewayasthecoatingofiodine。
Thefollowingarethebest。
Brominewater——ThissolutionismuchusedinFrance，and，Ishallthereforegiveitspreparation，andthemethodofusingit，inthewordsofM。Figeau。"Putintoabottleofpurewater，alargeexcessofbromine;shakethemixturewell，andbeforeusingit，letallthebrominebetakenup。Anascertainedquantityofthissaturatedwateristhendilutedinagivenquantityofdistilledwater，whichgivesasolutionofbrominethatisalwaysidentical。"
M。Figeaurecommendsonepartofthesaturatedsolutiontothirtypartsitsbulkofwater;butM。Lesebourfindsitmoremanageableifdilutedwithfortytimes。Incasepuredistilled，orrainwatercannotbeprocured，afewdropsofnitricacid——saysixtothequart——
shouldbeaddedtothecommonwater。
Putintothebromineboxagivenquantityofthissolution，sufficienttowellcoverthebottom;theplate，havingbeeniodizedtoadeepyellow，isplacedoverit;thetimetheplateshouldbeexposedmustbeascertainedbymakingafewtrials;itaveragesfromtwelvetofortyseconds。
Whenonceascertained，itisthesameforanynumberofplates，asthesolution，whichofcoursewouldbecomeweakerandweaker，ischangedaftereveryoperation，thesamequantitybeingalwaysputintothepot。
ChlorideofIodine。——Thisispreparedbyintroducingchlorinegassintoaglassvesselcontainingiodine;theiodineisliquified，andtheabovenamedcompoundistheresult。
Operatorsneednot，however，beatthetroubleandexpenseofpreparingit，asitcanbeobtainedprefectlypureofMr。Anthony，205Broadway，N。Y。，asalsoallofthechemicalshereinenumerated。
Thecompoundisdilutedwithdistilledwater，andtheplatesubmittedtoitsactiontillitisofarosecolor。Chlorideofiodinealone，isseldomifeverusednowbyAmericanoperators，asitdoesnotsufficientlycomeuptotheirlocomotiveprincipleofprogression。
Thenextisalsoeschewedbythemajority，althoughmanyofourbestartistsusenoother，onaccountoftheveryfinetoneitgivestopictures。
BromideofIodine。——Thisisacompoundofbromineandchlorideofiodine。Inmixingit，muchdependsuponthestrengthoftheingredients;anequalportionofeachbeinggenerallyused。
Perhapsthebestmethodofpreparingit，istomakeasolutioninalcoholofhalfanounceofchlorideofiodine，andaddthebrominedropbydrop，untilthemixturebecomesofadarkredcolor;
thendilutewithdistilledwater，tillitassumesabrightyellow。
Putabouthalfanounceofthiscompoundintothepot，andcoatoverittoavioletcolor，changethesolutionwhenitbecomestooweaktoproducethedesiredeffect。
Another。——Mixhalfanounceofbrominewithoneounceofchlorideofiodine，addtwoquartspuredistilledwater，shakeitwellandletitstandfortwelvehoursthenaddtwenty-fivedropsofmuriaticacid，andletitstandanothertwelvehours，occasionallyshakingitupwell。
Dilutesixpartsofthissolutioninsixteenofwater。Coatoverdryiodinetoadeepyellow，thenoverthesensitivetoadeeprosecolor——
approachingpurple——thenback，overdryiodinefromfourtoeightseconds。
Roach’sTrippleCompound。——Thisisoneoftheverybestsensitivesolutions，andisverypopularamongDaguerreotypists。
Tousethis，takeonepartinweight，sayonedrachm，ofthecompoundanddiluteitwithtwelveofwater;coatoverdryiodinetoyellow，thenoverthecompoundtoarosyred。
Theeffectinthecameraisquick，andproducesapictureofafinewhitetone。
Gurney’sSensitive。——Thisisanotherpreparationofbromine，andgivesafinetone。Totwopartsofwateraddoneofthesensitive，andputjustsufficientintheboxtocoverthebottom，orenableyoutocoatinfromeighttotenseconds。
Coatoverdryiodinetoadarkyellow，andoverthequicktillyouseeagoodchange，thenbackoverthedryiodinefromtwotothreeseconds。
BromideofLime，orDrySensitive。——Thisisacompoundbutrecentlyintroduced，andisbecomingsomewhatofitfavorite，owingprincipallytotheslighttroubleitgivesinitspreparation，andthetoneitimpartstothepicture。Toprepareit，fillyourjarabouthalforquarterfullofdryslackedlime，thendropintoitbromine，tillitbecomesabrightorangered。
Theplateisgenerallycoatedoverthiscompound，aftertheiodinecoatingtoyellow，toaviolet，orplumcolor;
