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means of a camel's hair pencil or feather; and if a copper or brass wire be placed at the bottom of it in contact with the fluid, and the whole sufiered to remain uudisturbed in a horizontal position, a beautiful vegetation of the silver will be formed. If a inicroscope be used for viewing the phenomena, it will appear in a beautiful manner.
Rationale. The copper, or brass, has a greater affinity for oxygen than the silver ; consequently the nia trate is decomposed, and the silver precipitated
Experiment 37. If one part of silver leaf, and seven of mercury be triturated in a mortar, an alloy posessing but little consistence will be produced.
Experiment 38. If, according to Lemery, one part of fine silver be dissolved in weak nitric acid to saguration, the solution diluted with about twenty parts of distilled water, and two parts of mercury added, the arbor Dianæ, or Dianæ's tree will be formeil; or,
Experim nt 39. According to Baume, mix together six parts of a solution of silver and four of a solution
mercury, both made with nitric acid, and completely saturated : add to them a little distilled water, and put the mixture into a conical vessel, into which have been previously introduced six parts of an alloy inade of seven parts of mercury and one of silver; or,
Experiment 40. Dissolve three drachms and fortyeight grains of pure silver, and half as much mercury, seperately, in a sufficient quantity of pure nitric acid. Mix the solution and add to it five or six ounces of distilled water. This must be poured upon seven drachms and twelve grains of an amalgam of silver of the consistence of butter, which has been previously put into a spherical vessel of glass. The vessel must be kept undisturbed, and in about 24 hours a very beautiful silver tree will be formed ; or,
Experiment 41. According to Homberg, make an alloy in the coll, of four parts of silver leaf and two parts of mercury; dissolve this alloy in a sufficient quantity of nitric acid, and add to the solution distilleri water. If we put into this liquor a small bull of
soft alloy of silver, a precipitation of silver immediately takes place.
Rationale, In all these experiments the silver is separated by means of the mercury. In experiment 40, the mercury held in solution, attracts that of the amalSam, and the silver in like manner, attracts that which is held in solution. The consequence is, that the silver is precipitated. The mercury in the amalgam being more abundant than would be necessary for preci. pitating the silver of the solution, has a tendency also to combine itself with the silver.
Experiment 42. If thin plates of silver and sulphur be laid alternately above each other in a crucible, they melt readily in a low red heat, and forin sulphuret of silver.
Remark. According to the analysis of Klaproth, it is composed of
100 Hence 100 parts of silver unite with about 17.6 parts of sulphur.
Silver contracts, when long exposed to the air, es. pecially · frequented places, as churches, theatres, &c. a covering of a violet colour, which deprives it of its lustre and malleability. This covering, which forms a thin layer, can only be detached fron the silver by bending it, or breaking it in pieces with a hammer. It was examined by Mr. Proust and found to be sulphul'et of silver,
On the principle of silver combining with sulphur, Mr. Hatchett informs us, is practised a deception in England by diminishing the current silver coin. It is done, says he, in the following manner: They expose the coin to the fumes of burning sulphur, by which a black crust of sulphuretted silver is soon formed, which, by a slight but quick blow, comes of like a scale, leaving the coin so little affected, that the operation may sometimes be repeated twice or thrice, without much hazard of detection,
Erperiment 43. If the sulphuret of silver obtained according to the foregoing process be exposed to heat, the sulphur will be disengaged from the silver.
Experiment 44. If the sulphuret be detonated with nitrate of potash, the silver will remain unaltered.
Experiment 45. If silver be fused with a fixed alkaline sulphuret, it is dissolved, and may be rendered miscible with water.
Experiment 46. If to this solution, an acid be added, the silver is precipitated, in the state of an hy drosulphuret. See Hydrosulphurets.
Experiment 47. If one ounce of silver, one ounce of phosphoric glass, and two drams of charcoal be mixed together, and heated in a crucible, phosphuret of silver is formed.
Rationale. The charcoal decomposes the phosphoric glass, or phosphoric acid, and the phosphorus thus disengaged, unites with the silver into a phosphuret. It is composed of four parts of silver and one of phosphorus.
