american hand book of the daguerreotype-第11部分

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ifies　by　standing；　may　be　regarded　as　a　solution　of　chloride　of　lime；　and　must　be　protected　from　the　air　and　light。　It　may　also　be　made　without　putting　in　the　water　with　the　hydrate　of　lime；　by　merely　passing　the　chlorine　into　the　hydrate　of　lime。　This　last　is　by　some　used　in　preparations　for　accelerating　the　operation　of　taking　Daguerreotypes；　but　when　used　for　this　purpose　it　is　in　small　quantities。

Chloride　of　Calcium。To　one　part　of　water　add　two　parts　of　muriatic　acid；　and　add　pieces　of　common　chalk　until　effervescence　ceases；　then　filter　through　cotton　cloth　and　evaporate　it　by　placing　it　in　all　earthen　or　porcelain　dish；　over　a　slow　fire；　to　the　consistency　of　a　syrup。　When　cooling；　large　prismatic　crystals　of　chloride　of　calcium　are　formed。　These　must　be　quickly　dried　by　pressing　between　folds　of　blotting　paper　and　kept　carefully　excluded　from　the　air；　as　it　readily　attracts　hydrogen。　For　most　daguerreotype　purposes；　the　syrup　may　be　at　once　evaporated　to　dryness。　　This　is　frequently　placed　in　the　iodine　coating　box　for　the　purpose　of　keeping　the　atmosphere　dry。　　It　is　so　easily　made　that　every　operator　can　provide　himself　with　it　in　a　short　time；　and　at　little　expense。

Chloride　of　Gold。Is　prepared　by　dissolving　gold　in　aqua　regia；　a　composition　of　one　part　of　nitric　to　two　parts　of　muriatic　acid。　Gold　foil　is　the　best　for　our　purposes；　coin；　however；　answers；　in　most　cases；　for　the　daguerreotype　operator；　as　the　alloy；　being　so　slight　is　not　noticed　in　the　gilding　process。　When　the　latter　is　used；　it　will　facilitate　the　operation　to　beat　it　out；　forming　a　thin　sheet；　and　then　cutting　in　small　strips。　Where　purity　is　required；　foil　is　better。　　The　gold　is　placed　in　three　or　four　times　its　own　weight　of　the　above　acids。　For　this　purpose；　an　evaporating　dish　is　best　（a　common　saucer　will　do）；　a　moderate　heat　may　be　applied　to　favor　the　action。　The　mixture　should　be　stirred　often　with　a　glass　rod；　care　should　be　observed　not　to　apply　too　much　heat；　for　at　a　temperature　of　about　300　deg。　　the　chlorine　would　be　expelled　and　leave　a　metallic　precipitate；　which　would　require　re…dissolving。　Acid　may　at　any　time　be　added　if　necessary　to　dissolve　the　gold；　but　it　is　advisable　to　add　as　little　excess　as　possible；　as　it　would　require　more　time　to　evaporate。　After　all　the　gold　has　dissolved；　and　the　liquid　assumes　a　deep　red　color；　the　solution　should　be　allowed　to　cool；　being　stirred　nearly　all　the　time。　　This　salt　is　of　a　reddish…brown　color。　It　is　rarely　we　find　in　our　market　good　chloride　of　gold；　as　common；　salt　is　used　for　the　bulk；　and　when　the　bottles　are　labelled　〃15　grains；〃　〃20　grains；〃　nine…tenths　do　not　in　reality　contain　exceeding　five　grains　of　chloride　of　gold。　The　salt　is　mixed　with　the　above　solution　when　it　is　cooling；　and　gives　bright　yellow　crystals；　which　some　of　our　uninformed　operators　conceive　to　be　the　best　quality。

Chloride　of　Silver。（Oxide　of　Silver。）Take　any　quantity　of　silver　coin　or　other　silver；　roll　or　hammer　it　thin；　cut　in　small　pieces。　This　in　order　to　save　time。　　Put　the　silver　in　a　glass　or　earthen　vessel　（Florence　flask　is　best）；　pour　in　nitric　acid　and　water；　about　three　parts　of　the　former　to　one　of　the　latter。　　The　operation　of　cutting　up　the　silver　may　be　facilitated　by　applying　a　gentle　heat。　This　blue　solution　consists　of　oxide　of　silver　and　oxide　of　copper；　both　combined　with　nitric　acid。　　Should　the　operator　wish　a　pure　solution　of　silver；　which；　however；　is　not　always　used；　he　may　obtain　it　in　the　following　manner：

