AT FlfKIBERG. 



419 



tlie little irregularities of surface are smoothed down with a file and brush. Its fineness must be now at least 99 per 

 cent, of silver. It is usually about 99.4, and contains only traces of copper, bismuth, and lead. The degree of fine- 

 ness is determined by a volumetric) analysis. 



After the silver lias been refined, the little buttons of silver arc collected from the hearth, and put aside to be 

 added at the next refining, 'flic part of the hearth into which the oxides of lead and bismuth have soaked (and 

 which contains from 15 to 20 per cent, of bismuth, and 0.15 to 0.3 per cent, of silver) is removed, and submitted to 

 the bismuth separation process. 



If the bliok-silver is to be treated for gold, it is freed from lead and bismuth in the manner indicated, but, instead 

 of being poured out into pans, it is granulated. The metal is ladled out into a cylindrical copper vessel tilled with 

 water. The ladle being filled is moved around and round, and the metal poured out in thin streams into the water, 

 whereby the silver is very finely granulated. 



It makes small porous masses of silver, and in this form is most easily attacked by acid. The copper vessel lias 

 two pipes, one above and one below. The cold water ponrs in through the lower, ami escapes from this upper pipe. 

 Unless the water is sufficiently cold, granulation will not take place. The separation of the gold from the silver is 

 undertaken exclusively at the Halsbrtickner Smelting Works, and consists in Cue treatment of the granulated and 

 refined blick-silver with concentrated sulphuric acid and the addition of heat, whereby the whole of the silver is dis- 

 solved as "silver vitriol," while the gold which was combined with it remains behind in the form of a powder. The 

 operation is performed in a, dissolving or separation kettle, of cast iron, which is walled in above a blast furnace. The 

 kettle is covered by a copper cap during the application of heat and the period of dissolving, and a pipe is connected 

 with this cover, through winch the sulphurio acid vapors are conducted to a small condensation chamber of sheet 

 lead, intended to catch all the little particles of sulphate of silver which may be carried off mechanically. From 

 here flic gases axe conducted into a chimney. In the copper cover is an aperture through which the contents of the 

 kettle can be constantly Stirred. Six centners of auriferous silver are dissolved at one time in such a, kettle ; and to do this 

 requires 12 centners of oil of vitriol, of which 5 centners are poured in at first, and the other 7 centners added from time 

 to time. In order that the silver may not stick fast to the bottom of the kettle, the mass must be stirred continuously 

 with, an iron rod. At first there is a violent disengagement of sulphurous acid, and great care is necessary in firing 

 to prevent the acid from boiling over. In eleven hours the dissolving is finished, and the solution is allowed to stand 

 for ten hours more, in order that it may cool and the gold residue may settle. At the expiration of this time the 

 concentrated solution of sulphate of silver is ladled into copper pans by means of a copper ladle, and transported to 

 a huge wooden vessel lined with sheet lead (silver precipitation vessel). It is here stirred with wooden poles ; a piece 

 of old copper sheeting is put into the tank, and it is heated by the introduction of steam to a temperature of about 

 70° C (158° Fahrenheit). The silver precipitates in flic form of a, grayisli-whifc crystalline mud. In proportion as 

 the metallic silver precipitates, copper vitriol is formed. 



Towards the hist, the liquor is tested for siver by chloride of sodium. When the dissolving is complete, 

 the liquor is allowed to stand for ten hours, in order to permit the line particles of silver to settle perfectly, and 

 is then drawn by means of leaden syphons, info a basin where the settling is completed. After this, the fully 

 desilverized liquor is conducted into the evaporation pans, where it is treated for copper vitriol. The "cement 

 silver" which remains in the silver precipitation vessel is sifted in a copper sieve, to get out any particles of copper 

 that may bo mixed with it, and is then placed in a tank provided with a false bottom, in which a sufficient number 

 of holes have been made for the escape of the liquid, and is well washed with hot water, until the, latter ceases to 

 give with chloride of barium the reaction for sulphuric acid. The waste water is collected, and as it contains 

 sulphate of copper in solution, it is used to dilute future charges of sulphate of silver in the precipitation tank. The 

 thoroughly washed cement silver is then pressed into bricks to expel the water as much as possible, and is brought, 

 In the form of small cylinders, into an iron retort, and heated to redness, to drive off the last trace of water. It is 

 then melted in Graphite crucibles in a, blast furnace, with stone-coal in masses of 410—420 pounds, and poured into 

 small cast-iron moulds, which have been smeared with tallow, a test of it having been previously taken to ascertain 

 the degree of fineness. This silver is delivered to the mint with a fineness of 09.9 per cent. 



