american hand book of the daguerreotype-第12部分

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　to　the　ferrocyanuret；　might　not　be　more　advantageously　employed；　because　the　residue　of　the　process　last　described　contains　a　large　quantity　of　cyanogen　which　the　acid　is　unable　to　set　free。

〃There　are　other　modes　of　procuring　prussic　acid；　besides　the　one　which　has　been　so　tediously　described；　but　these　are　found　to　be　more　expensive。　The　only　one　which　I　shall　now　notice　is　the　process　by　which　it　is　obtained　from　bicyanide　of　mercury。　　The　bicyanide　of　mercury　itself　is　formed　when　peroxide　of　mercury　is　digested　with　Prussian　blue；　the　peroxide　of　mercury　abstracting　the　whole　of　the　cyanogen　from　the　blue；　and　leaving　the　oxides　of　iron　at　the　bottom　of　the　vessel。　The　solution　may　be　evaporated　to　dryness；　and　one　part　of　the　salt　dissolved　in　six　of　water；　one　part　of　muriatic　acid；　sp。　　gr。　　1。15；　is　then　added；　and　the　solution　distilled；　when　the　whole　of　the　hydrocyanic　acid　passes　over；　and　by　being　conducted　into　a　solution　of　potassa；　as　in　the　former　process；　forms　cyanuret　of　potassium。　　This　process；　though　easier　than　the　first　described；　is　rather　given　as　a　resource　under　peculiar　circumstances　than　as　one　to　be　adopted　by　the　large　manufacturer。　The　expense　is　the　only　objection；　but　in　a　small　quantity　this　cannot　be　a　consideration。

〃In　giving　this　very　rough　outline　of　the　general　mode　of　forming　salts；　the　minutiae　necessary　for　chemical　work　have　altogether　been　avoided；　and　those　parts　alone　are　entered　upon　which　are　more　immediately　necessary　for　the　electro　metallurgist　to　know　and　practice　for　himself。　This　will　account　for　the　long　description　of　the　cyanuret　of　potassium；　while　the　preparation　of　the　equally　important　and　even　more　used　acids；　the　sulphuric；　muriatic；　etc。；　commonly　found　in　commerce；　are　altogether　neglected。

〃In　using　solutions　of　cyanide　of　potassium；　the　workman　should　not　immerse　his　arms　into　them；　otherwise　it　occasionally　happens　that　the　solution　produces　very　troublesome　eruptions　over　the　skin。〃


HYPOSULPHITE　OF　SODA。

Hyposulphite　of　Soda。This　salt　forms　one　of　the　important　chemicals　for　the　Daguerreotype　operator。　　Its　application　to　this　art　is　of　an　interesting　nature。　　It　is　used　to　dissolve　the　sensitive　salt　of　silver　which　remains　unchanged　during　the　exposure　in　the　camera。　It　has　the　property　of　readily　dissolving　the　chloride；　bromide　and　iodide　of　silver。　　It　should　be　pure　and　free　from　sulphuret　of　sodium；　should　this　last　be　present；　it　will　cause　brown　spots　of　sulphurated　silver　upon　the　Daguerreotype　impression。　　This　annoyance　is　a　great　source　of　complaint　from　many　operators；　and　ever　will　be；　so　long　as　it　is　prepared　by　men　who　have　no　reputation　to　lose；　and　whose　eyes　are　blinded　by　the　〃Almighty　Dollar。〃

A　good　article　may　be　prepared　as　follows：

〃Mix　one　pound　of　finely　pulverized　carbonate　of　soda　with　ten　ounces　of　flowers　of　sulphur；　and　heat　the　mixture　slowly　in　a　porcelain　dish　till　the　sulphur　melts。　　Stir　the　fused　mass；　so　as　to　expose　all　its　parts　freely　to　the　atmosphere；　whereby　it　passes　from　the　state　of　a　sulphuret；　by　the　absorption　of　atmospheric　oxygen；　into　that　of　a　sulphite；　with　the　phenomenon　of　very　slight　incandescence。　　Dissolve　in　water；　filter　the　solution；　and　boil　it　immediately　along　with　flowers　of　sulphur。　The　filtered　concentrated　saline　liquid　will　afford；　on　cooling；　a　large　quantity　of　pure　and　beautiful　crystals　of　hyposulphite　of　soda。〃

