SILVER 



461 



Nitrate of Silver, AgNO s , is one of the most 

 important salts of the metal. It crystallises in 

 colourless tabular plates belonging to the prismatic 

 system, has a specific gravity of 4 '355, ana fuses at 

 a low temperature, forming after solidification the 

 lunar caustic used as an escharotic by surgeons. 

 If during fusion the temperature is allowed to rise 

 above 383 F. (198 C.) the salt is decomposed. 

 Nitrate of silver dissolves in rather less ('783) than 

 its own weight of water at 51 -8* F. (11 C.), and is 

 more soluble at higher temperatures. It is pre- 

 pared by dissolving silver in moderately strong 

 nitric acid with the aid of heat, and has a very 

 bitter taste. Unless in contact with organic 

 matter, nitrate of silver is not blackened or dis- 

 coloured by the action of light. An ink for 

 marking linen or cotton is prepared by dissolv- 

 ing 2 parts by weight of nitrate of silver and 

 1 part of gum-arabic in 7 parts of water, a little 

 Indian ink being added. For the use of nitrate 

 of silver in taking photographic pictures, see 

 PHOTOGRAPHY. Black stains upon the hands or 

 upon linen caused by nitrate of silver may be 

 removed by a strong solution of iodide of potas- 

 sium, or more efficiently by cyanide of potassium, 

 which, however, is poisonous. When phosphorus 

 is kept immersed in an aqueous solution of nitrate 

 of silver the metal is reduced. This supplies a 

 means of coating delicate objects with a film of 

 silver. The article is dipped for a moment in 

 bisulphide of carbon containing ,', of its weight of 

 phosphorus in solution. As the bisulphide eva- 

 porates, phosphorus is left in a state of fine division 

 over the surface of the object, which in then dipped 

 into an aqueous solution of nitrate of silver, from 

 which silver is reduced by the phosphorus. Such 

 objects as insects, feathers, ana lace can be thus 

 coated with silver, but adroitness is necessary, as 

 finely-divided phosphorus takes fire spontaneously. 



Sulphate of Silver, Ag,SO 4 . This salt is formed 

 either by adding sulphate of soda to an aqueous 

 solution of nitrate of silver, when it is thrown down 

 as a precipitate, or by boiling granulated silver 

 with sulphuric acid. The process for ' parting ' an 

 alloy of silver and gold by sulphuric acid is referred 

 to below. 



Silver can be removed from old plated articles 

 by boiling them in a menstruum of 3 Ib. of sul- 

 phuric acid, 1 Ib. of water, and 1J oz. of nitrate of 

 potash. The silver in the solution is then precipi- 

 tated as the chloride, and from this the metal is 

 recovered. 



IKES OF SILVER. Native silver occurs in many 

 forms and in numerous localities. It crystallises 

 in the cubical system. Some specimens are of den- 

 dritic or arborescent form ; others are found in 

 laminae or foil ; others again are massive, or occur 

 in grains or specks disseminated through veinstone 

 of different kinds. Native silver is usually asso- 

 ciated with other ores of the metal. All native 

 gold contains more or less silver, and when the 

 proportion of the latter reaches about 20 per cent, 

 the native alloy is called electrum. The amount 

 generally varies between 3 and 25 per cent., but 

 some of the specimens of pale gold found in Tran- 

 sylvania contain 38 percent, of silver. In Europe 

 native silver has been found most largely at Kongs- 

 berg in Norway, where the mines have been worked 

 since 1623. Most of the silver produced by these 

 mines has l>een obtained in the native state. Some 

 very heavy single pieces have been found ; one in 

 the Copenhagen Museum weighs 560 Ib. , but 

 another lutnp was dug out nearly three times as 

 heavy. At Freiberg in Saxony a mass weigh- 

 ing 140 Ib. was once obtained. A mineral vein 

 on Silver Islet, Lake Superior, contains much 

 native silver ; and at Minnesota, on the same lake, 

 the native copper is sometimes studded with native 



silver in the form of lumps, or grains, or stringy 

 pieces. Native silver is or was abundant in the 

 great Comstock lode in Nevada, and is common in 

 the silver lodes of Mexico, Chili, and Peru. 



