808 SILVER 



Details of the Amalgamation Process, as formerly practised at Halsbrucke. All ores 

 containing more than 7 Ibs. of lead, or 1 Ib. of eoppefr, percent, are excluded from this 

 reviving operation (Anguickverfahreri) ; because the lead would render the amalgam 

 very impure, and the copper would be wasted. They are sorted for the amalgrmia- 

 tion in such a way that the mixture of the poorer and richer ores may contain 7^, or, 

 at most, 8 loths (of oz. each) of silver per 100 Ibs. The most usual constituents of 

 the ores are, sulphur, silver, antimonial silver (Speissglanzsilber'), bismuth, sulphides 

 of arsenic, of copper, iron, lead, nickel, cobalt, zinc, with several earthy minerals. 

 It is essential that the ores to be amalgamated shall contain a certain proportion of 

 sulphur, in order that they may decompose enough sea-salt in the roasting to disen- 

 gage as much chlorine as to convert all the silver present into chloride. With this 

 view, ores poor in sulphur are mixed with those that are richer, to make up a deter- 

 minate average. The ore-post is laid upon the bed-floor, in a rectangular heap, about 

 17 ells long and 4 ells broad (13 yards and 3); and upon that layer the requisite 

 quantity of salt is let down from the floor above, through a wooden funnel ; 40 cwts. 

 of salt being allotted to 400 cwts. of ore. The heap being made up with alternate 

 strata to the desired magnitude, must be then well mixed, and formed into small bings, 

 called roast-posts, .weighing each from 3 to 4 cwts. The annual consumption of salt 

 at Halsbrucke was 6,000 cwts., supplied by the Prussian salt-works. 



Boasting of the Amalgamation Ores. The furnaces appropriated to the roasting of 

 the ore-posts are of a reverberatory class, provided with soot-chambers. They are 

 built alongside the bed-floor, and connected with it by a brick tunnel. The prepared 

 ground-ore (Erzmehl) is spread out upon the hearth, and dried with incessant turnings 

 over ; then the fire is raised so as to kindle the sulphur, and keep the ore red hot for 

 one or two hours ; during which time, dense white-grey vapours of arsenic, antimony, 

 and water, are exhaled. The desulphuration next begins, with the appearance of a 

 blue flame. This continues for three hours, during which the ignition is kept up ; 

 and the mass is diligently turned over, in order to present new surfaces, and prevent 

 caking. Whenever sulphurous acid ceases to be formed, the finishing calcination is 

 to be commenced with increased firing ; the object being now to decompose the sea- 

 salt by means of the metallic sulphates that have been generated, and to convert them 

 intp chlorides, with the simultaneous production of sulphate of soda. The stirring is 

 to be continued till the proofs taken from the hearth no longer betray the smell of 

 sulphurous, but of hydrochloric acid gas. This roasting stage commonly lasts 

 three quarters of an hour; 13 or 14 furnaces are worked at the same time at Hals- 

 brucke, and each turns out in a week upon an average 5 tons. Out of the Nicht 

 chambers or soot-vaults of the furnaces, from 96 to 100 cwts. of ore-dust are obtained, 

 containing 32 marcs (16 Ibs.) of silver. This dust is to be treated like unroasted ore. 

 The fuel of the first fire is pitcoal ; of the finishing one fir-wood. Of the former 1 1 5i 

 cubic feet, and of the latter 294^, are, upon an average, consumed for every 100 cwts. 

 of ore. 



During the last roasting, the ore increases in bulk by one-fourth, becoming in con- 

 sequence a lighter powder, and of a brown colour. When this process is completed, 

 the ore is raked out upon the stone pavement, allowed to cool, then screened in close 

 sieve-boxes, in order to separate the finer powder from the lumps. These are to be 

 bruised, mixed with sea-salt, and subjected to another calcination. The finer powder 

 alone is taken to the millstones, of which there are 14 pairs in the establishment. The 

 stones are of granite, and make from 100 to 120 revolutions per minute. The roasted 

 ore, after it has passed through the bolter of the mill, must be as impalpable as the 

 finest flour. 



The Amalgamation. This (the Verquicken) is performed in 20 horizontal casks, 

 arranged in 4 rows, each turning upon a shaft which passes through its axis ; and all 

 driven by the water-wheel shown in the middle of Jig. 1797- The casks are 2 feet 

 10 inches long, 2 feet 8 inches wide, inside measure, and are provided with iron 

 ends. The staves are 3J inches thick, and are bound together with iron hoops. They 

 have a double bung-hole, one formed within the other, secured by an iron plug 

 fastened with screws. They are filled by means of a wooden spout terminated by a 

 canvas hose; through which 10 cwts. of the boiled ore-flour (Erzmehl} are intro- 

 duced after 3 cwts. of water have been poured in. To this mixture^from ^ to of a 

 cwt. of pieces of iron, 1| inch square, and thick, are added. When these pieces get 

 dissolved, they are replaced by others. The casks being two-thirds full, aro set to 

 revolve tor 1| or 2 hours, till the ore-powder and water become a uniform pap ; 

 when 5 cwts. of quicksilver are poured into each of them. The casks being again 

 made tight, are put in gear with the driving machinery, and kept constantly re- 

 volving for 14 or 16 hours, at the rate of 20 or 22 turns per minute. During this 

 time they are twice stopped and opened, in order to see whether the pap be of the 

 proper consistence ; for if too thick, the globules of quicksilver do not readily 



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