Hyposulphite　of　Gold。This　compound　salt　is　by　a　few　considered　preferable　to　the　chloride　of　gold；　but　our　experience　has　induced　us　to　use　the　latter；　believing　we　are　enabled　to　produce　a　more　brilliant　and　warm…toned　impression　with　it。　　When　the　hyposulphite　of　gold　is　used　in　gilding；　it　requires　less　heat　and　a　longer　application；　as　there　is　some　danger　of　producing　a　glossy　scum　over　some　parts　of　the　surface　of　the　plate。　I　prepare　this　salt　as　follows：

Dissolve　one　part　chloride　of　gold　and　four　parts　hyposulphite　of　soda　in　equal　quantities　of　distilled　water：　pour　the　gold　into　the　hyposulphite　solution；　in　the　same　manner　as　in　mixing　the　gilding　solution；　let　it　stand　until　it　becomes　limpid；　filter　and　evaporate　to　dryness。　Re…dissolve　and　add　a　few　grains　of　burnt　alum。

After　standing　a　few　hours；　filter　and　evaporate　again。　If　not　sufficiently　pure；　repeat　the　crystallization　until　it　is　so。　For　gilding；　dissolve　in　water　and　use　in　the　same　manner　as　the　common　gilding　solution。

N。B。The　four　following　mixtures　were　employed　in　Neipce's　process　in　his　earliest　experiments：

Aqueous　Solution　of　Bichloride　of　Mercury。Eight　grains　of　bichloride　of　mercury　in　10；000　grains　of　distilled　water。

Solution　of　Cyanide　of　Mercury。A　flask　of　distilled　water　is　saturated　with　cyanide　of　mercury；　and　a　certain　quantity　is　decanted；　which　is　diluted　with　an　equal　quantity　of　distilled　water。

Acidulated　White　Oil　of　Petroleum。This　oil　is　acidulated　by　mixing　with　it　one　tenth　of　pure　nitric　acid；　leaving　it　for　at　least　48　hours；　occasionally　agitating　the　flask。　　The　oil；　which　is　acidulated；　and　which　then　powerfully　reddens　litmus　paper；　is　decanted。　It　is　also　a　little　colored；　but　remains　very　limpid。

Solution　of　Chloride　of　Gold　and　Platinum。In　order　not　to　multiply　the　solutions；　take　the　ordinary　chloride　of　gold；　used　for　fixing　the　impressions；　and　which　is　composed　of　1　gramme　of　chloride　of　gold　and　50　grains　of　hyposulphate　of　soda；　to　a　quart　of　distilled　water。

With　respect　to　chloride　of　platinum；　4　grains　must　be　dissolved　in　3　quarts　of　distilled　water；　these　two　solutions　are　mixed　in　equal　quantities。

Acids。I　shall　not　go　into　the　preparations　of　the　various　acids　employed　in　the　Daguerreotype。　　This　would　be　useless　to　the　operator；　as　there　are　few；　if　any；　that　it　would　be　advisable　to　prepare。　It　is　only　necessary　for　the　experimenter　to　be　made　acquainted　with　their　properties；　and　this　in　order　to　prevent　any　haphazard　experiments；　which　are　too　common　among　operators。　　Any　person　who　may　be　desirous　to　try　an　experiment；　should　first　study　the　agents　he　wishes　to　employ。　By　so　doing　much　time　and　money　will　be　saved；　while　the　searcher　after　new　discoveries　would　rarely　become　vexed　on　account　of　his　own　ignorance；　or　be　obliged　to　avail　himself　of　the　experience　of　others　in　any　department　of　science。

Nitric　AcidExists　in　combination　with　the　bases；　potash；　soda；　lime；　magnesia；　in　both　the　mineral　and　vegetable　kingdoms；　and　is　never　found　insoluble。　　It　has　the　same　constituents　as　common　air；　but　in　different　proportions。　　The　strongest　nitric　acid　contains　in　every　pound；　two　and　a　quarter　ounces　of　water。　Pure　nitric　acid　is　colorless；　with　a　specific　gravity　of　1。5；　and　boiling　at　248　deg。。　It　is　a　most　powerful　oxidizing　agent；　and　is　decomposed　with　more　or　less　rapidity；　by　almost　all　the　metals；　to　which　it　yields　a　portion　of　its　oxygen。

