american hand book of the daguerreotype-第9部分

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high　temperatures；　or　when　the　thermometer　indicates　a　heat　above　60　deg。

Bromide　of　PotassiumIs　prepared　by　mixing　bromine　and　a　solution　of　pure　potass　together；　and　evaporating　to　dryness；　it　crystallizes　in　small　cubes；　and　dissolves　readily　in　water。　This　agent　is　extensively　employed　in　the　paper　and　glass　processes。

Bromide　of　Lime。　　This　the　principal　accelerator　used　in　the　American　practice；　and　is　the　best　of　all　dry　combinations　at　present　employed。　There　are　many　reasons　why　the　dry　is　advantageous；　these　are　too　familiar　to　repeat。

〃The　bromide　of　lime　may　be　produced　by　allowing　bromine　vapor　to　act　upon　hydrate　of　lime　for　some　hours。　　The　most　convenient　method　of　doing　this　is　to　place　some　of　the　hydrate　at　the　bottom　of　the　flask；　and　then　put　some　bromine　into　a　glass　capsule　supported　a　little　above　the　lime。　As　heat　is　developed　during　the　combination；　it　is　better　to　place　the　lower　part　of　the　flask　in　water　at　the　temperature　of　about　50　deg。　Fah。；　the　lime　gradually　assumes　a　beautiful　scarlet　color；　and　acquires　an　appearance　very　similar　to　that　of　the　red　iodide　of　mercury。　The　chloro…iodide　of　lime　may　be　formed　in　the　same　manner；　it　has　a　deep　brown　color。　　Both　these　compounds；　when　the　vapor　arising　from　them　is　not　too　intense；　have　an　odor　analogous　to　that　of　bleaching　powder；　and　quite　distinguishable　from　chlorine；　bromine；　or　iodine　alone。〃

Farther　on；　I　have　given；　in　connection　with　accelerators；　a　process　I　adopt；　which　is　far　less　tedious　and　equally　reliable。

Bromide　of　SilverMay　be　formed　by　pouring　an　alkaline　bromide　into　a　solution　of　nitrate　of　silver；　in　the　shape　of　a　white；　slightly　yellowish　precipitate；　which　is　insoluble　in　water　and　nitric　acid；　but　readily　dissolves　in　ammonia　and　the　alkaline　hyposulphites。　Chlorine　easily　decomposes　bromide　of　silver；　and　transforms　it　into　chloride。

M。　Biot　has　expressed　his　opinion；　that　it　is　not　possible　to　find　any　substance　more　sensitive　to　light　than　the　bromide　of　silver。　This　is　true　to　a　certain　extent；　but　in　combination　with　deoxidizing　agents；　other　preparations　have　a　decided　superiority　over　the　pure　bromide　of　silver。

Bromide　of　GoldIs　readily　prepared　by　adding　a　little　bromide　to　the　brown　gold　of　the　assayers；　and　allowing　it　to　remain　some　time　under　water；　or　assisting　its　action　by　a　gentle　heat。　It　forms　a　salt　of　a　bright　crimson　color；　but　in　its　general　properties　is　precisely　similar　to　the　chloride　used　in　gilding。

Bromide　of　MagnesiaIs　prepared　in　the　same　manner　as　bromide　of　lime。

This　mixture　is　particularly　adapted　for　hot　climates；　and　is　used　in　this　country　by　some　few　who　regard　its　use　as　a　valuable　secret。

Bromide　of　Starch。This　preparation　is　much　used；　but　not　alone。　It　is　combined　with　lime　by　putting　about　one　part　in　measure　of　starch　to　four　of　lime。　　It　is　prepared　by　adding　bromine　to　finely　pulverized　starch；　in　the　same　manner　as　bromide　of　lime。　（See　Accelerators。）

