SILVER 801 



metals. Pure atmospheric air does not affect silver, but that of houses impregnated 

 with sulphuretted hydrogen soon tarnishes it with a film of brown sulphide. It is 

 distinguished chemically from gold and platinum by its ready solubility in nitric acid, 

 and from almost all other metals, by its saline solutions affording a curdy precipitate 

 with a most minute quantity of sea-salt or any soluble chloride. 



The atomic weight of silver is 108 ; its chemical symbol is Ag (argentum). 



Silver occurs in nature under many forms : 



1. Native silver possesses most of the above properties ; yet, on account of its being 

 more or less alloyed with other metals, it differs a little in malleability, lustre, density, 

 &c. It sometimes occurs crystallised in octahedrons, in cubes, and cubo-octahedrons. 

 At other times it is found in dendritic shapes, or arborescences, resulting from minute 

 crystals implanted upon each other. But more usually it presents itself in small 

 grains without determinable form, or in amorphous masses of various magnitude. 



The gangues (mineral matrices) of native silver are so numerous, that it may be 

 said to occur in all kinds of rock. At one time it appears as if filtered into their 

 fissures, at another as having vegetated on their surface, and at a third, as if impasted 

 in their substance. Such varieties are met with principally in the mines of Peru. 



The native metal is found in almost all the silver mines now worked ; but especially 

 in those of Kongsberg in Norway, in carbonate and fluoride of calcium, &c. ; at 

 Schlangenberg in Siberia, in sulphate of baryta ; at Allemont, in a ferruginous clay, 

 &c. The mines of Chili and Peru have yielded large quantities of native silver. 



The metals most usually associated with silver in the native alloy, are gold, copper, 

 arsenic, and iron. At Andreasberg and Guadalcanal it has been found alloyed with 

 about five per cent, of arsenic. The auriferous native silver is the rarest. 



2. Antimonial silver, or Dyscrasite. This rare ore is destitute of malleability, 

 and very brittle ; spec. grav. 9'5. It melts before the blowpipe, and affords white 

 fumes of oxide of antimony: being readily distinguished from arsenical iron and arsenical 

 cobalt by its lamellar fracture. It consists of from 76 to 84 per cent, of silver, and 

 from 24 to 16 of antimony. 



3. Argentite, Sulphide of silver or Silver glance. This is an opaque substance, of 

 a dark-grey or leaden hue ; slightly malleable, and easily cut with a knife, when 

 it betrays a metallic lustre. The silver is easily separated by the blowpipe. It con- 

 sists of 13 of sulphur to 89 of silver, by experiment ; 13 to 87 are the theoretic propor- 

 tions. Its specific gravity is 6'9. It occurs crystallised in cubes, and is found in 

 the mines of Freiberg in Saxony, Joachimsthal in Bohemia, Schemnitz in Hungary, 

 and Mexico. 



4. Pyrargyrite, Red Silver ore, Ruby Blende, or Antimoniated sulphide of silver, is an 

 ore remarkable for its lustre, colour, and the variety of its forms. It is friable, easily 

 scraped by the knife, and affords a powder of a lively crimson-red. Its colour in mass 

 is brilliant red, dark red, or even metallic reddish-black. It crystallises in a variety 

 of hexagonal forms. Its constituents are : silver from 56 to 62 ; antimony from 20 to 

 24 ; sulphur from 16 to 18. It is found in almost all silver mines ; but principally 

 in those of Freiberg, Andreasberg, and Guadalcanal. 



5. Proustite, Light Red Silver ore, or Arsenical sulphide of silver, is a similar but 

 rarer mineral, in which arsenic takes the place of antimony. 



6. Steplianite, or Black sulphide of silver, is a blackish, brittle mineral, affording 

 globules of silver at the blowpipe. It is found at Allemont and at Freiberg ; but 

 more abundantly in the silver mines of Peru and Mexico. The Spaniards call it negrillo. 



7. Polybasite is a sulphide of silver and copper, generally with antimony and 

 arsenic. It occurs in Mexico, Chili, Nevada, and Idaho. 



8. Sternbergite is a rare sulphide of silver and iron. 



9. Chloride of silver, or Horn silver. In consequence of its semi-transparent aspect, 

 its yellowish or greenish colour, and such softness that it may be cut with the nail, 

 this ore has been compared to horn, and may be easily recognised. It melts at the 

 flame of a candle, and may be reduced when heated along with iron or black flux. It 

 is occasionally crystallised in forms belonging to the cubic system ; but occurs chiefly 

 in irregular forms, sometimes covering the native silver with a thick crust, as in Peru 

 and Mexico. Its density is only 4*74. It is found in considerable quantities at North 

 Dolcoath in Cornwall. 



Chloride of silver sometimes contains 60 or 70 per cent, of clay ; and is then called 

 ' butter-milk ore ' by the German miners. 



10. Bromide of silver or Bromyrite, and Iodide of silver or lodyrite, occur in the 

 mines of Chili and Mexico ; whilst a mineral called Embolitc. vhich is u chloro- 

 bromide of silver, is found rather abundantly, in some of the mines of Chili. 



11. Carbonate of silver, or Selbite, is a mineral of doubtful occurrence. 



Largo quantities of silver are annually obtained in this country, and in the lead- 

 producing districts of Europe, by the treatment of argentiferous galena ; but the New 

 VOL. III. 3 F 



