

SILVKII. 



SIL\ 



678 



IKT. at diffrmit place*, being associated with various matter*, require 

 diffarrat modifications of treatment. One metallurgist, Augtin, di- 

 ltwr* with the use of mercury altogether. Tiervogel at once obtaimi 

 ulphate u( silver by routing the ore at a particular temperature, and 



: .tiitrn the metal therefrom by copper. 



silvtr is almost pure white, baring only the faintest tinge of red. 

 In the native state it ftoinetimes occur* crystallised in cubes nr octo- 



It i moderately bard, ela*tic, and very ductile and mnl. 

 one grain may be drawn into : wire, nnd the thinue.-i 



r Kafailver, bai a thickness of only ,.!.., of an inch. Silver 



melU at a bright rod heat, and by repeated fusion* become* quite 

 l-rittle. It volatilise* in the lununoui arc of a powerful electric 

 current, yielding beautiful green-colon ml vapour. Of all metals, 

 ;1\ > r in. perhaps, the beat conductor of heat and electricity. It does 

 not oxidi at ordinary temperature*, but when melted ha* the pro- 

 f absorbing many time* its bulk of oxygen, which, however, a 

 ain at the moment of solidification. Though silver does 

 t iu the air. it rapidly tarnishes, owing to the formation of a 

 thin film "i mlphide of silver : this occurs more quickly in urban than 

 in rural districts, Milphur in the form of sulphuretted hydrogen being 

 far more abundant in the atmosphere of the former than in that of 

 tli.' I iti. r localities. 



Silver is not readily acted upon by alkalies, hence it is of peculiar 

 value in the manufacture of Venecia in which alkaline fusions have to 

 be made. Common salt, especially in the melted state, is slowly 

 decomposed by silver, soda being formed, from absorption of oxygen, 

 while liberated chlorine attacks the metal. Boiling sulphuric acid oxi- 

 dise* silver ; hydrochloric acid acts but slightly upon it ; aqua regia 

 attacks it readily ; but its best solvent is nitric acid. 



Perfectly pure silver may be obtained by dissolving the commercial 

 metal in nitric acid, precipitating with hydrochloric acid, and then 

 fusing the well-washed chloride with half its weight of dried carbonate 

 uf soda. In the place of carbonate of soda, carbonate of lime anil c liar- 

 coal are sometime* employed. Chloride of silver may also be reduced 

 |.y placing it in contact with zinc and dilute sulphuric acid. 



The equivalent of silver is 108. 



Silver and ojcygtn form three compound* : 



1. Snboxide of ilrtr 

 :. Protoxide of silver 

 . IVruxidc of silver 



Ag,0 



A0 



AgO, 



1 . Fiiboxide of tilcer (Ag,0). Citrate of silver is heated to 212 iu a 

 current f hydrogen ; on dissolving the resulting mass in water, and 

 adding an alkali, the suboxide is precipitated as a block powder. AVhen 

 dry, it acquires metallic lustre under the burnisher. 



Motybdate ofiuboxide of tilrer (Ag,0, 2MoO,). Wohler forms this 

 salt by pasiing hydrogen gas through an auimoniacal solution of inoly b- 

 date of silver at 90. It is a heavy brilliant block powder, iu which 

 occur regular octohedra. The tunyttate of the suboxide is mode in the 

 same manner as, and much resembles, the molybdate. Chrvmale of 

 suboxide of silver is black and amorphous. 



J. Protoxide of titter (AgO). A brown hydrated oxide of silver is 

 thrown down when solution of potash, soda, baryta, or lime is added 

 to solution of nitrate of silver. It becomes anhydrous when heated to 

 140* Fohr., and is reduced to the metallic state by increased heat, by 

 light, hydrogen, or almost any deoxidising agent. It is a powerful 

 base, forming salts, the chief of which are presently described. 



/'roxide of tilrcr (AgO,) occurs in dark gray acicular crystals 

 w In n a solution of nitrate of silver is electrolysed. It accumulates on 

 the positive pole, is a conductor of the electric current, but is very 

 unstable. 



fiilphiilr. nf rilrcr. (AgS). The elements sulphur and silver have a 

 great affinity for each other ; the compound produced by their union 

 occur* native in large quantities. [SILVER, in NAT. HIST. Div.] 

 Sulphide of silver may be formed artificially by passing a stream of 

 sulphuretted hydrogen gas through a solution containing silver, or on 

 adding a soluble sulphide to the silver solution, or, still more simply, 

 by heating together sulphur and silver in their equivalent proportions. 



Sulphide of silver readily fuse* and cools to a dark-gray, crystalline 

 mam, that is somewhat soft and malleable. It is decomposed and 

 dissolved when heated with concentrated sulphuric or nitric acids, and 

 i* also readily attacked by strong hydrochloric acid. Potash, soda, 

 iron, copper, or lead reduce it, by the aid of heat, to the metallic state. 



Chlorine and silver form two compounds, namely : 



1. Bubchloride of tilrer A(r,Cl 



t. Frotochlorldc of direr AgCl 



1. SuoMoride of Sitter (Ag,Cl). When silver leaf is digested in 

 solution of chloride of copper, or of perchloride of iron, block scale* of 

 snbchloride of silver are produced. Nitric acid does not affect them, 

 but ammonia resolves them into chloride of silver and metallic . 



2. 1'rotocHloridt nf filter (AgCl), Chlvride <if SUrer, or, Horn Hil,,r, 

 IK (..Mini native. [SILVER, in NAT. HIST. Div.] It falls as a white, 

 curd-like precipitate when hydrochloric acid or any soluble chl. 

 added to an aqueous solution of silver salt. 