To　separate　the　two　metals　contained　in　the　above　solution　from　each　other；　put　some　bright　copper　coins　into　the　solution　and　set　it　aside　in　a　warm　place　for　three　or　four　days；　occasionally　giving　it　a　circular　motion。　The　separated　laminae　are　pure　silver；　which　is　to　be　digested　with　ammonia　until　it　ceases　to　be　colored　blue。　　The　silver；　after　being　washed　and　dried；　is　again　dissolved　in　nitric　acid；　and　the　liquid；　diluted　with　water；　is　kept　as　solution；　of　silver。

Either　of　the　above　solutions　（the　one　of　oxide　of　silver　and　copper；　and　the　pure　silver　solution）　may　be　prepared　for　use　by　putting　them　in　a　bottle；　with　a　quantity　of　water；　and　adding　common　fine　salt；　you　obtain　a　white　curdy　precipitate　of　chloride　of　silver。　No　matter　how　much　salt　is　used；　provided　enough　be　added　to　throw　down　all　the　chloride　of　silver。　　This　solution　should　be　well　agitated　and　then　allowed　to　stand　for　a　few　minutes；　thus　the　white　precipitate　is　in　the　bottom　of　the　bottle。　　When　the　water　has　become　clear；　pour　it　off　with　care；　leaving　the　sediment　behind；　then　add　a　fresh　quantity　of　clean　water；　shake；　let　settle；　and　pour　off　as　before。　Repeat　the　same　for　several　times；　and　the　excess　of　salt　will　disappear；　leaving　the　white　precipitate；　which　may　be　drained　of　the　water　and　dried　in　the　dark；　and　kept　free　from　light　and　air。


CYANIDE　OF　POTASSIUM。

Cyanide　of　Potassium。This　important　article　is　worthy　the　undivided　attention　of　every　Daguerreotypist。　I　here　give　Mr。　Smee's　process　for　its　preparation。　This　is　from　that　author's　work　entitled；　〃Electro　Metallurgy；〃　American　edition：

〃The　cyanide　of　potassium；　so　often　alluded　to　while　treating　of　the　metallo…cyanides；　may　be　formed　in　several　ways。　It　may　be　obtained　by　heating　to　a　dull　redness　the　yellow　ferrocyanate　of　potash；　in　a　covered　vessel；　filtering　and　rapidly　evaporating　it。　The　objection　to　this　method；　however；　is　that　without　great　care　the　whole　of　the　ferrocyanate　is　not　decomposed；　a　circumstance　which　much　reduces　its　value　for　electro…metallurgy。　By　boiling；　however；　the　ignited　residue　with　spirits　of　wine　this　difficulty　is　said　to　be　overcome；　as　the　ferrocyanate　is　absolutely　insoluble　in　that　menstruum；　while　the　cyanuret；　at　that　heat；　freely　dissolves；　and　is　as　easily　re…deposited　on　cooling。

〃There　is；　however；　a　much　better　process　by　which　this　salt　may　be　formed；　viz。　　by　simply　transmitting　hydrocyanic　acid　through　potassium。　Although　the　modes　of　making　this　acid　are　very　numerous；　there　is　but　one　which　is　likely　to　be　employed　on　a　very　large　scale；　and　that　is　its　formation　from　the　yellow　ferrocyanate　by　means　of　sulphuric　acid。　This　process　is　performed　as　follows：　　any　given　weight　of　the　yellow　salt　is　taken　and　dissolved　in　about　five　times　its　weight　of　water；　this　is　placed　in　a　retort；　or　some　such　analogous　vessel；　to　which　is　then　added　a　quantity　of　strong　sulphuric　acid；　twice　the　weight　of　the　salt；　and　diluted　with　three　or　four　times　its　quantity　of　water。　A　pipe　is　carried　from　the　neck　of　the　retort　to　the　receiving　bottle；　which　should　be　kept　as　cool　as　possible。