butitwillworkwellunderanycircumstances，thecolorbeingoflittleconsequence，ifcoatedfromthirtytoninetyseconds，accordingtoitsstrength。
Mead’sAccelerator。——Imerelymentionthisasbeinginthemarket，notknowinganythinginregardtoitsmerits。
Thedirectionsgivenforitsuseareasfollows：
Mixone-thirdofabottlewithawineglassfullofwater，coattheplateoverdryiodinetoadarkgoldcolor，thenovertheacceleratortoaviolet，thenbackoverdryiodine，orchlorideofiodine，fromthreetofiveseconds。
ChlorideofBromine。——M。Bissou，aFrenchexperimentalist，hasfoundthatbromineassociatedwithchlorine，preparedinasimilarmannertochlorideofiodine，alreadydescribed，asolutionofbrominebeingsubstitutedfortheiodine，isaverysensitivesolution;bymeansofitdaguerreotypeproofsareobtainedinhalfasecond，and，thusveryfugitivesubjectsarerepresented，makingittheverybestcompoundfortakingchildren。
Soquickisitsoperation，thatevenpersonsoranimalsmaybetakenintheactofwalking。
HungarianLiquid。——This，Ibelieve，hasneverbeenusedhere，orimportedintothiscountry，andthecompositionofitisnotgenerallyknown，eveninEurope，whereithastakenprecedenceofallothers。
Itactsquicklyandwithconsiderablecertainty。Itisusedbydilutingitwithfromtentofifteentimesitsbulkofwater，puttingasufficientquantityintothejartocoverthebottom。
Theplatebeingpreviouslyiodizedtoalightyellow，issubmittedtothismixturetillitassumesalightrosetint。
BromineandFluoricAcid，incombination，areusedbysomeDaguerreanartistsasasensitive，butanyoftheabovecompoundsarebetter;
besidesthis，thefluoricacidisadangerouspoison，andthequickmadefromitwillnotrepaytherisktothehealthinusingit。
AsIhavebeforesaid，greatcautionshouldbeobservedinexaminingthecoloroftheplate，evenbythefeeblelightallowed，which，whenattained，mustbeimmediatelyplacedintheholderbelongingtothecameraandcoveredwiththedarkslide。
YouthenpasstotheTHIRDOPERATION。——SubmittingthePlatetotheactionofLightintheCamera。——Experiencealonemustguidetheoperatorastothetimetheplateshouldbeexposedtotheinfluenceofthelight;thisbeingdependentonavarietyofcircumstances，asclearnessoftheatmosphere——
andhere，areferencetothehygrometerwillbeofadvantage——
timeofday，objecttobetaken，andthedegreeofsensitivenessimpartedtotheplatebythequickstuff。AsIhavebeforesaid，theartistshouldbecarefultoseethattheinteriorofthecameraiscleanandfreefromdust，asthesmallparticlesflyingabout，orsetinmotionbytheslidingoftheholderintothebox，attachthemselvestotheplate，andcausethelittleblackspots，bywhichanotherwisegoodpictureisfrequentlyspoiled。
Careshouldalsobetakeninwithdrawingthedarkslide，infrontoftheplate，fromtheholder，asthesameeffectmaybeproducedbyatoohastymovement。Thelensisthelastthingtobeuncovered，bywithdrawingthecapc。fig。5。，whichshouldnotbedoneuntilyouhaveplacedthesitterinthemostdesirableposition。
When，accordingtothejudgmentandexperienceoftheoperator，theplatehasremainedlongenoughtoreceiveagoodinpression，thecapisreplacedoverthelens，andthedarkslideovertheplate，whichisthenremovedfromthecamera。
Daguerreotypistsgenerallymarktimebytheirwatches，arrivingatthenearestpossibleperiodforproducingagoodpicturebymakingseveraltrials。
Asareadymethodofmarkingshortintervalsoftimeis，however，averyimportantconsideration，andasanyinstrumentwhichwillenableanartisttoarriveattheexactperiod，mustbeanimprovement，andworthyofuniversaladoption，IwillheredescribeoneinventedbyMr。ConstableofEngland，whichhecallsaSandClock，orTimeKeeper。——"Itconsistsofaglasstube，abouttwelveincheslong，byoneindiameter，halffilledwithfinesand，similartothatusedfortheordinaryminuteglasses，and，likethem，ithasadiaphram，withasmallholeinthecentrethroughwhichthesandruns。
Thetubeisattachedtoaboardwhichrevolvesonacentrepin;
onthesideisagraduatedscale，dividedintohalfseconds;
thetubeisalsoprovidedwithamoveableindex。
Thisinstrumentisattached，inaconspicuousplace，tothewall。