Experiment 48. If the phosphuret, thus formed, be exposed to heat, the phosphorus will be disengaged, leaving the silver pure.
Remark. Silver unites readily with the greater numDer of metallic bodies.
One part of silver is sufficient to render twenty parts of gold considerably pale. This alloy, or mixture of gold and silver, is used for various purposes, and also for coin. As gold and silver have different solvents, their separation may be readily accomplished. See Gold.
Besides the use of nitro-muriatic acid for the separation of gold, and of nitric acid for the solution of silver, there is another mode of separating silver by a process called cementation. For this purpose the alloy of silver and gold is made into leaves, which are: placed stratum superstratum with a cementing powder, composed of such ingredients as would disengage either muriatic or nitric acid vapours by the action of a moderate red heat. Of the first kind is a composition of equal parts of muriate of soda and sulphate of
iron, calcined to redness, with four parts of brick dust; of the second, a mass of nitrate of potash and calcined sulphate of iron, blended with brick dust in the same proportions. Neither of these neutral salts should be contaminated with the other. The acid vapours disengaged in either cementing powder, corrode the silver, leaving the gold untouched. After the cement has been diligently separated from the plates, they are washed. As the cementing powder contains the silver, its separation is accomplished by melting the mass with litharge and charcoal dust, and by subsequent cupellation or scorification.
There is another process for separating silver from gold, founded on the affinity of silver with sulphur. It is called dry parting, or separation by casting and fusion. The alloy, being finely granulated, and mixed with a sixth or eighth part of sulphur, is fused in a black lead crucible, and then poured into a hollow metallic cone. The sulphur combines with the silver into a sulphuret, and after cooling the gold is found among the scoria of the sulphuret. In order to sepatate all the silver, the process is repeated. If the sulphuret of silver be roasted under the muffle, the silver is disengaged.
Silvering. This is an art which consists in giving a covering of silver to the surface of bodies, in the following manner :
Experiment 49. If two drachms of super-tartrate of potash, the same quantity of muriate of soda, and half a drachm of sulphate of alumina, mixed with fif. teen or twenty grains of silver, precipitated from nitrate of silver by copper, be applied to the surface of copper, by rubbing it with this powder, it will acquire a coat of silver. It may be afterwards polished with leather. For the purpose of covering the wares of saddlers and harness makers, the following cheap silvering is generally used:
Experiment 50. Half an ounce of silver that has been precipitated from nitrate of silver by the addition of copper, muriate of soda, and muriate of ammonia, of each two ounces, and one drachm of muriate of
mercury, are triturated together and made into a paste. with water.
Remark. Mr. Accum observes, that with this, copper utensils of every kind, that have been previously boiled with acidulous tartrate of potash, and sulphate of alumina, are rubbed; after which they are made hot, and then polished. The intention of this process appears to be little more than to apply the silver in a state of minute division to the clean surface of the copper, and afterwards to fix it there by fusion ; and accordingly this silvering may be effected by using the argentine precipitate here mentioned with supersaturated borate of soda, or mercury, and causing it to adhere by fusion. Various instruments, as well as dial plates, the scales of barometers, &c. may be silvered by rubbing them with the following mixture, viz. mu. riate of silver, muriate of soda, and super-tartrate of potash, and washing off the saline matter with water. The coating given by this mixture is not durable, but may be improved by heating the article, and continuing the operation until the covering becomes sufficiently thick.
Experiment 51. If silver leaf be triturated in a mortar with honey or mucilage of gum arabic, and afterwards the honey or gum washed off, and the silver put in shells, the shell-silver for the use of painters will be formed.
Plating, or the art of covering the surface of copper with silver, is performed in the following manner : plates of silver are bound with iron wire, on small ingots
copper, in the proportion of about one ounce of silver to twelve ounces of copper. Upon the edges of the copper, not covered with the silver, a little borax is put. When heat is applied, the borax melts, and contributes to fuse that part of the silver in contact with it. The ingot, in this situation is rolled under steel rollers, till it acquires a certain thickness.
In the manufacture of French plate, the copper is heated, silver leaf is then applied, and the burnisher is used to finish it.