Experiments　with　Bromine。Place　in　a　very　flaring　wine　glass　a　few　drops　（say　ten）　of　bromine；　then　place　a　small　piece　of　phosphorus　about　one…twentieth　of　an　inch　in　diameter。　Place　the　latter　on　the　end　of　a　stick　from　five　to　ten　feet　in　length。　So　place　it　that　the　phosphorus　can　be　dropped　into　the　glass；　and　in　an　instant　combustion　giving　a　loud　report　will　be　the　result。

b。　　Expose　a　daguerreotype　plate　to　the　vapor　of　bromine；　it　assumes　a　leaden…grey　color；　which；　blackens　by　light　very　readily。　Exposing　this　to　mercury　will　not　produce　any　decided　action　upon　the　lights。　Immerse　it　in　the　solution　of　the　muriate　of　soda；　and　the　parts　unacted　upon　by　light　becomes　a　jet　black；　while　the　parts　on　which　the　light　has　acted　will　be　dissolved　off；　leaving　a　clean　coating　of　silver。　This　will　be　a　most　decided　black　picture　on　a　white　ground。

c。　　Expose　an　impressioned　plate；　that　has　been　sufficient　time　in　the　camera　to　become　solarized；　to　the　vapors　of　bromine；　and　the　impression　will　be　fully　developed　and　exhibit　no　signs　of　solarization。　　The　exposure　over　the　bromine　most　be　very　brief。　Chlorine　or　iodine　will　produce　the　same　result。　The　latter　is　preferable。

Again；　should　the　impressioned　plate　be　exposed　too　long　over　the　vapor　of　bromine；　the　impression　would　be　rendered　wholly　insensitive　to　the　mercurial　vapor。　　Hence　this　method　is　resorted　to　for　restoring　the　sensibility　of　the　plate　when　there　is　reason　to　believe　that　the　impression　would　not　be　a　desirable　one；　as；　for　example；　if　a　likeness　of　a　child　be　wanted；　and　it　had　moved　before　the　plate　had　been　sufficiently　long　exposed　in　the　camera；　the　plate　may　be　restored　to　its　original　sensitiveness　by　re…coating　over　bromine；　as　above；　thus　saving　the　time　and　labor　of　re…preparing　the　plate　for　the　chemicals。

d。　　If　by　accident　（we　would　not　advise　a　trial　to　any　extent　of　this）；　you　should　inhale　a　quantity　of　the　vapor　of　bromine；　immediately　inhale　the　vapor　of　aqua　ammonia；　as　this　neutralizes　the　dangerous　effect　of　the　bromine　vapor。　every　operator　should　be　provided　with　a　bottle　of　ammonia；　as　a　little　sprinkled　about　the　chemical　room　soon　disinfects　it　of　all　iodine　or　bromine　vapor；　and　also　tends　to　facilitate　the　operation　in　the　camera。


IODINE。

History　of　Iodine。This　is　one　of　the　simple　chemical　bodies　which　was　discovered　in　1812　by　M。　Courtois；　of　Paris；　a　manufacturer　of　saltpetre；　who　found　it　in　the　mother…water　of　that　salt。　Its　properties　were　first　studied　into　by　M。　Gay　Lussac。　It　partakes　much　of　the　nature　of　chlorine　and　bromine。　Its　affinity　for　other　substances　is　so　powerful　as　to　prevent　it　from　existing　in　an　isolated　state。　　It　occurs　combined　with　potassium　and　sodium　in　many　mineral　waters；　such　as　the　brine　spring　of　Ashby…de…la…Zouche；　and　other　strongly　saline　springs。　This　combination　exists　sparingly　in　sea…water；　abundantly　in　many　species　of　fucus　or　sea…weed；　and　in　the　kelp　made　from　them。　It　is　an　ingredient　in　the　Salt　Licks；　saline；　and　brine　springs　of　this　country；　especially　of　those　in　the　valley　of　the　Mississippi。　It　is　sparingly　found　in　fresh…water　plants；　as　well　also　in　coal；　and　in　combination　with　numerous　other　bodies。

Fermented　liquors　contain　iodine；　wine；　cider；　and　perry　are　more　iodureted　than　the　average　of　fresh　waters。　Milk　is　richer　in　iodine　than　wine；　independently　of　the　soil；　with　which　it　varies；　the　proportion　of　iodine　in　milk　is　in　the　inverse　ratio　of　the　abundance　of　that　secretion。　Eggs　（not　the　shell）　contain　much　iodine。　　A　fowl's　egg　weighing　50　gr。　　contains　more　iodine　than　a　quart　of　cow's　milk。　Iodine　exists　in　arable　land。　　It　is　abundant　in　sulphur；　iron；　and　manganese　ores；　and　sulphuret　of　mercury：　but　rare　in　gypsum；　chalk；　calcareous　and　silicious　earths。　Any　attempt　to　extract　iodine　economically　should　be　made　with　the　plants　of　the　ferro…iodureted　fresh　waters。　Most　of　the　bodies　regarded　by　the　therapeutists　as　pectoral　and　anti…scrofulous　are　rich　in　iodine。

