the history and practice of the art of photography-第12节

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ine　from　two　to　three　seconds。

Bromide　of　Lime；　or　Dry　Sensitive。This　is　a　compound　but　recently　introduced；　and　is　becoming　somewhat　of　it　favorite；　owing　principally　to　the　slight　trouble　it　gives　in　its　preparation；　and　the　tone　it　imparts　to　the　picture。　　To　prepare　it；　fill　your　jar　about　half　or　quarter　full　of　dry　slacked　lime；　then　drop　into　it　bromine；　till　it　becomes　a　bright　orange　red。　The　plate　is　generally　coated　over　this　compound；　after　the　iodine　coating　to　yellow；　to　a　violet；　or　plum　color；　but　it　will　work　well　under　any　circumstances；　the　color　being　of　little　consequence；　if　coated　from　thirty　to　ninety　seconds；　according　to　its　strength。

Mead's　Accelerator。I　merely　mention　this　as　being　in　the　market；　not　knowing　any　thing　in　regard　to　its　merits。　The　directions　given　for　its　use　are　as　follows：　Mix　one…third　of　a　bottle　with　a　wine　glass　full　of　water；　coat　the　plate　over　dry　iodine　to　a　dark　gold　color；　then　over　the　accelerator　to　a　violet；　then　back　over　dry　iodine；　or　chloride　of　iodine；　from　three　to　five　seconds。

Chloride　of　Bromine。M。　Bissou；　a　French　experimentalist；　has　found　that　bromine　associated　with　chlorine；　prepared　in　a　similar　manner　to　chloride　of　iodine；　already　described；　a　solution　of　bromine　being　substituted　for　the　iodine；　is　a　very　sensitive　solution；　by　means　of　it　daguerreotype　proofs　are　obtained　in　half　a　second；　and；　thus　very　fugitive　subjects　are　represented；　making　it　the　very　best　compound　for　taking　children。　So　quick　is　its　operation；　that　even　persons　or　animals　may　be　taken　in　the　act　of　walking。

Hungarian　Liquid。This；　I　believe；　has　never　been　used　here；　or　imported　into　this　country；　and　the　composition　of　it　is　not　generally　known；　even　in　Europe；　where　it　has　taken　precedence　of　all　others。　It　acts　quickly　and　with　considerable　certainty。　　It　is　used　by　diluting　it　with　from　ten　to　fifteen　times　its　bulk　of　water；　putting　a　sufficient　quantity　into　the　jar　to　cover　the　bottom。　The　plate　being　previously　iodized　to　a　light　yellow；　is　submitted　to　this　mixture　till　it　assumes　a　light　rose　tint。

Bromine　and　Fluoric　Acid；　in　combination；　are　used　by　some　Daguerrean　artists　as　a　sensitive；　but　any　of　the　above　compounds　are　better；　besides　this；　the　fluoric　acid　is　a　dangerous　poison；　and　the　quick　made　from　it　will　not　repay　the　risk　to　the　health　in　using　it。

As　I　have　before　said；　great　caution　should　be　observed　in　examining　the　color　of　the　plate；　even　by　the　feeble　light　allowed；　which；　when　attained；　must　be　immediately　placed　in　the　holder　belonging　to　the　camera　and　covered　with　the　dark　slide。　You　then　pass　to　the

THIRD　OPERATION。Submitting　the　Plate　to　the　action　of　Light　in　the　Camera。Experience　alone　must　guide　the　operator　as　to　the　time　the　plate　should　be　exposed　to　the　influence　of　the　light；　this　being　dependent　on　a　variety　of　circumstances；　as　clearness　of　the　atmosphere　and　here；　a　reference　to　the　hygrometer　will　be　of　advantage　time　of　day；　object　to　be　taken；　and　the　degree　of　sensitiveness　imparted　to　the　plate　by　the　quickstuff。　　As　I　have　before　said；　the　artist　should　be　careful　to　see　that　the　interior　of　the　camera　is　clean　and　free　from　dust；　as　the　small　particles　flying　about；　or　set　in　motion　by　the　sliding　of　the　holder　into　the　box；　attach　themselves　to　the　plate；　and　cause　the　little　black　spots；　by　which　an　otherwise　good　picture　is　frequently　spoiled。　Care　should　also　be　taken　in　withdrawing　the　dark　slide；　in　front　of　the　plate；　from　the　holder；　as　the　same　effect　may　be　produced　by　a　too　hasty　movement。　　The　lens　is　the　last　thing　to　be　uncovered；　by　withdrawing　the　cap　c。　fig。　5。；　which　should　not　be　done　until　you　have　placed　the　sitter　in　the　most　desirable　position。　When；　according　to　the　judgment　and　experience　of　the　operator；　the　plate　has　remained　long　enough　to　receive　a　good　inpression；　the　cap　is　replaced　over　the　lens；　and　the　dark　slide　over　the　plate；　which　is　then　removed　from　the　camera。

Daguerreotypists　generally　mark　time　by　their　watches；　arriving　at　the　nearest　possible　period　for　producing　a　good　picture　by　making　several　trials。　As　a　ready　method　of　marking　short　intervals　of　time　is；　however；　a　very　important　consideration；　and　as　any　instrument　which　will　enable　an　artist　to　arrive　at　the　exact　period；　must　be　an　improvement；　and　worthy　of　universal　adoption；　I　will　here　describe　one　invented　by　Mr。　Constable　of　England；　which　he　calls　a