Argentite, Silver Glance, Vitreous Silver, Sul- 

 phide of Silver. A large amount of silver is 

 obtained from this ore, which is abundant in 

 Mexico and in the deep part of many mines in 

 Chili. It occurs in the Comstock lode, Nevada, 

 and sparingly in some European mines, including 

 some in Cornwall. Argentite crystallises in the 

 cubical system, and when pure contains 87 per 

 cent, of silver and 13 of sulphur. 



Stephanite, Brittle Silver Ore, Sulph-antimonite 

 of Silver, is another important ore of silver. It is 

 found accompanying other silver ores in a number 

 of the well-known metalliferous mines of Europe, 

 including those at Freiberg in Saxony, Andreas- 

 berg in the Harz, and in Bohemia and Hungary. 

 It is also one of the minerals mined in Mexico and 

 Peru. It crystallises in the prismatic system, and 

 when pure contains 71 per cent, of silver, 13 of 

 antimony, and 16 of sulphur. 



Pyrargyrite, Dark Red Silver Ore, Sulph-anti- 

 monite of Silver. This ore is found in the same 

 European localities as Stephanite, and likewise 

 occurs in Mexico, Chili, Idaho, and Nevada. 

 Small quantities of it have occasionally been got in 

 Cornwall. Crystallising in the rnombohedral 

 system, it often forms like Proustite, to be pres- 

 ently referred to, a very lieautiful mineral of a 

 blood-red colour, which, however, darkens by ex- 

 posure to light. When pure, pyrargyrite contains 

 60 per cent, of silver, 22 of antimony, and 18 of 

 sulphur. 



Prmutite, Light Red Silver Ore, Sulph-arsenite 

 of Silver, is, like the last, a rich silver ore, and 

 crystallises in the same system. It is found in 

 some of the same mines in Saxony and Bohemia, 

 and in one or two places in France and Spain. 

 Some of the silver-mines in Mexico, Chili, and 

 Nevada are also localities for it. When pure it 

 contains 65J per cent, of silver, 15 of arsenic, and 

 19J of sulphur. 



Stromeyerite, Sulphide of Silver and Copper. 

 The cupriferous silver ores of Chili are said to 

 consist chiefly of this mineral, but it is usually 

 so intimately mixed with felspathic vein-stuff that 

 it is difficult to separate pure pieces. It is also 

 found in Arizona, California, Silesia, and Siberia. 

 In its pure state, its composition is silver 53'1, 

 copper 31 '1, and sulphur 15 "8 percent. 



Chlorargyrite, Cerargyrite, Kerate, Horn Silver, 

 Chloride of Silver. The most important localities 

 for this valuable ore are Nevada (White Pine 

 District), California, Idaho, Arizona, British 

 Columbia (Fort Hope), certain districts in Mexico, 

 Chanarcillo in Chili, and in the Silverton district 

 and Barrier Ranges in New South Wales. But it 

 also occurs, though for the most part sparingly, at 

 Kongsberg in Norway, Allemont in France, the 

 Saxon and Harz mining districts, and in one or 

 two Cornish mines. It crystallises in the cubical 

 system, but is usually massive with a wax-like 

 appearance. It is malleable and sectile. This 

 ore when pure contains 75 per cent, of silver and 

 25 of chlorine. 



Embolite, Chloro-bromide of Silver, is the chief 

 ore obtained in the mines of Chanarcillo in Chili, 

 but it is believed that much of the ore called 

 chloride of silver is really this mineral. Embolite 

 contains from 61 to 68 per cent, of silver with 

 variable proportions of chlorine and bromine. 



Bromite, Bromyrite, Bromargyrite, Bromide of 

 Silver. This is the chief constituent of a silver ore 

 found in a few Mexican mines, and it also occurs 

 in Chili. The pure ore consists of 57J per cent, of 

 silver and 42J of bromine. 



