6G6 SILVER.. 



muffle, heated by a proper furnace. Air being allowed access to 

 the assay, the lead is rapidly oxidated, and its highly fusible 

 oxide imbibed, as it is produced, by the porous cupel. The 

 disposition of copper and other common metals to oxidate is 

 increased by the presence of the lead, and their oxides, which 

 form fusible compounds with oxide of lead, are removed in 

 company with the latter. When the foreign metal is nearly 

 entirely removed, the assay is observed to become rounder and 

 more brilliant, and the last trace of fused oxide occasions a 

 beautiful play of prismatic colours upon its surface, after which, 

 the assay becomes, in an instant, much whiter, or flashes, an 

 indication that the cupellation is completed. 



Pure silver is the whitest of the metals, and susceptible of 

 the highest polish ; when granulated by being poured from a 

 height of a few feet into water, its surface is rough, but its 

 aspect peculiarly beautiful. It crystallizes in the cube and re- 

 gular octohedron, both from a state of fusion and by precipita- 

 tion from solution. Silver is in the highest degree ductile and 

 malleable ; its density varies between 10.474 and 10.542, it fuses 

 at 1873. When in the liquid state, it is capable of absorbing 

 oxygen gas from the air, which is discharged again in the solidi- 

 fication of the metal, and gives rise to a sort of vegetation upon 

 its surface, or even occasions the projection of small portions 

 of the silver to a distance, an accident which is known in assay- 

 ing as the spitting of the metal. Gay-Lussac observed that 

 when a little nitre was thrown upon the surface of melted silver 

 in a crucible, and the whole kept in a state of fusion for half 

 an hour, a very considerable absorption of oxygen took place. 

 When the crucible was removed from the fire and quickly 

 placed under a bell jar filled with water, which can be done 

 without danger, the silver discharged a quantity of oxygen 

 equal to 20 times its volume. This property is possessed only 

 by pure silver, it does not appear at all in silver containing 1 or 

 2 per cent of copper. As oxide of silver is reduced by a red 

 heat, the absorption of the oxygen by the fluid metal must be 

 a phenomenon of a diiferent nature from simple oxidation. 



Silver does not combine with the oxygen of the air at the 

 usual temperature, nor even when heated; the tarnishing of 

 polished silver in air is occasioned by the formation of sulphuret 

 of silver. Silver does not dissolve in any hydrated acid, by 

 substitution for hydrogen, but on the contrary, it is displaced 