Chloride of silver is insoluble in water or dilute acids, and is only 

 very slightly acted on by strong nitric or hydrochloric acids. It i* 

 somewhat more soluble iu solutions of chlorides of alkalies or of 



alkaline earths, and is freely dissolved in solution of ammonia. It 

 fuse* when heated to about 600* Kalir., nn.l <>n U.K. ling forms a 



transparent horn-like mass. It is partially reduced to the state of 

 sub-chlnriilv on exposure to light. A current of hydrogen remove* the 

 whole of the chlorine from heated chloride of .-I'll. n. and 



some other metals also reduce it to the metallic state. Chl. 

 silver forms double salts with alkaline <K armies, sulphites, and l.\| 

 sulphites ; the solutions of the last-named have a most intensely sweet 

 taste, exceeding even that of sugar. 



air nf Filter (AgBr) occur* native. It may be prepared 

 artificially by precipitating nitrate of silver by bromide of potassium. 

 It much resembles chloride of silver, but is less soluble in auimoni.i, 

 and lias moreover a yellow colour. 



fixliilr uf Silver (Agl). This compound occur* native also. It fall* 

 as a yellow precipitate when on alkaline iodide is added t.. 

 nitrate of silver. It is insoluble in acids and nearly so in am; 

 but is very soluble in solution of iodide of potassium or hy j -sulphite 



. !' -...I.I. 



Xii/iihate of Silver (AgOSO,). When silver is U.ilnl in 

 sulphuric acid, sulphate of silver is formed according to the following 

 equation : 



Ag + 1{HO, 80,) = AgO, SO, + 80, + Sim 



Silver*. Sulphuric acid. 



Sulphate of Sulphurous 

 ilver. icid. 



Water. 



It is soluble in excess of the acid, but requires ninety parts of water 

 to dissolve it. 



M/rat' nf silrer (AgO, NO,). .This salt, now so largely used in 

 photography, and, when fused and cast into cylinders as on escharotic, 

 under the name of lunar eamtic, by surgeons, is formed on dis- 

 solving silver in strong nitric acid. By evaporation of the' solution, 

 colourless, transparent right rhombic crystals ore deposited. It has an 

 unpleasant bitter metallic taste, is soluble in water or alcohol, and is 

 not decomposed by exposure to light unless in contact with organic 

 matter. Solution of ammonio-nitrate of silver is formed by a.Min 

 ammonia to nitrate of silver until the resulting precipitate in nearly all 

 redissolved. 



The following are the principal remaining salts of silver that ore of 

 interest. They are produced by the ordinary process of double decom- 

 position. 



The triphosphate (3AgO, PO,) ia of yellow colour, alterable by tin; 

 action of light, readily soluble in excess of nitric acid or of ammonia. 



The pyropfiotpftatc (2AgO,PO,) is white and easily fusible. 



The metaphosphate (AgO, PO,) occurs as a gelattnoo* moss, soluble 

 in excess of nitrate of silver. The carbonate (AgO, CO 

 white, afterwards pale yellow. The karate (AgO, B0 a ) forms white 

 flakes which turn violet on exposure to light. The iotlatc (AgO. l< > > 

 in white, and crystallises from ammonia in brilliant little root i 

 prisms. The Morale is soluble in water, and crystallises iu white, 

 opaque, four-sided prisms. The monochromate (AgO, CrO s ) is of a 

 greenish-brown colour by reflected light and deep red by transmitted 

 light. The bichromate (AgO,2CrO a ) is a purple-red crystalline preci- 

 pitate. The areeniate (3AgO,AsO,) .is a dark brick-red precipitate, 

 soluble in ammonia and in carbonate of ammonia. 



Kor the salts which silver forms with organic acids, sec the articles 

 on those acids. 



Teittfor Silver. The production of the white curdy chloride on the 

 addition of hydrochloric acid, the precipitate being insoluble, in hot 

 nitric acid but readily soluble in ammonia, forms the characteristic. 

 test for silver salts. Reduction on charcoal in the blow-pipe I' 

 black precipitate by sulphuretted hydrogen, and a yellow one on the 

 adililion of an alkaline iodide, ore confirmatory tests. 



Kttimatim of Silctr. This is accomplished as described under 

 ASSAYING, or in the state of well-washed and fused chloride, 100 parts 

 of which contain 7.V-7 of metal. 



SII.VKH, Medical Properties uf. In a purely metallic state silver 

 has no action on the animal frame, and the only salt much used is the 

 nitrate, termed also lunar cauttit. This is always fused in proper 

 moulds, from which it is turned] out in the form of cylinders, about 

 three inches long, and the eighth of an inch iu diameter. They are at 

 first white, but quickly become of a dark gray or black colour, from 

 combining with organic matter in the air. To prevent this the 

 ders are generally wrapped up in blue paper. When nitrate of silver 

 is brought in contact with any part of the human frame, it cause* lir.^t 

 a white mark, which gradually changes to blue, purple, and at last Ui 

 block. This occurs more rapidly if moisture be present ; and is 

 to a chemical combination of the metal with the albumen and fibrin 

 of the animal tissues. If the port be wetted, and the caustic applie.1 

 several times at short intervals, vesication results. Nitrate of silver 

 acts therefore locally as an irritant and cornx, i r . When taken inter- 

 nally in small doses for a considerable time, such as six or twelve 



, it U absorbed and deposited in various parU ..f the Ixxl 

 when it is deposited in the rete mucorum of the skin it cans. 

 colorations, which in most coses prove permanent. It has been 

 time* employed with success in the treatment of >pi I . 

 some forms of angina pectorit,a well as morbid sensibility ..i th,- 

 ctomach. Larger doses can be l...rn.- when it is administered in 