It　is　probably　to　the　application　of　this　body　that　we　owe　the　discovery　of　the　daguerreotype。　　There　is　no　record　of　thep　recise　date　when　Daguerre　commenced　experimenting　with　iodine；　but　by　the　published　correspondence　between　him　and　M。　Neipce；　his　partner；　it　was　previous　to　1833。　There　is　no　doubt；　however；　that　the　first　successful　application　was　made　in　1838；　as　the　discovery　was　reported　to　the　world　early　in　January；　1839。

Preparation。Iodine　is　mostly　prepared　from　kelp；　or　the　half　vitrified　ashes　of　seaweed；　prepared　by　the　inhabitants　of　the　western　islands；　and　the　northern　shores　of　Scotland　and　Ireland。　It　is　treated　with　water；　which　washes　out　all　the　soluble　salts；　and　the　filtered　solution　is　evaporated　until　nearly　all　the　carbonate　of　soda　and　other　saline　matters　have　crystallized　out。　The　remaining　liquor；　which　contains　the　iodine；　is　mixed　with　successive　portions　of　sulphuric　acid　in　a　leaden　retort；　and　after　standing　some　days　to　allow　the　sulphureted　hydrogen；　etc。；　to　escape；　peroxide　of　manganese　is　added；　and　the　whole　gently　heated。　Iodine　distills　over　in　a　purple　vapor；　and　is　condensed　in　a　receiver；　or　in　a　series　of　two…necked　globes。

Properties。Iodine　is　solid　at　the　ordinary　temperature；　presenting　the　appearance　of　dark…grey　or　purple　spangles；　possessing　a　high　degree　of　metallic　lustre。　　It　somewhat　resembles　plumbago；　with　which　it　is　sometimes　diluted；　particularly　when　it　is　fine。　Operators　should　endeavor　to　secure　the　larger　crystals。　It　melts　at　224。6　deg。；　forming　a　brown　or　nearly　black　liquid。　It　boils　at　about　356　deg。；　and　emits　a　very　deep　violet　colored　vapor。　It　gives　off　a　very　appreciable　vapor；　sufficient　for　all　purposes　of　forming　the　iodide　of　silver　on　the　daguerreotype　plate；　at　a　temperature　of　45　deg。　　or　even　lower。　　Iodine　crystallizes　readily。　Every　operator　has　found　upon　the　side　of　the　jar　in　his　coating…box；　perfectly　regular　crystals；　deposited　there　by　sublimation。

Water　dissolves　but　a　small　proportion　of　iodine；　requiring　7000　parts　of　water　to　dissolve　one　of　iodine；

＇page　85＇

or　one　grain　to　the　gallon　of　water。　　Alcohol　and　ether　dissolve　it　freely；　as　does　a　solution　of　nitrate　or　hydrochlorate　of　ammonia　and　of　iodides。

The　density　of　solid　iodine　is　4。95；　that　of　its　vapor　8。716。　It　greatly　resembles　chlorine　and　bromine　in　its　combinations；　but　its　affinities　are　weaker。　　It　does　not　destroy　the　majority　of　organic　substances；　and　vegetable　colors　generally　resist　its　action。　　It　combines　with　several　organic　substances；　imparting　to　them　peculiar　colors。　It　colors　the　skin　brown；　but　the　stain　soon　disappears。

Chloride　of　IodineIs　formed　by　passing　chlorine　into　a　bottle　containing　some　iodine。　　This　can　be　readily　done　by　pouring　one　ounce　and　a　half　of　muriatic　acid　upon　a　quarter　of　an　ounce　of　powdered　black　oxide　of　manganese；　and　heat　it　gradually　in　a　flask；　to　which　is　adapted　a　bent　glass　tube。　This　tube　must　connect　with　the　bottle　containing　the　iodine；　and　the　yellowish…green　gas　disengaged　will　readily　combine　with　the　iodine；　forming　a　deep　red　liquid；　and　the　operation　is　complete。　The　use　of　chloride　of　iodine　will　be　referred　to　in　connection　with　the　Accelerators。

＇page　86＇

Iodides。The　iodide　treated　with　the　oil　of　vitri