Sand　Clock；　or　Time　Keeper。〃It　consists　of　a　glass　tube；　about　twelve　inches　long；　by　one　in　diameter；　half　filled　with　fine　sand；　similar　to　that　used　for　the　ordinary　minute　glasses；　and；　like　them；　it　has　a　diaphram；　with　a　small　hole　in　the　centre　through　which　the　sand　runs。　The　tube　is　attached　to　a　board　which　revolves　on　a　centre　pin；　on　the　side　is　a　graduated　scale；　divided　into　half　seconds；　the　tube　is　also　provided　with　a　moveable　index。　This　instrument　is　attached；　in　a　conspicuous　place；　to　the　wall。　The　glass　tube　being　revolved　on　its　centre；　the　index　is　set　to　the　number　of　half　seconds　required；　and　the　sand　running　down；　the　required　time　is　marked　without　the　possibility　of　error。　In　practice　it　will　be　found　to　be　a　far　more　convenient　instrument　for　the　purpose　than　either　a　clock　or　a　seconds　watch；　and　is　applicable　both　for　the　camera　and　mercury　box。〃

If　the　artist　finds　it　desirable　or　necessary　to　take　the　object　to　be　copied　in　its　right　position；　that　is　reverse　the　image　on　the　spectrum；　he　can　do　so　by　attaching　a　mirror　（which　may　be　had　of　Mr。　Anthony；　or　Mr。　Roach）　to　the　camera　tube；　at　an　angle　of　forty…five　degrees。

If；　after　taking　the　plate　from　the　camera；　it　be　examined；　no　picture　will　yet　be　visible；　but　this　is　brought　about　by　the

FOURTH　PROCESS。Bringing　out　the　Picture；　or　rendering　it　Visible。　We　now　come　to　the　use　of　the　mercury　bath；　Fig。　11。　　To　the　bath　a　thermometer　is　attached；　to　indicate　the　proper　degree　of　beat　required；　which　should　never　be　raised　above　170　deg。　Fahrenheit。　　The　plate　maybe　put　into　one　of　the　frames　（see　Fig。　11；）　over　the　mercury；　face　downwards；　and　examined　from　time　to　time；　by　simply　raising　it　with　the　fingers；　or　a　pair　of　plyers。　　This　operation；　as　well　as　the　others；　should　take　place　in　the　dark　closet。　　＇hipho_26。gif＇　Sometimes；　to　prevent　the　necessity　of　raising　the　plate；　an　additional　cover　or　top　is　made　use　of。　　It　consists　of　a　box　fitted　closely　to　the　inner　rim　of　the　bath；　and　having　an　inclined　top　（a；　Fig。　27。）　The　top　is　cut　through　and　fitted　with　frames　for　each　size　of　plate；　like　those　already　described；　and　in　the　back　is　a　piece　of　glass　（b；）　through　which　to　view　the　progress　of　mercurialization；　and　an　additional　piece　（c；）　on　one　side；　colored　yellow；　to　admit　the　light。　The　outline　only　of　the　top　is　here　given；　in　order　to　show　every　portion　of　it　at　one　view。

The　picture；　being　fully　developed；　is　now　taken　out　and　examined；　it　must　not；　however；　be　exposed　to　too　strong　a　light。　If　any　glaring　defects　be　perceived；　it　is　better　not　to　proceed　with　it；　but　place　it　on　one　side　to　be　re…polished；　if；　on　the　contrary；　it　appears　perfect；　you　may　advance　to　the

FIFTH　OPERATION。Fixing　the　Image　so　that　the　light　can　no　longer　act　upon　it。The　following　articles　are　required　for　this　purpose：

Two　or　three　porcelain　or　glass　dishes；　in　form；　something　like　fig。　24。

A　plate　support；　fig。　25。　　Few；　I　believe；　now　make　use　of　this；　although　it　is　a　very　convenient　article。

Hyposulphite　of　Soda；

A　pair　of　Plyers。

In　Europe；　they　also　use　a　drying　apparatus；　Fig。　27；　but　this；　like　the　plate　support；　　＇hipho_27。gif＇　is　a　matter　of　little　consequence；　and　may　be　dispensed　with。　I　will；　however；　describe　it；　for　the　benefit　of　those　who　may　wish　to　use　it。

A　vessel　made　of　copper　or　brass；　tinned　inside；　and　large　enough　to　take　in　the　largest　plate；　but　not　more　than　half　an　inch　wide；　is　the　most　convenient。　　It　must　be　kept　perfectly　clean。　Hot　distilled　water　is　poured　into　it；　and　the　temperature　kept　up　by　a　spirit　lamp。

Hyposulphite　of　Soda。Having　made　a　solution　of　hyposulphite　of　soda；　and　well　filtered　itthe　strength　is　immaterial；　about　half　an　ounce　of　the　salt　to　a　pint　of　distilled　water　is　sufficientpour　it　into　one　of　the　porcelain　dishes；　put　into　another　plain；　and　into　a　third　distilled　water。　Immerse　the　plate　with　its　face　downwards　into　the　hyposulphite；　and　the　whole　of　the　sensitive　is　removed；　and　the　light　has　no　farther　action　upon　it；　it　is　then　to　be　removed　from　the　hyposulphite　and　plunged　into　the　plain　water；　or　placed　upon　the　support；　fig。　25；　and　the　water　poured　over　it。　It　is　then　washed　in　a　similar　manner　with　the　distilled　water　and　well　examined；　to　see　that　not　the　slightest　particle　of　dust　rests　on　the　suface。　　The　next　step　is　to　dry　it。

This　may　be　readily　accomplished　by　holding　the　plate　with　your　plyers；　and　pouring　distilled　water　over　itif　it　is　hot；　so　much　the　better。　Apply　the　spirit　lamp　to　the　back；　at　the　corner　held　by　the　plyers；　at　the　same　time　facilitating　the　operation　with　the　breath；　pass　the　lamp　gradually　downwards；　finishing　at　the　extreme　corner。　The　last　drop　may　now　be　removed　by　a　little　bibulous　paper。　A　single　drop；　even；　of　distilled　water