The　nitric　acid　of　commerce；　is　generally　the　article　used　by　the　Daguerreotypist。　　This　usually　contains　some　chlorine　and　sulphuric　acid。　It　is　obtained　by　the　distillation　of　saltpetre　with　sulphuric　acid。　It　is　employed　in　the　Daguerreotype　process　for　dissolving　silver；　preparing　chloride　or　oxide；　nitrate　of　silver；　＇the　former　used　in　galvanizing；＇　and　in　combination　with　muriatic　acid　for　preparing　chloride　of　gold；　used　in　gilding。　　It　is　also　used　by　some　for　preparing　the　plate。

Acidulated　Solution。This　solution　is　used　for　cleaning　the　surface　of　the　Daguerreotype　plate。　　It　has　the　property　of　softening　the　silver；　and　bringing　it　to　a　state　in　which　it　is　very　susceptible　of　being　either　oxidized　or　iodized；　hence　it　contributes　to　increase　the　sensibility　of　the　plate。　The　proportions　are　to　one　drop　of　acid　add　from　15　to　20　drops　of　water；　or　make　the　solution　about　like　sharp　vinegar　to　the　taste。

Nitro…Muriatic　Acid。Aqua　Regia　is　a　compound　menstruum　invented　by　the　alchemists　for　dissolving　gold。　　It　is　composed　of　colorless　nitric　acid　（aqua…fortis）　and　ordinary　muriatic　acid；　the　mixture　is　yellow；　and　acquires　the　power　of　dissolving　gold　and　platinum。　These　materials　are　not　properly　oxidized；　it　nearly　causes　their　combination　with　chlorine；　which　is　in　the　Muriatic　acid。

Hydrochloric　Acid　（Muriatic　Acid）。This　acid　forms　a　valuable　addition　to　the　chemicals　employed　by　the　practical　Daguerreotypist。　This　acid　is　formed　by　acting　upon　common　salt　（which　is　chloride　of　sodium）　by　concentrated　sulphuric　acid。　　The　water　of　the　acid　is　decomposed；　and　its　hydrogen　combines　with　the　chloride　of　the　salt　to　form　muriatic　acid；　and　this　unites　with　the　sulphuric　acid　to　form　sulphate　of　soda；　60　parts　of　common　salt　and　49　parts　of　concentrated　sulphuric　acid；　afford；　by　this　mutual　action；　37　parts　of　muriatic　acid　and　72　parts　of　sulphate　of　soda。　The　muriatic　acid　of　commerce　has　usually　a　yellowish　tinge；　but　when　chemically　pure　it　is　colorless。　　The　former　is　commonly　contaminated　with　sulphurous　acid；　sulphuric　acid；　chlorine；　iron；　and　sometimes　with　arsenic。

Muriatic　acid；　from　the　fact　of　the　presence　of　the　chlorine；　is　used　in　the　Daguerreotype　process　for　dissolving　gold；　and　in　combination　with　various　accelerators。　　Its　presence　can　be　detected　by　ammonia。　A　strip　of　paper　dipped　in　this　and　waved　to　and　fro　will　emit　a　thick　white　smoke　if　the　acid　vapor　be　in　the　atmosphere。　The　ammonia　neutralizes　the　acid　fumes。　　By　reversing　the　experiment　we　can　determine　whether　vapor　of　ammonia　be　in　the　air；　and　also　deprive　these　suffocating　and　dangerous　gases　of　their　injurious　properties；　and　remove　them　from　the　air。　　Every　Daguerreotype　operator　should　be　furnished　with；　at　least；　a　six　ounce　bottle　of　aqua　ammonia。　Its　operation　is　very　nearly　the　same　on　bromine　and　iodine　vapor。

Hydrofluoric　Acid　（Fluorohydric　Acid）。This　acid　is　used　to　form　some　of　the　most　volatile　and　sensitive　compounds　employed　in　the　Daguerreotype。　It　is　one　of　the　most　dangerous　bodies　to　experiment　with：　it　is　volatile　and　corrosive；　giving　off　dense　white　fumes　in　the　air。　　It　combines　with　water　with　great　heat。　　At　32　deg。　it　condenses　into　a　colorless　fluid；　with　a　density　1。069。　It　is　obtained　from　decomposition　of　fluorspar　by　strong　sulphuric　acid。　It　readily　dissolves　the　silica　in　glass；　and　consequently　cannot　be　kept　in　a