〃For　small　operations；　those　invaluable　vessels；　Florence　flasks；　answer　well：　　a　bent　tube　being　connected　at　one　end　to　its　month；　the　other　passing　into　the　second　vessel；　heat　should　be　cautiously　applied　by　means　of　an　Argand　lamp；　a　little　vessel　of　sand　being　placed　under　the　flask；　which　helps　the　acid　to　decompose　the　salt。　Prussic　acid　is　then　generated　and　passes　through　the　tube　to　the　recipient　vessel；　which　is　to　be　charged　with　liquor　potassae。

〃When　the　potash　is　saturated；　the　operation　is　completed。　The　Germans　recommend　a　strong；　alcoholic　solution　of　potassa　to　be　used　in　the　second　vessel；　for　in　this　case；　the　hydrocyanic　or　prussic　acid　combines　with　the　potassa；　forming　a　hydrocyanate　of　potassa；　or；　the　water　being　abstracted；　the　cyanuret　of　potassium；　which　spontaneously　precipitates；　on　the　saturation　of　the　fluid；　the　cyanuret；　being　insoluble　in　strong　alcohol。　The　ferrocyanate　of　potash　may　be　considered　as　containing　three　equivalents　of　hydrocyanic　acid；　two　of　potash　and　one　of　iron；　but；　unfortunately；　we　can　only　obtain　half　the　acid　from　the　salt；　owing　to　the　formation　of　a　compound　during　its　decomposition　which　resists　the　action　of　the　acid。　The　decomposition　of　this　salt　taking　2　equivalents　or　426　grains　（to　avoid　fractions）　would　afford　3　equivalents　or　81　grains　of　hydrocyanic；　or　prussic　acid；　capable　of　forming　198　grains　of　cyanuret　of　potassium；　while　in　the　retort　there　would　remain　384　grains　or　3　equivalents　of　bisulphate　of　potash；　and　1　equivalent　or　174　grains　of　a　peculiar　compound；　said　to　contain　3　equivalents　of　cyanogen；　1　of　potassium；　and　one　of　iron　（Pereira）。　It　is　manifest　that；　but　for　this　later　compound；　we　might　double　the　quantity　of　hydrocyanic　acid　from　the　yellow　salt。〃

The　decomposition　just　described　is　the　one　usually　received；　but　too　much　reliance　must　not　be　placed　on　its　accuracy；　for　the　analysis　of　the　several　compounds　is　too　difficult　for　the　results　to　be　fully　admitted。　　The　residue　left　in　the　retort　speedily　turns　to　one　of　the　blues；　identical　with；　or　allied　to；　Prussian　blue。　　This　is　at　best　a　disagreeable　process　to　conduct；　for　the　hydrocyanic　acid　formed　adheres　so　strongly　to　the　glass；　that；　instead　of　being　freely　given　off；　bubbles　are　evolved　suddenly　with　such　explosive　violence　as　occasionally　to　crack　the　vessel。　This　may　be　remedied　as　far　as　possible　by　the　insertion　of　plenty　of　waste　pieces　of　platinumif　platinized；　so　much　the　better；　as　that　facilitates　the　escape　of　the　gas。　The　heat　should　be　applied　to　every　part　of　the　vessel；　and　the　flame　should　not　be　allowed　to　play　upon　one　single　part　alone。　Large　commercial　operations　are　performed　in　green　glass　or　stone…ware　retorts。

〃Now　for　one　word　of　advice　to　the　tyro：　　Remember　that　you　are　working　with　prussic　acid；　therefore；　never　conduct　the　process　in　a　room；　the　fumes　being　quite　as　poisonous　as　the　solution　of　the　acid　itself；　moreover；　have　always　a　bottle　of　ammonia　or　chlorine　by　your　side；　that　should　you　have　chanced　to　inhale　more　than　is　pleasant；　it　will　be　instantly　at　hand　to　counteract　any　bad　effects。　It　is　stated　by　Pereira；　that　a　little　sulphuric　acid　or　hydroferrocyanic　acid　passes　to　the　outer　vessel；　but　probably　the　amount　would　be　of　no　consequence　for　electro…metallurgy；　otherwise；　it　might　be　as　well　to　use　a　Woulfe's　apparatus；　and　discard　the　salt　formed　in　the　first　vessel。　To　the　large　manufacturer　it　may　be　worth　considering　whether　some　other　metallo…cyanuret；　formed　in　a　similar　manner　to　the　ferrocyanuret；　might　not　be　more　advantageously　employed；　because　the　residue　of　the　process